Properties of Hydroxypropyl methylcellulose keratin blends

Properties of Hydroxypropyl methylcellulose keratin blends

Food grade Hydroxypropyl methyl cellulose (HPMC) and keratin (CL), were selected to blend, and the rheological properties of their thermal-thermal blended gels at low temperature and high temperature were studied. , and the blending ratio, type of HPMC and temperature on HPMC/CL. Fried meat products are widely loved by consumers, but their high fat content is likely to cause many health risks. Hydrocolloids have a good oil-reducing effect on fried products. The influence of the structure and physical properties of the membrane material, and it is applied in the batter of fried products in order to obtain a good effect of oil resistance and water retention. The main findings are as follows:

(1) Using rheometer and scanning electron microscope (SEM), the effect of CL on the rheological properties and gel morphology of HPMC system was studied. The study shows that the blends have smaller linear viscoelastic region (LVR), higher gel strength and larger G at 82°C compared to the blends at 25°C. ＼ G 〃 , G ' , G 〃 , gel strength and viscosity increased with the increase of CL content. Repeated temperature scans resulted in increased G' and G' for the HPMC/CL blends. For samples with 6% and 8% CL content, the gel formation temperature of the repeated temperature scans was significantly lower than that of the first scan In the samples at 82 °C, all samples were yield-shear-thinning fluids except the sample with 8% CL, while the samples at 40 °C were shear-thinning fluids. The establishment of HPMC/CL-thermal-thermal blended gel system and its rheological research provide some methodological and theoretical references for other thermal-thermal blended gels.

(2) Using Small Angle X-ray Scattering (SAXS), Wide Angle X-ray Diffraction (XRD), SEM, Fourier Transform Infrared Spectroscopy (FTIR), Contact Angle, Tensile, Oxygen Transmission Rate, Light Transmission Rate, Water Vapor The effects of blending ratio and drying temperature on the microstructure and properties of HPMC/CL membranes were investigated using methods such as permeability (WVP) and water solubility. And the application of the blend system in oil reduction and water retention in fried products was preliminarily explored. Both the blending ratio and the drying temperature will have a certain effect on the intermolecular interaction, crystalline structure and morphology of the membrane, but the effect on the fractal structure is not obvious. At low temperature and high temperature, the transmittance decreases with the increase of CL content; except HPMC, the transmittance of other films at high temperature is higher than that at low temperature. The contact angle of the CL film is significantly higher than that of HPMC, and the contact angle of the blend film is similar to that of its high-component pure film. The oxygen permeability of the blend films decreased with the increase of CL content. Compared with other blend films, the tensile strength and elongation at break of the 7:3 blend films were higher at low and high temperatures; and the tensile parameters of the 7:3 films at high temperature were higher than those at low temperature. At 37 °C drying temperature, the WVP of HPMC/CL hybrid membrane and CL membrane had no significant difference, and was slightly higher than that of pure HPMC membrane; Membrane WVP value is high. With the increase of CL content, the water solubility of HPMC/CL films decreased. The addition of 7:3 HPMC/CL samples to the batter can significantly increase the moisture content in the inner core of fried battered chicken breast, and significantly reduce the oil in the meat core, without affecting the moisture and oil content in the outer shell. Healthier and more tender battered fried meat products can be obtained without compromising the crispy texture of such fried products.

(3) SAXS, XRD, SEM, FTIR, contact angle, tensile, transmittance, WVP and water solubility test methods were used to study the effect of HPMC molecular weight on HPMC and HPMC/CL at different drying temperatures (7 : 3) The effect of film microstructure and physical properties. Different molecular weight HPMC will have certain influence on the intermolecular interaction, crystal structure and morphology of the membrane. Except for the 10:0E50 sample at 85 °C, different HPMC molecular weights did not affect the fractal structure of HPMC pure membrane and 7:3 mixed membrane at high temperature and low temperature. At 37 °C, the light transmittance of the 7:3 film containing E50HPMC was the lowest. At 37 °C, with the increase of the molecular weight of HPMC, the contact angle of pure HPMC membrane and 7:3 membrane first decreased and then increased; at 85 °C, the contact angle of HPMC molecular weight with HPMC and 7:3 membrane angle had no significant effect. At 37 °C, the molecular weight of HPMC had different effects on the tensile strength, elongation at break and elastic modulus of the membrane; at 85 °C, the molecular weight of HPMC had a significant effect on the tensile strength of the membrane. However, there was no significant effect on the elongation at break and elastic modulus of the membrane. HPMC with different molecular weights had some effect on the WVP of HPMC at 37 °C, 7:3 membrane and HPMC at 85 °C, but had no significant effect on 7:3 membrane at 85 °C. The molecular weight of HPMC did not affect the water solubility of pure HPMC membrane and 7:3 membrane.

Keywords: hydroxypropyl methyl cellulose（HPMC ）; keratin ; thermal gel ; edible film

Chapter 1 Introduction

1.1 Application of thermogel and edible film in oil-blocking and water-retention of fried food

Some edible coatings, especially those based on hydrophilic polymers, are good barriers to grease. When frying coated foods, the gel coat forms a fine "invisible" film that hinders the absorption of oil and reduces the fat content and calories of the final product. The application of gel coats to reduce oil absorption in fried foods has become increasingly important in recent years, as oil intake in fried products has become a health problem associated with obesity and coronary heart disease. The purpose of frying is to seal the surface of the food by dipping it in hot oil, thereby retaining flavor and juices, but this involves heat and mass transfer, resulting in the transfer of oil into the product and the transfer of water from the product into the oil . During frying, the moisture in the outer shell evaporates and some of the water migrates from the inner core to the outer shell. Since this water leaves voids for fat to enter, water loss and fat absorption are closely related. The microstructure of the shell is a major determinant of oil absorption, which occurs through a capillary action mechanism. Coatings make food surfaces stronger, more brittle, with fewer voids, reducing moisture evaporation and reducing oil absorption; likewise, coatings alter water retention by trapping moisture inside the food and preventing oil from displacing water.

HPMC is a cellulose ether with the unique property of forming a structured gel at elevated temperatures, the gelling properties of which are reversible upon cooling. If included in the batter system during deep frying, the paste-like gel formed during the first stage of heating can act as a barrier to prevent moisture loss during the final stages of frying when the coated food is subjected to high temperatures. This helps reduce oil absorption into food products during cooling. This unique property of HPMC makes it very effective in reducing the amount of oil absorbed during frying. HPMC is widely used to reduce the oil absorption rate of fried foods such as meat, such as poultry, starchy foods, dough, etc. Hinterstois sei et al. coated HP MC and MC films on the surface of fried chicken fillets, and studied the changes in oil consumption, free fatty acid content and color value during frying. Pre-coating the food can reduce the oil absorption rate and increase the use time of the oil. In one study, spraying a coating of HPMC onto chicken meatballs resulted in moisture retention and fat reduction in deep frying, with moisture retention rates as high as 16.6% being observed. 4%, while the fat loss rate was as high as 17.5% in the superficial layer. 9%, up to 33.3% in the core. 7%. This oil blocking effect is related to the thermal gelation ability of HPMC. Above the initial gelation temperature, the viscosity increases sharply because intermolecular association occurs very rapidly and the solution gels in the HPMC temperature range of 50–90 °C. The gel layer controls the migration of water and oil during frying. Adding HPMC to the rice flour based batter was found to contain 26% less oil than the control crust. The performance of the coatings may be attributed to wetting properties related to interfacial tension and acting as a mechanical barrier to lipids. In the batter-coated fried foods, the batter components contained HPMC, xanthan gum and guar gum respectively, and the food with HPMC batter coating had the lowest oil absorption rate. HPMC reduced oil content by about 54%, while xanthan and guar gums reduced oil content by 40% and 33%, respectively.

When cellulose derivatives are added to fried food, it can reduce the absorption of oil and fat during the food frying process. When the frying temperature is above the initial gelling temperature of the cellulose derivative, it reduces the oil absorption of the fried food by film formation. CL has thermal gelling properties similar to some cellulose derivatives and can be considered as a potential oil barrier forming component in fried foods. Funami et al. evaluated the effect of CL on reducing oil absorption and moisture loss in fried doughnuts, and evaluated its effects on doughnut physical properties and dough viscoelasticity by comparison with cellulose derivatives. The results showed that CL was more effective than cellulose derivatives in reducing oil uptake or moisture loss of doughnuts during frying. CL may reduce these indicators through its thermal gelation and film-forming effects, indicating that the gel has the effect of oil-blocking and water-retaining. Both HPMC and CL thermal gels can be used in fried foods alone or in combination with other samples, both of which have the effect of blocking oil and water. And the application effect is practical.

In summary, both HPMC and CL thermogels can have the effect of blocking oil and water in fried food. We know that the compound system is expected to combine the advantages of the two polymers to achieve a certain synergistic effect. Therefore, HPMC was studied. The rheological properties of the blended system with CL, the structure and performance of the blended film system have certain guiding significance for the oil and water retention of fried food.

1. 2. Rheological behavior of thermogel-based polysaccharides

1. 2. 1 Rheological study of hydroxypropyl methylcellulose

HPMC is a modified cellulose derivative, which can be widely used in the food industry as pre-coating of fried foods, food preservation due to its thermal gelation, film-forming properties, thickening properties, dispersibility and solubility. Films, thickeners, suspensions, and sustained-release materials for food and medical applications. The main functional groups of HPMC are hydroxypropoxy (-[OCH2CH(CH3)]nOH) and methoxy (-OCH3) substituents. There are many types of HPMC based on the content of the two substituents; in addition, samples containing the same hydroxypropoxy and methoxy substituent content can also be classified according to their viscosity. Different types of HPMC generally have different properties and uses. Domestic commercially available HPMC has many viscosity grades, mainly 3, 6, 15, 30, 50, 100, 4000, 10000, 15000, 100000 mPa.s . Among them, HPMC with a viscosity below 100 mPa.s is mainly used for adhesives and film coating materials, while the viscosity is 4000 mPa.s. HPMC above s is mainly used as the backbone material for sustained and controlled release formulations.

HPMC is a thermogel, and the formation of the gel is temperature- and concentration-dependent. The widely accepted gelation mechanism of HPMC is the intermolecular association of hydrophobic groups on the polymer chain, which leads to HPMC cross-linking and gel formation. It is of great significance to study the rheological properties of HPMC and its mixtures. Talukdar et al studied the rheological properties of xanthan gum (XG) and HPMC by performing oscillatory and steady-state shear measurements at lower temperatures. XG solution in pure water and pH 7. 4 exhibited a "gel-like" behavior in phosphate buffer, whereas HPMC behaved as a typical polymer solution. The addition of HPMC enhanced the gel properties and thermal stability of fish gelatin (FG) in this system, and the composite gel exhibited reversible cold and hot gel properties, which could expand the application range of FG in the food industry. Especially in edible casings for refrigerated and high temperature processed products. The rheological properties of HPMC-based composite gels and other cold gels, such as hydroxypropyl starch (HPS) and collagen, which increased the viscosity of HPMC at lower temperatures, were also investigated. . In addition, their blends can form gels at lower and higher temperatures.

1. 2. 2 The rheological study of keratin

CL is a linear triple helical polysaccharide composed of 1,3-P-D-glucose units, produced by a strain of Alcaligenes faecalis, and is a thermogel. Since it was first discovered by Harada in 1966, CL has attracted considerable attention in the food and non-food industries due to its unique physicochemical properties. It is insoluble in alcohol, cold water and many organic solvents, but can be dissolved in solvents with hydrogen bond breaking function, such as formic acid, urea (Urea), dimethyl sulfoxide (DMSO), sodium hydroxide (NaO) H) (pH 12) and trisodium phosphate, etc. Although it is insoluble in water, CL can form two types of gels when heated: low-setting gels and high-setting gels. The low cure CL gel is a thermoreversible gel that forms when an aqueous dispersion is heated to a lower temperature between 55 and 65 °C. However, when this aqueous dispersion is heated to higher temperatures, it forms a thermally irreversible gel that is stable at both low and high temperatures. In low-coagulation gels, cross-linking occurs between CL micelles, and CL micelles are occupied by single helical molecules through hydrogen bonds, while in high-coagulation gels, CL micelles are occupied by triple-chain molecules through hydrophobic interactions. Spiral cross-linking In addition, CL can also form a neutralizing gel, which can be formed by dissolving CL in an alkaline solution and then neutralizing the suspension. Due to its unique thermogelling properties, CL has been widely used in various foods, such as tofu, noodles, jelly and low-fat meat products such as Zhang, etc. by dynamic rheological measurements, differential scanning calorimetry and pulsed 1H-NMR measurements have molecularly described the gelation mechanism of CL. Different molecular weights and different concentrations of CL have different gelling phenomena. Ye et al. studied the interaction between konjac glucomannan (KGM) and CL from the perspective of sol state and gelation process, the apparent viscosity of the blend system in an alkaline environment, and the flow during heating and cooling. Metamorphic properties, thermodynamic properties, gelling properties and water holding capacity. The results show that the addition of CL can help to reduce the gelation temperature of KGM, increase the gelation rate and inhibit the thinning phenomenon of KGM gel at low temperature (2-20 °C), increasing the hardness and gel strength of KGM. It is of great significance to study the rheological properties of CL and its mixtures for its application.

1. 2. 3 The rheological study of the compound system

The rapid development of science and technology makes people's requirements more and more diverse, and it is difficult for a single-component material to meet the diverse practical application needs of human beings. Combining two or more polymers is the most direct and effective method to obtain polymer materials with good performance, processing convenience and wide application, which has attracted the attention of many researchers, and more and more people are concerned.

In the process of material processing, flow and deformation will inevitably occur, and rheology is the science that studies the flow and deformation laws of materials. Studies have shown that in the polymer compound system, the partially compatible compound system will show the phenomenon of compatibility or phase separation, which is mainly affected by factors such as the compound ratio, shear rate, temperature and component structure of the system. The change from compatibility to phase separation will inevitably lead to a significant change in the viscoelasticity of the compound system. In recent years, the viscoelastic behavior of partially compatible polymer complexes has attracted the attention of many researchers. The research shows that the rheological behavior of the complex system in the compatibility zone shows the characteristics of a homogeneous system, and in the phase separation zone, the rheological behavior shows a completely different and extremely complex feature from the homogeneous zone.

Understand the rheological properties of the compounding system under different conditions (concentration, compounding ratio, shear rate, temperature, etc.) Energy consumption, etc. are of great significance. For example, for some materials that are extremely sensitive to temperature, the viscosity of the material can be changed by adjusting the temperature, thereby improving the processing performance of the material; when studying the shear thinning zone of the material, a certain shear rate is selected to Control processing properties and improve material production efficiency.

1. 3 Research progress of thermogel-based high molecular composite edible films

1. 3. 1 Research progress of hydroxypropyl methylcellulose-based composite edible film

HPMC is a kind of food additive with high safety, because it has good film-forming properties, the film prepared from it not only has good flexibility and mechanical properties, but also has high transparency, and can also prolong the shelf life of food. longevity, so it is used as an edible membrane. Osorio et al. reduced the water vapor transmission rate of the film by adding carrageenan, plasticizer and carnauba wax emulsion to the HPMC film, and applied it to the preservation of blueberries. A better fresh-keeping effect on blueberries is achieved. PRIYA et al. added chitosan, TiO2 and neem powder to the HPMC film, and found that the film had better physicochemical and biological properties, and the shelf life of grapes and plums was extended by 10 days, with good sensory and texture. The incorporation of sodium alginate and essential oil (DEO) into the HPMC membrane material significantly improved the water barrier properties, water vapor transmission rate, water solubility and mechanical properties of the membrane, and also enhanced the antioxidant activity of the membrane. , In conclusion, the fabricated hybrid films show considerable potential in active food preservation.

Takes into account the effect of polymer molecular weight (corresponding to viscosity grade) on the film. Cespi et al. studied HPMC films and found that at room temperature, the mechanical properties of free films were independent of molecular weight. Glass transition temperature, apparent activation energy and brittleness depend on polymer chain length. In particular, low molecular weight materials show higher glass stability, higher brittleness. Espinoza-Herrera et al. studied the thermal, mechanical and microstructural properties of different cellulose derivative films including HPMC. Cellulose derivative films exhibited different physical properties, among which, CMC film had better mechanical properties, higher crystallinity and thermal diffusivity, followed by HPMC film. Larson et al. showed that the degree of substitution of HPMC affects the glass transition temperature and water plasticization of HPMC-based films. Otoni et al. studied the effects of hydroxyl substitution degree and molecular weight on the mechanical properties and water-barrier properties of HPMC films, and proved the following hypothesis: both chain length and main chain side groups affect the mechanical and water-barrier properties of HPMC films. Thermal and rheological properties are also affected by the chemical structure of HPMC. The degree of substitution (SD) has a significant effect on the hydrophilicity, moisture resistance, glass transition, tensile resistance and ductility of HPMC films. This effect is attributed to the reduced polarity provided by the methoxy substitution. The molecular weight mainly affects the rheological behavior of HPMC solution and the mechanical properties of its thin films. This result is due to higher levels of physical entanglement and a decrease in free volume for longer chains.

1. 3. 2 Research progress of keratin-based composite edible film

The application of CL in food is relatively late, but because of its strong thermal stability, gelation, safety and non-toxicity, CL has been widely used as a food additive in recent years. The insoluble nature of CL can be used to improve the hydrophobicity of some systems, especially edible membrane systems. Since most edible film systems are easily soluble in water, they cannot provide good protection for foods with high moisture content, or cannot be used in high humidity environments. However, its solubility properties when mixed with other materials should be addressed, and so far there have been few reports on edible films of CL.

Sun et al. reported that dissolving CL in 1% NaOH and forming a mixture with a chitosan (CS) solution required stirring the mixed solution for several hours before pouring it onto a film-forming plate. Although CL/CS blend films were prepared, the mechanical properties still need to be further improved. Wu et al. M prepared KGM/CL hybrid membranes. They dissolved CL in an aqueous solution of pH 8, heated at 90 °C and stirred for 3 h to form CL microgels. These gels were then mixed with the KGM solution by stirring for another 3 h. It was found that strong intermolecular hydrogen bonds occurred between KGM and CL, and when the KGM content in the hybrid film was about 70 wt%, it showed excellent mechanical and physical properties. Ahmad et al. reported a gelatin/CL hybrid film. However, all of these films were prepared at pH 12 to prepare CL blends with gelatin. Wang et al. prepared CL/CS/carboxymethylcellulose (CMC) ternary membranes and characterized their properties by controlling the temperature and adjusting the pH of the solution. Compared with pure CS membranes, CS/CL/CMC blend membranes exhibited better mechanical properties, permeability and thermal stability. In addition, the visible light properties of the ternary blend films were improved. SEM and Fourier transform infrared spectroscopy analysis showed good compatibility among CS, CL and CMC. However, the mixing conditions of CL with other materials require further study.

1. 4 Influence of processing factors on the structure and properties of the composite edible film

1. 4. 1 Effects of processing factors on the structure and properties of hydroxypropyl methylcellulose-based composite edible films

Studies have shown that processing factors can have an impact on the structure and properties of the resulting edible films. Pedley et al. used polarized attenuated total reflection infrared spectroscopy to study the structure of polymeric HPMC films under dry and ambient humidity conditions. Spectra were recorded in the C-H and 0-H stretch regions of films deposited on silicon, germanium, and ZnS internal reflective elements (IREs) in particular. For the C-H band, all three polarization spectra (s-, p-, and z-spectra) show no change in the preferred orientation of transition dipoles between wet and dry films on germanium or silicon , but the orientation parallel to the ZnSe surface increases slightly. On the other hand, the 0-H spectra show an increased orientation of transition dipoles parallel to the surface for both wet and dry films of all three IREs compared to the corresponding C-H spectra. In dry films, i.e. with free water removed, this effect is greater than in wet films. Mixing of the two biopolymers may lead to phase separation due to their thermodynamic incompatibility under certain conditions, which in turn affects the structure and properties of the films formed after drying of the biopolymers. Nuzzo et al. studied the effect of HPMC/maltodextrin blend solids content and phase (composition) on component localization in individual dry granules. It was observed that the phase separation of HPMC and maltodextrin was caused by solvent evaporation in membrane drying, single particle drying and spray drying. Contrast is an important parameter that affects the localization of the HPMC-enriched phase and the maltodextrin-enriched phase, i.e. affecting the particle surface, core and distribution in a more or less bicontinuous manner. It was found that the drying time, which is affected by the solids content, controls the progress of phase separation, which in turn affects the structure and properties of the membrane. Menegalli et al. found that drying at high temperatures can lead to the formation of gels for MC and HPMC, resulting in different membrane properties. Perfeti et al. studied the physical properties of HPMC films used for coatings at different drying and storage temperatures. The drying temperature had no effect on the polymer properties, while the storage temperature had an effect on the HPMC films and glass. The changes in the transition temperature and the magnitudes of the storage modulus E and loss modulus E ” are only partially correlated. Zhang et al. studied the effect of processing conditions on these effects of HPMC/hydroxypropyl starch (HPS) with different ratios. Influence of the microstructure and mechanical properties of the blends. It was found that higher temperature resulted in higher storage modulus of the hybrid gel, more solid-like behavior and tighter self-similar structure. Moreover, by drying at high temperature The films prepared from the gel showed higher crystallinity and denser amorphous structure, thus resulting in increased tensile strength and elastic modulus, but decreased elongation at break. Pastor et al. The optical, mechanical and water repellency properties of the dry films were evaluated when HPMC films of propolis were equilibrated under different humidity conditions, and it was found that at low moisture content (samples were equilibrated at 53% and 59% relative humidity), The water absorption enthalpy in the samples is greatly reduced, which indicates that the hydrophobicity of the matrix is enhanced; when the moisture content of the film increases, the elongation at break and elastic modulus of the film decrease, but the moisture content does not affect the stretchability of the film In conclusion, the present study shows that the drying time, drying temperature, storage temperature and equilibrium humidity conditions of the membranes all have an impact on the structure and properties of HPMC-based membranes.

1. 4. 2 Effects of processing factors on the structure and properties of keratin-based composite edible films

In the film preparation process, drying is one of the most important conditions affecting the structure and performance of the film. During the drying process of the membrane, factors such as the concentration of the membrane-forming liquid, the equipment used for drying the membrane, the drying temperature, humidity and time will all affect the structure and performance of the membrane. Researchers use different methods to dry the membrane, such as room temperature drying, microwave, oven, vacuum, infrared or low pressure superheat drying. At present, drying conditions have been studied for membranes prepared from various substances, such as gelatin, CS, alginate, soy protein, whey protein, amylose and amylopectin. Studies have shown that the selection of drying conditions is closely related to the characteristics of the raw materials, such as the state of the gel phase before drying, or whether the gel is formed or depolymerized during the drying process. In addition, the drying process is accompanied by other phenomena, such as the transition from the rubbery state to the glassy state, the formation of recrystallization, or the occurrence of phase separation. Therefore, the degree of influence of the drying conditions of the membrane on the structure and properties of the polymer membrane is inseparable from the physical and chemical properties of the polymer.

CL forms different gel structures under different temperature conditions, so it is necessary to study the drying conditions of CL membranes. Antibacterial films prepared by the mixture of CL and CS were studied by Sun et al. When the temperature is higher (90 °C), the elongation at break of the CL/CS blend films can be greatly improved due to the formation of CL gel and the interaction between the hydroxyl groups of CL and the amino groups of CS. and water vapor transmission rate, and make the membrane have higher storage modulus and lower water absorption. Therefore, drying conditions will have an important impact on the final properties of the membrane.

1. 5 The research purpose, research significance and research content of this paper

1. 5. 1 Research purpose

(1) The HPMC/CL thermo-thermal gel blend system was established, and the rheological properties of the HPMC/CL thermo-thermal gel blend system were clarified.

(2) HPMC/CL composite edible film was prepared, and the influence of blending ratio and drying temperature on the structure and physical properties of the composite film was clarified. The purpose of reducing oil and water retention of chicken breast meat products.

(3) Prepare HPMC/CL composite edible film, and clarify the influence of HPMC type and drying temperature on the multi-scale structure and physical properties of the composite film.

1. 5. 2 Research significance

Thermal gel polysaccharide is expected to achieve a certain effect of oil resistance and water retention by forming a gel layer and further drying to form a film during the frying process of high temperature fried products. There are few thermal curdlan, the common ones are HPMC and methyl cellulose, CL is also a thermal curdlan, but it was discovered later, and its application in food is still less. The compound gel system is expected to form a co-gel to achieve better application effects, but the research on the thermal-thermal gel system is still very limited, and there is no relevant research on the HPMC and CL thermal-thermal gel blend system. The rheological study of this blended gel system can not only provide a theoretical basis for its application in fried products such as oil resistance and water retention, but also provide methodological and theoretical references for the research of other thermal-thermal co-gel systems.

On the basis of studying the rheological gel properties of the blend system, further research on the structural properties of the composite membrane may clarify the mechanism of the blend system in oil resistance and water retention of fried products, and can expand the application approach of the blend system. The composite edible film can combine the advantages of two polymer materials and improve the defects of a single film material. HPMC edible film has good mechanical properties, but its strong hydrophilicity and poor barrier properties limit some of its applications. CL membrane material has a certain degree of hydrophobicity, and excellent oxygen barrier properties. And these two polymers are linear polysaccharides, thermal gels, and have certain compatibility. In this study, a new composite edible film with excellent performance was prepared, the influence of processing factors on its structural properties was clarified, and its application in water blocking and oil retention of fried products was preliminarily explored. Because this composite film has excellent oxygen and water vapor barrier properties, and certain hydrophobic properties, it also has a wide range of application prospects, such as edible fresh-keeping coatings for fruit and vegetable products and new edible packaging materials.

1. 5. 3 Research content

(1) The HPMC/CL thermo-thermal gel blend system was constructed, and the effect of CL on the rheology and gel structure of HPMC was studied.

(2) Prepare HPMC/CL composite edible film, study the effect of blending ratio on the multi-scale structure and physical properties of HPMC/CL composite edible film prepared at different temperatures, and further study the effect of blend system on fried chicken breasts. The effect of oil reduction and water retention in meat products.

(3) To study the effects of HPMC species on the multi-scale structure and physical properties of HPMC/CL composite edible films prepared at different temperatures.

Chapter 2 The effect of keratin on the rheological properties of hydroxypropyl methylcellulose

2. 1 Introduction

Both HPMC and CL are thermal curdlan, but CL was discovered later, and its application in food is still less. The composite gel system is expected to form a co-gel to achieve better application effects, but most of the current research mainly focuses on the combination of cold-cold gel and cold-hot gel. The research is still very limited, and there are no related studies on HPMC and CL thermo-thermogel blends.

In this study, a HPMC/CL thermo-thermal blended gel system was established, and the linear viscoelastic region, the degree of solid-like behavior, the sol-gel effect of CL on the HPMC system at low temperature and high temperature were investigated by rheometer and scanning electron microscopy. The effects of transition properties, viscosity properties, fluid properties and gel morphology and structure provide methodological and theoretical references for the study of other thermal-thermal cogel systems. This study will also provide some theoretical guidance for the application of HPMC/CL blends in fried food.

2. 2 Materials and methods

2. 2. 1 Main reagents

Hydroxypropyl methylcellulose (ZW-E6) (Methoxy content: 29%; Hydroxypropyl oxygen content: 8.4%; 2% (w/w) Hydroxypropyl methylcellulose solution viscosity: 6 mPa.s, pharmaceutical grade) was purchased from Huzhou Zhanwang Pharmaceutical Co., Ltd. Kederan gum (CG-01, water content of 7.85%, food grade) was purchased from Jiangsu Yiming Biotechnology Co., Ltd.

2. 2. 2 Main instruments

Rotational rheometer (Kinexus Pro+) Malvern Instruments Ltd, UK

Digital display constant speed powerful electric mixer (JB90-SH) manufactured by Shanghai Specimen Model Factory

Lyophilizer (Alpha-2LDPlus) Beijing Bomoxing Instrument Co., Ltd.

Zeiss Field Emission Scanning Electron Microscope System (Gemini SEM 300) Carl Zeiss, Germany

2. 2. 3 Sample preparation

HPMC was dispersed in deionized water (90 °C) by slow stirring for 20 min, then stirred at 30 rpm for 40 min and cooled to room temperature to prepare a 10% (w/w) HPMC solution , and then CL was added to prepare 0%, 2%, 4%, 6% and 8% CL (wCL/w(water + hpmc)) HPMC/CL suspensions. Finally, the above suspension was continuously stirred at room temperature at 60 rpm for 1 h and then at 40 rpm for 1 h for rheological testing. HC0, HC2, HC4, HC6 and HC8 were used to label the five suspensions, respectively.

2. 2. 4 Rheological test

The rheological properties of the HPMC/CL blends were measured using a rheometer through strain sweeps, frequency sweeps, temperature sweeps and shear rate sweeps. The strain scan, frequency scan and temperature scan were selected with a diameter of 40mm and a gap of 1. 0mm plate rotor PU40SR1343SS, with a diameter of 25mm and a gap of 1.5mm for shear rate scanning. 0mm Cylindrical Rotor C25SW1114SS. Except for the temperature scan, all other scan tests were preprocessed. During the pretreatment, all samples were heated to 95 °C and kept in the sample holder for 5 min, then cooled to 82 °C and 25 °C, respectively, and the scanning was started after the samples stabilized. All samples tested at higher temperatures were sealed with silicone oil to prevent water evaporation. The specific method is as follows:

Strain scanning is mainly to obtain the linear viscoelastic region (LVR). For strain sweeps, the samples were at 0. The test is carried out in the range of 01-100%, the test temperature is 25°C and 82°C, and the test frequency is 1Hz.

in O. The frequency sweep was carried out in the frequency range of 1-10 Hz, the test temperature was 25°C and 82°C, and the test strain was 0 . 1%.

Shear rate scans were performed at 40°C and 82°C using the Toolkit_V001 shear rate/equilibrium flow curve program with a scan range of 1-500/s. Flow patterns can be determined by fitting shear stress (ct) and shear rate (Y) to the corresponding fluid equations.

The temperature sweep range was 25–90 °C, the heating rate was 2 °C/min, and the strain was 0. 1%, the frequency is 1Hz. The samples are sealed with silicone oil to prevent evaporation of moisture. Immediately after the first scan, a second temperature scan was repeated under the same conditions. The two temperature scans are divided into -1 and -2, eg HC0-1 for the first and HC0-2 for the second. For HC8, two temperature sweeps in the range of 25–95 °C were performed as a comparison, demonstrating that the pretreatment temperature has a great influence on the formation of thermally irreversible gels. After the first temperature scan was heated to 90°C and 95°C, the second temperature scan of HC8 was recorded as H90-2 and H95-2, respectively.

All rheological tests were performed in triplicate and the data used were the average of the triplicates.

2. 2. 5 Scanning electron microscope (SEM) observation

The HC0, HC2 and HC6 (prepared according to Section 2.2.3) samples were placed in a water bath at 82 °C for 5 min to form a gel. According to the method of Zhang et al., with some modifications, the gel was pre-frozen in liquid nitrogen for 3 min, placed in a -80 °C freezer for 12 h, and then freeze-dried. Freeze-dried samples were stored in a desiccator prior to SEM measurement. The freeze-dried HPMC/CL blends were gold-sprayed and then observed.

2. 2. 6 Statistical analysis

Data were analyzed using SPSS Statistics 25 (IBM Software, Inc., New York, USA) and expressed as mean standard deviation (SD). Means were compared using one-way or two-way analysis of variance (ANOVA) followed by Duncan's multiple comparisons test. Numbers with different letters indicate significant difference (p<0.05), numbers with the same letter indicate no significant difference (P>0.05).

2. 3 Results and discussion

2. 3. 1 The effect of CL on the linear viscoelastic region of the HPMC system

2. 3.2 The effect of CL on the degree of solid-like behavior of HPMC system

2. 3. 3The effect of  CL on the sol-gel transition of HPMC solution

2. 3. 3.1 The effect of CL on the first sol-gel transition behavior of HPMC solution

Effective molecular chain stiffness, linking region strength, and number of bonds contribute to G', while frictional energy consumption in the liquid state (including mobility of small molecules, motion, friction, and vibration and rotation of functional groups) all contribute to the value of G' . These moduli can be used to analyze gel behavior, rate of gel network formation, and structural characteristics. They also reflect the internal structure development and molecular interactions during gel network formation. It can be seen from the red curve in e that all samples experienced three stages during the heating process: the initial plateau region, the gel structure formation region and the final plateau region. In the initial plateau stage, the values of G ' and G ″ vary with temperature This may be due to the thinning phenomenon at room temperature. When the temperature further increases, both G ' and G 〃 rise rapidly, and the intersection of G 1 and G 〃 appears, which is the condensation point. Gel formation stage. HP MC can form a gel structure through the hydrophobic interaction of methoxy groups in the molecule and the interaction of hydroxyl groups. CL can form a single helix through hydrogen bonding or a triple helix gel structure through hydrophobic interaction. In addition to these gels In addition to the structure, a co-gel structure can also be formed. The gel formation temperature of the first temperature scan is shown in Table 2-1. The gel formation temperature of HCl is 63.0 °C, while the temperature of HC2, The gel formation temperatures of HC4, HC6 and HC8 were 63.5T, 63.00C, 62.1 °C and 60.2 °C, respectively. From the results of the significance analysis The gelation temperature of HC8 was significantly lower. This may be because higher CL content can promote the formation of CL gels and co-gels. In the final plateau region, the samples have higher G' and G' values. and stable, indicating that the gel network of the sample has been fully formed.

Moreover, in the three stages, the G' and G' values of the samples all increased with the increase of CL content. At higher temperatures, with increasing CL content, both G' and G' increased significantly for all samples. The increase in HC8 was especially dramatic. At lower temperatures (below the gel formation temperature), the Gfn G" values of the HC0, HC2, HC4, HC6, and HC8 samples were smaller and increased with increasing CL content. smaller, which corresponds to their liquid properties at lower temperatures.

2. 3. 3. 2Effect of 2CL on the repeated sol-gel transition behavior of HPMC solutions

2. 3. 4 The effect of CL on the viscosity and fluid properties of HPMC system

2. 3.5 The effect of CL on the gel morphology and structure of HPMC system

Morphological structure of HPMC/CL blends at 82 °C. The surface of pure HPMC gel has a porous structure, and the pores are slender or round, while the pore size of pure HPMC is larger. After adding 2% CL, the pores of the blended gel were more and smaller. After adding 6% CL, the blended gel had a regular round, smaller and denser porous structure, indicating that a denser gel was formed. To sum up , with the increase of CL content , the pore size of the blended gel becomes smaller , which makes the G \ gel strength and viscosity of the blended gel increase .

2. 4 Chapter Summary

Compared with the blends at 25°C, the blends at 82°C have a smaller linear viscoelastic region (LVR), higher gel strength and larger G', G ", G", gel strength and viscosity increased with increasing CL. Repeated temperature sweeps resulted in increased G' and G" for HPMC/CL blends. For HC6 and HC8, the gel formation temperature of repeated temperature scans was significantly lower than that of the first scan. The samples at 82 °C are yield-shear-thinning fluids, except for the samples with 8% CL, while the samples at 40 °C are shear-thinning fluids. The establishment of the HPMC/CL thermal-thermal blended gel system and its rheological study provide some methodological and theoretical references for other thermal-thermal blended gels.

Chapter 3 Effects of blending ratio and drying temperature on the microstructure and properties of HPMC/CL blend membranes

3. 1 Introduction

The composite edible film can combine the advantages of two materials and improve the defects of a single film material. HPMC edible film has good mechanical properties, but its strong hydrophilicity and poor barrier properties limit some of its applications. CL membrane has certain hydrophobicity and excellent barrier properties. In addition, both materials are polysaccharide-based thermogels. According to the rheological study of HPMC/CL blend system in the previous chapter, the two materials may form co-gels at high temperature, indicating that the system has a certain phase. Capacitance.

On the basis of mastering the rheology of HPMC/CL blend system, in this chapter, we prepared HPMC/CL blend films with different blending ratios and drying temperatures, and studied the effects of blending ratio and drying temperature on blending. The effects of film multi-scale structure (intermolecular interaction, crystal structure, microdomain ordered structure, morphological structure) and physical properties (water solubility, contact angle, water vapor barrier, oxygen barrier, mechanical properties and light transmittance). On this basis, HPMC/CL systems with different blending ratios were further added into chicken breast batter to prepare fried chicken breast products, and the effect of blending system on oil and water content of fried products was preliminarily investigated.

3. 2 Materials and methods

3. 2. 1 Main reagents

Hydroxypropyl methylcellulose (Methoxy content: 29%; Hydroxypropyl oxygen content: 8.4%; 2% (w/w) Hydroxypropyl methylcellulose solution viscosity: 15mPa_S , pharmaceutical grade) were purchased from Huzhou Zhanwang Pharmaceutical Co., Ltd. Kederan gum (CG-01, water content of 7.85%, food grade) was purchased from Jiangsu Yiming Biotechnology Co., Ltd. Chicken breast meat was purchased from Jiangsu Yonghui Supermarket . Wheat flour (universal flour) was purchased from Xinxiang City Xinliang Grain and Oil Processing Co., Ltd. Corn flour was purchased from Xinxiang Liangrun Whole Grain Food Co., Ltd. Baking soda was purchased from Inner Mongolia Prairie Dajiang Food Co., Ltd. Table salt was purchased from China Salt Shanghai Salt Industry Co., Ltd. Petroleum ether (30-60 °C, analytical grade) was purchased from Sinopharm Chemical Reagent Co., Ltd.

3. 2. 2 Main instruments

X-ray diffractometer (D8Advance) Bruker AXS, Germany

Small angle X-ray scatterometer (NanoSTAR) Bruker AXS, Germany

Zeiss Field Emission Scanning Electron Microscope System (Gemiini SEM 300) Carl Zeiss, Germany

Microscopic Infrared Spectroscopy IR (Cary 610/670) Varian, USA

Video optical contact angle measuring instrument (OCA20) German dataplusics company

UV-Vis Spectrophotometer (759S) Shanghai Prism Technology Co., Ltd.

Texture Analyzer (TMS-Pro) Food Technology Corporation, USA

Gas permeability tester (BSG-33D) Guangzhou Xitang Electromechanical Technology Co., Ltd.

High-speed desktop refrigerated centrifuge (H1850R) Hunan Xiangyu Laboratory Instrument Development Co., Ltd.

Collecting type constant temperature heating magnetic stirrer (DF-101S) Shanghai Lichen Bangxi Instrument Technology Co., Ltd.

Electric blast drying (101-3B) Changge Mingtu Machinery Equipment Co., Ltd.

Electric Blast Drying Oven (DGX9053B-2) Shanghai Fuma Experimental Equipment Co., Ltd.

Electric fryer ( EF - 191V ) Guangzhou Colorful Trading Co., Ltd.

Fat Tester (S0X406) Shandong Haineng Scientific Instrument Co., Ltd.

3. 2. 3 Membrane preparation

(1) Weigh a certain amount of HPMC powder and disperse it into hot water (85°C), cool the film-forming liquid to room temperature under stirring to dissolve the polymer, and prepare the HPMC film-forming liquid (1% w/w) .

(2) Disperse CL in deionized water for 1 h, then add 3M NaOH, and mix in a magnetic stirrer for 5 h. Subsequently, 1M HCl was added dropwise to neutralize the (pH 7) CL-base solution. The resulting CL suspension was centrifuged at 5,000 g for 20 min, and the precipitate was washed three times with deionized water. The gelatinous CL suspension was adjusted to 1% (w/w) and then homogenized for 5 min (10 x 30 s) to prepare the CL film-forming solution.

(3) Mix the two types of solutions together in different weight ratios (10:0; 7:3; 5:5; 3:7; 0:10), add (accounting for the dry matter of the film-forming liquid) 10%) glycerol, stirring for 3h. Defoamed in a vacuum drying oven for several hours, poured into polystyrene petri dishes (0.015 cm), and dried in an oven at 37 °C and 85 °C, respectively.

(4) After drying, the membrane was peeled off from the plate and placed in 59% RH (saturated NaBr solution to control moisture balance, 20°C) to equilibrate.

3. 2. 4 Thickness test

Use a digital electronic micrometer to measure the thickness of the film. Seven random locations around each film sample were used to determine thickness. The average thickness value for each sample was taken and used in the calculation of water vapour transmission, light transmission and mechanical properties.

3. 2. 5 Wide-angle X-fiber diffraction (XRD) test

The crystalline structure of the film can be analyzed by wide-angle X-ray diffraction. When the X-ray irradiates the atomic plane at the complementary angle 0 of the incident angle (the lattice plane spacing is d), and the angle conforms to Bragg's law, diffraction lines will appear in the reflection direction. The reflection is obtained from each reflecting surface that meets the Bragg condition at 0 angle. After measuring e, use the Bragg formula to determine the lattice plane spacing, cell type and size. From the intensity of the diffraction lines, the arrangement of atoms in the unit cell can also be determined.

3. 2. 6 Small angle X-ray scattering (SAXS) test

Small Angle X-ray Scattering (SmallAngel X-ray Scattering, SAXS) refers to the scattering phenomenon produced by the measured sample in a small angle near the X-ray beam when the X-ray beam irradiates the measured sample. . Because of the difference in electron density between the scatterer and the surrounding medium in the nanoscale range, SAXS is often used in the research of liquid polymer materials, solid state and colloid state in the nanoscale range. And SAXS can be used to analyze the polymer molecular chain conformation, long-period structure, and the phase structure and phase distribution of the polymer molecular complex system.

3. 2. 7 Scanning electron microscope (SEM) observation

The samples were observed using a Zeiss field emission scanning electron microscope system (Gemini SEM 300). Each sample was first cut into a size of 6cmX6mm, and then brittle with liquid nitrogen to obtain a cross-section, and then different samples were glued to the sample box, and the cross-section of the sample box was vertically upward for gold spray observation. Observe and take images at 1000x and 4000x, respectively.

3. 2. 8 Fourier transform infrared spectroscopy test

Fourier transform infrared spectroscopy (FTIR) is a type of molecular absorption spectrum that can be used for quantitative and qualitative analysis, and can also be used to identify functional groups and structures of molecular compounds.

3. 2. 9 Light transmittance test

3. 2. 9. 1. Principle of UV-Vis Spectrophotometric Ageing

The UV-Vis spectrophotometer can emit light in the wavelength range of 200-8000 mn. When light is irradiated on the test material, some specific wavelengths of light in the incident light are absorbed by the test material, and molecular vibrations and electronic energy level transitions occur.

When a beam of light hits an object, part of the incident light is absorbed by the object, and the other part is transmitted through the object; light transmittance is the ratio of the transmitted light intensity to the incident light intensity.

3. 2. 9. 2 Test method

The transmittance of the film was measured using the method of Liu et al. Cut the film sample into 10mm x 40mm rectangular strips, put them in a quartz cuvette, and make the edible film stick to the inner wall of the cuvette. A 759S UV-Vis spectrophotometer was used to scan the samples at the full wavelength of 200-800 nm, and each sample was tested 3 times.

3. 2. 10 Contact angle test

In this experiment, a video optical contact angle measuring instrument (OCA20) was used to measure the contact angle of the samples. The film sample (7 x 2 cm2) was pasted on a glass slide and placed on a movable platform in a horizontal position. A drop of ultrapure water is quickly dropped onto the film surface using the attached micro-syringe. The test results were repeated 5 times and the average value was calculated.

3. 2. 1 1 Mechanical property test

The mechanical property test refers to applying a tensile force along the longitudinal axis to the test sample at a certain tensile speed in a specific test environment until the sample is pulled off. This test can obtain the force applied to the sample and the deformation value of the sample, and obtain the stress-strain curve of the sample during the tensile process. The tensile strength, elongation at break, and elastic modulus of the samples can be calculated from stress-strain curves. These data are often used to evaluate the tensile properties of materials, and then provide some necessary parameters for practical applications.

Cut the membrane into a rectangular strip size of 60mm x 6mm. Measure the thickness of all rectangular strips. The load cell is 1000N, the original gripping distance is 40mm, and the crosshead speed is 8mm/min. The tensile properties of the film samples were tested in the tensile mode of the texture analyzer. Each sample was repeated 7 times.

3. 2. 1 2 Oxygen permeability test

3. 2. 12. 1 Principle of oxygen permeability analysis

The test cavity is divided into two parts, A and B. Among them, a certain flow rate of high-purity oxygen flow is passed into the A cavity, and a certain flow rate of nitrogen flow is passed into the B cavity. During the sample testing process, the oxygen in chamber A penetrates into chamber B through the sample, and the oxygen infiltrated into chamber B is carried by the nitrogen stream and leaves chamber B to reach the oxygen sensor. The oxygen sensor measures the oxygen content in the nitrogen stream and outputs the corresponding value. The electrical signal was used to calculate the oxygen transmission rate of the sample.

3. 2. 12. 2 Test method

Select undamaged film samples, cut them into 10 x 10 cm square shapes, coat the edge surfaces of the grips with vacuum grease, and mount the samples on the test block. According to YBB 00082003-2015 standard, the test area of each sample is 50cm2.

3. 2. 13 Water Vapor Transmission Rate (WVP) Test

The water vapor transmission rate (WVP, g＾mnrls+Pa4) of the films was determined according to the method of Liu et al. with some modifications. The film samples (6.5 cm x 6.5 cm) were sealed in 50 mL centrifuge tubes containing 40 g of anhydrous cassia gum. Then, place the centrifuge tube in an environmental chamber filled with distilled water at 20°C. The weight changes of the centrifuge tubes were recorded at 24-h intervals for 7 consecutive days.

3. 2. 1 4 Water solubility test

Membranes were first dried to constant weight at 105 °C, then cut into squares (4 cm x 4 cm), accurately weighed (recorded as Mi), immersed in 50 mL of distilled water and continuously incubated at 20 °C. Stir for 1 h to measure water solubility. Undissolved membrane samples were removed and dried at 105 °C to constant weight (recorded as Mf).

3. 2. 15 chicken breast preparation

Wash the chicken breast and put it in the refrigerator at 6 °C 1 . 5 h in order to be able to cut out samples of uniform shape and size. After removing fat and connective tissue, cut into 4cm x 1cm x 1cm shape, and thaw the chicken at room temperature. Then, press with kitchen paper to absorb moisture from the surface of the chicken.

3. 2. 16 Preparation of the batter

The ingredients of the batter mainly include wheat flour, corn flour, sodium bicarbonate, salt, HPMC and CL, etc. Six kinds of batter were prepared according to different proportions. Mix it well and mix it with water in a mass ratio of 1:1. 25. Mix and stir, and it is advisable to mix evenly without bubbles.

3. 2. 17 Cooking of chicken breast

The sample is immersed in the mixed slurry, and the weight of the slurry on the sample is about 5g. Fry samples at 160 °C oil temperature. Deep fry about 3. 5min is mature. Remove the samples, drain, cool, and store in a 5-8°C refrigerator for later use.

3. 2. 18 Chicken breast fried batter Test for moisture in the outer shell and inner core meat

The moisture content refers to GB/T 9695. 15-2008 "Determination of Moisture Content of Meat and Meat Products". The chicken breast shell and core meat samples were placed in a constant temperature drying oven and dried to constant weight at 105 °C to determine the moisture content.

3. 2. 19 Test of oil content in chicken breast batter shell and core meat

Refer to GB/T 9695 for the determination of oil content. 7-2008 "Determination of total fat content in meat and meat products". Soxhlet extraction was performed on the chicken breast shell and inner meat samples with petroleum ether for 6 h to remove the remaining petroleum ether to determine the oil content.

3. 2. 20 Statistical analysis

Data were analyzed using SPSS Statistics 25 (IBM Software, Inc., New York, USA) and expressed as mean standard deviation (SD). Means were compared using one-way or two-way analysis of variance (ANOVA) followed by Duncan's multiple comparisons test. Numbers with different letters indicate significant difference (P<0.05), numbers with the same letter indicate no significant difference (P>0.05).

3. 3 Results and discussion

3. 3. 1 Thickness analysis

Film thickness is a crucial parameter because it is closely related to the physical properties of the film such as WVP, light transmittance, and mechanical properties. Under the drying condition of 37 °C, with the increase of CL content, the thickness of HPMC/CL membrane showed a trend of increasing first and then decreasing. Among them, when the CL content is 30%, the thickness of the film reaches the highest value, which is 0.0%. 036mm. It is possible that the addition of CL promoted the development of a heterogeneous membrane matrix and thus increased the thickness of the membrane. At 85 °C, there was no significant difference in the thickness of HPMC/CL films ( /; > 0.05), but the HPMC/CL (7:3, 3:7 and 0:10) ratios of mixed films The corresponding film thicknesses at 37°C were significantly reduced.

3. 3. 2. Crystal structure analysis

3. 3. 3 Fractal structure analysis

3. 3. 4. Cross-sectional morphology analysis

3. 3. 5 Fourier transform infrared spectroscopy analysis

3. 3. 6 Light transmittance analysis

Under the drying temperature of 37 °C, the light transmittance of pure HPMC film is the highest, and gradually increases with the increase of wavelength to reach equilibrium at about 250 nm; while the light transmittance of pure CL film is the lowest, but also reaches 9. 4%, its film forms shoulder peaks at 250 and 310 nm with the increase of wavelength, and then gradually reaches equilibrium after 400 nm; the light transmission curve of the mixed film is consistent with CL, and the light transmission The ratio is between pure HP MC and CL, and gradually increases with the increase of CL ratio, indicating that the system has a certain compatibility. Under drying at 85 °C, the change trend of the transmittance of all films with the blending ratio is consistent with that at low temperature. Comparing the films at different drying temperatures, the light transmittance of pure HPMC films is lower at high temperature than at low temperature, mainly due to the rough morphology and structure caused by the gel at high temperature; the light transmittance of other films at high temperature drying The ratios of these samples were higher than those at low temperature, indicating that the compatibility of these samples was improved at high temperature drying, which was consistent with the results observed by scanning electron microscopy of these samples at high temperature.

3. 3. 7 Contact angle analysis

Generally, membranes with higher contact angle values exhibit lower surface hydrophilicity, while biopolymer membranes with lower contact angle values exhibit higher surface hydrophilicity to enhance the hydrophobicity of natural polymer membrane materials. The preparation of degradable hydrophobic packaging films has always been a technical problem and research focus of natural polymer materials, because it has a great market demand. The contact angle of HPMC is significantly smaller than that of CL membrane, indicating that CL has strong hydrophobicity; the blended sample 7:3 membrane and pure HPMC show similar contact angles, and there is no significant difference between them, while sample 5:5 and There is no significant difference between the contact angles of 3:7 and pure CL films, the reason for the above phenomenon may be that the continuous phase of 7:3 is HPMC, while the continuous phase of 5:5 and 3:7 is CL, because the continuous phase of 7:3 is HPMC. The contact angle of the relative system has a great influence, and the blended film will show a contact angle similar to that of the continuous phase film. At 85 °C, the contact angle of the HPMC/CL hybrid film did not change significantly, but the contact angle of the 5:5 film was significantly lower than that of the CL pure film, mainly due to the close ratio of the two components. In some cases, the system may form a co-continuous phase (HPMC/hydroxypropyl starch 4:6 exhibits a co-continuous phenomenon), and it may be that HPMC/CL 5:5 does not use CL as the continuous phase at high temperature, resulting in a significant decrease in the contact angle. Comparing the films prepared at different temperatures, except for the sample 7:3, there is no significant difference among other films. The contact angle of the 7:3 film prepared at 85°C is significantly higher than that of the film at 37°C. The main reason is that the compatibility of the 7:3 film at high temperature is better from the infrared spectrum, scanning electron microscope and light transmittance. Therefore, although the 7:3 sample still uses HPMC as the continuous phase at high temperature, it may appear In order to avoid the phenomenon of interphase mixing, there are also dispersed CL molecular chain clusters in the continuous phase of HPMC, thereby increasing its contact angle value.

3. 3. 8 Mechanical properties analysis

At 37 °C, the tensile strength of the pure HPMC film was 37 MPa, the tensile strength of the pure CL film was 22 MPa, and the tensile strength of the mixed film was lower than that of the pure HPMC and pure CL. Membrane material, indicating that although the system has a certain compatibility, it is not completely compatible, and there is a certain degree of phase separation, because the tensile strength of a completely compatible system will gradually increase with the increase of one component; 3:7 Tensile The tensile strength is lower than that of 5:5, which may be related to its morphology and structure compared with coarse sugar. At 85 °C, the tensile strength of the pure HPMC membrane was lower than that of the pure CL membrane, the tensile strength value of the 5:5 membrane was not significantly different from that of the pure CL membrane, and the tensile strength of the 3:7 membrane was lower than that of the pure CL membrane. The tensile strength value is lower than that of pure CL membrane, while the tensile strength value of 7:3 membrane is higher than that of pure HPMC membrane, which is related to its relatively smoother cross section than pure HPMC. Compared with the films with the same blending ratio, the tensile strength of the HPMC film at 85 °C is lower than that at 37 °C, which may be related to the formation of a certain degree of phase separation of the gel structure, resulting in a rough morphology; other The tensile strength of the samples at high temperature is higher than that at low temperature. For 7:3, it is mainly related to the enhanced intermolecular hydrogen bonding and smooth morphology and structure at high temperature; 5:5, 3:7 and pure CL The increase in tensile strength of the film at high temperature is mainly due to its smoother morphology and structure than that at low temperature drying.

At 37 °C, with the increase of CL content, the elongation at break of the film first decreased and then increased, and the elongation at break of the 7:3 film in the blend film was the highest, and there was no significant difference with the pure CL film; 85 At °C, there was no significant difference in the elongation at break of all blend films, and there was no significant difference in the elongation at break between the 7:3 and 5:5 films and the pure HPMC and pure CL films; pure HPMC The elongation at break of the high temperature film is lower than that of the low temperature film, the elongation at break of the high temperature film of 5:5 and 3:7 is higher than that of the corresponding low temperature film, and its morphological structure is smoother and its crystallization peak is wider at high temperature. , the crystalline area is smaller.

At 37 °C, the elastic modulus of the 7:3 sample is slightly lower than that of the pure CL film, but it is not significantly different from other films; at 85 °C, the elastic modulus of the 5:5 sample is the lowest, and all the other samples have the lowest elastic modulus. There were no significant differences in elastic modulus. The elastic modulus of the high temperature film of 5:5 is lower than that of the low temperature film, and there is no significant difference between the high temperature film and the low temperature film of other blending ratios.

In terms of comprehensive mechanical properties, the mechanical properties of 7:3 in the blended sample are better, especially at high temperature, its tensile strength, elongation at break and elastic modulus are not significantly different from those of pure HPMC film and CL film. .

3. 3. 9 Oxygen transmission rate analysis

Edible composite film is used as food packaging material to extend the shelf life of food, and its oxygen barrier performance is one of the important indicators. The oxygen permeability of HPMC membrane is the highest, which is 703. 45cm3/m2_24h*0. 1 MPa, possibly due to the low viscosity of HPMC and the existence of the amorphous region, it is easy to form a relatively loose low-density structure in the film. This is higher than the oxygen permeability results of the HPMC membranes prepared by Wang et al., mainly due to the different thicknesses of the membranes and the different types of HPMCs. The oxygen transmission rate of pure CL membrane is 6 . 77cm3/m2*24h. 0.1 MPa, the oxygen permeability of the blend film decreases sharply with the increase of CL content, which may be related to the intermolecular hydrogen bonds formed between the systems. It can be seen from the infrared spectrum that the intermolecular hydrogen bonds increase with CL. The content increases gradually (with the increase of CL, the stretching vibration of the -0-H bond gradually shifts from 3423 cm-1 to 3275 cm force, in addition, HPMC due to low viscosity Compared with the existence of the amorphous region, it is easy to form a relatively loose low-density network structure in the film. Compared with this, CL has a higher tendency to recrystallize, and it is easy to form a dense structure in the film. Addition can increase the tortuosity of the oxygen channel in the composite membrane, which in turn leads to a decrease in the oxygen permeation rate, which ultimately leads to a lower oxygen permeability of the hybrid membrane. 7.27, 15.66 and 65.68 times higher. The addition of CL endows the HPMC membrane with excellent antioxidant effect, which can enhance the HPMC membrane to some easily oxidized foods, such as vegetables and vegetables. Protective effects.

3. 3. 10 Analysis of water vapor transmission rate

One of the main features to consider when using biodegradable polymers for edible films is their ability to avoid mass transfer mechanisms. In this way, a good barrier to aromas, water vapour and gases is generally desired. At 37 °C, the WVP of the HPMC/CL hybrid membrane was not significantly different from that of the CL membrane, and was slightly higher than that of the pure HPMC membrane. Compared with other films, the HPMC/CL (5:5) of the films prepared at 85 °C has a lower WVP, which may be due to the formation of a co-continuous phase at this blending ratio. . Compared with the films with the same blending ratio, the WVP value of the films prepared at 85 °C is higher than that of the films prepared at 37 °C. Gel is formed during the process, resulting in a certain phase separation, resulting in a rough and discontinuous section; except for HPMC, the section of other membrane materials is more continuous and smooth at high temperature, and the system compatibility increases, which should generally lead to a decrease in the WVP value of the membrane material, resulting in The opposite result may be due to the reduction of the crystallization peak area and width of these films at high temperature, that is, the decrease of crystallinity and crystalline integrity, which can lead to a decrease in the water vapor barrier performance of the system.

3. 3. 1 1 Water solubility analysis

For the membranes prepared at both temperatures, the water solubility of pure HPMC is about 100%, while that of pure CL membrane is about 20%. With the increase of CL content, HPMC/C The significantly reduced water solubility of the L membranes may be due to the structural integrity and water resistance provided by the water-insoluble polymer chains of CL. In addition, intermolecular interactions can improve the cohesion of the biopolymer matrix, resulting in fewer hydrophilic sites, thereby reducing water sensitivity. For the films with the same blend ratio, the water solubility of the film at 85 °C was similar to that of the film at 37 °C, indicating that the drying temperature had no significant effect on the water solubility of the blended films with the same content of CL.

3. 3. 12. Analysis of water content in chicken breast, deep-fried batter, outer shell and inner core meat

Moisture is an important factor affecting the crispness of the outer shell and the tenderness of the inner meat. In this study, the moisture content of the outer shell and inner meat of chicken breast meat was determined. Among them, the moisture content of raw chicken breast is 68.8%. 93%. Regarding the moisture content of the shell, there was no significant difference in the moisture content of the fried chicken products between the four other experimental groups and the control group (batter-coated), but there was a significant difference between the batter samples containing CL and the control group (p < 0.05). ), in which the water content of the shell of the control group was 36.6%. 13% , and the moisture content of the shell of the batter pulped product containing CL was 42 . 67%, but an increase in the moisture content of the shell is not what we want, as it will affect the crispness of the product. In terms of the water content of the core meat, the batter pulped product containing 7:3 had a significant difference with the control group, which had a water content of 62.3. 69%, and the water content of the batter and pulped products containing 7:3 is 64.4%. 95%, which increases the tenderness and juiciness of the core meat. To sum up, when HPMC/CL of 7:3 was added to the batter, the water content of the inner meat could be increased without increasing the water content of the outer shell. The crispness of the crust plays a big role.

3. 3. 13 Analysis of oil content in chicken breast fried batter shell and core meat

Excessive oil content in fried food can cause human health effects. In this study, the oil content of chicken breast meat was determined in shell and inner meat. Among them, the oil content of raw chicken breast is 1. 92%. In terms of the oil content of the shell, compared with the control group, only the oil content of the experimental group 5 was significantly lower (p < 0.05), which may be related to the high water content of the shell, because the channels formed by the evaporation of water can further become the migration of oil. aisle. Different from the oil content of the outer shell, after adding CL, the oil content of the inner core meat of the batter products with HPMC and CL blending system was significantly lower than that of the control group. Effectively control the oil content of chicken belly during processing, which is mainly because HP MC and CL are both thermal gels, which appear in a gel state during frying and heating and can be further dried into a hydrophilic film to reduce oil from the fryer. Penetrates into the shell and into the chicken. In terms of the total oil content of the outer shell and core meat, only the 7:3 and CL-containing batter coatings showed a significantly lower trend than the control group. Therefore, considering the oil content of the outer shell and the inner core meat, the batter coating containing 7:3 and containing keratin can effectively control the migration of external oil in the process of frying chicken breast.

3. 4 Chapter Summary

In terms of structure: At two drying temperatures, the blended film showed the same crystalline form as its high-component pure film, but the area and width of the crystalline peak increased with the increase of the content of the component. The crystallization peak area and peak value of the film material were lower than those at low temperature. At low temperature, the smoothness of CL fractal structure is slightly higher than that of other blend films. At high temperature, there is no significant difference in the fractal structure dimension of the films with different blend ratios, and the drying temperature has no significant effect on the fractal dimension of the films. Under drying at 37 °C, the cross-sectional structure of HPMC original film was smoother, while the cross-sectional structure of CL film and blend film was rough; under drying at 85 °C, the cross-section of HPMC film was rougher than other films; 85 °C The dried HPMC films were rougher than the corresponding films at low temperature, and the other films dried at 85 °C were smoother than the films of the same blend ratio at low temperature. Regardless of low temperature or high temperature, the -0-H peak of the blend film gradually red-shifted from the higher wavenumber of pure HPMC to the lower wavenumber of pure CL with the increase of CL content. There are more inter-hydrogen bonds than at low temperatures.

In terms of performance: at both drying temperatures, the transmittance decreased with the increase of CL content; except for HPMC, the transmittance of other films at high temperature was higher than that at low temperature. At both drying temperatures, the contact angle of the CL film was significantly higher than that of HPMC; at 37 °C drying, when the CL content was not more than 30%, the contact angle of the sample was similar to that of HPMC; The contact angle of the sample is similar to that of CL at %; the contact angle of the blend films 7:3 and 3:7 has no significant difference with HPMC and CL; except that the contact angle of the 7:3 film at high temperature is significantly higher than that at low temperature The contact angles of the films with this blending ratio have no significant difference between the contact angles of other films at low temperature and high temperature. In terms of comprehensive mechanical performance indicators, the mechanical properties of 7:3 in the blended sample are better, especially at high temperature, its tensile strength, elongation at break and elastic modulus are not significantly different from those of pure HPMC film and CL film. difference. The oxygen permeability of the blend films decreased with the increase of CL content . At 37 °C drying temperature, the WVP of HPMC/CL hybrid membrane and CL membrane had no significant difference, and was slightly higher than that of pure HPMC membrane; the membrane prepared at 85 °C, Compared with other membranes, HPMC/CL (5:5) had lower WVP; membranes prepared at 85 °C had higher WVP values than their corresponding membranes at 37 °C. For the films prepared at the two temperatures, with the increase of CL content, the water solubility of HPMC/CL films decreased significantly; the drying temperature had no significant effect on the water solubility of the blend films with the same content of CL. Impact.

Application: Adding a sample of 7:3 HPMC/CL to the batter can significantly increase the moisture content in the core of fried battered chicken breast and significantly reduce the oil in the core, allowing us to obtain a more tender and healthier taste The addition of 7:3 HPMC/CL will not affect the crispy taste of such fried products because there is no significant change in the moisture and oil content in the shell.

Chapter 4 Influence of HPMC molecular weight on the microstructure and properties of HPMC/CL blend membranes at different drying temperatures

4. 1 Introduction

In the previous chapter, we successfully prepared HPMC/CL mixed membranes with different blending ratios. On the whole, the 7:3 HPMC/CL membrane has relatively good physical properties, so this chapter uses 7:3 The blending ratio of HPMC/CL was used for follow-up studies. In the previous chapter, the effect of blending ratio on the microstructure and properties of HPMC/CL hybrid membranes prepared at different temperatures was systematically studied. Since the molecular weight of HPMC is also an important factor affecting the performance of HPMC-based blend membranes, HPMC with different molecular weights can interact with CL differently, resulting in different aggregated structures, compatibility and physical properties of the blend membranes. Based on this, we carried out the research of this chapter.

In this study, we mixed three different molecular weight HPMCs (ZW-E6, ZW-E15, ZW-E50) with CL to prepare HPMC/CL blend films, and studied the effect of HPMC molecular weight on HPMC/CL. Effects of blend films on microstructure, contact angle, water solubility, water vapor transmission, light transmittance and tensile properties.

4. 2 Materials and methods

4. 2. 1 Main reagents

Three kinds of hydroxypropyl methylcellulose (ZW-E6, ZW-E15, ZW-E50) are all pharmaceutical grades, purchased from Huzhou Zhanzhan Pharmaceutical Co., Ltd. The content of methoxy group is 29%, and the content of hydroxypropyl group is 8. 4%; ZW-E6, ZW-E15, ZW-E50 weight average molecular weight were 2. 441x104g/mol, 2. 650 x 104 g/mol, and 5. 401x104 g/mol; 2% hydroxypropyl methylcellulose solution viscosity was 6mPas, 15mPa_s and 50mPas, respectively. Kederan gum (CG-01, water content of 7.85%, food grade) was purchased from Jiangsu Yiming Biotechnology Co., Ltd.

4. 2. 2 Main instruments

Ray diffractometer (D8Advance) Bruker AXS, Germany

Small-angle X-ray scatterometer (NanoSTAR) Bruker AXS, Germany

Zeiss Field Emission Scanning Electron Microscope System (Gemini SEM 300) Carl Zeiss, Germany

Micro-infrared spectrometer IR (Cary 610/670) Varian Company, USA

Video optical contact angle measuring instrument (OCA20) German data ploysics company

UV-Vis Spectrophotometer (759S) Shanghai Prism Technology Co., Ltd.

Texture Analyzer (TMS-Pro) Food Technology Corporation, USA

High-speed desktop refrigerated centrifuge (H1850R) Hunan Xiangyi Laboratory Instrument Development Co., Ltd.

Collecting type constant temperature heating magnetic stirrer (DF-101S) Shanghai Lichen Bangxi Instrument Technology Co., Ltd.

Electric blast drying oven (101-3B) Changge Mingtu Machinery Equipment Co., Ltd.

Electric blast drying oven (DGX9053B-2) Shanghai Fuma Experimental Equipment Co., Ltd.

4. 2. 3 Membrane preparation

(1) Take a certain amount of HPMC (ZW-E6, ZW-E15, ZW-E50) powders and disperse them into hot water (85°C) respectively, and cool the film-forming liquid to room temperature under stirring. The polymer was dissolved to prepare different HPMC film-forming solutions (1% w/w).

(2) Prepare 1% CL film-forming solution: Same as 3. 2. 3(2).

(3) Mix the four types of solutions in different weight ratios (10:0; 7:3; 0:10), add (accounting for 10% of the dry matter of the film-forming liquid) glycerol, and stir for 3 h. Defoamed in a vacuum oven for several hours, poured into polystyrene petri dishes, and dried in an oven at 37°C and 85°C, respectively.

(4) After drying, the film was peeled off from the plate and placed in 59% RH (saturated NaBr solution to control moisture balance, 20°C) to equilibrate.

4. 2. 4 Thickness test

Same as Chapter 3 3. 2. 4.

4. 2. 5 Wide-angle X-ray diffraction (XRD) test

Same as Chapter 3 3.2.5

4. 2. 6 Small angle X-ray scattering (SAXS) test

Same as Chapter 3 3. 2. 6

4. 2. 7 Scanning electron microscope (SEM) observation

Same as Chapter 3 3. 2. 7

4. 2. 8 Fourier transform for spectral testing

Same as Chapter 3 3. 2. 8

4. 2. 9 Light transmittance test

Same as Chapter 3 3. 2. 9

4. 2. 10 Contact angle test

Same as Chapter 3 3. 2. 10

4. 2. 1 1 Mechanical property test

Same as Chapter 3 3. 2. 1 1

4. 2. 12 Water vapor transmission rate (WVP) test

Same as Chapter 3 3. 2. 1 3

4. 2. 1 3 Water solubility test

Same as Chapter 3 3. 2. 1 4

4. 2. 14 Statistical analysis

Data were analyzed using SPSS Statisti Cs 25 (IBM Software, Inc., New York, USA) and expressed as mean standard deviation (SD). Means were compared using one-way or two-way analysis of variance (ANOVA) followed by Duncan's multiple comparisons test. Numbers with different letters indicate significant difference (P < 0.05), numbers with the same letter indicate no significant difference (P > 0.05).

4. 3 Results and discussion

4. 3. 1 Thickness analysis

At 37 °C drying temperature, there was no significant change in the thickness of pure HPMC films and HPMC/CL 7:3 mixed films containing HPMC with different molecular weights. At the drying temperature of 85 °C, the thicknesses of HPMC/CL hybrid films containing HPMC with different molecular weights had no significant difference, while the thicknesses of pure HPMC films containing E15 and E50 were significantly higher than those containing E6. HPMC pure membrane. Compared with the film at 37 °C, the thickness of HPMC containing E6, 7:3 film and 7:3 film containing E15 decreased significantly at high temperature, which may be related to the formation of thermal gel by HPMC at high temperature, and the chain segment due to tighter integration.

4. 3. 2. Crystal structure analysis

At 37°C, the three pure HPMC membranes containing E6, E15, and E50 HPMC were all at 8° and 20. There are two diffraction peaks around 0 °, which are typical semi-crystalline peaks of HPMC, indicating that the molecular weight of HPMC does not affect the crystal form of HPMC, but the crystalline peak width and peak area of E15 are similar to those of the other two films. ratio decreased; pure CL membrane at 6°, 11 . 6° and 21° showed a strong peak and two broad peaks, respectively; the 7:3 blend films containing E6, E15, and E50 HPMC showed crystalline peaks of pure HPMC, and 6 The 6° peak of CL is more obvious in the 7:3 film containing E50HPMC, it can be inferred that the high molecular weight HPMC interacts weakly with the CL segment and cannot effectively hinder C L segment crystallization, the peak at 8 ° of the 7:3 blend film containing E6 and E15 HPMC is flatter than its corresponding pure HPMC film, the peak is broadened, and the peak area is reduced, indicating that this peak is completely crystalline The degree and crystallinity decreased, it can be inferred that CL can have a better interaction with the lower molecular weight HPMC segment, which can hinder the crystallization of HPMC segment to a certain extent, while the 7 with E50 HPMC: 3 The peak at 8° of the blend film is higher and narrower than its corresponding pure HPMC film, and the peak area has increased, indicating that the crystalline integrity and crystallinity of this peak are increased. The HPMC segments have good interactions and cannot effectively hinder the aggregation of HPMC segments, and even promote their aggregation and crystallization.

At 85 °C, the three pure HPMC membranes of E6, E15, and E50 are all at 8 ° and 20. There are two diffraction peaks around 0°, and with the increase of the molecular weight of HPMC, the peak area gradually becomes larger; the pure CL film shows a strong peak and a broad peak at around 6° and 21°, respectively; The 7:3 blend films of 6, E15, and E50 HPMC showed crystalline peaks similar to those of pure HPMC, without CL 6 ° crystalline peaks, indicating that 70% of HPMCs with different molecular weights had different crystalline peaks at high temperature. The addition of CL can prevent the recrystallization of CL; the peak area of the 7:3 blend film containing E50 HPMC is larger than that of the 7:3 film containing E6 and E15; E6, E15 and E5 The peaks at 8° and 20° of the 7:3 blend film of 0 HP MC are flatter than those of the corresponding pure HP MC film, the peak is broadened, and the peak area is reduced, indicating that the crystalline integrity and degree of crystallinity of this peak are reduced. , it can be inferred that at high temperature, CL can interact better with the HPMC segments of different molecular weights used in the experiment, which can hinder the crystallization of HPMC segments to a certain extent.

At high temperature, the crystallization peak area of HPMC pure films containing E15 HPMC and E50 HPMC increased, which may be related to its high molecular weight, and it is easy to form gel at high temperature, resulting in increased crystallinity; Compared with the corresponding film at low temperature, the 7:3 sample of E50 HPMC does not show a peak of 6 °, indicating that high temperature promotes the stronger interaction between HPMC and CL segment and hinders the recrystallization of CL segment.

4. 3. 3 Fractal structure analysis

At a drying temperature of 37 °C, the scattering intensities of film samples prepared from different types of HPMCs were arranged in the following order: 7 :3E15 >7 :3E6 >7 :3E50 >10 :0E50 >10:0E6>10:0E15>CL. With the increase of the molecular weight of HPMC, the scattering intensity of HPMC pure film first decreased and then increased, while the scattering intensity of HPMC/CL 7: 3 film material first increased and then decreased, and the scattering intensity of HPMC and 7: 3 film material The strengths of the 7:3 membranes containing HPMC with different molecular weights are higher than those of the pure membranes containing the same molecular weight HPMC, indicating that the HPMC membranes with different molecular weights after blending in the 7:3 ratio have different molecular weights in the crystallization area and The difference in electron cloud density between the amorphous regions has increased to varying degrees. For the films containing E6 and E15, the crystalline integrity and crystallinity are lower than those of the corresponding original films. The increase in the electron density difference between the amorphous regions can only result in a greater reduction in the electron cloud density in the amorphous region, which means that the amorphous region is looser.

At 85 °C, the scattering intensities of film samples prepared from different types of HPMCs are arranged in the following order: 7 : 3 E 1 5 > 7 : 3 E 6 > 7 : 3 E 5 0 > CL = 1 0 : 0 E 15>10:0E6>10:0E50; the scattering intensity of pure HPMC film is 10:0E15>10:0E6>10:0E, opposite to that of 37 °C 50 , but the variation of scattering intensity of HPMC/CL films with different types of HPMC is similar to that of 37 °C; the intensity of 7:3 films with different molecular weight HPMCs is higher than that of pure films with the same molecular weight HPMC, indicating that with 7:3 After blending in 3 ratios, the difference in electron density between the crystalline region and the amorphous region of HPMC films with different molecular weights increased to different degrees. Both the crystallinity and the crystallinity are lower than that of the corresponding original film. To satisfy the increase in the electron density difference between the crystalline region and the amorphous region, the electron cloud density in the amorphous region can only be reduced to a greater extent, which also means that the amorphous region is looser. , indicating that the blending of CL with HPMC of different molecular weights can reduce the density of the amorphous region at high temperature. Except for the pure HPMC film containing E50 HPMC, the scattering intensity of all films at high temperature is higher than that of the corresponding films at low temperature, which may also be caused by the looseness of the amorphous region.

At 37°C, all membrane samples showed surface fractal, and the addition of different HPMC molecular weights and 30% CL did not affect the self-similar structure fractal dimension of HPMC pure membrane and 7:3 mixed membrane. However, pure CL membranes show a more compact self-similar structure. Except for the 10:0E50 sample, all membrane samples also showed surface fractal at 85 °C, and the addition of different HPMC molecular weights and 30% CL did not affect the pure HPMC membrane and 7% CL. : 3 is influenced by the fractal dimension of the self-similar structure of the mixed membrane. Except for the 10:0E50 sample, there is no significant difference between the fractal dimensions of HPMC and 7:3 films at high temperature and their corresponding low temperature films. For the 10:0E50 sample at 85 °C, a linear region also exists, indicating the existence of a self-similar structure. but , ? If it is greater than 4, the fractal dimension cannot be used for analysis, but we can judge that the self-similar structure of this sample is more compact. In general, the addition of a small amount of HPMC and CL with different molecular weights and the drying temperature had no significant effect on the fractal structure of pure HPMC membranes and 7:3 membranes.

4. 3. 4. Cross-sectional morphology analysis

At 37 °C, pure HPMC membranes containing HPMC with different molecular weights showed cross-sections with different roughness. With the increase of HPMC molecular weight, the roughness of HPMC and 7:3 membranes increased gradually; Compared with the corresponding pure HPMC membranes, the 7:3 membranes with E50 HPMC have increased cross-sectional roughness, mainly due to phase separation. At 85 °C, pure HPMC membranes with different molecular weights showed different degrees of roughness in cross-section. With the increase of HPMC molecular weight, the section roughness of HPMC membranes first increased and then decreased. The section roughness of 7:3 membranes The roughness of the 7:3 membranes containing E6 and E50 HPMC was higher than that of the corresponding pure HPMC membranes, and the cross-sectional roughness of the 7:3 hybrid membranes containing E15 HPMC was lower than that of the pure HPMC membranes. The cross section of pure HPMC film containing E15 HPMC at high temperature is rougher than that at low temperature, while the cross section of pure HPMC film containing E6 and E50 HPMC at high temperature is smoother than that at low temperature; the 7:3 film containing E6 HPMC at high temperature The cross section of 7:3 film with E15 and E50 HPMC is rougher than that at low temperature, while the cross section of 7:3 film containing E15 and E50 HPMC is smoother at high temperature than at low temperature.

Both HPMC and CL membranes are polysaccharide-based materials and have similar peaks. The peaks near nSO-MGO cm-1 are attributed to the stretching vibration of CH and CH2 functional groups. The peak near 1 corresponds to the stretching vibration of CH3, the stretching vibration of C-O-C and C-0 is near 1050CHT1, and the peak near 1640CHT1 corresponds to free water. (H-0-H) stretching vibration, the absorption peak of hydroxyl stretching vibration is around 3400 cmH.

At 37 °C, the absorption peak of -0-H stretching vibration peak of pure HPMC film containing E6 is at 3440cnT1, and that of pure HPMC film containing E15 is at 3423 cnT1, the pure HPMC membrane with E50-O-H stretching vibration absorption peak shifts at 3415cnT1, which are all smaller than the corresponding CL peak 3275cnT1. With the increase of , the -O-H absorption peaks of pure HPMC membranes related to hydrogen bonds shifted red, indicating that the higher the molecular weight, the more hydrogen bonds were formed between the systems; The absorption peak of -H stretching vibration is located at 3390 cm-1, and the absorption peak of -O-H stretching vibration of 7:3 film containing E15 HPMC is located at 3382 cm-1, containing E The -O-H stretching vibration absorption peak of the 7:3 film of 50 HPMC is located at 3386 cm-1; with the increase of molecular weight, the -O-H bond of the 7:3 film first shifts to red and then to blue, indicating that mixing Compared with the pure HPMC membranes containing HPMC of the same molecular weight, the 7:3 membranes containing E6, E15 and E50 HPMCs were red-shifted, respectively. The wave numbers of 50, 41 and 29 indicate that the intermolecular hydrogen bond between E6 type HPMC and CL is the most, followed by E15, and the least in E50.

At 85 °C, with the increase of molecular weight, the absorption peaks related to hydrogen bonds of pure HPMC films first shifted red and then blue shifted, indicating that with the increase of molecular weight, hydrogen bonds between systems first increased and then decreased; With the increase of molecular weight, the -O-H peak of 7:3 membrane shifted blue, indicating that the hydrogen bond in the mixed membrane gradually decreased with the increase of molecular weight; The 7:3 films of 0 are red-shifted by 84, 76 and 54 wavenumbers, respectively, indicating that the intermolecular hydrogen bonds between E6 type HPMC and CL are the most, followed by E15, and the least E50.

Compared with the pure HPMC film containing E 6 , E 1 5 and the 7 : 3 film containing E 50 at high temperature and low temperature, the -O-H peaks related to hydrogen bonds did not migrate, indicating that the difference between the systems at high temperature and low temperature did not occur. The number of hydrogen bonds remained unchanged; the 7:3 film containing E6 and E15 HPMC had a red shift in the -0-H peak associated with hydrogen bonds at high temperature compared with low temperature, indicating that high temperature promoted the formation of more hydrogen. Compared with the low temperature, the -0-H peak associated with hydrogen bonds has a blue shift, indicating that the number of hydrogen bonds is reduced.

4. 3. 6 Light transmittance analysis

For all samples, the transmittance of the film increases first and then equilibrates with increasing wavelength. At 37 °C, different types of HPMC pure films showed similar equilibrium light transmittance, about 99%, indicating that the pure HPMC film has good light transmittance, and the light transmittance of pure CL film is about 96%. , the transmittance values of the two 7:3 films containing E6 and E15 HPMC were similar, and were between the pure HPMC and pure CL films, and the transmittance balance value was about 97%. , indicating that the light transmission properties of the two blend films are also very good. The transmittance of the E50 type 7:3 film at equilibrium is about 69%, which is lower than that of the E50 type pure HPMC film and pure CL film. Important factors affecting light transmittance are crystallinity, phase separation, pore structure, etc., because these structures can cause differences in refractive index. The reason for the reduced transmittance of the 7:3 film containing E50HPMC in this study may be due to its increased crystallinity and more obvious phase separation. Compared with the 7: 3 film of E 6 and E 15 HPMC, the cross-sectional morphology of this film is rougher than that of the 7 : 3 film containing E 6 and E 15 HPMC.

At 85 °C, the light transmittance of different kinds of HPMC pure films decreased slightly with the increase of HPMC molecular weight, which may be due to the fact that the crystallinity (crystalline area) of the films containing high molecular weight E50 was higher than that of E6 and E15. The pure membrane is large. However, the 7:3 films prepared with different kinds of HPMC have similar transmittance, and they are between HPMC and CL pure films.

Except for the 7:3 film containing E50 HPMC, the light transmittance of pure films containing different molecular weight HPMC and 7:3 film at high temperature is similar to the corresponding low temperature film. The transmittance at high temperature of the 7:3 film containing E50 HPMC is increased by nearly 30% compared with its corresponding low temperature film, mainly due to its reduced crystallinity and weakened phase separation (relatively smooth morphology).

4. 3. 7 Contact angle analysis

At 37°C, with the increase of the molecular weight of HPMC, the contact angle of pure HPMC membrane and 7:3 membrane first decreased and then increased. The contact angle of the pure membrane of 7:3 is low, which may be related to its small crystallization peak area. The change trend of the 7:3 membrane and the pure HPMC membrane with the molecular weight of HPMC is consistent, which may be because the continuous phase is HPMC. We know that the contact angle of the blend system is affected by its continuous. Compared with the HPMC/CL membrane, there is no significant difference between the pure HPMC membrane containing the same molecular weight HPMC and the HPMC/CL membrane, which may be mainly due to the continuous phase of HPMC 7:3 membranes with different molecular weights. Phases are HPMC. At 85 °C, the molecular weight of HPMC had no significant effect on the contact angles of HPMC and 7:3 films. There was no significant difference between pure HPMC membranes and 7:3 membranes containing HPMC with different molecular weights at 85 °C compared with the corresponding membranes at low temperature.

4.3. 8 Mechanical properties analysis

At 37 °C, with the increase of the molecular weight of HPMC, the tensile strength of HPMC pure film also increased, but there was no significant difference between the tensile strength of E15 and E50 type HPMC pure film. It is due to the high viscosity of high molecular weight HPMC, which can increase the adhesion between molecules and increase the tensile strength of the film [116], but there is no significant difference between E15 and E50. A larger value can increase the intermolecular adhesion and enhance the tensile properties, but because its cross-sectional morphology is rougher than that of the E15 HPMC film, the tensile properties can be reduced. With the increase of the molecular weight of HPMC, the tensile strength of HPMC/CL 7:3 membrane decreased, but the tensile strength of HPMC/CL membrane of E15 and E50 had no significant difference. The difference is mainly related to the increasing roughness of its cross-sectional morphology; the tensile strength of the 7:3 membranes containing HPMC with different molecular weights and their corresponding pure HPMC membranes are both lower, due to the blending of the two polymer components. , There are very few completely compatible systems, and a certain degree of phase separation generally occurs, and phase separation can lead to a decrease in tensile strength . At 85 °C, with the increase of the molecular weight of HPMC, the tensile strength of HPMC pure film decreased, but the tensile strength of E15 and E50 type HPMC pure film had no significant difference; The tensile strength of HPMC's 7:3 membrane is significantly higher than that of E6 and E50 type 7:3 membranes, which may be related to the relative smoothness of the cross section. Compared with the film, the tensile strength has no significant change, which may be due to the higher tensile strength of the CL film at high temperature, so the addition of 30% CL in the system can increase the tensile strength of the film, offsetting the phase separation. produced impact. The tensile strength of pure films containing E15 and E50 HPMC at high temperature was significantly lower than that of the corresponding low temperature films; the 7:3 films containing E15 and E50 HPMC at high temperature were significantly higher than the corresponding low temperature films. The high ＾ is mainly due to its relatively smooth section.

At 37 °C, there is no significant difference in the elongation at break of HPMC pure membrane; among the mixed membranes, the elongation at break of the 7:3 membrane of E50 type is the lowest, which may be related to the rougher fracture surface. Moreover, the elongation at break of the 7:3 membranes containing HPMC with different molecular weights was lower than that of the corresponding pure HPMC membranes, which may be due to the lower elongation at break of the CL membrane at low temperature, so the 30% C in the system The addition of L can reduce the elongation at break of the membrane. At 85 °C, there was no significant difference in elongation at break for all membranes. The elastic modulus data are shown in Figures 4-6c. At 37 °C, with the increase of the molecular weight of HPMC, the elastic modulus of HPMC pure film also increased, but the tensile strength of HPMC pure film of E15 and E50 type had no significant difference; 7 There was no significant difference in the elastic modulus of the : 3 membranes; and there was no significant difference in the elastic modulus between the 7 : 3 membranes containing HPMC with different molecular weights and their corresponding pure HPMC membranes. At 85 °C, the elastic modulus of HPMC pure membrane, 7:3 membrane and the elastic modulus of 7:3 membrane with different molecular weight HPMC and its corresponding pure HPMC membrane have no significant difference.

From the comprehensive mechanical properties analysis, the molecular weight of HPMC has different degrees of influence on the tensile length, elongation at break and elastic modulus of the film at 37 °C; The elongation at break and elastic modulus of the film have no significant effect on the tensile length of the film.

4. 3. 9 Analysis of water vapor transmission rate

At 37 °C, the WVP of the pure HPMC membrane containing E50 HPMC was significantly higher than that of the HPMC membrane containing E6; while the WVP of the 7:3 membrane first decreased and then decreased with the increase of the molecular weight of HPMC. The 7:3 membranes containing HPMC with different molecular weights have higher WVP than their corresponding pure HPMC membranes, which may be due to the compatibility between the two phases after adding CL to the system, but it also shows a certain degree of compatibility. Phase separation leads to an increase in WVP.

At 85 °C, with the increase of the molecular weight of HPMC, the pure membrane containing E6 HPMC was significantly lower than the pure membrane containing E15 HPMC; The WVP of the membranes was not significantly affected; the 7:3 membranes with E6 and E50 HPMC had higher WVP than their pure HPMC counterparts, mainly due to the higher WVP of E6 and E50 HPMC at this high temperature. The cross-sectional morphology of the : 3 film was rougher than that of the pure HPMC film, while the WVP of the 7 : 3 film containing E15 HPMC and its corresponding pure HPMC film had no significant difference.

The pure HPMC membranes with different molecular weights at high temperature have higher WVP values than their corresponding membranes at low temperature. There was no significant difference in WVP between 7:3 films containing E6 and E50 HPMC at high temperature and their corresponding films at low temperature, although the decrease in crystallinity of 7:3 containing E50 HPMC at high temperature resulted in an increase in WVP , but its morphology is smoother, which leads to weakened phase separation, which can reduce WVP, and the two effects are offset, resulting in the same WVP.

4. 3. 10 Water solubility analysis

At 37 °C, the molecular weight of HPMC did not affect the water solubility of pure HPMC membrane and 7:3 membrane; after adding CL, the water solubility of 7:3 membranes containing HPMC with different molecular weights was lower than that of the corresponding ones. Pure HPMC membrane. At 85 °C, the change of molecular weight and the addition of CL had no effect on the water solubility of HPMC and HPMC/CL membranes, which was the same as their effect on membranes at 37 °C. And there is no significant difference between pure HPMC membranes and 7:3 membranes containing HPMC with different molecular weights and their corresponding cryogenic membranes.

4. 4 Chapter Summary

In terms of structure: at 37°C, the molecular weight of HPMC does not affect the crystal form of HPMC, but the crystallization peak width and peak area of E15 are smaller than those of E6 and E50 films; The crystallization peak of the 7:3 film of E50 HPMC has a significant influence, so that the 7:3 film of E50 HPMC has a peak of 6°of the CL film; at 85 °C, with the increase of the molecular weight of HPMC, the The peak area of the material gradually increased; the peak area of the 7:3 blend membrane with E50 HPMC was larger than that of the 7:3 membrane with E6 and E15. Divide by 85. (Except for the 10:OE50 sample of : , at high temperature and low temperature, the addition of different HPMC molecular weights and 30% CL did not affect the self-similar structure fractal dimension of HPMC pure membrane and 7:3 mixed membrane. At 37 T, with the increase of the molecular weight of HPMC, the roughness of HPMC and 7:3 membranes increased gradually; After decreasing, the section roughness of the 7:3 membrane decreased gradually. At 37 °C, with the increase of molecular weight, the -0-H peak of the pure HPMC membrane shifted to red, and the formation of hydrogen bonds between the systems increased, 7:3 The -0-H bond of the membrane first shifted to red and then to blue, and the hydrogen bond in the mixed membrane first increased and then decreased. At 85 °C, with the increase of molecular weight, the -O-H peak of pure HPMC membrane first shifted to red and then decreased. Blue-shift, the hydrogen bonds between the systems first increased and then decreased. The -0-H peak of the 7:3 film was blue-shifted, and the hydrogen bonds in the mixed film gradually decreased with the increase of molecular weight.

In terms of performance: at 37°C, HPMC pure films with different molecular weights showed similar equilibrium transmittance, and the transmittance values of two 7:3 films containing E6 and E15 HPMC were higher than those of E50 type 7 : 3 transmittance of the film at equilibrium; at 85 °C, the transmittance of different types of HPMC pure films decreased slightly with the increase of the molecular weight of HPMC, and the 7: 3 films prepared with different types of HPMC had similar properties. of light transmittance. At 37 °C, with the increase of the molecular weight of HPMC, the contact angle of pure HPMC membrane and 7:3 membrane first decreased and then increased; at 85 °C, the contact angle of HPMC molecular weight with HPMC and 7:3 membrane angle had no significant effect. At 37 °C, the molecular weight of HPMC had different effects on the tensile length, elongation at break and elastic modulus of the membrane; at 85 °C, the molecular weight of HPMC had a significant effect on the tensile length of the membrane. However, there was no significant effect on the elongation at break and elastic modulus of the membrane. 37°C, the WVP of pure HPMC membrane containing E50 HPMC was significantly higher than that of HPMC containing E6, while the WVP of 7:3 membrane first decreased and then increased with the increase of HPMC molecular weight; With the increase of HPMC molecular weight, the WVP of the pure membrane containing E6 HPMC was significantly lower than that of the pure membrane containing E15 HPMC, and the molecular weight of HPMC had no significant effect on the WVP of the 7:3 membrane. Whether it is high temperature or low temperature, the size of HPMC molecular weight will not affect the water solubility of HPMC pure membrane and 7:3 membrane.

Epilogue

1. Conclusion

In this study, a HPMC/CL-thermal-thermal blended gel system was established, and the effects of processing factors on the rheology, structure and physical properties of the HPMC/CL blended system were investigated. Oil resistance and water retention in deep-fried battered products. The main conclusions are as follows:

(1) The establishment of HPMC/CL thermal-thermal blended gel system and the study of its rheological properties provide a certain methodology and theoretical reference for other thermal-thermal blended gels. At 82 °C, the viscosity, modulus, gel strength and compactness of the gel network of the HP MC/CL blends were significantly higher than those of the gel network at lower temperature, which contributed to its thickening in hot beverages. It provides a certain theoretical guidance for the application of agent, bakery product skeleton, fried food pre-coating water-retaining agent and so on.

(2) Both the blending ratio and the drying temperature will have a certain influence on the intermolecular interaction, crystal structure and morphological structure of the film, but the effect on the fractal structure is not significant. Regardless of the low temperature and high temperature, the transmittance decreases with the increase of CL content; except for HPMC, the transmittance of other films at high temperature is higher than that at low temperature. The contact angle of the CL film is significantly higher than that of HPMC. When the CL content is not more than 30%, the contact angle of the sample is similar to that of HPMC; when it is not less than 50%, the contact angle of the sample is similar to that of CL. The oxygen permeability of the blend films decreased with the increase of CL content . At 37 °C drying temperature, the WVP of HPMC/CL hybrid membrane and CL membrane had no significant difference, and was slightly higher than that of pure HPMC membrane; the membrane prepared at 85 °C was higher than 37 °C. The WVP value of the membrane material is high. Compared with other blend films, the tensile strength and elongation at break of the 7:3 blend films are better. With the increase of CL content, the water solubility of HPMC/CL films decreased significantly. The addition of HP MC/CL7:3 samples to the batter can significantly increase the moisture content in the inner core of fried battered chicken breast, and significantly reduce the oil in the meat core, without affecting the moisture and oil content in the outer shell. Healthier and more tender battered fried meat products can be obtained without compromising the crispy texture of such fried products.

(3) At high temperature and low temperature, HPMC with different molecular weights affects the crystal structure of pure HPMC membrane and 7:3 membrane. Except for the 10:0E50 sample at 85 °C, the addition of different HPMC molecular weights and 30% CL did not show the self-similarity of HPMC pure membrane and 7:3 mixed membrane at high and low temperature. Structural fractal dimension. At 37 °C, with the increase of the molecular weight of HPMC, the roughness of the HPMC and 7:3 membranes increased gradually; at 85 °C, with the increase of the molecular weight of HPMC, the section roughness of the HPMC membrane decreased, and the section roughness of the 7:3 membrane material gradually decreased. At 37°C, with the increase of molecular weight, the hydrogen bonds formed between pure HPMC membrane systems increased, and the hydrogen bonds in 7:3 membranes increased first and then decreased; at 85°C, with the increase of molecular weight, pure HPMC membranes The hydrogen bonds between the systems first increased and then decreased, and the hydrogen bonds in the 7:3 film gradually decreased with the increase of molecular weight. HPMC with different molecular weights had no significant effect on the light transmittance of pure HPMC film at 37 °C and 7:3 film at 85 °C, but had no significant effect on the transmittance of 7:3 film at 37 °C and 8.5 °C. The pure HPMC membrane of C has a certain influence. At 37 °C, with the increase of the molecular weight of HPMC, the contact angle of pure HPMC membrane and 7:3 membrane first decreased and then increased; at 85 °C, the contact angle of HPMC molecular weight with HPMC and 7:3 membrane angle had no significant effect. At 37 °C, the molecular weight of HPMC has different effects on the tensile strength, elongation at break and elastic modulus of the membrane; at 85 °C, the molecular weight of HPMC has a significant effect on the tensile strength of the membrane. 9 HPMC with different molecular weights has a certain influence on the WVP of HPMC at 37 °C, 7:3 membrane and HPMC at 85 °C. , had no significant effect on the 7:3 membrane at 85 °C. The size of HPMC molecular weight will not affect the water solubility of HPMC pure membrane and 7:3 membrane.

2. Innovation

A new type of thermal-thermal gel blend system-HPMC/CL system was established, and the effects of processing factors on the rheology of the blend system and the microstructure and physical properties of the blend membrane were systematically studied.

3. Outlook

In this paper, a thermal-thermal gel blend system-HPMC/CL system was established, and the influence of processing factors on the rheology, structure and physical properties of the HPMC/CL blend system was studied. The following research can be carried out in the future. :

(1) The oxygen barrier properties and hydrophobicity of HPMC/CL films are improved to a certain extent compared with HPMC films, which can broaden the application range of HPMC/CL blend films. The protective effect of foods with multiple antioxidants.

(2) Antioxidant and antibacterial functional substances can be added to HPMC/CL film to prepare functional edible film material or packaging to further improve its protective effect on food.