| The application of biodegradable packaging materials to replace petroleum-based plastics in food packaging has become a research hotspot today.Bio-based films have great application prospects in food packaging due to their special biological activity and sustainability,but most bio-based films have great application prospects in food packaging.Both have high hydrophilicity and weak mechanical properties,which limit the application of bio-based films.How to improve the hydrophobicity and mechanical properties of such packaging films and improve their applicability has become the focus of research.Based on the team’s previous research on the properties of protein-based films,this paper continued to use whey protein isolate,sodium caseinate and pullulan as film-forming substrates,and glycerol as plasticizer to prepare protein-polysaccharide composite films.At the same time,the composite film was heated to promote the Maillard cross-linking reaction,and the physical and chemical changes of the film during the Maillard reaction and its effect on properties were studied.At the same time,composite film and kraft paper were combined,and the technology of composite material and its application in beef preservation were studied.The main contents are as follows:1.The effect of Maillard crosslinking with different heat treatment time on the properties of WPI-Na Cas-PUL composite films.The WPI-Na Cas-PUL composite films were subjected to Maillard cross-linking reaction at 95℃ with different heat treatment times of 0,4,8,12,16,20 and 24 h.The changes of chromaticity,browning index,FTIR,SDS-PAGE and amino acid content of composite films after Maillard cross-linking reaction with different heat treatment time were studied.The results showed that the thin film changed from light yellow to dark brown,and the b*value and browning index of the thin film increased significantly with the prolongation of heat treatment time.In the infrared spectrum analysis,the bands in the amide I region and the amide II region of the protein shifted,and the two bands in the carbohydrate region gradually merged into one,indicating the denaturation of the protein and the consumption of sugar.Decreased protein band intensity in the SDS-PAGE and amino acid content also verified protein consumption.This indicates that the amino group of WPI-Na Cas undergoes condensation reaction with the carbonyl group of PUL,and with the prolongation of heat treatment time,the degree of Maillard reaction becomes more and more intense,and more and more Maillard reaction products are produced.At the same time,the changes of UV resistance,thermal properties,solubility,hydrophobicity,barrier properties,mechanical properties,antioxidant properties and microscopic morphology of Maillard crosslinked films were observed under different heat treatment time.The results showed that with the increase of heat treatment time,the UV-visible light absorption capacity of the film increased significantly,the glass transition temperature（Tg）increased to 162.48℃,the water content decreased by22.45%,the water solubility decreased by 56.38%,the water vapor transmission coefficient（WVP）and oxygen permeability decreased significantly,the WVP decreased to 5.72×10-12g·cm/cm2·s·Pa,and the oxygen transmission rate decreased by 34.25%.Mechanical strength increases.At the same time,the film obtained antioxidant activity,the DPPH free radical scavenging activity reached 81.25%,and the reducing ability increased by 237%,and the total antioxidant activity reached256.2μmol/mL equivalent ofα-tocopherol.The microscopic morphology of the film cross-section shows that the film is densely cross-linked and a large amount of polymer is produced,which is related to the Maillard cross-linking reaction and its products.2.In this study,whey protein isolate-sodium caseinate-pullulan composite colloid was compounded with kraft paper to prepare high-barrier biodegradable food packaging materials in order to develop alternatives to plastic-coated paper.Taking the oxygen transmission rate of the product as the objective function,the influence of factors such as the volume ratio of the film-forming composite solution,the pH value,and the amount of glycerin added was analyzed,and the process was optimized by orthogonal experiments with three factors and three levels.The results show that when the volume ratio of whey protein isolate-sodium caseinate to pullulan is 1:2,the pH value is 9,and the glycerin content is 60%,the oxygen barrier performance of the composite coated paper is the best.The transmittance is as low as 3.824cm3/m2·24h·0.1MPa.In addition,its water vapor transmission coefficient is9.241×10-12 g·cm/cm2·s·Pa,and the water contact angle and oil contact angle are69.9°,48.4°,the transverse/longitudinal tensile strength is 13.894 MPa/24.731 MPa,the transverse/longitudinal elongation at break is 8.2%/6.6%,and its performance can meet the actual packaging application requirements.3.Application of high oxygen-barrier protein-polysaccharide-kraft paper base-edible film composite material in beef preservation.In this study,fresh beef was packaged with high oxygen-barrier protein-polysaccharide-kraft paper-based-edible film composite material,and compared with commercially available PE films and cooking bags.The changes of pH,color,NMR,texture,TVB-N content,TBARS value,ferromyoglobin content and total number of colonies were studied to study the application effect of composite materials in beef preservation.The results show that,compared with PE film,the composite material can better maintain the sensory,color,pH and water holding capacity of fresh beef,improve beef quality,enhance meat-like taste,and inhibit beef TVB-N content,TBARS value and high iron muscle.The increase of hemoglobin content also has a certain inhibitory effect on the total number of colonies.Although its preservation effect is slightly lower than that of cooking bags,it has great application prospects in food preservation. |
PDF Full Text Request