Study On Preparation And Application Of Edible Fresh-keeping Films Based On Chitosan And Alginate

Nowadays, people’s life in China is greatly troubled by hazy weather and food safetyissues. With higher awareness of environmental protection and the requirement forsafety of food fresh-keeping films, it has become a focus of research to preparebiodegradable or eatable fresh-keeping films using natural polymers. However, thesefilms were found to be poorly waterproof, which significantly contributed to the waterloss of food during storage and greatly hindered its application in food packaging.In this study, by physical blending modification, a kind of edible fresh-keeping filmwas prepared based on chitosan and alginate. The influence of each ingredient on thefunctions of films was investigated. The properties of the composite films werestudied as well. In addition, the applications of composite films to package andpreserve chilled pork were evaluated. The results are as follows:1. The composite films were prepared with chitosan and alginate, using glycerin asplasticizer. The effects of different lipids and emulsifiers on properties especiallywater resistance of the composite films were investigated. Optimum preparation ofcomposite films was determined by single factor and response surface analysis.Meanwhile, clove oil was added into the composite film, and its effect on thecomposite film was evaluated. The results showed that the decreasing order of fivelipids, in terms of the water vapor barriers is beeswax, stearic acid, palmitic acid,lauric acid, oleic acid. Span40has been proved to have excellent emulsifying effect onbeeswax among the four selected emulsifiers. The composite films had the optimalproperties under chitosan concentration1.42%, alginate concentration1.5%, glycerolcontent0.2%beeswax content0.39%and Span40content0.22%. The composite filmhad perfect properties with a water vapor permeation (WVP) of0.33×10-10g/Pa·s·m,tensile strength of25.23MPa, elongation at break of29.36%. Optimization of the composite film resulted in a78%decrease in WVP. Clove oil increased waterresistance of the film, while decreased the light transmittance.2. Infrared spectrum (FT-IR), scanning electron microscopy (SEM) and differentialscanning calorimetry (DSC) were used to characterize the microscopic structure andanalyze thermal stability of the composite films. The results showed that beeswaxuniformly fulfilled the surface and mesh structure of chitosan layer, creating a smoothand dense composite film without bubbles and cavities. There were strong interactionsamong the molecules of components, creating new chemical bonds to form a stablemesh structure. The boundaries of different layers were not obvious. All thosechanges ensured the thermal stability, mechanical stability and excellent hydrophobicproperties of composite films.3. Chitosan-alginate films were used as pallet coating during chilled pork storage toexplore its possibility as alternative to traditional plastic wraps. In terms ofappearance quality, the composite films were colorless and transparent, and had goodmechanical strength. Moreover, water vapor was not identified to condense on thesurface of the composite films at low temperatures, which indicated good anti-mistproperties. As for the physical and chemical indicators, it was shown that B/C/A filmand C/C/A film could effectively restrain TVB-N and the total number of microbecolonies compared with C/A film and PE film, maintaining a low weight loss of pork.Based on the indexes being synthesized, product shelf life using B/C/A film andC/C/A film were prolonged for1-2more days compared with the PE control film,Composite films prepared in this study were identified to be of high mechanicalperformance, non-toxic, bacteriostatic, water-resistant, and biodegradable, It isexpected to be widespread used as an alternative to traditional plastic wrap and couldbe beneficial to economic, society and food safety.