Preparation,properties And Application Of Fish Skin Gelatin-Sodium Alginate Composite Films

Fish gelatin is a partial hydrolyzate of collagen,which is inexpensive,rich in source and has good film-forming properties.Therefore,more and more researchers have turned their attention to the development of edible gelatin film.Edible packaging film refers to the natural macromolecules as raw materials,which through the interaction between different polymers to form thin film.It can naturally degrade and thus will not cause environmental pollution.In this paper,tilapia skin gelatin and sodium alginate was employed as the main raw material,together with the crosslinking agent,plasticizer,hydrophobic agent and other substances to prepare gelatin-alginate composite membrane.The main results of this thesis are as follows:Three kinds of gelatin samples were obtained from tilapia skin with hydrochloric acid,sodium hydroxide and pepsin,respectively.Their protein content was all over 87%.The gel strength of acid,alkali and pepsin gelatin were 325.38 g,287.26 g and 170.87 g,respectively.The gelling points of these three gelatin were 15.05 ?,15.96 ? and16.83?,respectively.The melting points of them were 25.17?,26.24? and 27.23?,respectively.The thermal denaturation temperatures of three gelatin were 109.88 ?,81.60? and 76.36?,respectively.SDS-Gel electrophoresis showed that these three kinds of gelatin contained ?,?1 and ?2 bands.Acid and alkali gelatin kept relatively complete bands.Amino acid analysis indicated that glycine was the main amino acid in the gelatin and the content of imino acid was also high.UV spectrum showed that the maximum absorption peak of the three gelatin were all at 218 nm,Infrared spectrum of the three gelatins showed the corresponding absorption peaks of amide A,amide B,amide I,amide II and amide III.The wave number of absorption showed different degrees of deviation due to different treatment methods.Acid gelatin and sodium alginate was used as film-forming materials,and a series of gelatin-sodium alginate composite membranes were prepared with different proportions of the two matrix.Their structures and properties were studied,such as Fourier transform infrared spectroscopy(FTIR),X-ray diffraction Analysis,scanning electron microscopy analysis,thermal stability analysis and so on.The results showed that the two film-forming matrix had good compatibility.With the increase of sodium alginate,the film tensile strength and elongation at break appeard the maximum value.Combined with various properties,it was found that when the ratio of gelatin and sodium alginate in the composite membrane is 60:40(w/w),the performance of the compositemembrane was better.In order to improve the mechanical properties and barrier properties of the gelatin-alginate composite membrane,hydrophilic and hydrophobic modifiers were used respectively to modify them.Glycerol and PEG 400 were used as hydrophilic modifiers.The effects of different plasticizers on the mechanical properties,hygroscopicity,water solubility,thermal stability and crystallinity of gelatin-sodium alginate composite films were studied.According to various properties,it was considered that glycerin could be used as the plasticizing matrix with the content of 6%in gelatin-sodium alginate composite film.Using stearic acid as hydrophobic modifier,the film-forming process of gelatin-sodium alginate-stearic acid composite film was optimized.Addition of stearic acid improves the water resistance of the composite membrane.The optimal technological conditions were as follows: sodium alginate2.23%,glycerin 4.36% and stearic acid 1.37%.Finally,the composite film obtained tensile strength of 7.34 Mpa,water vapor permeability of 1.08 g.mm.m-2.h-1.Kpa-1.Finally,the composite film was used to the coating preservation of chilled porke meat.as fresh meat coating.The results showed that both the bacteriostatic agent group(sodium diacetate)and the coating group had longer shelf life of chilled pork meat than the control group.The bacteriostatic membrane group had the most obvious effects on chilled meat,and made the shelf life of chilled meat prolong two times compared with the control group.