Study On Collagen Extracted From The Tilapia Fish Skin By Fermentation Method And Its Electrospun Film Fabrication And Application

The tilapia fish production high in China,and the export of tilapia filles is large.However,it is easy to produce a large amount of fish skins during produce fish filles,in which collagen(Col)is abundant,which have high utilization value.Chemical method,a traditional fish skin pretreatment method,have positive effect for removal of impurity protein and fat in tilapia fish but also with some problems such as time consuming,solvent consuming,reagent residue,and environmentally hazardous.Therefore,it is of great significance for collagen production industry to develop new,environment-friendly,and safe pretreatment method.In this study,firstly,it is investigated to the effect of fermentation method on the removal non-collagenous proteins and collagen properties,in order to explore the feasibility of fermentation method as fish skin pretreatment approach.Secondly,collagen electrospun films were prepared by electrospinning to solve the problems of its poor hydrophobicity and thermal stability,and weakly antioxidant and antibacterial property by the way of addition zein(ZN)and gallic acid(GA).Finally,it was surveyed to the preservation properties of collagen/zein/gallic acid(Col/ZN/GA)electrospun film on the tilapia fish meat.The main research results are as follow:(1)Study on technology of removing non-collagen proteins from tilapia fish by fermentation method.There are about 14.19%impurity proteins in dry tilapia fish skin.The number of non-collagenous proteins removed was 81.35%(g/g dry skin)and the number of losing of hydroxyproline in the fish skin was 0.89(mg/g dry skin),when the inoculum size was 12%(v/v),solid-liquid ratio was 1:20(g/m L),and fermentation time was 12 h.(2)Effect of fermentation(F)method on the structure and physical properties of collagen.Chemical method(C)as contrast,characterization and comparison of structure and physical properties of the four collagens extracted from tilapia fish by acid extraction and enzymes extraction method,respectively.The four extractions were identified as type I collagen,as confirmed through amino acid composition;compared with pepsin soluble collagen(PSC),fermentation method has a greater impact on the amino acid content of acid soluble collagen(ASC).SDS-PAGE and ultraviolet(UV)absorption spectra indicated the four collagens have high purity.Fourier transform infrared(FTIR)spectroscopy and circular dichroic(CD)spectrum revealing that the four collagens possess complete triple helix structure.The results indicated that fermentation-acid soluble collagen(FASC)and fermentation-pepsin soluble collagen(FPSC)yields(4.76 and 8.14 wt%,respectively)were slightly higher than chemical-acid soluble collagen(CASC)and chemical-pepsin soluble collagen(CPSC)yields(4.27 and 7.60 wt%,respectively),suggesting that fermentation method can promote the collagen extraction.The denaturation temperature(T_d)of FASC,FPSC,CASC,and CPSC is around 37?;all collagens had good solubility at p H 1–4 and Na Cl concentration?3%(w/v).Compared with chemical method,the microstructure of collagens extracted from tilapia fish pretreated by fermentation method present more loose and porous structures.(3)Study on technology of fabricating collagen/zein electrospun film and the effect of zein on collagen electrospun film properties.Using FASC and ZN as raw material,the Col/ZN electrospun film was prepared by electrospinning.The results indicated that Col/ZN electrospun film was in good condition,such as the diameter of nanometer fiber distributed evenly,smooth fiber surface,and without bead,when the ratio of 60%(v/v)acetic acid solution and absolute ethanol was 2.33%(v/v),the concentration of the total protein(collagen and zein)was 28%(w/v),the voltage was12 k V,the rate of pushing column speed was 0.06 mm/min,and the receiving distance was 12 cm.The scanning electron microscopy(SEM)results showed that the diameter of Col/ZN electrospun films was significantly increased from 209.71 nm to312.14 nm with the increasing zein ratio.Col and ZN interaction and form the hydrogen bonds;when the weight ratio of Col and ZN was 4:6 and 5:5,the molecular interaction between Col and ZN was stronger.The addition of ZN enhanced hydrophobic and thermal properties and promote the form of ordered structure and?-helix crystal structure of Col/ZN electrospun film.When the weight ratio of Col and ZN was 4:6,Col/ZN electrospun film fiber surface is smooth and its diameter is evenly distributed,and have good thermal stability and hydrophobic properties.(4)The effect of gallic acid content on structure,properties,and preservation ability of collagen/zein electrospun films.Using FASC,ZN,and GA as raw material,the Col/ZN/GA electrospun films with different GA concentration were prepared by electrospinning,GA uniformly distributed and incorporated in the system composed with ZN and Col and increased fiber diameter of Col/ZN electrospun film.The interaction force between GA and proteins is strong and the new chemical bonds was formed.GA decreased the hydrophobic properties,destroyed the crystal structure,but significantly(P<0.05)increased the antioxidant properties of Col/ZN/GA electrospun film.When the addition of GA was 8%(w/w),Col/ZN/GA electrospun film morphology,the structure stability,hydrophobic,and antioxidant properties were good,and it can prolong the shelf life of tilapia fish meat for at least two days.This study proved that fermentation method is a viable pretreatment method,solved the problems of poor hydrophobic property,poor thermal stability,and weak antibacterial and antioxidant properties of collagen electrospun film,and confirmed that collagen/zein/gallic acid electrospun film have potential as active food packaging material.Therefore,this study not only provided new ideas for the pretreatment of collagen raw materials,but also broaden the application scope of collagen in food packaging field.