Preparation And Physicochemical Properties Of Fish Gelatin Antibacterial Composite Film And Evaluation Of Its Fresh-keeping Property On Strawberry

Therefore,in this study,fish gelatin was used as the main film-forming substrate and the combined modification of chitosan and glutamine transaminase(TGase)was used to improve the water solubility of pure fish gelatin film.Through the single factor test and response surface test,the optimal dosage ratio among fish gelatin,chitosan and TGase can be obtained.Then under the optimal film-making process conditions,TiO₂-Ag with different concentrations were further added to enhance the antibacterial properties of the composite films,and then to study the effect on the physical-chemical properties and microstructure of the fish gelatin composite films.The optimal TiO₂-Ag concentration will be determined through comprehensive comparison.Finally,the fish gelatin/chitosan/TiO₂-Ag(FG/Ch/TiO₂-Ag)composite films were prepared under the optimum TiO₂-Ag concentration.Then the strawberry preservation test was carried out in conjunction with low temperature to study the ability to preserve strawberries of FG/Ch/TiO₂-Ag composite films.The main conclusions obtained through research are as follows:(1)Taking the water solubility of the film as an indicator,the single factor test results showed that when the dosage of fish gelatin,chitosan and TGase were 2%,1.25%and0.03%,the film had the lowest water solubility of 33.5%,28.7%and 33.5%,respectively.The results of the response surface indicated that the optimal film-making process conditions are 2.33%(7 g)fish gelatin,1%(3 g)chitosan,and 0.04%(0.12 g)TGase.Under this condition,the film water solubility had a minimum value of 21.1%.(2)TiO₂-Ag had a certain improvement on the physical and chemical properties of the film.When the concentration of TiO₂-Ag was high(0.4%,0.5%),the optimal water vapor permeability(WVP)was 2.63×10^-12g·cm/cm²·s·Pa,oxygen permeability coefficient(OP)was 4.928×10^-14cm³·mm/(m²·24 h·0.1 MPa),the elongation at break(EAB)was72.71%,the size of the inhibition zone for E.coli,Staphylococcus aureus and Botrytis cinerea was 20.06,22.86 and 23.72 mm,respectively.When the concentration of TiO₂-Ag was low(0.1%),the TS and transmittance of the film were 17.39 MPa and 79.6%,respectively.The addition of TiO₂-Ag will not change the film thickness but reduce the film's water solubility.The results of SEM showed the agglomeration of TiO₂-Ag on the surface of the film and the closure of the small channels inside the film.XRD,XPS,and ATR-FTIR results showed that the presence of TiO₂-Ag crystals in the film could enhance the interaction between the components.(3)FG/Ch/TiO₂-Ag composite film showed a certain fresh-keeping ability for strawberries.At the 10th day of freshness testing,with a treatment of FG/Ch/TiO₂-Ag composite film packaging,the spoilage of strawberry was 70%,the weight loss rate of strawberry was 8.53%,fruit hardness of strawberry was 3.42 kg/cm²,and the a*value of strawberry decreased by 31%,which shows that the FG/Ch/TiO₂-Ag composite film has the best preservation effect.In terms of maintaining the total phenol,soluble solids,and vitamin C content of strawberries,the FG/Ch/TiO₂-Ag composite film showed a gentler downward trend.However,FG/Ch/TiO₂-Ag may adversely affect the production of nutrients during the post-ripening stage of strawberries.