Improvement And Application Study Of Fresh-water Fish Surimi Edible Films

China is one of the major freshwater fish farming countries with the increasing production of freshwater fish year by year.However,the commercial value of freshwater fish is not utilized sufficiently,partly because of the unitary fresh sales in the market and the lack of new production introduction.Therefore,to exploit new products with of the freshwater fish source and improve its added value,edible films were successfully prepared from fish muscle and fish skin,and the improvement of the properties of films were also investigated.In Chapter 2,edible films were prepared from silver carp surimi and the effects of TGase on the properties of surimi films were evaluated.The results showed that the tensile strength(TS)of films increased markedly with increasing TGase content,but decreased slightly with a further increase of the content of TGase.The highest TS value(8.3 MPa)was obtained when the content of TGase was 2.5 %(w/w).The film water solubility(FWS)and soluble protein(SP)of surimi films were 42.41 % and 34.60 %,repectively,and both of them decreased significantly when TGase was added.According to the result of SDS-PAGE analysis,it was suggested that TGase promoted the crosslinking between myosin heavy chains(MHC)of surimi.The effect of ?-PL content on the properties of surimi edible films was investigated in Chapter 3.The mechanical properties of surimi films could be improved by adding ?-PL at the concentration of 0.15 % in surimi film-forming solutions,while slightly declined with the additon of ?-PL of higher concentration.It was of interest to concern that surimi films containing?-PL revealed a wide range of antimicrobial activity,especially effective at preventing the growth against of gram-positive bacteria.For preservation of fresh fish meats with the external packing help of edible films,the increase of total viable counts and total volatile basic nitrogen values was suppressed during storage at 4 ?.In the next section of Chapter 4,the effects of gelatin extraction time and adding glutaraldehyde on the properties of gelatin films prepared from fish skin were investigated.TS of films increased with increasing gelatin extration time during the initial 1.0 h,and reached a higheat value(69.78 MPa)when extracted for 1.0 h,while a gradual decrease of TS was observed with the further increase of extraction time.On the other hand,the TS,elongation at break(EAB),water vapor permeability(WVP)and FWS of gelatin films decreased whenglutaraldehyde was incorporated into the film-forming solutions at 1 to 4 %(w/w)of protein.The SDS-PAGE analysis showed that the cross-linking reaction induced by glutaraldehyde mainly involved the high molecular weight polymers of gelatin.Then in Chapter 5,composite films were prepared from surimi and gelatin with different ratio.The TS,FWS and SP of composite films increased with the increasing proportion of gelatin,while EAB decreased.The TS of neutral films with the same ratio of surimi and gelatin were the lowest,while increased at acidic or alkaline conditions.The effects of cross-linking with glutaraldehyde and transglutaminase on the properties of surimi-gelatin composite films was evaluated in Chapter 6.When glutaraldehyde concentration was adjusted to 0.025-0.1 % of protein,the TS of films was not significantly influenced,while the EAB increased gradually with adding glutaraldehyde.When glutaraldehyde concentration was further increased to 0.2 %,both TS and EAB were decreased.Conversely,TS and EAB of films gradually increased with increasing TGase concentration.The addition of glutaraldehyde and TGase in the composite films could both promote cross-linking within protein film network,resulting in the decrease of FWS and SP of films.However,the FWS and SP of films modified by glutaraldehyde decreased faster than those of films modified by TGase.Furthermore,the yellowness of films containing glutaraldehyde was increased,while the addition of TGase did not affect the color of films but improved the film transparency.Whether the films contained glutaraldehyde or TGase,the polymerization of protein in surimi-gelatin composite films was found by SDS-PAGE analysis.The FTIR data revealed that hydrogen bonds in the films were weakened by adding TGase,but they were strengthened following in the initial gradual weakness when glutaraldehyde was added.In conclution,colorless and transparent edible films with certain mechanical strenghth could be prepared using fresh-water surimi protein,TS of surimi films could be improved by incorporating of TGase or ?-PL,and antimicrobial packaging materials could be obtained simultaneously after adding ?-PL.The TS of surimi films could be improved after adding gelatin which exhibited excellent film-forming properties.Furthermore,the FWS and SP of surimi-gelatin composite films reduced significantly after adding TGase or glutaraldehyde.Gelatin films could be obtained using casting method on steel belt cast machine,but the process remains to be further optimized.