Effects Of Vacuum Impregnation With Fish Gelatin Coating On Chilled Tilapia Fillets

Oreochromis Niloticus is not only easy for consumption, but also easy for processing.The yield, processing capacity and the amount of exports of tilapia increase year after year in China. The main form of tilapia processing is basically processed into fillets. However, some undesirable modifications still occur in cold storage including protein degradation, drip loss and lipid oxidation. Therefore, how to extend the shelf life of the fillets attracts more and more researchers’ attention. The effect is better with the aid of vacuum impregnation(VI) for it can make gelatin solution penetrating into fillets more evenly and quickly. Fish gelatin comes from the byproduct of the fish processing and it is a natural, non-toxic food material.Fillets samples were coated with fish gelatin solutions(180 bloom) at 3 concentrations(0%,3%, 5%) containing 10 g glycerol and their effects on fillets stored at 4°C and-18°C,respectively were investigated. A vacuum pressure of 0.02 MPa was applied at room temperature for 10 min, and the system was then restored to atmospheric pressure for 15 min.Physical properties(yield, drip loss, texture profile analysis(TPA) and sensory quality),biochemical properties(microbiological indexes, ɑ-glycosidase enzymes, pH, thiobarbituric acidreactive substances(TBARS), peroxide value(POV) of reactants and the fatty acid composition) and structural characterisation of proteins were studied during cold/freezing storage in order to reveal the effect of fish gelatin on storing fillets.First, we studied the influences of gelatin on the yield of fish. The results showed that the gelatin solution improved the yield of tilapia fillets significantly. The yield of 3% gelatin treated fillet was 101.8% while the drip loss of the same group was 2.4%. The drip loss of the control was 4.4% and the drip loss of 5% gelatin treatment was 3.0% during 4oC storage for 7days. And the drip loss of 3% gelatin treated group was 4.1%. For frozen storage, the drip loss of the control was 6.6% while it was 5.3% for 5% gelatin treated group after 180 days of storage. At the end of the storage time, the changes of drip loss and TPA of 3% treated group were smaller than the other two groups, significantly. Furthermore, there was no significant difference of sensory analysis among the three treatment groups during the storage.At the end of the cold storage, psychrotrophic bacterial count of the control, 3% gelatin treatment and 5% gelatin treatment groups were 5.8%, 6.1% and 6.0%, respectively. There was no significant difference among the three groups. For frozen storage, at the end of thestorage, psychrotrophic bacterial count of the control, 3% gelatin treatment and 5% gelatin treatment groups were 7.5%, 6.1% and 7.1%, respectively. Psychrotrophic bacterial count of3% gelatin treatment group was obviously lower than the other two groups, and it was within an acceptable level(< 7.0 logCFU/g). The changes of ɑ-glycosidase enzymes, pH, TBARS,POV of reactants and the fatty acid composition of gelatin treatment were less than those of the control group. It indicates that gelatin inhibited the changes of physical and biochemical properties of fillets during cold/frozen storage. The reasons attributed to these two aspects include two aspects. On the one hand, gelatin solution enterred into the fillets and filled in the cell of fillets after vacuum impregnation, reducing the damage of low temperature on the fillets; On the other hand, coating with gelatin solutions inhibited the contact of oxygen with aerobic microorganisms.To further investigate the effects of gelatin on protein denaturation and degradation of fillets during storage, the structural changes of protein, the degradation and variation of the subunits were studied via fourier transform infrared spectroscopy(FTIR) and sodium dodecylsulfate polyacrylamide gel electrophoresis(SDS-PAGE). The results revealed that the structure of protein of gelatin treated protein was an important part of fish. The denaturation of protein had a direct effect on the drip loss, TPA, sensory quality of fillets. And the degradation of protein was closely related to the growth of microorganism and enzyme activity. The results indicate that vaccum impregnation with gelatin solution is effective in maintaining quality attributes of fish fillets during cold/frozen storage.