Abstract: Changes in the physicochemical properties of muscle proteins are among the leading causes of quality deterioration during the storage of freshwater fish. The effect of preservative treatment on changes in the physicochemical properties of muscle proteins from freshwater fish is not yet well understood nowadays. Therefore, in this study, two groups of grass carp fillets treated separately with a natural preservative combination of 10 mg/mL chitosan + 5 mg/mL tea polyphenol + 2 000 U/mL lysozyme and sterile water (control group) were analyzed and compared for changes in total volatile basic nitrogen (total volatile basic nitrogen (TVB-N) content, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) pattern, molecular mass distribution, active sulfhydryl group content and surface hydrophobicity, with the aim of evaluating the effectiveness of the mixed preservative for preventing changes in fish muscle proteins. The results showed that the preservative treatment group exhibited lesser changes in any of the protein properties than did the control group, especially from Day 6 to 9 of cold storage. The preservative treatment prevented the increase in TVB-N content and the decrease in active sulfhydryl group content as well as the change in surface hydrophobicity, indicating reduced protein breakdown, oxidation and denaturation. The slower change in SDS-PAGE and size exclusion-high-performance liquid chromatography profiles provided further evidence supporting the role of the preservative treatment in inhibiting protein degradation and structural change. These results provided evidence that the mixed preservative can stabilize the structure and properties of grass fish muscle proteins to a certain extent and consequently prevent quality deterioration.

Key words: grass carp, chitosan, muscle protein, preservative treatment