Physicochemical changes of myosin and gelling properties of washed tilapia mince as influenced by oxidative stress and microbial transglutaminase.

Physicochemical properties of myosin from tilapia subjected to oxidation via Fenton's reaction using H2O2 (0, 0.05, 0.1, 1 and 5 mM) were determined. With increasing H2O2 concentrations and times (from 0 to 12 h), sulfhydryl group content and Ca(2+)-ATPase activity decreased, while carbonyl content and surface hydrophobicity increased to a higher extent. After being subjected to oxidation, cross-linking via disulfide bond along with increased storage modulus (G´) was observed. Microbial transglutaminase (MTGase) induced polymerization of myosin in both non-oxidized and oxidized forms and increased gel G´. Gel properties of washed mince and oxidized washed mince were determined in the presence and absence of MTGase. A stronger gel was observed when 0.3 unit MTGase/g was added, regardless of oxidation process. Nevertheless, the gel strengthening effect of MTGase was hampered when mince was subjected to severe oxidation. Excessive protein aggregation of oxidized samples prior to gelation resulted in the reduction of gel strength and water-holding capacity. Negative effect of protein oxidation on gelation could therefore be alleviated to some degree by MTGase addition.