Image and chemical analyses of freezing-induced aggregates of fish natural actomyosin as affected by various phosphate compounds

The impact of various phosphate compounds [sodium tripolyphosphate (STPP), tetrasodium pyrophosphate (TSPP), STPP/TSPP, trisodium pyrophosphate (3SP), sodium hexametaphosphate (SHMP), and disodium phosphate anhydrous (DSPA)] on retarding freeze-induced protein denaturation and aggregation was evaluated. Using natural actomyosin (NAM) extracted from fresh Pacific whiting, the phosphate treatments were evaluated at various concentrations (0.1%, 0.3%, and 0.5%), with and without cryoprotectants (CP) (4% sorbitol and 5% sugar), after different freeze/thaw cycles (F/TC) (0, 3, and 9F/TC). Trimethylamine-N-oxide demethylase (TMAOase) activity, formaldehyde (FA) content, solubility, and turbidity were measured. The other NAM mixture containing the 0.5% STPP/TSPP, STPP, or TSPP along with CP showed low TMAOase activity, low FA production, high salt-soluble proteins solubility, and high turbidity. Among the phosphate treatments, STPP seemed to be the most effective compound in retarding both FA- and freeze-induced protein denaturation and aggregation. NAM without CP was more rapidly denatured and aggregated than NAM with CP as F/TC increased, resulting in a gradual increase in the degree of aggregation (DA). The DA, which was calculated based on graphical images, correlated with biochemical properties.