Physicochemical characteristics and protein degradation during fermentation of Plaa-som, A traditional fermented fish product of North-Eastern Thailand

The involvement of lactic acid fermentation in physicochemical characteristics and fish protein degradation of Plaa-som, a Thai fermented fish produced from common silver barb (Barbonymus gonionotus), was investigated. pH of Plaa-som gradually decreased to 5.16 after 120 hrs of fermentation. In contrast, titratable acidity of Plaa-som rapidly increased and reached a peak of 0.73% (w/w) after 48 hrs then it slightly declined. Concentration of lactic acid was enhanced to 2.13% (w/w) after 120 hrs. Small amounts of other organic acids such as acetic, citric, succinic, and formic acids were also detected. Peptide content demonstrated an increasing trend while protein concentration illustrated a decreasing trend. Protein degradation was also observed using electrophoresis. Actin and tropomyosin were degraded after 96 and 120 hrs, respectively. Simultaneously, small proteins of 18 and 21 kDa were detected between 24 and 48 hrs and eventually degraded after 72 hrs, indicating complete degradation. Therefore, the degraded products, such as small proteins and peptides, could lead to development of health-promoting areas for the functional peptides obtained from Plaa-som consumption.