Ka-pi-plaa fermented using beardless barb fish: physicochemical,microbiological and antioxidant properties as influenced by production processes

Production of Thai fish paste Ka-pi-plaa fermented using beardless barb, Cyclocheilichthys apogon was monitored. The physicochemical, microbiological and antioxidant properties were compared after each process, that is autolysis, salting, sun-drying and fermentation. Colour parameters L* decreased while a* and b* increased during production (P < 0.05). The Ka-pi-plaa finished product presented an intense brown colour as shown with the increase in browning intensity (A₄₂₀). Contents of formal nitrogen, ammonia nitrogen and amino nitrogen showed continuous increase (P < 0.05) indicating the formation of peptides and free amino acids, which were verified by protein patterns. Populations of total, halophilic, proteolytic, lipolytic and lactic acid bacteria (LAB) generally increased. Halophilic bacteria grew rapidly after salting. LAB counts were correlated with the pH change. It was suggested that a few biochemical reactions occurred during production, including protein hydrolysis by microbial and fish proteases, lipid oxidation as presented by the increasing thiobarbituric acid reactive substances value, and Maillard reaction based on the determined precursors and products. Antioxidant activities generally increased during production particularly fermentation, suggesting Ka-pi-plaa possessed 2,2-diphenyl-l-picrylhydrazyl and 2,2-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) scavenging and metal chelating activities, and ferric reducing power. This study provides important information on the relationship among production steps, various properties and chemical reactions for fish fermentation.