Autolysis and the endogenous proteinases characterised in beardless barb (Anematichthys apogon) muscle

Beardless barb is a common fish species used in fermentation of fish paste Ka-pi-plaa. Autolytic profile of beardless barb muscle showed the maximum autolysis was at 50 °C, at both acidic and alkaline pH values. With augmentation concentration of NaCl, autolytic activity slightly decreased. Endogenous proteinases isolated from fish muscle in crude extract forms were also characterised. The acidic proteinases had optimum activity at pH 3.0 and 50°C, and they showed higher proteolytic activity than the alkaline proteinases which were optimally active at pH 9.0 and 50 °C. Proteinases in peak at pH 3.0 were inhibited by pepstatin A, but those in peak at pH 9.0 were highly inhibited by PMSF, TLCK and soybean trypsin inhibitor, suggesting that both aspartic and serine proteinases were existed in beardless barb muscle. The proteinases were stable in pH range of 2.0-5.0 but unstable at the temperatures higher than 40 °C. NaCl suppressed the proteolytic activity, ATP activated the proteinase activity, while CaCl₂, MgCl₂ and CoCl₂ exhibited no influence on the activity. The results implied that cathepsin D is the predominant proteinase responsible for autolysis in beardless barb. The findings were useful to improve the processing and qualities of Ka-pi-plaa product using beardless barb as raw material.     

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.