PHYSICOCHEMICAL AND MICROBIAL CHANGES IN SKIPJACK TUNA (Katsuwonus pelamis) VISCERA DURING SALT FERMENTATION

Abstract

Tuna viscera is often regarded as waste by many canning industries around the globe. However, it also represents a potential source of various proteinases that can enhance fish fermentation. Salt-fermented fish viscera locally known as dayok, is a traditional fermented food popular in Mindanao, Philippines. This study aimed to investigate the changes in physicochemical properties and microbial populations of salt-fermented skipjack tuna (Katsuwonus pelamis) viscera over a 150-day fermentation period. The skipjack tuna viscera primarily consisted of 76.42% moisture, 17.27% protein, 3.64% lipid, and 1.37% ash. Results showed that during the salt fermentation of tuna viscera, pH decreased to 5.71, while titratable acidity (TA) and degree of hydrolysis (DH) increased to 1.64% and 69.60%, respectively. Salt concentration remained stable ranging from 28.10% - 30.28% (w/w) throughout the fermentation period, eliciting a preservative effect. Changes in microbial population revealed a decline in the total viable count to 1.36 log CFU.g^-1 at the later stages of fermentation, and an increase in lactic acid bacteria (LAB) count to 2.32 log CFU.g^-1 during the early stages of fermentation. The dominant bacteria identified belonged to the genera Bacillus, Staphylococcus, and Enterococcus, potentially affecting the physicochemical and microbial properties of the salt-fermented tuna viscera. The most abundant bacterial genera may have contributed to the enhancement of flavor and aroma of the final product. This study will lay a foundation for standard tuna viscera fermentation systems and quality improvement of fish paste and fish sauce made from tuna viscera.