Mechanism of histamine formation and control in fermented viscera 'dayok' from yellow fin tuna [Thunnus albacares (Bonnaterre)]

Dayok, is a fermented fish product prepared from tuna viscera. This study aimed to determine the formation and control of histamine in fermented tuna viscera as influenced by different salt concentrations (10%, 17.5% and 25%), fermentation temperature (30-35 deg C and 40 deg C) and fermentation period (3 and 7 days). The effect of inoculation of selected lactic acid bacteria (LAB) cultures on the histamine levels of dayok was also investigated. Different parameters such as pH, lactic acid, microbial counts, amino nitrogen, total volatile base nitrogen (TVB-N) and histamine level during fermentation were monitored at regular time intervals. The formation of histamine during fermentation of dayok is influenced by salt concentration and fermentation period and not by fermentation temperature. As salt concentration (greater than or equal to 17.5%) and fermentation period increases (7 days) histamine content decreases. Histamine levels above FDA [Food and Drug Administration] standard limit of 50 ppm are formed at low salt concentrations (10% NaCl) with total plate count 10 sup 7 cfu/g. No significant differences on histamine content were observed on samples inoculated with LAB starter cultures (Pediococcus acidilactici and Lactobacillus delbrueckii) compared to control due to high salt concentration of the medium causing low LAB counts. The levels of pH, lactic acid, amino nitrogen and TVB-N increased during fermentation of tuna viscera. To minimize or prevent the formation of histamine in raw material, immediate washing, icing or storage at low temperature should be practiced. In fermentation, the application of greater than or equal to 17.5% salt concentration, use of higher inoculum size of LAB starter culture at salt concentrations not higher than 18% NaCl and pasteurization after fermentation to inactivate histidine decarboxylase are also suggested to minimize or control histamine formation.