Determination of histamine levels in long-tail tuna (Thunnus tonggol) stored at different temperature

Histidine is precursor for histamine (4-(2-aminoethyl) imidazole) formation through a process called decarboxylation with the aid of histidine decarboxylase enzyme possessed by particular bacterial species. Since storage temperature is highly influenced the formation of histamine, a study regarding histamine and bacterial count was conducted. Long-tail tuna was stored at -20, 4, 15, 25 and 37 ̊C and analysis of bacteria and histamine was done for every 48 hours till reaching 196 hours for freezing and chilling storage temperature. Histamine determination and bacterial count was taken for every 0, 6, 12,18 and 24 hours for 15, 25 and 37 ̊C. At 0 day of storage for -20̊ C, gut and non gut fish samples showed histamine level of 3.496 mg/100. Reduction of histamine levels took place after 48 hours of storage but increased later throughout the storage period up to 8 days, reaching a value of 4.84 and 3.78 mg/100 g for gut and non gut tuna, respectively. Similar trend of result was seen at 4 ̊C where a gradual increase of histamine concentration was observed throughout the storage period. However, the histamine level in gut tuna exceeded the safety level at day 8. At temperature 15 and 25 ̊C, the gut fish meat is not safe for consumption at 24 hours. Meanwhile, the safety limit can be seen within 12 hours and 18 hours of storage in gut and non gut fish stored at 37 ̊C, respectively. For bacterial cell enumeration, at -20 ̊C, the initial count of bacteria is 5.4 Log CFU/g for both fish condition. The count then slightly increased to 6.28 and 5.91 for gutted and non gutted respectively at 48 hours till reaching last storage time. Similar trend was recorded at 4, 15, 25 and 37 ̊C from time to time. However, bacterial count is largely seen at 37 ̊C. This may be due to the presence of spoilage bacteria that can deteriorate the quality of fish.