Fish sauce is popular for fermenting food in Southeast and Eastern Asia, while black bean is used to ferment condiments in Taiwan. Researchers have recently investigated the use of fish and black bean sauce in places where combining both fish and black bean is rare. This study was focused on fish sauce made from concentrated tuna cooking juice mixed with black bean koji. The experiment was divided into two stages. In the pre-fermentation stage, a suitable fermentation time with no salt added was determined. In the later fermentation stage, two preformatted samples of 4 and 7 days were added to salt water at 20 °Bé. In the pre-fermentation stage, the results show that the protease activity increased as time passed, but the pH value decreased. The highest browning degree was achieved after 120 days. In the later fermentation period, the total nitrogen contents for both experimental groups of 4 days and 7 days reached up to twice that of soy sauce. The total nitrogen content increased with time. In addition, the level of ammonia nitrogen increased from 0.08 to 0.15 g/dL in the first month. In conclusion, a new flavor of fermented sauce was produced in a shorter time and more effectively by combining tuna cooking juice and black bean.
Keywords: by-product; fish sauce; gradient salt-adding method; koji; tuna cooking juice.