Biogenic amine formation and bacterial contribution in Cheonggukjang, a Korean traditional fermented soybean food

To evaluate the safety of Cheonggukjang, 60 different samples collected from 8 provinces all across the country were analyzed for biogenic amine contents by HPLC. The aromatic vasoactive amine (beta-phenylethylamine and tyramine) contents in some Cheonggukjang samples exceeded safe levels for consumption. Bacterial and enterococcal counts of Cheonggukjang samples were 9.70 +/- 0.43 and 6.00 +/- 1.52 Log CFU/g, respectively, and strains of Bacillus (n = 433) and Enterococcus (n = 55) isolated from Cheonggukjang samples were tested for biogenic amine production in assay media. Histamine and putrefactive amines (putrescine and cadaverine) were detected more abundantly in cultures of Bacillus strains, while tyramine was detected in larger quantities in cultures of Enterococcus strains. Subsequently, strains selected based on their specific abilities to produce the aforementioned respective biogenic amines were applied to soybeans to undergo fermentation, and biogenic amine contents in the soybeans were measured during the fermentation period. Unexpectedly, Bacillus strains produced slightly lower levels of histamine, but significantly higher levels of beta-phenylethylamine and tyramine than Enterococcus strains. Altogether, this study suggests that Bacillus species are as significant as Enterococcus species for biogenic amine production in Cheonggukjang, including tyramine, and should be controlled accordingly for the reduction of biogenic amine contents in the food.