Biogenic amine reduction by vasoactive amine-degrading Bacillus licheniformis CH7P22 in Enterococcus faecium-contaminated Cheonggukjang, Korean fermented soybean paste

This study was performed to screen and select biogenic amine (BA)-degrading Bacillus strains originating from Cheonggukjang and to examine the practical effects of the Bacillus strains on BA reduction during Cheonggukjang fermentation in the presence or absence of Enterococcus faecium known to be the principal species of tyramine production. Out of a total of 327 strains isolated, three BA-degrading and low BA-producing strains were selected through in vitro tests and were identified as B. licheniformis CH7P22, B. haynesii CH7P24, and B. velezensis CH7P28. The selected strains were used for the fermentation of Cheonggukjang with or without E. faecium inoculation. During fermentation, the sample inoculated with B. licheniformis CH7P22 showed the largest reduction in tyramine (43.25–91.50%) and spermine contents (40.35–69.93%) compared to the negative controls (samples inoculated with non-BA-producing Bacillus strains) and positive control (sample inoculated with a prolific tyramine-producing Bacillus strain). This sample also showed the largest reduction in histamine content (100.00%) compared to the blank sample (sample prepared without an inoculum). In the fermentation of Cheonggukjang in which a prolific tyramine-producing strain of E. faecium was inoculated, the sample inoculated with B. licheniformis CH7P22 exhibited a reduction in tyramine content (17.02–63.26%) compared to the controls, as well as in histamine (100%) and spermine content (59.32%) compared to the blank sample. The findings of this study indicate that B. licheniformis CH7P22 could be applied to Cheonggukjang as a starter and/or protective culture to reduce food safety risks associated with BAs, regardless of Enterococcus contamination.