The Role of Enterococcus faecium as a Key Producer and Fermentation Condition as an Influencing Factor in Tyramine Accumulation in Cheonggukjang

Abstract

The study evaluated the role ofEnterococcus faeciumin tyramine production and its response to fermentation temperature in a traditional Korean fermented soybean paste,Cheonggukjang. Tyramine content was detected in retailCheonggukjangproducts at high concentrations exceeding the recommended limit up to a factor of 14. All retailCheonggukjangproducts containedEnterococcusspp. at concentrations of at least 6 Log CFU/g. Upon isolation ofEnterococcusstrains, approximately 93% (157 strains) produced tyramine at over 100 mu g/mL. The strains that produced the highest concentrations of tyramine (301.14-315.29 mu g/mL) were identified asE.faeciumthrough 16S rRNA sequencing. The results indicate thatE. faeciumis one of the major contributing factors to high tyramine content inCheonggukjang. During fermentation, tyramine content inCheonggukjanggroups co-inoculated withE. faeciumstrains was highest at 45 degrees C, followed by 37 degrees C and 25 degrees C. The tyramine content of mostCheonggukjanggroups continually increased as fermentation progressed, except groups fermented at 25 degrees C. At 45 degrees C, the tyramine content occasionally exceeded the recommended limit within 3 days of fermentation. The results suggest that lowering fermentation temperature and shortening duration may reduce the tyramine content ofCheonggukjang, thereby reducing the safety risks that may arise when consuming food with high tyramine concentrations.