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

The study evaluated the role of Enterococcus faecium in tyramine production and its response to fermentation temperature in a traditional Korean fermented soybean paste, Cheonggukjang. Tyramine content was detected in retail Cheonggukjang products at high concentrations exceeding the recommended limit up to a factor of 14. All retail Cheonggukjang products contained Enterococcus spp. at concentrations of at least 6 Log CFU/g. Upon isolation of Enterococcus strains, approximately 93% (157 strains) produced tyramine at over 100 µg/mL. The strains that produced the highest concentrations of tyramine (301.14-315.29 µg/mL) were identified as E. faecium through 16S rRNA sequencing. The results indicate that E. faecium is one of the major contributing factors to high tyramine content in Cheonggukjang. During fermentation, tyramine content in Cheonggukjang groups co-inoculated with E. faecium strains was highest at 45 °C, followed by 37 °C and 25 °C. The tyramine content of most Cheonggukjang groups continually increased as fermentation progressed, except groups fermented at 25 °C. At 45 °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 of Cheonggukjang, thereby reducing the safety risks that may arise when consuming food with high tyramine concentrations.

Formation and destruction of biogenic amines in Chunjang (a black soybean paste) and Jajang (a black soybean sauce).

Chunjang and Jajang samples were analysed for biogenic amine contents by using HPLC equipped with a UV-Vis detector. Chunjang samples contained relatively large amounts of histamine (up to 273mg/kg) and tyramine (up to 131mg/kg), whereas Jajang samples had relatively small amounts of biogenic amines (mostly less than 40mg/kg). There appeared to be a strong relationship between biogenic amine contents in Chunjang and Jajang, and the biogenic amines in Chunjang were found to be pyrolysed during frying thereof to prepare Jajang. Meanwhile, the total plate counts of Chunjang samples ranged from 5 to 8logcfu/g, and most strains that were isolated from Chunjang samples were identified to be Bacillus subtilis (91.0%). The strains isolated from a sample in which relatively small amounts of biogenic amines were detected showed significantly weak abilities to produce biogenic amines. This indicates that biogenic amine contents in Chunjang are primarily attributed to bacterial abilities to produce biogenic amines.

Occurrence of biogenic amines in Miso, Japanese traditional fermented soybean paste.

The objective of this study was to analyze overall contents of biogenic amines in Miso and thereby evaluate the safety of the food. Through HPLC analysis of 22 different Miso products, it was found that most samples had low biogenic amine contents. However, some samples contained both histamine and tyramine close to hazardous levels of the amines, which indicate that the amounts of biogenic amines in Miso are not completely within the safe level for human health. Meanwhile, the biogenic amine contents showed no clear relationship with physicochemical parameters, whereas they revealed a good relationship with the ratio of soybean to other grains used in raw material. Thus, it turned out that biogenic amine contents in Miso are primarily affected by the ratio of raw ingredients, especially soybeans. The aerobic plate counts of Miso samples ranged from 3 to 8 Log CFU/g, and all the strains isolated from Miso samples were found to produce biogenic amines. Most strains were identified to be Bacillus subtilis, often regarded as the predominant contaminant bacteria in Miso, and highly capable of producing tyramine and spermine. Taken together, therefore, this study suggests that variability of biogenic amine contents in Miso are primarily attributed to the ratio of raw ingredients in the food that affects the relative contribution level of bacterial contaminants to the contents.

Biogenic amine formation and bacterial contribution in Natto products.

Twenty-one Natto products currently distributed in Korea were analysed for biogenic amine contents and tested to determine physicochemical and bacterial contributions to biogenic amine formation. Among them, nine products (about 43%) had ß-phenylethylamine or tyramine contents greater than the toxic dose (30mg/kg and 100mg/kg, respectively) of each amine, although no products showed total amounts of biogenic amines above the harmful level (1000mg/kg), which indicates that the amounts of biogenic amines in some Natto products are not within the safe level for human health. From four different Natto products, that contained noticeable levels of ß-phenylethylamine and tyramine, 80 bacterial strains were isolated. All the strains were identified to be Bacillus subtilis and highly capable of producing ß-phenylethylamine and tyramine. Therefore, it seems likely that the remarkable contents of ß-phenylethylamine and tyramine in Natto predominantly resulted from the strains highly capable of producing those amines present in the food.