Tyramine reduction by tyrosine decarboxylase inhibitor in Enterococcus faecium for tyramine controlled cheonggukjang.

This study was carried out to find a method to control tyrosine decarboxylase activity (TDC) of a strain of Enterococcus faecium capable of producing high levels of tyramine. To select a TDC inhibitor, enzyme assay was first performed using purified TDC enzyme and 0.1% of TDC inhibiting chemicals. When 0.23% of nicotinic acid was added, tyramine content (363 ug/mL) was lower than that of the control group (873 ug/mL). At the same time, bacterial growth was decreased 1 log cycle from 8.62 to 7.56 log CFU/mL. TDC expression level in E. faecium was measured by using RT-qPCR. Lower expression level (below 0.7) was observed after the addition of 0.23% nicotinic acid (in vitro). When cheonggukjang was manufactured with addition of nicotinic acid, tyramine contents were decreased from 698.67 to 117.27 mg/kg when the concentration of nicotinic acid added was increased from 0.10 to 0.30%. These results suggest that nicotinic acid could be used as an agent (TDC inhibitor) to reduce tyramine content in cheonggukjang.

Quantitative analysis of volatile flavor components in Korean alcoholic beverage and Japanese sake using SPME-GC/MS.

Quantitative analysis of the volatile flavor components in Korean alcoholic beverages (makgeolli and yakju) and Japanese sake was carried out using SPME-GC/MS. Fusel oils (n-butyl alcohol, isobutyl alcohol, isoamyl alcohol, and phenethyl alcohol), ethyl esters (ethyl acetate, isoamyl acetate, ethyl caproate, ethyl caprylate, and ethyl caprate) and aldehydes (furfural and benzaldehyde) were analyzed quantitatively by an 85 µm SPME fiber (carboxen/polydimethylsiloxane) using internal standards (1-pentanol-1-13C and methyl nonanoate). Phenethyl alcohol (85-216 ppm) and isoamyl alcohol (38-115 ppm) constituted the majority of fusel oils in all the samples. Acetic acid was detected in sour makgeolli at a high level (0.02-0.14 ppm) compared with yakju and sake. A very high level of total ethyl esters (ethyl acetate, isoamyl acetate, ethyl caprate, and phenethyl acetate), having fruit and flower flavor, was found in makgeolli. Processing the volatile flavor data by multivariate partial least squares discriminant analysis, makgeolli, yakju, and sake showed cluster separation.