Changes in contents of γ-Aminobutyric Acid (GABA) and Isoflavones in traditional Korean Doenjang by ripening periods

This study was performed to investigate changes in γ-aminobutyric acid (GABA) and isoflavones in traditional Korean Doenjang according to ripening periods. The traditional Korean Doenjang used in this research was produced at Seowon Agricultural Cooperative in Gangwon-do Province, and samples fermented for periods of 1, 3, 5, 7, and 10 years were used. Doenjang that was not fermented after production was used as a control group. The analysis results of general constituents indicated a decreasing tendency for moisture after a momentary increase until three years of fermentation. The pH and Hunter color values of the Doenjang samples decreased overtime. In the case of amino acids, generally there were no notable differences during fermentation, but glutamic acid, the precursor of GABA, significantly decreased with fermentation. GABA content for the control group was 24.9±0.8 mg/kg, while the traditional Korean Doenjang fermented for 1 year contained 43.8± 0.2 mg/kg and after 3 years it increased to 120.6±3.9 mg/kg. Furthermore, samples fermented for 5 and 7 years contained 569.5±3.9 mg/kg and 930.7±7.1 mg/kg, respectively, and a 10 year old specimen had 77 times more GABA than the control group, with 1,938.7±4.8 mg/kg. This confirmed that GABA content increased with fermentation time. There were no significant differences in the isoflavone glycosides daidzin, genistin, and glycitin, but genistein and daidzein, which are aglycones, increased along with fermentation period by the actions of enzymes and microorganisms during fermentation.