Change in phytoestrogen contents and antioxidant activity during fermentation of Cheonggukjang with bitter melon

In this study, the β-glucosidase activity and total phenolic and isoflavone contents and antioxidant activities during Cheonggukjang fermentation with bitter melon powder (BMP) were investigated and evaluation of the same was performed. The level of β-glucosidase activity was increased at 48 hr and decreased after 72 hr, and the total phenolic and isoflavone-malonylglycoside and aglycone contents increased, while the antioxidant activities increased, but the total isoflavone and isoflavone-glycoside contents decreased during the Cheonggukjang fermentation. In particular, the soybean with 5% BMP fermented at 37°Cfor 72 hr displayed the highest antioxidant activities, among all the samples. The highest levels of total phenolic and daidzein contents and DPPH radical scavenging activity, ABTS radical scavenging activity and FRAP assay results after 72 hr fermentation in Cheonggukjang with 5% BMP were found to be 13.5 mg/g, 390.57 μg/g, 90.74%, 99.79%, and 1.705 (OD593 nm) respectively. In addition, the more BMP was added to the Cheoggukjang, the more the off-odor of the Cheonggukjang decreased. These results suggest that BMP can be used to come up with a new type of Cheonggukjang with improved palatability and antioxidant activity.