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

In this study, the ${\beta}$-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 ${\beta}$-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 $37^{\circ}C$ for 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, $390.57{\mu}g/g$, 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.

여주 첨가 청국장 발효 중 phytoestrogen 함량 및 항산화 활성 변화

본 연구에서는 여주 분말(bitter melon powder, BMP) 첨가 청국장 발효 중 ${\beta}$-glucosidase 활성 변화, 총 phenolics와 isoflavone 함량, 항산화 활성 변화 및 관능평가를 조사하였다. 청국장 발효 중 ${\beta}$-glucosidase 활성은 48 hr까지는 증가한 후 72 hr에는 감소하였으며, 총 phenolics, isoflavone-malonylglycoside 및 isoflavone-aglycone 함량은 증가하였고 이에 상응하여 항산화 활성 역시 증가하였으나, 총 isoflavone 및 isoflavone-glycoside 함량은 감소하였다. 한편, 발효종기 5% BMP 첨가 청국장은 또 다른 시료들과 비교하여 가장 높은 항산화 활성을 나타내었다. 특히, 발효 72 hr 후 5% BMP 첨가 청국장의 총 phenolics와 daidzein 함량 및 DPPH 라디칼 소거 활성, ABTS 라디칼 소거 활성 및 환원력은 각각 13.5 mg/g, $390.57{\mu}g/g$, 90.74%, 99.79% 및 1.705($OD_{593nm}$) 있었다. 부가적으로 여주 분말이 첨가될수록 청국장의 이취도는 감소하였다. 이들 결과로부터 여주 분말 첨가로 기호성과 항산화 활성이 개선된 새로운 타입의 청국장 제조가 가능할 것으로 판단되었다.