Characteristics of fermentation and bioavailability of isoflavones in Korean soybean paste (doenjang) with application of Bacillus sp. KH‐15

Abstract

SummaryWe attempted to increase the fibrinolytic activity and aglycone contents of isoflavone in doenjang prepared with Bacillus sp. KH‐15. An initial rapid increase of viable cells was observed in the first 30 days followed by a gradual decrease to 1.78 × 108 CFU g−1 wet weight. The amino type nitrogen sharply was increased after 15 days, and showed the highest level (788.7 mg%) after 90 days. The total nitrogen was increased from 2.21% to 2.52% of final content after 90 days. Soluble carbohydrate was increased to 32.9 mg g−1 for 60 days, and after 60 days, the content was slowly decreased to 29.5 mg g−1. A rapid increase in fibrinolytic and caseinolytic activities were observed in the first 30 and 45 days of fermentation followed by a gradual decrease to 2.54 and 144.5 U g−1, respectively. β‐Glucosidase activity also showed a similar change pattern of the caseinolytic and fibrinoytic activities. Daidzein and genistein were increased to the maximum level of 764.5 and 561.4 mg kg−1 at day 30, respectively. At day 90, the contents of daidzein and genistein were 661.5 and 524.9 mg kg−1, respectively. The rats were fed a diet supplemented with either doenjang powder prepared with Bacillus sp. KH‐15 (D‐1 group) or commercial doenjang powder (D‐2 group) for 40 days. The level of serum total isoflavones in the D‐1 group was significantly higher than that in the D‐2 group.