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

We 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. γ-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.