Chemical components of Aspergillus-type Douchi, a Chinese traditional fermented soybean product, change during the fermentation process

Douchi, a traditional fermented soybean product that originated in China, has been consumed since ancient times as a food seasoning. The influence of fermentation on the chemical components of naturally fermented douchi and Aspergillus egypticus pure-cultured douchi was investigated. Changes in per cent and/or concentration of amino-type nitrogen, total acid, reducing sugar, organic acid, amino acids (AA) and isoflavone, along with the neutral protease and beta-glucosidase activities during the fermentation, were analysed. The results indicated that fermentation had a significant effect on the concentration of chemical components. The concentration of all free amino acids (FAA) increased gradually during fermentation, to a maximum of 109.54 mg g(-1) in 15-day fermented products. The main organic acids in douchi are 7.788 and 17.778 mg g(-1), respectively. During fermentation, the contents of daidzin and genistin decreased from 160.7 and 207.9 to 7.54 and 24.12 mu g g(-1) respectively. Daidzein and genistein increased from 18.2 and 16.9 to 63.4 and 84.6 mu g g(-1), respectively.