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

Summary 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 β ‐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 μ g g −1 respectively. Daidzein and genistein increased from 18.2 and 16.9 to 63.4 and 84.6 μ g g −1 , respectively.