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

Abstract

SummaryDouchi, 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 μg g−1 respectively. Daidzein and genistein increased from 18.2 and 16.9 to 63.4 and 84.6 μg g−1, respectively.