The fermentation
caused a sharply increase in the content of the free amino nitrogen from 99.7 mmol/g to 301.9 mmol/g,
390.1 mmol/g and 529.1 mmol/g in the solid fermented soybean products, due to the multiplication of
microorganism and the effect of enzyme system. Furthermore, the levels of soybean peptide with molecular
weight less than 1000 Da increased 30.7%, 71.2% and 81.3% relative to that of the control group at
48 h.