What You Need to Know
During fermentation, Aspergillus oryzae secretes proteases and lipases that hydrolyze soy proteins and fats. The resulting peptides and free fatty acids undergo further oxidation and condensation to form volatile sulfur compounds such as methanethiol and dimethyl disulfide. Concurrently, the pH drops from ~6.5 to ~5.0 and ammonia accumulates, contributing to the characteristic pungent aroma.
The Science
Primary Reaction
Proteolysis and lipolysis of soy proteins and fats by Aspergillus oryzae enzymes, producing peptides, free fatty acids, volatile sulfur compounds, and ammonia