Protein hydrolysis during soybean tempe fermentation with Rhizopus oligosporus

Hydrolysis of soybean protein during fermentation in a rotating drum reactor (RDR) was compared with hydrolysis during the traditional stationary tempe fermentation process. An increase of watersoluble nitrogen was observed. After 72 h of fermentation, 18.5, 25.4, 27.1, and 34.0% (w/w) of total N were found for the traditional stationary process at 25, 30, and 37 °C and for the RDR at 36 °C, respectively, compared to 2.0% in cooked soybeans at the start of the fermentation. The fungal activity in the RDR continued longer than in the traditional process. This was achieved by avoiding heat and mass transfer limitations. In the RDR a higher degree of hydrolysis, as well as higher levels of water-soluble and TCA-soluble nitrogen, were found after 72 h of fermentation compared with the stationary process at 37 °C. β-Conglycinin was hydrolyzed more rapidly than glycinin, which is probably related to the chemical structure ; β-conglycinin is more sensitive toward protease activity.