Chemical and Enzymic Changes During the Fermentation of Bacteria-Free Soya Bean Tempe

Abstract

Amounts of dry matter, ash, protein, free ammonia, crude lipid, glyceride–glycerol, free fatty acids, free glycerol, glucosamine, protease activity and lipase activity were monitored during the fermentation of bacteria-free tempe made with acidified soya bean cotyledons and Rhizopus oligosporus NRRL 2710 at 30°C. During the phase of mycelial growth (0–32 h) the total dry matter decreased by approximately 10% (w/w), accounted for by losses of crude lipid (3% of initial dry matter), protein/amino acids (0·5%), and unidentified compounds (6·5%). During the phase of mycelial senescence (60–180 h), decrease in dry matter (12% of initial dry matter) was due almost entirely to loss of crude lipid. Lipase activity and the production of free fatty acids occurred from the earliest stages of the fermentation. The production of only small amounts of free glycerol indicates that triglycerides were primarily hydrolysed to partial glycerides and free fatty acids. Protease activity and production of free ammonia were also detected at the earliest stages of the fermentation. During the phase of mycelial senescence, amounts of crude lipid and glycerol decreased in the absence of fungal growth, possibly due to the activity of enzymes released from senescent mycelium.