Ecology of soybean acidifications and some biochemical changes during controlled kinema production

Biochemical changes occurring during the manufacture of kinema were studied. In the process, spontaneous fermentation of soybeans was found to take place in the soaking stage prior to Bacillus fermentation: Lactococcus, accompanied by other bacteria, brought down the pH of the beans from 6.6 to 5.3. Soaking with recycled soak water established an additional growth of Lactobacillus, resulting in further decline in pH of the beans to 4.3. But, soaking in acidified water did not help in the growth of any lactic acid bacteria. Although the soaking stage tvas essential for the optimum sensory quality of kinema, all such variations in soaking had no apparent influence on the downstream processes of kinema-making. Oligosaccharide contents of soybeans (62.8 g sucrose, 19.2 g ranffinose and 43.2 g stachyose per kg dry wt) were significantly reduced during soakings; the extent of reduction being maximum in inoculated soaking and minimum in acidified cooking. Spores of Bacillus subtilis, which are normal inhabitants of soybeans, passed through soaking and cooking treatments to initiate and carry out the alkaline fermentation. During 48 h-fermentation of beans, the oligosaccharide content dropped below the limit of detection (1.0 g kg(-1) dry wt) within 24 h. While sucrase activity reached its peak at 12 h and declined thereafter, alpha -amylase and lipase activities increased steadily with the progress of fermentation. The hexanal (the probable cause of beany flavour) content (1.1 g kg(-1) dry wt) of unfermented soybeans decreased gradually below the limit of detection (0.5 mg kg(-1) dry wt) after 24 h of fermentation. On the other hand, the ammonia content of unfermented soybeans (0.08 g kg(-1) dry wt) showed 34-fold increase in kinema.