The purpose of this study was to investigate effect of fermentation time on the proteins of steamed soybean inoculated with Bacillus subtilis (natto).The result was found that the contents of trichloroacetic acid soluble nitrogen (TCA-N) and drgree of hydrolysis (DH) of protein increased with the fermentation time increased, but the protein solubility was declined with increasing the fermentation time in advance, then increased. The most bands of soy proteins were found to disappear from the Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) electrophoretogram after 24 h of fermentation. Some of nonessential amino acids were found to remarkedly decline, but some of them were remained unchanged after 24-48 h of fermentation., However the most essential amino acids were found to declined after 36h of fermentation, then all of them increased after 48 h of fermentation except histidine.

The objective of this study was to investigate effect of the steamed soybeans inoculated with Rhizopus oligosporus in advance then Bacillus subtilis on the protein of fermentd soybeans. Soluble nitrogen content and degree of hydrolysis of soy protein increased with increasing fermenting time both of the two-step fermentation and single starter culture of B. subtilis. The amino acid composition of the two-step fermented product fluctuant during fermentation, of which glutamic and aspartic acids had the highest content. However, The most bands of soy protein components with molecular weight above 20 kDa on electrophoretogram of the product by the two-step fermentation became faint. It meant the concentration of these proteins decreased after 24 h of fermentation.

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This study investigated purification and milk-clotting activity of the enzymes produced by Bacillus subtilis var, natto and Rhizopus oligosporus compared with that of commercial rennet. The clotting time, viscosity, tension and microstructure of the curd and electrophoretic patterns of milk proteins were determined. The milk-clotting activity/proteolytic activity ratios (MCA/PA ratio) of B. subtilis, R. oligosporus and commercial rennet were also compared. The results revealed that the curd formed by the commercial rennet had the highest viscosity and curd tension and the shortest clotting time among the three enzymes. However, curd produced by Rhizopus enzymes was ranked as second. From the MCA/PA ratio and electrophoretogram analyses it could be concluded that the enzyme produced by B. subtilis had the highest proteolytic activity, while the commercial rennet had the highest milk-clotting activity. Observations of microstructures of SEM showed that the three-dimensional network for curd formed by commercial rennet was denser, firmer and more smooth. The milk-clotting activity, specific activity, purification ratio and recovery of the purified enzymes produced by both the tested organisms were also determined with ion exchange chromatography and gel filtration.