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.
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.
This study investigates the effects of drying methods on angiotensin‐converting enzyme (ACE) inhibitory activity, γ‐polyglutamic acid (γ‐PGA) and isoflavone contents of steamed soybeans fermented by Bacillus subtilis (natto). In this study, the fermented steamed soybeans (natto) are dried in different methods, namely conventional oven‐drying at 50C, vacuum‐drying at 40C and freeze‐drying at −50C, and ground into powder for analysis after drying for 2 days. Results indicate that vacuum‐drying, freeze‐drying or conventional oven‐drying does not affect the stability of γ‐PGA and isoflavone contents but does affect ACE inhibitory activity in all dried natto samples. PRACTICAL APPLICATIONS Natto is a traditional fermented soybean food product containing functional compounds, but it is not acceptable to most consumers because of its strong unpleasant smell. Its odor sometimes causes problems with natto product quality control, and a fresh product has a short shelf life. To avoid these problems, some biotechnical and functional food companies have tried drying it into powder form or into capsulized form and sell it as a functional food. The results obtained from this research demonstrate that natto dried by vacuum‐drying, freeze‐drying or oven‐drying does not affect the stability of γ‐PGA or isoflavone but has an effect on the ACE inhibitory activity in natto. The drying process is useful to commercial production of natto and product quality, minimizing the risk of secondary fermentation releasing ammonia. The greatest advantage of the drying process is that it can maintain the functional compounds of the product.
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