Studies On The Application Of Rhizopus Oryzae R₁ In Tempeh Preparation

Tempeh was prepared with R.oryzae which isolated from the koji used in naturally fermented Liuyang brown bean in this dissertation, and compared with R.oligosporus which is a kind of commercial starter.The culture condition for maximum yield of acid protease from R.oryzae and the properties of the protease system were studied in this research. The results showed that though differences were present between the two strains, there were similarities in some degree: the optimum conditions for maximum acid protease production of Rhizopus oryzae grown on wheat bran were cultivated at 57～59% moisture,pH2.5～3.0,28～31℃for 36 h; the secreted protease system had most catalytic activity around pH4.0 or pH6.0, and were relatively stable at pH3.0～6.0, it exhibited maximum activity at 50°C, but the temperature stable was very low. The optimum conditions for maximum acid protease production of Rhizopus oligosporus grown on wheat bran were cultivated at 52～55% moisture,pH2.5～3.0,31℃for 48 h, and the enzyme activity was relatively higher at 35℃for 36 h; the secreted protease system had most catalytic activity around pH3.0 or pH6.0, and were fairly stable at pH4.0～6.0, the enzyme system had maximum activity at 55～60℃, and the thermal stability was also low.The optimum condition for preparing tempeh by R.oryzae and the products'shelf-life were dicussed. Compared with the comprehensive quality of tempeh prepared in different conditions, the optimal fermentation conditions by R.oryzae were as follow: fermentation temperature at 32℃, relative humidity 85～88%, 60h fermentation; and the optimal fermentation conditions by R.oligosporus were: fermentation temperature at 32℃, relative humidity 85～88%, 36h fermentation. The shelf-life was determined by measuring the physicochemical microorganism index and quality changes of tempeh during storage, and the result showed that tempeh should edibled within three days under cold storage.The flavor components and nutritional ingredient of tempeh were also investigated. Due to the difference between various enzyme systems produced by R.oryzae and R.oligosporus respectively, the contents and categories of nutritional ingredient, free amino acid and free fatty acids in two tempehs had a major discrepancy. Volatile components analysis indicated there are many kinds of volatile components appeared during fermentation, and mainly with alcohols, aldehydes, alkanes. Because of the differences between the two strains, volatile components in two tempeh had apparent differences, and the flavor compounds in tempeh prepared using R.oryzae were more complex than R.oligosporus, and the flavor of tempeh prepared by R.oryzae was more suitable for Chinese people.