Production of a New Type of Acid Carboxypeptidase of Molds of the Aspergillus niger Group

The ability of 88 fungi, which had been obtained as high-potency strains for acid proteinase production, to produce a new type of acid carboxypeptidase (having on optimal pH of about 3 for hydrolysis of benzyloxycarbonyl-glutamyltyrosine) in surface koji culture was determined. Among the aspergilli, substantial amounts of this new acid carboxypeptidase were produced by Aspergillus saitoi, A. usamii, A. awamori, A. inuii, and A. niger. Maximum yields of acid carboxypeptidase per gram of substrate were obtained by submerged culture in a medium containing 0.9% defatted soybean and 0.6% wheat bran. However, the maximum enzyme concentration per milliliter was obtained with a medium containing 3% defatted soybean and 2% wheat bran. The terminal pH could be controlled by varying the concentrations of soybean oil meal and wheat bran. The maximum enzyme production was reached after 4 days or more at 30 C.     

Selection of starter cultures for the production of kinema,a fermented soybean food of the Himalaya

Kinema, a traditional fermented soybean food, serves as a low-cost source of protein in the diet of the people of the Himalaya. The traditional method of kinema preparation results in a product with inconsistent quality. Forty five strains of spore-forming bacteria were isolated from nine samples of kinema collected from markets in the Darjeeling hills and Sikkim in India. Of these, 10 strains, identified as Bacillus subtilis (Ehrenberg) Cohn, were selected as possible starter cultures on the basis of enzyme activities and the production of slimy material. Protease activity (U/ml), -amylase activity (U/ml) and relative viscosity of the selected strains were 6.5 to 81.5, 0.1 to 9.3, and 1.1 to 20.1, respectively. Kinema produced by these strains showed nitrogen contents (expressed as a percentage of the total nitrogen content) of: water-soluble N, 48.4 to 76.5; TCA-soluble N, 16.0 to 27.6; formal N, 5.0 to 12.5; ammonia-N, 4.4 to 7.8%. Reducing sugar was 1.1 to 2.0% of the wet weight and relative viscosity was from 2.0 to 35.2. Correlation matrices of the biochemical parameters and sensory attributes of the kinema produced by these B. subtilis strains were statistically analysed. Strains KK-2:B10 and GK-2:B10 of B. subtilis were the best starter cultures for improved kinema production.     

Effect of temperatures during pure culture fermentation of Kinema

Kinema was prepared by fermenting whole cooked soybeans with pure culture of Bacillus subtilis KK2:B10 (MTCC 2756) strain at 35°C, 40°C and 45°C for 24h. Temperature, mesophilic plate counts, relative viscosity, water-soluble nitrogen, formal nitrogen contents and reducing sugars of fermenting soybeans were investigated during fermentation. At higher temperatures the growth rate of B. subtilis KK2:B10 was faster. A remarkable increase in the relative viscosity of kinema was observed at 40°C during fermentation. Water-soluble nitrogen and formol nitrogen to total nitrogen contents increased throughout the 24h of fermentation. Reducing sugars increased during the log phase and then decreased sharply. Kinema matured below 10°C for 1 day after the desired fermentation showed a significant increase in relative viscosity. The quality of kinema was maintained with pure culture fermentation by B. subtilis KK2:B10 at 40°C for 20h and matured at 5°C for 1 day.