Effect of Temperature and Inoculum Size on Natto's Enzyme activities during Fermentation

Abstract

Natto's protease, γ-glutamyltranspeptidase (γ-GTP) and levansucrase (L.S) activities, solubilization and hydrolysis ratios of proteins, and the stringiness of a viscous substance were investigated during fermentation at different incubation temperatures (30, 35, 40, 45°C) with different inoculum sizes (10², 10⁴, 10⁶ cells/g). The protease activity increased contintously during the 30 hours of fermentation, and the activity increased in the order of pH 5.7 <10.0≤7.0. With lowering the temperature the protease activity appeared later but the protease production rate was faster. Solubilization and hydrolysis of proteins also increased through out the 30 hours of fermentation with a rice in temperature, but these increasing rates were slowed down at 45°C. The γ-GTP activity increased during the 30 hours of fermentation, and the rate of Natto's γ-GTP production at 45°C was slowest. L.S activity increased at log phase, and decreased after than. The stringiness of Natto in creased with time in fermentation at 30°C during 30 hours. At 35-45°C the stringiness showed maximum values, and decreased a little after than, in samples with karge inoculum size. The protease activity was kept high in Natto produced at 30-40°C, and γ-GTP activity, solubilization and hydrolysis of proteins and stringiness were kept high in Natto produced at 35, 40°C at 18-20 fermentation hours.