Enhanced effectiveness of Rhizopus oryzae by immobilization in a static bed fermentor for L-lactic acid production

摘要

The static bed fermentor was successfully employed for cell immobilization in this study. By complete immobilization of Rhizopus oryzae on a fibrous matrix, cell-free fermentation broth resulted in improved mass transfer and easy operation compared with free cell fermentation in a typical stirred fermentor. Environmental conditions generated in this fermentor configuration favoring the immobilized R. oryzae to grow and produce lactic acid without substrate repression at high initial glucose concentration during batch cultivation. Approximately 67% of the theoretical lactate yield (0.50 g/g) with the productivity of 1.05 g/Lh and the final titer of 75.28 g/L was obtained from fermentation with high glucose concentration (150 g/L). Complete cell immobilization supported the continuous operation of lactic acid production by R. oryzae since cell wash out was diminished. When operating the continuous culture at an appropriate dilution rate, a sufficiently high concentration of lactic acid (72.32 g/L) with a small amount of remaining glucose (<5 g/L) was obtained. Impurities remaining in the hydrolysates were generally considered toxic to microbial conversion; nevertheless, immobilized cells in the static bed fermentor exerted high tolerance to the salt impurities (Na+, Cl-) remaining in the cassava pulp hydrolysates to be used in lactate fermentation medium. (C) 2016 Elsevier Ltd. All rights reserved.