Effect of Product Inhibitions on L-Lactic Acid Fermentation From Fresh Cassava Roots in Tofu Liquid Waste by <I>Streptococcus bovis</I>

Abstract

The ef fects of product inhibition on lactic acid fermentation from fresh cassava roots in tofu liquid waste by Streptococcus bovis were studied in batch culture. The lactic acid production and growth rate gradually decrease with increase of inhibitor (lactic acid) concentration. The effects of product inhibition on productivity and specific growth rate were confirmed by the Lineweaver-Burk plot to noncompetitive inhibition. The product inhibition was evaluated by two inhibitions constants: inhibition constant for productivity (Ki) and inhibition constant for specific growth rate (Ksi). They decrease with increasing of inhibitor concentration. The values of Ki and Ksi in a rich media are smaller than those in a poor media and the Ki is larger than the Ksi in those media. The experiment results on batch fermentation agree with the noncompetitive inhibition model for about four days, but they deviate from the inhibition model after four days due to high inhibitor concentration. It is supposed that accumulation of lactic acid in broth decidedly causes damage on viable cell.