Lactic acid production from lactose by Lactobacillus plantarum: kinetic model and effects of pH, substrate, and oxygen

Abstract

Batch fermentation of lactose to lactic acid was conducted using Lactobacillus plantarum under aerobic and anaerobic conditions (operation without aeration). Synthetic lactose medium was used as the culture medium and the effects of pH and substrate concentration on cell growth and lactic acid production were investigated. Lactic acid fermentation with this bacterium is found to be homolactic and primarily growth associated. Optimum pH for cell growth and acid production was found to be between 5 and 6. Anaerobic fermentation gave a higher lactic acid yield of about 2.3 times that for aerobic fermentation. Cell growth rate was about two times higher, but cell yield was only about 80% of that for aerobic fermentation. Batch fermentation studies with no pH control indicate that lactose slightly inhibits cell growth in the exponential growth phase but there are no effects in the stationary and death phases. The high lactic acid yield (0.95∼1.03 (w/w), the complete conversion rate is 1.05 (w/w)), tolerance of low pH conditions and the high cell growth rate indicate a great potential for the use of L. plantarum in lactic acid fermentations for industrial applications. Taking pH variations into account in a Monod's model, a nonlinear parameter estimation procedure using the Gaussian method and numerical integration of the differential equation by the fourth-order Runge–Kutta method are used to obtain optimal kinetic model parameters.