Optimization of process parameters and estimation of kinetic parameters for lactic acid production by Lactobacillus casei MTCC 1423

Abstract

Central composite rotatable design was employed for the optimization of process parameters for maximizing the production of lactic acid (LA) by Lactobacillus (Lb.) casei MTCC 1423 from sugarcane molasses. The optimized conditions obtained were sugar concentration 190 g/L, CSL content 2.75% (v/v), pH 6.75, incubation temperature 38 °C, and incubation time 59.5 h with predicted 119.45 g/L maximal LA production. Validation experiments using these optimized condition has resulted in 120.23 ± 2.21 g/L lactic acid production. A Monod model and kinetic model proposed by Luedeking and Piret were considered to obtain kinetic parameters of relevance. Maximum specific growth rate (μmax.), Monod’s constant (Ks) and substrate inhibition constant (Ki) were determined as 0.7163 ± 0.0058 (h−1), 0.6203 ± 0.0013 (g/L), and 362.75 ± 0.76 (g/L), respectively. Maximum biomass concentration 14.98 ± 0.32 g/L (cell dry weight, CDW) under the optimized condition was found. The growth cell yield, YX/S (g/g) and product yield, YP/S (g/g) were determined as 0.3289 ± 0.0012 (g/g) and 0.9194 ± 0.0078 (g/g), respectively under the optimized conditions. Under the optimized condition obtained, growth (α) and non-growth associated constant (β) values were found as 0.4231 ± 0.0194 (gLA/gcells) and 0.1517 ± 0.0022 (gLA/gcells-h), respectively, demonstrating (since α/β > 1.0) that lactic acid production by Lb. casei MTCC 1423 was more contributed by growth associated segment as compared to non-growth associated segment and was directly proportional to concentration not depending on their growth. Kinetic parameter values at optimized conditions for sugar consumption, γ, η, and maintenance factor, m were obtained as 3.492 ± 0.0061 (gLA/gcells), 0.1663 ± 0.00528 (gsugar/gcells-h), and 0.00142 ± 0.0022 (gsugar/gcells-h), respectively.