A low-cost Kodo millet bran residue was utilized as feedstock for the production of D (-) lactic acid (DLA) using Lactobacillus delbrueckii NBRC3202 under anaerobic condition. Data culled from a series of batch fermentation processes with different initial Kodo millet bran residue hydrolysate (KMBRH) and DLA concentrations were used for kinetic model development. Both simulated and experimental data were in good agreement for cell growth, KMBRH utilization, and DLA formation. The values of kinetic constants specific growth rate, (μm = 0.17 h-1); growth (αP = 0.96 g.g-1) and non-growth (βP = 1.19 g.g-1.h-1) associated constant for DLA production and the maximum specific KMBRH utilization rate, (qG, max = 1.18 g.g-1.h-1) were in good agreement with the literature reports. Kinetic analysis elucidated that L. delbrueckii growth was predominantly influenced by KMBRH limitation and highly sensitive to DLA inhibition. Fed-batch fermentation studies demonstrated the existence of substrate and product inhibition paving the scope for process intensification.
Keywords: D (−) lactic acid; Luedeking-Piret equation; kinetic modeling; millet bran; product inhibition; substrate inhibition.