Kinetic modeling of lactic acid production from molasses using Enterococcus faecalis RKY1

A kinetic model has been developed for batch fermentation of cane-sugar molasses for lactic acid production by Enterococcus faecalis RKY1. Parameters of the kinetic model have been determined based on experimental data by using genetic algorithm. The values of key kinetic constants are maximum specific growth rate (μmax), 1.6 h−1, growth-associated constant for lactic acid production (α), 0.26 g g−1; maximum specific lactic acid production rate (qp,max), 3 g g−1 h−1; maximum specific sugar utilization rate (qs,max), 3.33 g g−1 h−1. It has been observed that the growth of biomass and lactic acid production are affected by lactic acid inhibition and it has been taken into account with an exponential term. However, effects of substrate limitation and substrate inhibition have been found to be relatively small. When compared with batch experimental data, the model provides good predictions for growth of biomass, sugar consumption and lactic acid production profiles on media with initial molasses concentration ranging from 130 to 333 g/l with few exceptions. Effect of pH on kinetic parameters has also been studied. It has been found that the growth of biomass and lactic acid production are strongly influenced by pH. Optimum pH is found to be 7.