Simultaneous saccharification and fermentation of starch to lactic acid

Abstract

Batch experiments were conducted to establish optimum operating conditions for the simultaneous saccharification and fermentation (SSF) of starch to lactic acid acid using Lactobacillus delbrueckii. A predictive model was developed for SSF by combining the kinetics of saccharification and fermentation. Saccharification kinetics were determined through experiments on starch hydrolysis in which the effects of temperature, pH and different fermentation products as inhibitors were studied. Fermentation kinetics was studied using glucose as substrate and effect of initial lactate on growth of Lactobacillus delbrueckii was also examined. The saccharification kinetics were fitted using a Michaelis–Menten type equation, while the growth kinetics of L. delbrueckii was represented by a Monod expression incorporating lactic acid inhibition. The kinetic model was used to predict the performance SSF accurately. The saccharification rate was always higher SSF than in simple saccharification (SS) at all substrate concentrations. Lactate productivity was 1.21 g/l h for SSF conducted under optimum conditions with 250 g/l potato starch, higher than that of lactic acid productivity by fermentation after saccharification. Potato tuber and pearl tapioca are good raw materials for the production of lactic acid using SSF with yields up to 70%.