Lactic acid production from starch hydrolysates using lactococcus lactis IO-1

Enzymatic hydrolysis of 20 percent w/v sago and cassava starches was studied at pH 6.5, 95 deg C, 2 h for liquefaction and at pH 4.3, 60 deg C, 72 h for saccharification, using 0.05 percent v/v Termanyl 120 L TYPELS and 0.06 percent v/v Dextrozyme, respectively. When 99.6 percent of sago and cassava starches were used after 74 h of hydrolysis, 146.70, 289.0 g/l and 143.87, 287.46 g/l of dextrose equivalent (DE) and glucose were produced, respectively. The optimum saccharifying time for sago and cassava starches was found to be 48 and 24 h, respectively. Enzyme concentrations did not significantly affect cassava starch hydrolysis at high ratios of starch (S) : Termamyl (T) : Dextrozyme (D). The following Response Surface Analysis model for enzymatic hydrolysis of cassava starch was obtained; Y = 18.07S + 1332.99T + 1.05D - 0.29S**(2) + 32.64ST - 7586.89T**(2) + 54.05SD - 6814.79TD + 1661.62D**(2). When Lactococcus lactis IO-1 was used in a batch fermentation at 37 deg C and pH 6.0, it produced lactic acid with more than 90 percent conversion yield of glucose in a basal complex medium containing glucose as carbon and energy source. Corn steep liquor was found not suitable substitute for yeast extract and polypeptone as a nitrogen source. Cassava starch hydrolysate was very appropriate carbon source for growth and lactic acid production in a basal complex medium. Very high product yield (Y sub(p/s) = 1.05 g/g, based on glucose concentration) and volumetric productivity (Qp = 3.45 g/l h) of lactic acid were obtained in batch fermentation with 25.04 g/l glucose from starch hydrolysate. Based on kinetic modeling on the batch lactic acid fermentation, the concomitant substrate and product inhibition and Luedeking-Piret kinetics can sufficiently describe the growth and product formation with modified saturation constant (K sub(s)) and non-growth associated constant (alpha) reported previously from lactic acid fermentation of sago starch hydrolysate.