Batch and continuous fermentation of lactic acid by Lactococcus Lactis using sago starch hydrolysate

Paula @ Paulawati, Jolhery (2002) Batch and continuous fermentation of lactic acid by Lactococcus Lactis using sago starch hydrolysate. Masters thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

Sago starch was hydrolysed enzymatically for use in both the batch and continuous fermentation studies. The best parameters for enzymatic hydrolysis were obtained from a glucose concentration of 20% DS sago starch, liquefaction and saccharification at pH 6.5 and pH 4.5 respectively, with the incubation period for liquefaction at 2 hours. Optimum enzyme concentration for hydrolysis were 0.5μl/g and 0 6μl/g for Termamyl 120L and Dextrozyme, respectively. Batch fermentation trials utilising different initial glucose concentration of either 60g11 or 70g/1 exhibited only minimal differences in the amount of lactate and biomass produced kligher initial glucose concentration results in higher residual glucose, thus needed longer i riod for complete consumption. Batch fermentation trials under controlled pH (pH6) induced faster with almost complete glucose consumption (98% consumption, residual glucose 1. lOg/l) compared to uncontrolled pH (75.8% consumption, residual glucose 13.4g/I) after 48 hours. The other advantage is the higher lactate production (37.3g/l compared to 30.7g/l) and volumetric lactate productivity (0 78g/Ihr compared to 0.64g/Ihr). Continous fermentation trials were analysed and limited to dilution rates of 0.05hr1, 0.06hr' and 0.08hr' where lactate concentration was reduced gradually from 37. lg/1 to 34.4g/l and to 30.3g11, respectively. Biomass (DCW) was highest at the lowest dilution rate of 0.05hr', at 2.11g/1. This decreases at higher dilution rates of 0.06"' and 0.08hr' to 1.97g/l and 1.83g/l, respectively. As such, higher dilution rates were not feasible due to possible wash-out of viable cells from the fermemor. Apart from the decreasing concentration of the biomass, high dilution rate (0.08hr"') also suffers from uneconomically high concentration of residual glucose (22.2g/1). In order to maintain high cell density in the fermentation while working at higher dilution rate (thus increasing lactate productivity), a hollow fibre filter module (HFM) was introduced into the system, at dilution rates 0.1 lhr', 0.24hr' and 0.33hr-', resulting in higher lactate concentrations at 41 Og/l, 38.4g/1 and 35.4g/l, respectively. Consequently, volumetric lactate production was highly amplified at 4.51 g/l, 9 22g/1 and 1 1.70g/l while maintaining high cell density in the fermentor at 2.87g/l, 3.35g/l and 3.60g/l, respectively. The high cell concentration at high dilution rate managed to reduce the concentration of residual glucose while generating higher lactate production in the system

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