Abstract
Batch fermentation by Streptococcus bovis was carried out in order to investigate the characteristics of L-lactic acid fermentation from raw cassava as a substrate in tofu liquid waste (TLW) as a fermentation medium. The use of raw cassava-TLW system is intended to produce low cost L-lactic acid for the production of polylactic acid, a polymer used as biodegradable plastic, since raw cassava is an inexpensive raw material and TLW is cost-free. The raw cassava was compared to glucose and to tapioca and the TLW was compared to the standard basal medium, trypro-soya broth (TSB) at the 1% w/w sugar concentration. In order to maintain pH not to be lower than 5.0, 2 mol equivalent calcium carbonate (CaCO3) were added at initial fermentation. The results revealed that the maximum of L-lactic acid concentrations (CLa) obtained with addition CaCO3 in TSB and in TLW were 2.2 times and 1.6 times, respectively higher than that in TSB without CaCO3 addition. The maximum of L-lactic acid concentrations obtained with TLW were about 75 ± 5% of those obtained with TSB. The L-lactic acid productivities (PLa) with TLW were 1/3∼1/2 of those in TSB. Furthermore, experiments were also carried out in TLW at various sugar concentrations: 5, 10, 15, 20% w/w to investigate its effect on the L-lactic acid production. The maximum L-lactic acid concentrations was found to be (in decreasing order): raw cassava (6.66% w/w) > tapioca (5.36% w/w) > glucose (3.41% w/w) were reached at 10% w/w of sugar concentration.
