Abstract
To utilize kitchen refuse as a substrate for polylactic acid (PLA), it is essential to eliminate the L-and D-lactate initially contaminated, while preserving the glucose in it. Both the specific growth rate (μ) and the substrate consumption rate (rs) of Propionibacterium sheymanii on kitchen refuse medium (KRM) were compared at each pH 5.0, 5.5, 6.0 and 6.5 with artificial kitchen refuse medium (AKRM), lactate medium (LM) and lactate-glucose medium (LGM) which respectively contains glucose, lactate, and a mixture of these substrates. Lactate initially contaminated in KRM was assimilated prior to glucose by P. sheymanii at each pH. In KRM and LGM, enhancement and reduction of cell growth by lactate were observed at pH 6.5 and 5.0, respectively, when compared with that in AKRM. As a result, a glucose consumption rate in KRM was more than twice, but was significantly lower than that in AKRM at pH 6.5 and 5.0, respectively. Glucose could be preserved by a low glucose consumption rate when pH was changed from 6.5 to 5.0 after lactate exhaustion in KRM. Preferential substrate utilization of P. sheymanii and a pH change from 6.5 to 5.0 can increase the optical purity of lactic acid while preserving glucose.
