초록
Uninvestigated control factors of meta-fermentation, the fermentative production of pure chemicals and fuels in a mixed culture system, were examined for production of optically pure l-lactic acid (LA) from food waste. In meta-fermentations by pH swing control, l-LA production with 100% optical purity (OP<SUB>l-LA</SUB>) was achieved even using unsterilized model kitchen refuse medium with preferential proliferation of l-LA-producing Bacillus coagulans, a minor member in the seed, whereas agitation decreased OP<SUB>l-LA</SUB> drastically. pH constant control shortened the fermentation time but decreased OP<SUB>l-LA</SUB> and LA selectivity (S<SUB>LA</SUB>) by stimulating growth of heterofermentative Bacillus thermoamylovorans. Deliberately switching from pH swing control to constant control exhibited the best performance for l-LA production: maximum accumulation, 39.2gL<SUP>-1</SUP>; OP<SUB>l-LA</SUB>, 100%; S<SUB>LA</SUB>, 96.6%; productivity, 1.09gL<SUP>-1</SUP>h<SUP>-1</SUP>. These results present a novel pH control strategy for efficient l-LA production in meta-fermentation based on a concept different from that of pure culture systems.