Abstract
To utilize kitchen refuse as renewable substrate for producing biodegradable poly lactic acid (PLA), it is critical to eliminate the initial L (+)/D (-) lactic acid contaminated in kitchen refuse and preserve glucose during removal of initial lactic acid. Several semi-anaerobic batch fermentations by P. shermanii were conducted with kitchen refuse and synthetic medium at various pH. Lactic acid was preferentially assimilated than glucose in kitchen refuse and synthetic medium at all pH conditions. P. shermanii exhibited diauxic growth without any obvious intermediate lag phase during sequential utilization of lactic acid and glucose. Effect of pH on specific growth rate of P. shermanii at kitchen refuse was more considerable than that at synthetic medium. According to decreasing pH, propionate yield was increased; 0.33g/g used lactic acid and glucose at pH 6.5 and 0.49g/g at pH 5.0. Acetic acid yield was also increased but not radically by each pH. The metabolites of pyruvate and succinate were significantly different by means of used substrates. By pH control from 6.5 to 5.0 after lactic acid consumption, growth of P. shermanii was entirely ceased and glucose could be preserved. This study indicates that removal of initial lactic acid by preferential substrate utilization of P. shermanii and glucose preservation by pH control may increase optical purity of lactic acid fermented from kitchen refuse medium.
