Abstract
Improvement methods of polysaccharide degradation and lactate yield in thermophilic L-lactic acid fermentation were evaluated with kitchen garbage and high-yielding rice as materials for biodegradable plastics. Based on the batch experiments, it was cleared that low decomposition ratio of total sugar and lactate yield were obtained from kitchen garbage without banana skin, comparing to those from kitchen garbage. It was found that pretreatment of starch by heat from 55°C to 100°C had little influence on polysaccharide degradation and lactate yield of kitchen garbage. Addition of nitrogenous organic compounds i.e. yeast extract and polypeptone were investigated in order to evaluate influences of organic nitrogen concentrations on decomposition ratio of total sugar and lactate yield with high-yielding rice. Compared to the case without addition of nitrogenous organic compounds, higher polysaccharide decomposition ratio and lactate yield can be obtained, and it is determined that addition of both 0.25 g/L of yeast extract and 0.25 g/L of polypeptone is desirable for thermophilic L-lactic acid fermentation with high-yielding rice. Meanwhile, little influences of addition of minerals on the fermentation were found. In addition, it was suggested that the suitable operationg condition for thermophilic L-lactic acid fermentation with high-yielding rice was that of pH 5.5 and 55°C.
