Abstract
For bio-recycling of food waste to produce value added-products, lactic acid fermentation from kitchen refuse as a renewable substrate for high concentration and high purity of L(+)-lactic acid by Rhizopus oryzae KPS 106 was studied in this work. To modify kitchen refuse as medium, pretreatment methods by saccharification, natural precipitation, freezing and thawing technique, centrifugation and chromatography were adopted. The main sugar in saccharified kitchen refuse (SKR) was glucose (98.51% of total sugar). And freezing and thawing method was major technique for remove suspended solids (SS) in SKR. We was found that it was possible to separate sugar from SKR by ion-exclusion chromatography and use as a substrate for lactic acid fermentation by R. oryzae KPS 106 in submerged culture. The sugar consumption and lactic acid fermentation by R. oryzae were significantly affected by composition in separated sugar from kitchen refuse (KRS). This fungus required addition of some inorganic supplements in KRS to enhance sugar consumption and lactic acid production abilities. When comparing lactic acid production from KRS medium with glucose medium, R. oryzae could assimilate sugar and produce lactic acid from KRS medium as well as glucose in synthetic medium. The lactic acid yield from KRS and glucose medium were 63.43±2.31 and 73.28±2.92% (w/w) (based on initial total sugar concentration), respectively after 72 h, at 35°C in rotary shaking rate 100 rpm. In addition, the lactic acid production from KRS medium was 98.67±0.28% L(+)-form.
