Acid hydrolysis and lactic acid fermentation of Korean food waste by engineered Saccharomyces cerevisiae

The acid hydrolysis is one of the most promising processes for the conversion of various biomass to value-added products among the several biomass conversion process. Korean food waste squeezed water by screw press contains about 25.7 % of glucose. The acid hydrolysis was performed using a 1L Parr stainless steel reactor. A reactor was loaded with 100g of air dried food waste and 400mL liquid (a final ratio of solid to liquid =1:4). Dilute sulfuric acid hydrolysis was applied at conditions 160°C, 0.4% (w/v) H₂SO₄, and 64.5 min residence time. After reaction, liquid was separated from solid and second hydrolysis was performed by liquid at 121 C, pH 0.7 for 60min in an autoclave. Autoclaved liquid was concentrated 5 times and extracted organic acid by Liquid-Liquid extraction using TAPO (Trialkylphosphine oxide). The concentration of glucose in the extracted liquid was about 69.7g/L. In addition, a recombinant S. cerevisiae harboring a plasmid containing a codon-optimized lactate dehydrogeases (LDH) gene derived from Lactobacillus casei was constructed. We have also constructed another lactic acid producing S. cerevisiae in which pyruvate decarboxylases (PDC1 & PDC5) were replaced with lactate dehydrogease (LDH) on the chromosome. These strains were used to produce lactic acid from the glucose derived from food waste. This system with food waste as a biomass can be applied to produce other organic acids such as 3-hydroxypropionic acid, adipic acid, succinic acid, and other biochemicals such as isobutanol and isobutylene which will result in producing cost-effective biochemicals against petroleum-based chemicals.