Optimization of dilute sulfuric acid pretreatment of kitchen garbage for increased lactic acid production

Based on previous studies on lactic acid (LA) production from food waste (FW, “cooked” waste from canteens and restaurants), the present study explored the feasibility of LA production from kitchen garbage (KG, “raw” waste from household kitchens). A considerable pretreatment method for fermentable sugar release in KG was investigated, and acid pretreatment was found to significantly promote polysaccharide hydrolysis. Furthermore, the optimal conditions of acid pretreatment were investigated through response surface methodology and determined to be 1.45% (w/v) sulfuric acid, 118.14 °C and 0.66 h, respectively, resulting in a polysaccharide conversion rate of 72.88%. Fourier transform infrared spectroscopy and X-ray diffraction revealed that the hemicellulose and lignin of KG were dissolved, which increased polysaccharide conversion in KG during acid pretreatment. Enterococcus mundtii was used in LA fermentation because it could metabolize a variety of fermentable sugars, including glucose, xylose, and fructose. Finally, the feasibility of LA production from KG hydrolysate with acid pretreatment was explored, and the maximum LA concentration and yield reached 60.3 g/L and 0.83 g/g total sugar, and 0.31 g/g KG (dry weight), respectively, which were 11% higher than those without acid pretreatment.