Enhanced lactic acid production from food waste in dark fermentation with indigenous microbiota

Abstract

This study investigated the effects of pH, total solids (TS) content, and enzymatic pretreatment on lactic acid (LA) production from food waste with indigenous microbiota. A multilevel factorial design was applied to all the essential factors for making LA production the most efficient and productive. The experimental data revealed that all the tested factors had a significant effect on the LA produced. The production of LA was progressively increased with the increase of TS content from 50 to 150 g-TS/L. With enzymatic pretreatment, the maximum production of volatile fatty acids (VFAs) and LA was, respectively, 26.17 g/L and 12.87 g/L at a pH of 6 and 150 g-TS/L. A LA yield of 0.09 g/g-TS with a productivity of 1.29 g/L day was achieved at mesophilic temperature of 37 °C and optimal operating conditions. Interestingly, the production of VFAs was 2.6-fold, and LA was 3-fold higher compared to those obtained with untreated food waste under same conditions. These results showed that enzymatically pretreated food waste at TS 15% can provide high production of VFAs and LA. The high selectivity of LA in the fermentative product, along with others, could make downstream processing economical. The multilevel factorial design predicted optimum conditions and presented a good agreement with a mean error of less than 5%.