Comparison of indigenous and exogenous microbiota: necessity of inoculation for lactic acid production

Lactic acid (LA) production from food waste fermentation offers a promising route for organic waste valorization and aligns with a circular economy concept. However, the microbial metabolic interactions remain poorly understood. This study demonstrates that regulating indigenous microbiota with eggshell (EG) buffer can achieve efficient LA production (33.2 ± 2.6 g COD/L), a yield only 3.6 % lower than that obtained with anaerobic sludge inoculation. Metabolic pathway analysis indicated that EG addition not only stabilized fermentative pH but also redirected the carbon flux toward LA. High-throughput sequencing showed that homofermentative LA bacteria (Streptococcus and Enterococcus) accounted for 37.3 % of the microbial community under EG addition alone. Additionally, EG modulated genes in the Embden-Meyerhof-Parnas, the hexose monophosphate, and the hexokinase pathway. This study confirms that an EG-buffered fermentation system can activate indigenous microbiota for high-efficiency LA production, demonstrating that exogenous inoculation is non-essential and offering a cost-effective approach for sustainable LA synthesis.