Caproic acid production from food waste using indigenous microbiota: Performance and mechanisms

Caproic acid (CA) production from food waste (FW) is a promising way for waste recycling, while the fermentation processes need further exploration. In this study, FW acidogenic fermentation under different pH (uncontrolled, 4, 5, 6) using indigenous microbiota was investigated. Result showed that substrate hydrolysis, carbohydrate degradation and acidogenesis increased with the increase of pH. Although various microbial communities were observed in FW, lactic acid bacteria (Lactobacillus and Limosilactobacillus) were enriched at pH lower than 6, resulting in lactic acid accumulation. CA (88.24 mM) was produced at pH 6 accounting for 31.23% of the total product carbon. The enriched lactic acid bacteria were directionally replaced by chain elongators (Caproicibacter, Clostridium_sensu_stricto, unclassified_Ruminococcaceae) at pH 6, and carbohydrates in FW were firstly transformed into lactic acid, then to butyrate and CA through lactate-based chain elongation processes. This work provided a novel CA fermentation pathway and further enriched the FW valorization.

Automated summary

Caproic acid (CA) production from food waste (FW) is a promising way for waste recycling. In this study, the fermentation process of FW acidogenic fermentation under different pH conditions was explored. The results showed that substrate hydrolysis, carbohydrate degradation, and acidogenesis increased with the increase of pH. Lactic acid bacteria were enriched at lower pH, leading to the accumulation of lactic acid. At pH 6, CA was produced through lactate-based chain elongation processes. This study provides a new pathway for CA fermentation and enriches the valorization of FW.