Tailored production of butyric acid from mixed culture fermentation of food waste

Volatile fatty acids (VFA) are high-value-added products obtained from the fermentation of waste feedstock. These are generally produced as a VFA mixture of C2 - C6 acids through mixed culture fermentation. The prospect of tailoring the process conditions in mixed culture fermentation is attractive since it can produce a predominance of a target VFA without the need for a sterile, pure culture-based process. Among VFAs, butyric acid has a wide range of industrial applications which are currently met by chemical synthesis. This study showed a targeted production of butyric acid in a mixed culture VFA fermentation under psychrophilic temperature. Compared to mesophilic conditions, the butyric acid produced at 17°C accumulated to up to 7 days at 0.5 g/L compared to in 37°C where it was not detected after day 1. The microbial community study showed the increased abundance of Sporosarcina and Solibacillus genus which degrades proteins, aiding the Clostridium_sensu_stricto spp. in producing butyric acid potentially through protein degradation. Within the detected bacterial diversity showing a lower Shannon index of 0.84 at 17ºC, these genera also showed a higher abundance. For further enhancing the hydrolysis, thermal-alkaline pretreatment of food waste was performed. However, it reduced the subsequent production of butyric acid as compared to untreated food waste. Under 17ºC, butyric acid’s concentration was 0.06 g/L, while at 37ºC, it was 0.12 g/L. This showed that intrinsic microflora of food waste was essential for its production. This selective accumulation of butyric acid over other VFAs offers a means of targeted VFA production using mixed culture fermentation under psychrophilic temperature. • Sustained accumulation of butyric acid under 17°C than 37°C. • Most abundant genus found were Solibacillus and Sporosarcina. • Butyric acid is generated under 17°C potentially due to protein degradation.