Steering microbial communities via the lactate route to selectively produce high concentrations of propionate from food waste

Propionate is a valuable platform chemical, in particular as a precursor for the production of sustainable jet fuel. However, its biological production remains a challenge, particularly in mixed-culture waste fermentation, where a mixture of volatile fatty acids is typically generated with a low propionate selectivity. This study investigates a two-stage fermentation process to convert food waste into propionate using two different inocula. The strategy relies on driving microbial metabolism toward lactate production in the first-stage fermentation, which will serve as the intermediate for propionate production during the second step of the fermentation. With both inocula, lactate was effectively consumed and preferentially converted into propionate and acetate, with propionate concentrations reaching up to 17.90 ± 0.35 g L −1 , representing 45.51 ± 1.81% of total COD metabolites. This production was associated with the growth of Anaerosporobacter , Tyzzerella and some Clostridium genera, in both inocula, suggesting their pivotal role in the lactate-propionate pathway. Overall, these results demonstrate that a two-stage fermentation strategy can efficiently target high propionate concentrations and reasonable selectivity using mixed cultures, by specifically targeting the lactate-propionate pathway, regardless of the initial inoculum.