Biorefining food waste through the anaerobic conversion of endogenous lactate into caproate: A fragile balance between microbial substrate utilization and product inhibition

•Food waste fermentation and chain elongation occurred in the same bioreactor.•High caproate yields obtained without external electron donor supplementation.•Coexistence of lactate-producers and chain elongators in the reactor microbiome.•High carboxylic acids content in the fermentation broth hampered lactate uptake.•Insights into the inhibitory role of caproate on chain elongation in batch systems.