High-value caproate synthesis from food waste: mechanisms, regulation, and sustainable scaling-a comprehensive review.

The global surge in food waste (FW) generation, coupled with the growing demand for sustainable alternatives to fossil fuels, has driven intensive research on valorizing FW into high-value caproate. This review systematically summarized the mechanisms, competing pathways, fermentation configuration, and performance of caproate production from FW. Key influencing factors, challenges, and emerging strategies for enhancing caproate production were comprehensively analyzed. Moreover, the environmental and economic assessment of this technology were discussed. Caproate biosynthesis from FW typically involves sequential hydrolysis, acidogenesis and chain elongation (CE), with methanogenesis, acrylate pathway and excessive ethanol oxidation as the primary competing pathways. Laboratory-scale studies have employed integrated, multistage and secondary fermentation configurations. Fermentation processes and caproate yield were governed by a combination of environmental parameters (pH, temperature), operational conditions (hydraulic retention time (HRT), substrate loading and concentration), inoculum sources, and ammonium content. Efficient caproate synthesis is hindered by substrate heterogeneity, microbial competition, inhibition from toxic substances, and unstable microbial communities. Strategies including co-fermentation, fermentation configuration optimization, carbon materials addition, substrate pretreatment and microbial community reinforcement have been validated to effectively promote caproate production. Environmental and economic assessment support the feasibility of this technology as an eco-friendly and cost-competitive approach. Finally, future research perspectives were proposed to address current bottlenecks and promote industrial application.