Beyond enzymes and organic acids, solid-state fermentation as an alternative for valorizing fruits and vegetable wastes into novel bio-products in a circular economy: A critical review

The magnitude of the global fruit and vegetable waste (FVW) generated and its contribution to environmental pollution and greenhouse gas emissions are alarming and necessitate appropriate remediation measures. In addition to typical FVW applications such as landfilling and manure production, our previous article critically explored the added value of FVWs for producing enzymes and organic acids by deploying various microbial processes. However, with the advancement of novel solid-state fermentation (SSF) technology, several products (other than enzymes and organic acids) have been developed from FVWs. This review article addresses the valorization of FVWs into the production of various bioproducts (i.e., microbial inoculants, single-cell proteins, aquafeeds, bioinsecticides, antimicrobial agents, or prebiotics), platform chemicals (i.e., polyphenols, biocolorants, exopolysaccharides, biosurfactants, biocomposites, or carbon dots), and biofuels. Upscaling and downstream aspects, techno-economic feasibility reports, and lifecycle assessments are also covered in the article. Rather than an overburden, FVWs can be regarded as a potential substrate for SSF, and successful transformation to novel bioproducts further contributes to a circular economy.