Valorisation of Market Food Waste for Sustainable Polyhydroxyalkanoate Production: A Critical Review of Feedstock Variability, Bioprocess Integration and Scale-Up

Abstract

Market food waste is a concentrated, spatially identifiable stream of discarded fruits, vegetables and other perishables generated at wholesale and retail food markets. Its high moisture content, rapid degradability and variable carbohydrate composition create disposal problems but also provide a renewable carbon source for polyhydroxyalkanoate (PHA) production. This critical narrative review evaluates the evidence for converting market food waste to PHA, with particular attention to the acidogenic fermentation-volatilised fatty acid (VFA) route, microbial selection, polymer recovery, scale-up and sustainability. The literature shows that direct, fully integrated demonstrations using genuine market waste remain scarce. Stronger evidence exists for individual links in the chain: market vegetable and fruit wastes rapidly generate VFA-rich leachates; mixed food waste, organic municipal waste and food-industry residues can support PHA accumulation; and feast-famine mixed microbial cultures can operate without sterilised substrates. Pure cultures, especially Cupriavidus necator, can achieve high intracellular storage when waste-derived carbon is sufficiently clarified and appropriately dosed, whereas mixed microbial cultures reduce sterility requirements but introduce ecological and product-composition variability. The critical interface is not PHA biosynthesis alone but upstream control of hydrolysis and acidogenesis, because VFA concentration and acid spectrum govern inhibition, carbon conversion and the 3-hydroxybutyrate/3-hydroxyvalerate balance. Downstream stabilisation and extraction can also erase upstream gains by lowering molecular weight or increasing solvent, energy and chemical demand. Market-waste valorisation therefore cannot be assumed to be sustainable merely because the feedstock is discarded. The strongest deployment case is a source-segregated, short-haul biorefinery that prioritises prevention and edible redistribution, converts unavoidable residues to VFAs, directs selected carbon to PHA, and valorises residual solids and process liquors. Future work should prioritise market-specific seasonal campaigns, continuous pilot validation, contaminant tracking, harmonised mass balances, polymer-quality endpoints, and integrated techno-economic and life-cycle assessment.