From fruit waste to foods via fermentation
The increasing generation of fruit waste represents a major environmental and economic challenge for the agri-food sector, while also offering significant opportunities for sustainable valorisation within the framework of the circular economy. Fruits rejected for cosmetic reasons, together with processing by-products, are rich sources of dietary fibre, sugars and bioactive compounds that can be converted into value-added products. This review aims to provide a comprehensive overview of microbial fermentation as a sustainable strategy for fruit waste valorisation, with particular emphasis on the role of lactic acid bacteria, acetic acid bacteria, yeasts and microbial consortia in improving the nutritional, technological and functional properties of fruit-derived substrates. Current evidence demonstrates that microbial fermentation not only preserves fruit biomass but also enhances its value through the degradation of complex carbohydrates, the biotransformation of phenolic compounds, the production of bioactive metabolites and the generation of functional ingredients. This review further discusses the contribution of viable microorganisms and postbiotic components to product functionality, as well as the importance of microbial viability, processing conditions and storage stability for the development of safe and functional fermented foods. In addition, it highlights recent advances in the use of microbial consortia and identifies the mechanisms governing microorganism–plant matrix interactions as a key area requiring further investigation. Overall, the available literature supports fermentation as a versatile and effective strategy for transforming fruit waste into high-value food products. By integrating current knowledge on microbial metabolism, functionality and processing challenges, this review identifies the main scientific and technological gaps and outlines future research priorities, including microbial consortium design, process scale-up, regulatory considerations and life cycle assessment, to facilitate the industrial implementation of sustainable fruit waste biorefineries.