Fermentation of Fruit By-Products as a Tool for Nutritional and Environmental Sustainability.

Mounting volumes of fruit processing by-products pose an environmental challenge, yet these wastes harbor rich polyphenol reservoirs locked within plant cell walls. Fermentation has emerged as a green biotransformation strategy to unlock these bound antioxidants without the need for chemical solvents, converting waste streams into value-added nutraceutical ingredients. This review summarizes recent advances in fermenting fruit by-products to boost their total polyphenol content (TPC) and antioxidant capacity, illustrating fermentation's role in both functional enhancement and sustainable waste valorization. Across diverse fruit substrates, microbial fermentation consistently increases TPC and enhances antioxidant activity, demonstrating significant functional enrichment. More importantly, unlike conventional solvent extraction, fermentation-driven valorization reduces chemical waste and allows full incorporation of the biomass into edible products, including bakery products, beverages, and fermented dairy alternatives. This sustainable approach aligns with circular economy principles by turning food waste into functional ingredients, effectively bridging nutritional enhancement with environmental responsibility. Overall, the findings highlight fermentation as an innovative pathway for waste upcycling in the food system, opening new avenues for antioxidant-rich, zero-waste products and their integration into sustainable food ingredient development, while also indicating that the main barrier to industrial translation lies not in functional efficacy but in process compatibility, reproducibility, and scalability under realistic food processing conditions.