Chestnut and Grapevine By-Products: Bioactivity, Biotransformation, and Nutraceutical Applications

The growing interest in sustainable food systems has spurred research into the valorisation of agro-industrial by-products as sources of bioactive compounds. This review provides a comprehensive overview of the phytochemical composition, bioactivity, biotransformation, and potential nutraceutical applications of by-products from chestnut (Castanea sativa Mill.) and grape (Vitis vinifera L.). Recent studies identify matrices such as chestnut leaves, shells, and burs, as well as grape pomace, skins, seeds, stems, and vine shoots, as rich in phenolic compounds, dietary fibres, vitamins, and minor bioactives, with antioxidant, anti-inflammatory, and antimicrobial properties. Emerging evidence highlights the importance of gastrointestinal digestion and microbial biotransformation in modulating the bioavailability and biological efficacy of phenolic compounds, particularly fibre-bound phenolics. The review further discusses state-of-the-art analytical approaches for chemical characterisation, including chromatographic and spectrophotometric methods, as well as emerging strategies for extraction, encapsulation, and delivery to enhance stability and bioavailability. Finally, the integration of chestnut and grapevine by-products into nutraceuticals, functional foods, and natural preservatives is critically examined from technological, safety, regulatory, and sustainability perspectives. Overall, this synthesis underscores the potential of these underutilised biomass streams as multifunctional raw materials that support waste valorisation, resource efficiency, and the development of next-generation health-promoting ingredients aligned with circular bioeconomy principles.