Bioactive Compounds in Chestnut (Castanea sativa Mill.): Composition, Health-Promoting Properties, and Technological Applications

Chestnut (Castanea sativa Mill.) is a Mediterranean staple food valued for its cultural heritage, gastronomic identity, nutritional profile, bioactivities, and socio-economic and environmental relevance. This narrative review synthesizes current knowledge on chestnut fruits and by-products, linking ecophysiology and genetic diversity to chemical composition and functionality. It summarizes the nutrient profile (high starch and dietary fiber; gluten-free; B vitamins; essential minerals; and favorable fatty acids) and the diversity of phytochemicals—particularly phenolic acids, flavonoids, and ellagitannins (e.g., castalagin and vescalagin)—that underpin antioxidant, anti-inflammatory, antimicrobial, anti-proliferative, and metabolic effects demonstrated across in vitro, cellular, and in vivo models. We compare conventional and green extraction strategies (e.g., hydroethanolic, ultrasound-/microwave-assisted, and supercritical and subcritical water), highlighting method-dependent yields, composition, and bioactivity, and the valorization of shells, burs, and leaves within circular bioeconomy frameworks. Technological applications span functional foods (gluten-free flours, beverages, and emulsions), nutraceuticals, and cosmetics (skin-protective and regenerative formulations), and active packaging/biopolymers with antioxidant and antimicrobial performance. We discuss sources of variability (cultivar, environment, maturation, and processing) affecting bioactive content and efficacy, and outline future directions. Finally, this review emphasizes the importance of university-facilitated co-creation with companies and consumers—within the framework of Responsible Research and Innovation—as a pathway to strengthen the economic valorization and full utilization of the chestnut value chain, enhancing its societal relevance, sustainability, and health-promoting potential.