Food-Grade By-Products as Sustainable Sources of Phytochemicals: Green Extraction Strategies, Encapsulation Technologies, and Applications in Functional Food Development

Food-industry by-products, including fruit and vegetable pomace, peels, and seeds, are increasingly recognized as sustainable sources of bioactive compounds, particularly phenolic compounds and carotenoids, including anthocyanins and lycopene. These phytochemicals exhibit a range of biological activities; however, their application in food systems is often limited by poor stability, low bioavailability, and susceptibility to environmental degradation. This review summarizes recent advances in the recovery and stabilization of bioactive compounds from food-industry by-products. Particular attention is given to green extraction technologies, including ultrasound-assisted, microwave-assisted, pressurized liquid, and supercritical fluid extraction, which can improve extraction efficiency while reducing solvent consumption and environmental impact. Furthermore, conventional and emerging encapsulation approaches, such as spray drying, ionic gelation, nanoemulsions, Pickering emulsions, liposomes, and lipid nanoparticles, are discussed as strategies to improve the stability, bioaccessibility, and delivery of recovered phytochemicals. The integration of green extraction and encapsulation technologies offers a promising strategy for the valorization of food processing residues and the development of innovative functional food ingredients. Such integrated approaches may contribute to waste reduction, improved resource efficiency, and the implementation of circular economy principles in food production.