Valorization of Food Industry By-Products for Sustainable Functional Food Production: Recent Advances and Future Perspectives

Food industry by-products represent an abundant and underexploited source of bioactive compounds, dietary fibers and proteins with significant potential for functional food development. Recent studies estimate that up to 30 to 50% of processed raw materials are discarded as by-products, while food waste contributes approximately 8–10% of global greenhouse gas emissions, equivalent to nearly 3.3 billion tons of CO2 annually. This review critically evaluates advances (2015–2026) in the valorization of food industry by-products, with a focus on technological efficiency, health-related evidence, and environmental impact. Specifically, it addresses the following research question: to what extent do current valorization strategies provide measurable technological, nutritional, and environmental advantages over conventional food production systems? Emerging extraction technologies including ultrasound- and microwave-assisted extraction (20–40 kHz, 30–60 °C), supercritical fluid extraction (200–350 bar, 35–60 °C), enzymatic hydrolysis, and fermentation demonstrated improvements in extraction yields (up to 20–50% increases compared to conventional methods) and higher purity in the recovered compounds. These approaches enable the isolation of compounds such as pectins from citrus peels, polyphenols from grape pomace, galacto-oligosaccharides from dairy whey, and collagen from fish by-products. From an environmental perspective, valorization strategies can reduce waste disposal and associated emissions by up to 30%, depending on the scale and type of by-product processing. Furthermore, these approaches contribute directly to circular economy models and support multiple Sustainable Development Goals, particularly SDG 12 (responsible consumption and production) and SDG 13 (climate action). However, challenges remain, including variability in raw material composition, scalability limitations, and the limited availability of high-quality clinical evidence supporting health benefits. By integrating nutritional potential, technological feasibility, and sustainability indicators, this review provides a comprehensive and critical assessment of the current state of by-product valorization and identifies key gaps for future research.