Orange peel waste valorization: A comprehensive review of sustainable production and high-value resource recovery

Citrus processing generates large quantities of agro-industrial residues that pose environmental challenges but also offer valuable opportunities for sustainable valorization. Among them, orange peel waste (OPW), one of the most abundant citrus by-products, is rich in pectin, polyphenols, flavonoids, carotenoids, and essential oils, particularly d -limonene. Growing interest in circular and bio-based economy strategies has driven research on recovering these bioactive compounds. This review provides a comprehensive overview of sustainable OPW valorization. It first discusses the chemical composition of OPW and its importance for downstream processing, then critically evaluates conventional and green extraction technologies, including enzyme-, ultrasound-, microwave-assisted, deep eutectic solvent (DES), and supercritical CO₂ extraction, considering efficiency, scalability, and environmental performance. Integrated biorefinery approaches aimed at maximizing resource utilization and minimizing waste are also examined. OPW is highlighted as a versatile renewable feedstock for producing high-value compounds and bio-based materials. Advances in green extraction and hybrid bioprocessing have improved recovery while reducing solvent use and environmental impact. Citrus-derived compounds show broad applications in functional foods, nutraceuticals, biodegradable materials, environmental remediation, and emerging nanomaterials. Unlike previous reviews, this work integrates extraction technologies, environmental applications, and citrus-derived nanotechnology within a unified framework supporting circular bioeconomy, waste reduction, and sustainable resource management.