Cascade Valorisation of Lemon Processing Residues (Part I): Current Trends in Green Extraction Technologies and High-Value Bioactive Recovery

The global citrus processing industry generates 15–32 million tonnes of waste annual-ly, representing substantial environmental and economic burdens. However, lemon processing residues—peels, seeds, and pomace—constitute complex matrices rich in high-value compounds, amenable to cascade valorisation within circular biorefinery frameworks. This comprehensive review examines current trends in green extraction technologies for recovering bioactive compounds and functional materials from lemon waste streams. Following systematic bibliometric analysis of 847 publications span-ning 2003–2025, this work delineates the compositional heterogeneity of lemon frac-tions, quantifies typical industrial residue yields, and establishes a hierarchical framework for value-added products encompassing essential oils, pectin, polyphenols, seed oils, citric acid, industrial enzymes, α-cellulose, and nanocrystalline cellulose. Particular emphasis is placed on emerging sustainable extraction methodolo-gies—including ultrasound-assisted extraction, microwave-assisted extraction, super-critical fluid extraction, and enzyme-assisted extraction—which demonstrate yield improvements of 16–112% compared to conventional approaches whilst reducing en-ergy consumption by up to 95%. Critical research gaps are identified, including frag-mented valorisation approaches, insufficient techno-economic assessment, and limited industrial implementation at commercial scales. This review establishes that integrat-ed cascade biorefineries employing sequential green extraction protocols offer eco-nomically viable pathways for transforming lemon processing waste into diversified revenue streams, thereby advancing circular economy principles within the citrus in-dustry.