Two-step pressurized liquid extraction: Sustainable recovery of phenolic antioxidants and high-purity limonene from orange peel waste

This study presents a novel biorefinery approach for the sustainable valorization of orange peel waste using pressurized liquid extraction (PLE) to selectively recover phenolic compounds and limonene. A consecutive two-step PLE strategy was developed, employing water for polyphenol extraction followed by ethyl acetate for limonene recovery. To maximize extraction efficiency and purity, a Box-Behnken design was employed to optimize temperature and extraction time of the two consecutive extractions. The optimal PLE extraction conditions were determined as 100 °C for aqueous extraction and 125 °C for ethyl acetate extraction, with 9 min per process. The first extraction involved three static cycles, while activated carbon was incorporated in the second step to minimize carotenoid co-extraction, yielding high-purity limonene. The aqueous extract was rich in flavanones, known for their antioxidant and health-promoting properties, while the ethyl acetate extract contained high-purity limonene, free from other volatiles or terpenes. Given its bioactive potential, limonene has applications in food, cosmetics, and as a bio-based alternative to petroleum-derived monomers in biopolymers. This optimized PLE process provides a rapid, efficient, and environmentally friendly alternative to conventional extraction techniques, supporting the circular economy by transforming agri-food waste into high-value bioactive compounds for food, nutraceutical, cosmetic, and biopolymer industries.