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Description
Orange peel is an abundant agro-industrial by-product and a valuable source of essential oil rich in terpenes, particularly D-limonene. This study aimed to develop and optimize a solvent-free supercritical CO₂ extraction process for the recovery of high-value essential oil from waste orange peel and to evaluate the influence of extraction conditions on the yield and chemical profile of the obtained extracts. Supercritical CO₂ extraction was performed at pressures of 10 and 12 MPa and temperatures of 40, 45, and 50 °C. The obtained extracts were characterized using GC–MS method and Raman spectroscopy to assess changes in their chemical composition associated with the processing conditions. Extraction yields ranged from 0.552 to 1.752%, demonstrating a clear influence of pressure and temperature on the amount and characteristics of the recovered extracts. GC–MS analysis revealed D-limonene as the predominant compound in all samples, accounting for 92.7–96.7% of the total composition, while other mono- and sesquiterpenes were detected in lower amounts. Raman spectra confirmed the terpene-rich profile of the extracts and showed characteristic bands associated with D-limonene and other unsaturated hydrocarbon structures. Variations in Raman spectral profiles reflected changes in the relative contribution of lighter monoterpenes and higher-molecular-weight and oxidized components resulting from different extraction conditions. The consistency between Raman and GC–MS results demonstrate the potential of Raman spectroscopy as a rapid and non-destructive tool for comparative characterization and quality control of supercritical CO₂ extracts. Overall, the developed approach provides an environmentally sustainable route for converting orange peel waste into a high-value terpene-rich product with potential applications in the food, cosmetic, and pharmaceutical industries.
Keywords: Supercritical CO₂ extraction, orange essential oil, GC–MS analysis, Raman spectroscopy, waste valorization
Acknowledgements: This work was supported by the Ministry of Science, Technological Development and Innovation of the Republic of Serbia (Contracts No. 451-03-33/2026-03/200135 and 451-03-33/2026-03/200287) and the Western Balkans Innovation Voucher Programme (WBIV Application No. 09-2789; Contract No. 09-1007), within the Horizon Europe SPIN project (Grant Agreement No. 101058873).