Green Extraction of Citrus Peels via Supercritical CO₂ Technology with a Focus on Limonene

The peels generated during the processing of citrus fruits—specifically mandarin (Citrus reticulata L.), grapefruit (Citrus paradisi L.), lemon (Citrus limon L.), and orange (Citrus sinensis L.)—serve as a rich source of essential oils and bioactive compounds. In this study, essential oils and limonene components were recovered via eco-friendly Supercritical Fluid Extraction (SFE) from citrus peels whose structural integrity was preserved through freeze-drying (lyophilization).

Key Findings and Details

High Extraction Yield: Compared to conventional methods, maximum yields were achieved by utilizing the PEX1002C supercritical fluid extraction system developed by Polat Makina alongside freeze-dried citrus peels:

Orange Peel (C. sinensis): 7.50% yield.

Grapefruit Peel (C. paradisi): 6.95% yield.

Mandarin Peel (C. reticulata): 6.88% yield.

Lemon Peel (C. limon): 5.56% yield.

Critical Bioactive Compound (Limonene Analysis): GC-MS analysis confirmed that limonene constitutes the primary active component across all extracted citrus essential oils:

Orange Oil: 98.5% limonene, 1.7% beta-myrcene, 1.4% gamma-terpinene.

Grapefruit Oil: 97.9% limonene, 1.8% myrcene, 1.5% linalool.

Mandarin Oil: 85.8% limonene, 6.2% beta-myrcene, 5.1% gamma-terpinene.

Lemon Oil: 79.8% limonene, 15.1% beta-pinene, 9.5% gamma-terpinene.

Significance of Pre-treatment: The freeze-drying (lyophilization) pre-treatment—comprising crystallization (-80 °C for 24 hours), sublimation, and desorption stages—safeguarded the chemical integrity of thermolabile (heat-sensitive) compounds, ensuring maximum extraction efficiency and product purity.

These findings demonstrate that citrus processing waste—when valorized using eco-friendly green extraction technologies (SFE)—can be transformed into high-value natural ingredients for the food, cosmetics, and pharmaceutical industries.

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