GREEN extraction of antioxidant carotenoids from fresh ORANGE PEEL USING CO₂-expanded ethanol

Carotenoids are valuable bioactive pigments widely used in the food, pharmaceutical, and cosmetic industries due to their potent antioxidant properties. The growing demand for sustainable extraction processes has driven interest in valorizing agro-industrial by-products, such as orange peel, which is particularly rich in carotenoids. Traditional extraction methods typically rely on toxic organic solvents and energy-intensive procedures, raising environmental and safety concerns. In this study, a green and efficient method based on CO₂-expanded ethanol (CXE) was developed for the extraction of antioxidant carotenoids from fresh orange peel waste. To the best of our knowledge, this is the first report exploring CXE for carotenoid recovery from citrus by-products. A theoretical evaluation using Hansen solubility parameters (HSP) was conducted to predict the solubility behaviour of key carotenoids in CXE, guiding the selection of optimal solvent compositions. A D-optimal response surface design was employed to optimize key extraction parameters, including CO₂ molar fraction, temperature, pressure, and solvent flow rate. The optimized CXE process (57.6 °C, 6.3 MPa, 1 mL/min, and 50% v /v CO₂ in ethanol) achieved significantly higher carotenoid yields and antioxidant capacities (ABTS and DPPH assays) than conventional solid-liquid extraction using acetone, hexane, or ethanol. Notably, the CXE method enabled direct extraction from fresh peel, circumventing the need for a drying step and thereby preserving thermolabile compounds and reducing energy consumption. These results confirm the potential of CXE as a scalable and sustainable alternative for the recovery of high-value compounds from citrus waste, aligning with green chemistry principles and circular economy strategies.