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Abstract
The orange tree (Citrus sinensis) is a species of fruit shrubs of the Rutaceae family. Essential oils from citrus peels are widely used in various agro-food and pharmaceutical preparations and hence they must be recovered using green extraction methods. In this study, we compare the efficiency of five extraction techniques (conventional hydro-distillation (HD), Salt-assisted extraction by HD (S-HD), Ultrasound-assisted extraction by HD (US-HD), Enzymes-assisted extraction by HD (E-HD), and Solvent-free microwave extraction (SFME)) for the extraction of essential oil from Citrus sinensis peels. The essential oils were compared with regard to their chemical compositions, light microscopy analysis, total energy consumption, and antioxidant activity. GC/MS analysis allowed the identification of 28 compounds in the different essential oils. The principal identified component was limonene (86.7 %, 87.9 %, 88.2 %, 88.3 %, 85.4 % for HD, S-HD, US-HD, E-HD, and SFME, respectively), followed by β-pinene, sabinene, linalool and α-terpineol. The obtained essential oils were analyzed for their antioxidant activity using the 2,2-diphenyl-1-picrylhydrazyl radical scavenging method. Results indicated that essential oil extracted by SFME showed the highest antioxidant activity (IC50 = 0.0175 mg/ml) and extraction yield (3.58 % ± 0.05) consuming lower energy (0.312 kW h-1) in a shorter extraction time (30 min) comparing with the other tested techniques. Hence, the SFME would be an interesting green method for the recovery of essential oil from C. sinensis peels useful in agro-food, cosmetic, and pharmaceutical preparations as an alternative for undesirable chemical additives.