Antioxidant Effects of Essential Oils from the Peels of Citrus Cultivars.

Essential oils from citrus cultivars are widely used in food, cosmetic, and pharmaceutical industries, and they have been extensively studied in the last decades. This study investigates the antioxidant activities of essential oils from 21 citrus cultivars and the active antioxidant constituents of the oils. Essential oils are extracted from the peels of citrus cultivars via hydrodistillation, and their chemical compositions are analyzed by gas-chromatography-mass-spectroscopy. The antioxidant activities of the citrus cultivars are determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS), and ferric-reducing antioxidant potential (FRAP) assays. Based on the results, the major constituent of the oils is d-limonene (50.88-97.19%). The essential oil from Citrus junos shows the highest phenolic content (360.04 ± 24.75 mg GAE/100 g), followed by that from Citrus × latifolia (339.42 ± 31.14 mg GAE/100 g), [(Citrus unshiu × Citrus sinensis) × Citrus reticulata] × Citrus reticulata (327.05 ± 14.29 mg GAE/100 g), and [(Citrus unshiu × Citrus sinensis) × Citrus reticulata] × Citrus reticulata (322.92 ± 21.43 mg GAE/100 g). The essential oil from [(Citrus unshiu × Citrus sinensis) × Citrus reticulata] × Citrus reticulata shows the highest DPPH and ABTS radical scavenging activity, with an EC(50) of 86.17 ± 4.87 and 0.16 ± 0.06 mg/mL, respectively. The essential oil from Citrus reticulata and [(Citrus unshiu × Citrus sinensis) × Citrus reticulata] × Citrus reticulata shows the highest ferric-reducing activities (2302.55 ± 237.26 and 2213.12 ± 35.54 mg/100 g, respectively). These results indicate that the essential oil from [(Citrus unshiu × Citrus sinensis) × Citrus reticulata] × Citrus reticulata has a higher antioxidation effect than that from other cultivars. By comparing the chemical compositions of the essential oils, 12 compounds are selected as the major contributors to the antioxidant activities of the oils, and α-phellandrene and α-terpinene are the most active constituents of the oils.