Antioxidant and antimicrobial activity of essential oil from round kumquat (Fortunella japonica) peel using supercritical CO2 extraction

In this study, the highest oil yield of kumquat peel essential oil extraction of 3.89±0.03% was achieved under the supercritical carbon dioxide (SC-CO2) extraction condition including 250 bars, 50°C, fluid rate of 20 g/min and 120 min of extraction. Limonene comprising 39.25% was the main component of the oil. It showed 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) cation radical (ABTS•+) scavenging activity and ferric reducing antioxidant power (FRAP) value of 25.29±0.17mM Trolox equivalent (mM TE)/g dry weight and 6.25±0.15 mM TE/g dry weight, 4565 and 4623 folds lower than those of vitamin C, respectively. Inhibition zone diameter (IZD) of pure oil equaled to that of (i) 9.2 µg/mL Ampicillin solution against Bacillus subtilis, (ii) 23.4 µg/mL Ampicillin solution against Staphylococcus aureus, (iii) 7.2 µg/mL Streptomycin solution against Klebsiella pneumoniae, (iv) 35.1 µg/mL Amikacin solution against Pseudomonas aeruginosa, and (v) 37.7 µg/mL Amikacin solution against Proteus mirabilis. Meanwhile, minimal inhibitory concentration (MIC) value of the oil was 5 mg/mL for B. subtilis and 10 mg/mL for the rest bacteria.