Characterization and Evaluation of the In Vitro Antioxidant, α-Glucosidase Inhibitory Activities of Camellia longii Orel and Luu. (Theaceae) Flower Essential Oil and Extracts From Vietnam

Objective/Background:Camellia longii Orel and Luu was discovered for the first time in Cat Tien National Park of Lam Dong Province, Southern Vietnam, was determined as a new species. To the best of our knowledge, this is the first report on the phytochemical and bioactivity of this species. Methods: The chemical profile of essential oil (EO) prepared from C. longii flowers was determined by GC/MS analysis and comparison of the recorded retention indices and the corresponding literature values. The total phenolic and flavonoid contents in different flower extracts were estimated by Folin-Ciocalteu and aluminum chloride methods with a spectrophotometer, respectively. The antioxidant activities of the extracts were determined by various bioassays, including DPPH free radical scavenging, ferric reducing power, and cupric reducing antioxidant capacity. The alpha-glucosidase inhibitory activity of the extracts was evaluated using p-nitrophenyl alpha-D-glucopyranoside solution as a substrate and acarbose as the positive control. Results: Fifty-seven compounds were identified from the EO of C. longii flowers. Among these, the main components were alpha-eudesmol (16.1%), followed by (E)-nerolidol (13.0%), beta-eudesmol (8.9%), tau-cadinol (6.5%), and gamma-eudesmol (5.8%). The total phenolic and flavonoid contents were found high in ethyl acetate, n-butanol, and ethanol extracts (206.8-378.6 mg gallic acid equivalents/g crude extract and 298.5-390.3 mg rutin equivalents/g crude extract, respectively). These extracts were shown to possess potent antioxidant activities in the examined bioassays. As for the alpha-glucosidase inhibitory assay, the ethyl acetate, butanol, and ethanol extracts were shown to be more potent than acarbose with IC50 values of 2.16 +/- 0.04, 1.95 +/- 0.05, and 1.53 +/- 0.04 mu g/mL, respectively. Conclusion: The findings first provide the phytochemical profiles of Camellia longii Orel and Luu and its bioactivities, indicating moderate potentials in antioxidant activity and strong alpha-glucosidase inhibition.