2.2.3 Antioxidant capacity assay
Antioxidant capacity assay (DPPH, FRAP, ABTS and ORAC) was performed according to Shi et al. (Shi et al., 2017) with a few modifications. Polar extract was acquired from 2.0 g of oil. The oil was mixed with 7.5 mL methanol in a brown bottle and vigorously stirred for 20 min. The supernatant was carefully separated as polar extract, and the residue was extracted four times with 7.5mL of methanol each. All polar extracts were transferred into a brown vial and stored at -20 °C in darkness until analysis. Detailed information associated with the methods used for DPPH, FRAP, ABTS and ORAC were all presented in the supplementary material.