Antioxidant components and antioxidant capacity analysis
Tocopherol analysis was performed by HPLC as described previously using Hitachi instruments equipped (Hitachi, Japan) with a C18–Varian column (25 cm×4 mm; Kanto Chemical Co., Inc., Japan), and detection was applied using a UV detector at 298 nm (Yang et al., 2017). The calibration curves of each standard were initiated by plotting peak area versus the corresponding concentration, respectively. Phytosterol analysis was performed by GC/MS as described previously using Agilent instruments equipped with a DB–1 column (60 m×0.25 mm i.d.; Agilent, Palo Alto, CA, USA). The 5α–cholesterol was taken as an internal standard, and the ratio of the peak area of the analyte and internal standard was used as an analytical signal (Jun–Hua et al., 2008).
The total phenolic and total flavonoid contents were analyzed using the method mentioned in previous literature (Yang et al., 2018). Each oil sample (5g) was mixed with acetone/methanol (2:8) to 50 ml. The total phenolic content and total flavonoid content of oil samples were evaluated by methods described inprevious literature (Yang et al., 2018). The antioxidant activity of each peanut oil sample was evaluated using, the biochemical methods of DPPH and Ferric ion reducing antioxidant power (FRAP) assays. The DPPH radical–clearing capacity was measured following to previous research (Lin et al., 2019). Each oil sample was diluted with acetone/methanol (2:8) to concentrations of 1 mg/mL, and then mixed together with DPPH radicals (0.2mM) of methanol solution. After vigorously shake, the mixture was incubated at room temperature for 30 min, and then measured absorbance at 517 nm. The FRAP was measured following to the method used in previous research (Fernández–Arroyo et al., 2011). Each oil sample was diluted with acetone/methanol (2:8) to concentrations of 2 mg/mL, and then mixed with FRAP reagent (acetate buffer, FeCl3 solution, and TPTZ; 10:1:1). After vigorously shake, the mixture incubated at room temperature for 10 min, and next, measured absorbance at 595 nm. Trolox was used as the positive control.