All the reagents, chemicals and standards used in this research were of analytical grade. The 53 phenolic compounds including phenolic acids, benzoic acids, phenolic aldehydes, cinnamic acids, phenolic terpenes, flavones, flavanols, proanthocyanidins and stilbenes were purchased from Sigma-Aldrich (Steinheim, Germany). Curcumin (cur, 98% purity) was also obtained from Sigma-Aldrich, while demethoxyCurcumin (dmc, >95% purity) and bisdemethoxyCurcumin (bdmc, >95% purity) were purchased from Biopurify Chemicals Ltd. (Chengdu, Sichuan, China). LC–MS grade water, methanol and acetonitrile solvents, formic acid (98–100%) and dimethyl sulfoxide (DMSO) were also provided by Sigma-Aldrich.
Stock standard solutions of all targeted bioactive compounds (1000 mg/L) were prepared in methanol and were kept in amber glass vials. Working intermediate solutions were prepared by appropriate dilution of the stock standard solutions with water. All the solutions were stored in the refrigerator at 4 °C for not more than 1 month.
Stock standard solutions of all targeted bioactive compounds (1000 mg/L) were prepared in methanol and were kept in amber glass vials. Working intermediate solutions were prepared by appropriate dilution of the stock standard solutions with water. All the solutions were stored in the refrigerator at 4 °C for not more than 1 month.