Potassium bichromate

Iodized salt (food grade) was obtained from China National Salt Industry Corporation (Shanghai, China). 2,2-Diphenyl-1-picrylhydrazyl (DPPH), 3,4-dihydroxy-l-phenylalanine (l-DOPA), and tyrosinase were purchased from Sigma-Aldrich (Shanghai, China). Diethyl ether, disodium hydrogen phosphate, monosodium phosphate, anhydrous ethyl alcohol, dimethyl sulfoxide, potassium bichromate, potassium iodide, chloroform, and acetic acid were purchased from Sinopharm (Shanghai, China). Instant cornstarch was obtained from Shanghai Rongshi (Shanghai, China). 2,6-Di-tert-butyl-4-methylphenol (BHT) and ascorbic acid (vitamin C) were purchased from Yingyuan (Shanghai, China) and Fine Chemicals Institute (Shanghai, China), respectively. All commercial essential oils were purchased from Pan'an Tianlan fragrance Co., Ltd (Zhejiang, China), manufactured via steam distillation. All commercial chemicals were used without further purification.