2.2. L‐DOPA assay for tyrosinase enzymatic activity

This assay measures dopachrome formation from L‐DOPA (or tyrosine) by tyrosinase by its absorbance at 475 nm. Phenols were incubated at a concentration of 100 or 300 µM with 10 U/ml mushroom tyrosinase in 50 mM sodium phosphate buffer pH 7.1 (NaP_i) (Merck, Schiphol‐Rijk, NL) for 60 min at room temperature (RT) in the dark. Subsequently, L‐DOPA was added at a concentration of 250 µM. An incubation without test phenol served as a positive control. The formation of dopachrome was monitored on fixed intervals during maximal 2 hr. Fixed wavelength measurements were performed in plastic 1‐cm cuvettes on a Jasco V‐560 double‐beam spectrophotometer (Jasco Corp. Jas.co Benelux BV, de Meern, NL). The area under the curve (AUC) of samples with (B) or without (A) phenolic compounds were compared. The inhibition of tyrosinase activity on the conversion of L‐DOPA to downstream melanin precursors was calculated as (A/B) × 100%.