Tyrosinase inhibitory components of immature calamondin peel

There is broad range of applications in the use of tyrosinase inhibitors for suppressing unwanted hyperpigmentation in human skin and enzymic browning in fruits. In searching effective tyrosinase inhibitors from natural products, the components in unripe calamondin (Citrus mitis Blanco) peel were investigated by performing bioassay-directed fractionation and chromatographic separation coupled with tyrosinase inhibition assay. Herein it is reported for the first time that (1) there is a rich content of 3′,5′-di-C-β-glucopyranosylphloretin in unripe calamondin peel, 3.69 ± 0.44 g/100 g dry basis, (2) this C-glycosylated flavonoid showed the strongest inhibitory activity against tyrosinase among the components in this fruit, with an IC50 of 0.87 mg/ml, and (3) that unripe calamondin peel is also a rich source of naringin and hesperidin, 1.25% and 0.73% by dry weight, respectively, which also expressed strong tyrosinase inhibitory property.