Evaluation of antityrosinase and antioxidant activities of Raphanus sativus root: Comparison between freeze-dried juice and methanolic extract

Abstract

Two types of extracts (freeze-dried juice and methanolic extract) from the root of Thai radish (Raphanus sativus L.) were evaluated for antityrosinase and antioxidant activities to determine their potential as a skin-whitening and anti-aging agent in cosmetic applications. The contents of total phenolics, total flavonoids and L-ascorbic acid (as per 1 mg of the dried extract) were found to be 10.09, 0.51 and 24.11 μ g for the freeze-dried juice and 6.59, 0.33 and 8.28 μ g for the methanolic extract, respectively. The freeze-dried juice showed higher potency of tyrosinase inhibition (IC50 = 3.09 mg/ml) than the methanolic extract (IC50 = 9.62 mg/ml). Also, the scavenging effects of the freeze-dried juice on DPPH radical, superoxide anion radical and singlet oxygen were greater than the methanolic extract, with the respective IC50 values of 0.64, 4.20 and 1.42 mg/ml for the freeze-dried juice and 1.25, 6.28 and 2.40 mg/ml for the methanolic extract. The higher contents of phenolic compounds and L-ascorbic acid in the freeze-dried juice appeared to be responsible for its greater antityrosinase and antioxidant activities. However, the activities of both extracts were much less than that of the reference antityrosinase agent (purified licorice extract) and the pure antioxidants (L-ascorbic acid and Trolox©) used as positive controls. Measurements of LDH leakage from fibroblast cells indicated that both extracts exhibited only mild cytotoxicity. Thus, provided that a more refined extraction process is developed with further evaluation, the extract of R. sativus root appeared to be a good candidate for application as a natural skin whitening/skin anti-aging agent due to its abilities to inhibit tyrosinase and scavenge several types of reactive oxygen species.