RESUMO
The flowers of African marigold [Tagetes erecta L], a medicinal plant widely cultivated in Thailand, were subjected to evaluation for total phenolics, DPPH scavenging and thiobarbituric acid-reactive substance [TBARs] assays as well as tyrosinase inhibitory activity. In preliminary studies, the ethyl acetate [EA] extract obtained by continuous extraction showed the highest activities with highest phenolic content among all extracts. Bioassay-guided fractionation of EA extract led to isolation of a flavonoid identified as quercetagetin. Interestingly, it was found that quercetagetin exhibited potent DPPH scavenging activity with IC50 of 3.70 Micro g/ml which is about 2-3 times higher activity than standard quercetin [IC50 5.07 Micro g/ml] and trolox [IC50 9.93 Micro g/ml]. Moreover, it exhibited tyrosinase inhibitory activity on L-tyrosine [IC50 89.31 Micro g/ml], higher than Alpha - and Beta -arbutins [IC50 157.77 and 222.35 Micro g/ml] and slightly higher [IC50 128.41 Micro g/ml] than ellagic acid [IC50 151.1 Micro g/ml] when using L-DOPA as substrate. Testing with skin fibroblasts, all the extracts and quercetagetin demonstrated no toxic effect. These finding strongly indicate that African marigold flower is a promising source of natural antioxidative and tyrosinase inhibitory substances with safe to skin