Anti-tyrosinase, total phenolic content and antioxidant activity of selected Sudanese medicinal plants

The flora of Sudan is relatively rich in medicinal plants and represents an important component of traditional medicine. Fifty methanolic extracts of selected Sudanese medicinal plants were evaluated for their in vitro tyrosinase inhibitory effect, antioxidant activity and total phenolic content (TPC). The standard method of antioxidant evaluation, ferric reducing ability of plasma (FRAP), was employed to determine the antioxidant activity while the enzyme based tyrosinase inhibition was used for the anti-tyrosinase activity. Acacia nilotica (pods, bark) and Acacia seyal var. seyal (wood) demonstrated comparable anti-tyrosinase inhibitory activity using L-tyrosine as substrate (08.61, 10.47 and 10.77 μg/ml respectively) to Kojic acid (10.02 μg/ml) which was used as a positive control. A. nilotica (bark) and Acacia seyal var. fistula (bark) exhibited good tyrosinase inhibitory activity using L-DOPA as substrate (IC50: 31.93, 36.32 μg/ml) compared to positive control (IC50: 37.63 μg/ml). The results revealed significant differences in TPC between plants extracts. The highest level of phenolic content was found in Terminalia brownii (bark; 46.02 μg GAE/mg) while the lowest was in Ziziphus spina-christi (fruits; 09.63 μg GAE/mg). The study indicated significant differences in total antioxidant capacity between the extracts. Terminalia laxiflora (wood), A. nilotica (pods, bark), T. brownii (bark), A. seyal var. seyal (bark), Khaya senegalensis (bark), T. brownii (wood) Combretum hartmannianum (bark), Polygonum glabrum (leaves), Z. Spina-christi (bark) and Guiera senegalensis (leaves) extracts displayed the high antioxidant equivalent concentration (EC) values. A. nilotica (pods, bark) expressed promising activity that warrant further research since it has high tyrosinase inhibitory activity, antioxidant activity and could be a good source of phenolic compounds. To the best of our knowledge, this is the first data presenting comprehensive data on anti-tyrosinase, TPC, antioxidant activity of the Sudanese medicinal plants.