Tyrosinase Inhibition, Antioxidant Activity and GC-MS Analysis of the Hexane Extracts of the Aerial Parts of Astragalus vegetus Bungi. and Gundelia turnifortii L.

The enzyme tyrosinase is a copper-containing polyphenol oxidase, which is involved in melanogenesis. It catalyzes the conversion of tyrosine to melanin pigments in mammals. Tyrosinase plays an important role in enzymatic browning, which causes discoloration and loss economic value of many plant food products. This enzyme is widely distributed in fungi, higher plants and animals. The aim of this study was to determine the tyrosinase inhibitory effect of hexane extracts of different aerial parts of Astragalus vegetus Bungi and Gundelia turnifortii L. Later the kinetics and antioxidant activities of the extracts with the highest inhibitory properties were assessed. Aerial parts of the plants were divided to stems, leaves and flowers and air-dried. Hexane extract of each part has obtained by maceration in n-hexane. Inhibitory effects assayed at four different concentrations, using a microplate reader at 492 nm. Kojic acid used as positive control. DPPH method used to determine the antioxidant activities of the extracts and ascorbic acid (positive control). GC/MS device utilized to determine the composition of the extracts. Main inhibitory activity detected at 1 mg/ml concentration of hexane extract of leaves of Astragalus vegetus Bunge (66.6%), and the leaves and flowers of Gundelia turnifortii L. (71.7 and 68.7 percent respectively). IC50 values for Astragalus vegetus Bungi leaves was 0.5 mg/ml. and for Gundelia turnifortii L. leaves and flowers, were 0.5 and 0.32 mg/ml respectively. Astragalus vegetus Bungi.plant leaves also showed a considerable antioxidant activity. GC/MS analysis of extracts didn't show any reliable result. These results suggest that some of the most effective extracts from analyzed plants in this study, may be worthy for further investigation to obtain some new tyrosinase inhibitors with pharmacological applications.