Comparative chemical investigation and evaluation of antioxidant and tyrosinase inhibitory effects of Withania somnifera (L.) Dunal and Solanum nigrum (L.) berries

Abstract

In the present study, berries of two different species of Solanaceae family, Withania somnifera (WS) and Solanum nigrum (SN), were extracted in methanol and then fractionated with solvents, ranging from non-polar to polar, for their phytochemical profiling and investigation of antioxidant and tyrosinase enzyme inhibition capacity. The methanolic extract and n-hexane, ethyl acetate (WSEA, SNEA) and aqueous fractions were chemically analyzed and evaluated for biological activity. Total flavonoids and total phenolics were quantified in WSEA (96.91 ± 1.56 μg QE mg-1 sample and 178.45 ± 2.78 μg GAE mg-1 s ample, r esp.) and S NEA (89.58 ± 0.98 μg QE mg-1 sample and 120.15 ± 2.33 μg GAE mg-1 sample, resp.). HPLC-DAD analysis of ethyl acetate fractions of WS and SN measured 13.74 and 5.34 μg GAE mg-1 dry fraction and 3.72 and 3.41 μg QE mg-1 dry fraction, resp. WSEA and SNEA fractions showed the highest 2,2-diphenyl-2-picryl hydrazyl (DPPH) radical scavenging, total antioxidant capacity and iron reducing power activity. The highest inhibition of tyrosinase enzyme was also exhibited by WSEA and SNEA (59.6 and 58.7 %) resp. This investigation justifies the medicinal value of W. somnifera and S. nigrum berry extracts as potential and readily available sources of natural antioxidants. Marked tyrosinase enzyme inhibition activity and antioxidant activity of both plant extracts might be due to polyphenols and flavonoids.

Keywords: HPLC-DAD; Solanum nigrum; Withania somnifera; antioxidant; polyphenols; tyrosinase inhibition.