Preliminary screening of Nicotiana glauca extracts for determination of antioxidant activity by different methods

Nicotiana glauca (Solanaceae), or tree tobacco, is found in dry arid climates of North America, Africa and Europe. It has been reported to have both toxic and medicinal properties. The main aim of this study was to analyze the phytochemical screening and quantitative estimation of polyphenols, flavonoids and flavonols of crude extracts from the leaves of Nicotiana glauca and to evaluate its in vitro antioxidant properties. Three different solvents were used to extract bioactive compounds from powdered leaves of Nicotiana glauca: dichloromethane (DCM), ethyl acetate (AE) and n-buthanol (n-BuOH). The three extracts were then subjected to qualitative phytochemical screening using standard procedures. Total phenolics, total flavonoids and total flavonols contents of the extracts were measured by Folin Ciocalteu and Aluminium chloride methods respectively. Furthermore, the antioxidant capacity evaluation was performed using the DPPH, ABTS, DMSO alcalin, Phenantroline, FRAP and CUPRAC methods. The three extracts were then subjected to qualitative phytochemical screening using standard procedures. These methods showed the presence of polyphenols and comarines in all extracts. Moreover, flavonoids, tannins, steroids and quinones were reported in the AE and n-BuOH extracts. In addition, alkaloids were seen to be present in DCM extract, while saponines and phlobatannins were absent in all extracts. The antioxidant capacity evaluation was performed using the DPPH, ABTS, DMSO alcalin, Phenantroline, FRAP and CUPRAC methods.

Results using the DPPH method showed strong free radical scavinging activity for three extracts. This activity decreased with increasing concentration in the following order: n-BuOH>AE>DCM. In other assays, all extracts showed good antioxidant activity which decreased with increasing concentration in the following order: AE > n-BuOH > DCM. Extracts were compared with standards: BHT, BHA, Tanic acid and α-Tocopherol. The antioxidant of these extracts is probably related to polyphenols content (351.55±0.07, 284.98±0.08 and 133.8±0.06 mg/g), flavonoids (105.97±0.04, 164.44±0.07 and 1.18±0.005 mg/g) and flavonols (22.41±0.24, 18.75±0.46 mg/g) in AE and n-BuOH, respectively.

As a conclusion, the results of the present study indicate that Nicotiana glauca leaves could be considered as a potential source of natural antioxidants.