Isolation and characterization of antioxidant constituents of the fruit of &lt;i&gt;Telfairia occidentalis&lt;/i&gt; Hook F (Cucurbitaceae)

Olorunfemi A Eseyin,Aniekan Ebong,Uduak Benedict,Ukeme Akpan,Zubaid Munavvar,Paul S Thomas,Ekarika Johnson,Iweh Etim,Emmanuel Essien,Ashfaq Ahmad,Afzal Sheryar

doi:10.4314/tjpr.v17i10.9

Abstract

Purpose: To evaluate the antioxidant property of the fruit of Telfairia occidentalis and isolate the components responsible for the antioxidant activity.Methods: The fruit pericarp was macerated with methanol and the extract obtained successively partitioned with n-hexane, dichloromethane and ethyl acetate. The in vitro antioxidant activity of the extract and fractions was evaluated using 2,2-diphenyl-1-picryl hydrazyl (DPPH) radical scavenging, reducing power, nitric oxide scavenging, total antioxidant and hydrogen peroxide scavenging assays. The n-hexane fraction, which had the highest DPPH scavenging and total antioxidant activities, was subjected to column and thin layer chromatography to isolate the components. The isolated compounds were identified by ultraviolet-visible (UV), nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy and mass spectrometry.Results: Among the fractions tested, n-hexane had the best total antioxidant activity of 99.44 % at 20 mg/ml (p < 0.05) compared to ascorbic acid at 99.71 % of 20 mg/ml. This fraction also had the highest DPPH radical scavenging activity of all the fractions (p < 0.05) at all test concentrations. For nitric oxide scavenging activity, the whole extract, and the chloroform and aqueous fractions exhibited activity ranging from 92.29 to 97.66 % compared to 98.93 % for ascorbic acid. The hydrogen peroxide scavenging activity of the extract and fractions ranged from 92.60 to 96.23 % compared with of the standard, ascorbic acid (101.68 %). The major components of the n-hexane fractions were α- amyrin and β-amyrin.Conclusion: The fruit pericarp of Telfairia occidentalis possesses good DPPH radical scavenging activity. This is the first time the antioxidant activity of the fruit (pericarp) and the presence of α- and β- amyrins in Telfairia occidentalis have been reported.Keywords: Telfairia occidentalis, Fluted pumpkin, Amyrin, Antioxidants

Highlights

Telfairia occidentalis is popularly known mainly because of its nutritionally valuable leaves [1]
There were significant variations in the antioxidant activity of the different fractions based on the method used
In COSY analysis δH 3.16 (H-3) correlates with δH 1.66 (H-2), 5.15 (H-12) with 1.96 (H-11). These nuclear magnetic resonance (NMR) features are consistent with the established features of triterpenoid amyrins

Summary

INTRODUCTION

Telfairia occidentalis is popularly known mainly because of its nutritionally valuable leaves [1]. Telfairia occidentalis possesses antioxidant property [3]. There is no available report on the antioxidant activity or isolated component of the fruit pericarp of Telfairia occidentalis. Since the leaf and seed of Telfairia occidentalis have been found to possess significant antioxidant properties, the authors decided to screen the fruit pericarp for antioxidant property and isolate the antioxidant components of the pericarp. The fruit of Telfairia occidentalis (Fluted pumpkin) was obtained from the medicinal plant farm of the Faculty of Pharmacy, University of Uyo, Akwa Ibom State, Nigeria in June 2015. The dried methanol extract (85 g) was dissolved in 500 mL of distilled water and partitioned successively with n-hexane, dichloromethane and ethyl acetate to obtain their respective fractions. Each of the fractions was concentrated in a rotary evaporator to dryness

Evaluation of antioxidant properties

RESULTS

DISCUSSION