Comparative Evaluation of Sutherlandia frutescens and Tulbaghia violacea Antioxidant Potential

Aims: To evaluate the antioxidant properties of Sutherlandia frutescens and Tulbaghia violacea to justify their medicinal uses and values.

Study design: Experimental

Place and Duration of Study: Department of Biochemistry, Faculty of Science, Lagos State University and Department of Biotechnology, University of The Western Cape, Cape Town, between June 2019 to July 2021.

Methodology: The antioxidant and free radical scavenging activity of Sutherlandia frutescens and Tulbaghia violacea extracts were determined by several standard methods including ferric-ion reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC), trolox equivalent absorbance capacity (TEAC) and the thiobarbituric acid reactive substances (TBARs) assays.

Results: All S. frutescens extracts exhibited higher FRAP activities (ranging from 687.43 ± 11.90 to 974.31 ± 6.21 µMAAE/g) compared with corresponding extracts of T. violacea. Aqueous extract of S. frutescens produced the highest trolox equivalent absorbance capacity (1603.12 ± 5.50 µMTE/g), copper-initiated prooxidant activity (51.40 ± 1.25 µMTE/g) as well as peroxyl (1049.45 ± 0.54 µMTE/g) and hydroxyl (3911.27±18.67 µMTE/g) scavenging activities. The peroxyl and hydroxyl scavenging activities of aqueous methanolic extracts of S. frutescens and T. violacea increased in a concentration dependent manner. The inhibition of Fe2+-induced microsomal lipid peroxidation showed that aqueous methanolic extracts of Sutherlandia frutescens and Tulbaghia violacea significantly inhibit this process when compared with ethylacetate, dichloromethane and water only extracts.

Conclusion: The results suggest that S. frutescens and T. violacea antioxidant capacities depend on the extractive solvent. The antioxidant activity of the plants could be related to inherent phenolic bioactive compounds. However, further study is required to determine the precise mechanism of action and active constituents responsible for the antioxidant properties of these plants.