Chemical profile, phenol content and antioxidant activity of Massularia acuminata, Rhaphiostylis beninensis, Telfairia occidentalis and Platostoma africanum

The leaf of Massularia acuminata (G. Don) Bullock ex Hoyle (Mal), Rhaphiostylis beninensis (Hook. f.) Planch (Rbl), Telfairia occidentalis Linn. (Tol) and the whole plant of Platostoma africanum P. Beauv. (Pal) are ethnomedicines in Nigeria used to treat malaria and other diseases. Extracts of Mal, Rbl and Tol were already tested using the β-haematin formation inhibitory assay and showed an inhibitory effect [1,2]. 70% ethanol extracts of these medicinal plants were submitted to a preliminary phytochemical screening by TLC and LC-UV/DAD. Subsequently the phenol, flavonoid and triterpenoid content and the free radical scavenging activity (FRSA) [3], the total antioxidant (phosphomolybdate assay) activity (TAP) [4] and the ferric reducing/antioxidant power assay (FRAP) were also determined. TLC analysis revealed the presence of terpenoids (mainly triterpenoids) and phenolic compounds in all the extracts, and of alkaloid in Rbl extract. LC-UV/DAD profiles obtained support these results. Total phenolic content (expressed as gallic acid) was 1.23 ± 0.03, 0.33 ± 0.01, 0.30 ± 0.02 and 0.07% w/w, respectively, for Pal, Rbl, Mal and Tol. Total flavonoid content of Pal expressed as catechin was 1.66 ± 0.02% w/w. Total triterpenoid content (as oleanolic acid) was 3.31 ± 0.18, 0.69 ± 0.03, 0.004 ± 0.002% w/w and vestigial in Rbl, Pal, Mal and Tol, respectively. Concerning the FRSA, Pal extract was most active (IC₅₀ = 258 µg/ml); others showed slight activity (IC₅₀ > 2500 µg/ml). TAP (as ascorbic acid equivalents) was 48.8 ± 1.0, 48.3 ± 2.7, 42.2 ± 4.5, 30.1 ± 1.0 mg/g to Pal, Rbl, Mal and Tol, respectively. FRAP was shown to be mostly directly correlated with the concentration of phenolic compounds.

Keywords: Antioxidant activity, Ethnopharmacology, Massularia acuminata, Plastostoma africanum, Rhaphiostylis beninensis, Telfairia occidentalis, Total phenol content

References:

[1] Adeyemi A, Moody J. Inhibition of haematin formation by selected Nigerian ethnomedicines Planta Med 2013; 79:PI4.

[2] Adeyemi A 2014; Unpublished results.

[3] Brand-Williams W. et al. Use of free radical method to evaluate antioxidant actibity Lebensm Wiss Tech 1995; 28:25 – 30.

[4] Prieto P et al. Spectrophotometric quantitation of antioxidant capacity through the formation of a phosphomolybdenum complex: specific application to the determination of vitamin E. Ann Biochem 1999; 269:337 – 341.