Determination of total phenolic content and antioxidant activity of Commiphora mollis (Oliv.) Engl. resin

In this study, total phenolic contents (TPC) and antioxidant activity of Commiphora mollis (Oliv.) Engl. (Burseraceae) resin were investigated. The resin was extracted using petroleum ether, chloroform, and methanol to give 27.46 ± 0.48, 46.56 ± 0.42, and 53.00 ± 1.39% extractable solids, respectively. The Folin-Ciocalteu (F-C) redox assay was optimized considering relevant parameters such as reaction time, maximum wavelength, and sample dilution effect before the determination of TPC. The concentration of antioxidants necessary to decrease by 50% the initial concentration of DPPH (EC₅₀) was determined at 60 min. The reaction kinetics was analyzed using the pseudo-first-order kinetics model. For the F-C assay, the optimum conditions for the maximum absorbance and analysis time were 760 nm and 30 min, respectively. Under these conditions, the method exhibited good sensitivity and linear instrumental responses over wide ranges of concentrations. The highest TPC;168.27 ± 3.44, 137.43 ± 1.32, and 136.16 ± 0.42 mgGAE/g were recorded in the diluted samples (500 µg/mL) of methanol, chloroform, and petroleum ether extracts, respectively. By using different concentrations of the test sample, exhaustive reduction of phenolics and/or antioxidant substrates was achieved. Regarding the DPPH radical scavenging capacity, the EC₅₀ values for methanol, chloroform, and petroleum ether extracts were 295.03 ± 3.55, 342.75 ± 9.72, and 353.69 ± 7.30 µg/mL, respectively. The standard (L-ascorbic acid), however, exhibited much lower EC₅₀ value (44.72 ± 0.48 µg/mL). The methanol extracts showed kinetic behavior (k₂ values,115.08 to 53.28 M^-1 s^-1; steady-state time, < 29 min) closer to that of L-ascorbic acid (k₂ values, 190 to 109 M^-1 s^-1; steady-state time, < 16 min), than other two extracts (k₂ values,14 to 28 M^-1 s^-1; steady-state time, 63 to 130 min). For all tested samples, the rate of the DPPH radical scavenging increases with concentration from 50 to 250 µg/mL. The current study demonstrated that the polar solvent (methanol) extract has a better F-C reducing capacity and DPPH radical scavenging activity than the nonpolar solvents extracts. This could be due to phenolics and other oxidation substrates extracted by methanol from the C. mollis resin. For a better understanding of the antioxidant constituents of the resin, a further study including isolation of its compounds is recommended.