Determination of Total Phenolic Content and Antioxidant Activity of Commiphora mollis (Oliv.) Engl. Resin

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Abstract In this study, total phenolic contents (TPC) and antioxidant activity of Commiphora mollis (Oliv.) Engl. (Burseraceae) resin was investigated. The resin was extracted using petroleum ether, chloroform, and methanol and yielded 27.46 ± 0.48, 46.56 ± 0.42, and 53.00 ± 1.39% extractable solids, respectively. The Folin-Ciocalteu redox (F-CR) assay was optimized considering relevant parameters such as reaction time, maximum wavelength, and dilution effect before the determination of TPC. The amount of antioxidant necessary to decrease by 50%, the initial concentration of DPPH (EC50) was determined at 60 min. The kinetics of the reaction was analyzed taking into account the pseudo-first-order model. For the F-CR assay, the optimum conditions for the maximum absorbance and analysis time were 760 nm and 30 min, respectively. Under these conditions, the method was valid and the instrumental response was linear and sensitive. Relatively, higher TPC was obtained in diluted samples (500 µg/mL): 168.27 ± 3.44, 137.43 ± 1.32, and 136.16 ± 0.42 mgGAE/g from 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. The obtained DPPH radical scavenging capacity index (EC50) was 44.72 ±0.48 for ascorbic acid, and 295.03 ± 3.55, 342.75 ±9.72 and 353.69 ± 7.30 µg/mL for methanol, chloroform, and petroleum ether extracts, respectively. The methanol extracts showed better kinetic behavior (k2 values: 115.08 to 53.28 M-1s-1 and steady-state time < 30 min), which was closer to the standard L-ascorbic acid (k2 values; 190 to 109 M-1s-1), than other extracts. Results of the current study showed that polar solvent, methanol resulted in better F-CR reducing capacity and DPPH radical scavenging activity than nonpolar solvents which displayed similar effects (p > 0.05). This could have resulted from different antioxidants extracted from C. mollis resin. In conclusion, C. mollis resin could be a useful source of antioxidants. For better understanding, further study accompanied by isolation of pure compounds is recommended.

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