Phytochemical study and in vitro antioxydant activities of combinations of extracts from the leaves of Gnetum africanum welv. and Gnetum buchholzianum engl. (Gnetaceae), two food plants in Carmeroon

The study was carried out to estimate the phytochemical composition of ethanolic extracts (EE) and to measure the antioxidant activities of combination extracts (CE) obtained from the leaves of Gnetum africanum (welw.) and, Gnetum buchholzianum (engl.) (Gnetaceae). The biological material was obtained by maceration for 72 hours in ethanol – distilled (70-30) % then filtered. and concentrated on a Heidolph brand rotary evaporator and then stored at laboratory temperature until the actual analyzes. These different samples were firstly analyzed by liquid chromatography – mass spectrophotometry (LC-MS) for the characterization of chemical compounds. On the other hand, the antioxidant activities were measured respectively by the diphenyl picryl hydrazyl (DPPH) method and the iron capacity reduction method (FRAP) after combination extracts 30-70; 50-50; 70-30 respectively E1, E2 and E3. Finally, the total flavonoids and polyphenols were evaluated using the complex mixture of phosphotungsten acid (H3PW12O40) and phosphomolybdenum (H3PMo12O40) and a colorless sodium nitric solution (NaNO 2.5%) and chloride, respectively. aluminum (AlCl3, 10%). The phytochemical composition of EEs showed an abundance of chemical compounds depending on the m / z ratio and retention times. These compounds are 7 and 8 respectively for the africanum and buchholzianum species. The contents of flavonoids and total phenolic compounds are respectively 29.870 ± 2.485 mg EQ / g extract for EE of Gnetum africanum welv. (EEa) and 2.233 ± 0.251 mg EQ / g extract for EE of Gnetum buchholzianum engl. (EEb). On the other hand, the total polyphenol contents are between 14.520 ± 0.557 mg EQ / g of extract and 4.560 ± 0.010 mg EQ / g of extract for the same extracts. The antioxidant power (PA) measured at DPPH varies respectively from 0.003 ± 0.002 and 0.060 ± 0.009 while the reducing power (PR) measured at FRAP varies between 124, 500 ± 1, 00 and 75, 630 ± 4, 754 for both cash. This could thus justify their antioxidant activities. The results of the present study suggest that EEs are rich in chemical compounds of pharmacological interest and taken in isolation would be very important potential sources of natural antioxidants.

Keywords: Gnetum africanum (welv.), Gnetum buchholzianum (engl.), Antioxidant activity, anti-free radical, reducing power, liquid chromatography – mass spectrophotometry