DETERMINATION OF ESSENTIAL METAL, POLYPHENOL CONTENT, ANTIOXIDANT AND ANTIBACTERIAL ACTIVITIES OF METHANOLIC ROOT EXTRACTS OF CROTON MACROSTACHYUS AND PHYTOLACCA DODECANDRA

Abstract

medication to treat various diseases. The present study aimed at investigating elemental composition, polyphenol content, antioxidant and antibacterial activities of methanolic root extracts of both plants collected from six sites in Chiliga district, Central Gondar Zone, Ethiopia. For the analyses of metals, an optimized wet-digestion procedure was applied with 0.5 g of root sample using HNO3:HCl:H2O2 (v/v) in the ratio of 8:2:1 at 240 °C for 3:00 h, and 5:2:2 at 300 °C for 3:00 h for Phytolacca dodecandra and Croton macrostachyus, respectively. Then, concentrations of metals were determined in the digested samples using flame atomic absorption spectrophotometer; validity of the optimized procedure was evaluated by spiking experiments. An optimized procedure was also employed for the extraction of total polyphenols with 80% aqueous methanol for 24 h maceration. The Folin-Ciocalteu, Aluminium Chloride and DPPH radical-scavenging spectrophotometric assays were used to quantify, respectively, the total Polyphenol and flavonoid contents, and antioxidant activities of root extracts. Finally, the antibacterial activities of both plant root samples were evaluated by disk diffusion method. Results of metals revealed good accuracy and repeatability of the method, with recovery rates ranging from 87% to 102% for Croton macrostachyus and 85% to 103% for Phytolacca dodecandra. The concentrations of metals (mg/kg) in both plant root samples ranged from: Cu (5–12), Zn (17–196), Mn (62–479), Fe (182–1455), Cr (0.1–3), Ca (550–1407), and Mg (1019– 1318). The total polyphenol contents were in the range of 802 ± 53 – 1557 ± 75 and 950 ± 38 – 4214 ± 45 mg GAE/100 g, respectively, for Croton macrostachyus and Phytolacca dodecandra, whereas the flavonoid content ranged 342 ± 25.60 – 745± 32.00 and 451 ± 25.60 – 828 ± 16.11 mg CE/100 g. Similarly, the antioxidant activities varied from 3.53 ± 0.38 to 6.38 ± 0.62 and 3.80 ± 0.41 to 14.29 ± 0.99 mg AAE/g sample. The root extracts showed inhibition zones of 6.4, 7.6, 6.2 and 8.1 mm (Phytolacca dodecandra) and 5.8, 6.2, 5.9 and 6.0 mm (Croton macrostachyus), respectively, for Staphylococcus aurous, Staphylococcus pneumonia, Escherichia coli and Klebsiella pneumonia, which are more potent than Gentamicin antibiotic. One-way ANOVA revealed significant differences (p < 0.05) among the mean concentrations of all metals in both plant root samples. The result of Pearson correlation showed a strong association between total polyphenol concentrations and their respective antioxidant activities (r = 0.996). To summarize, the root extracts of both medicinal plants contained highest levels ofxi Mg followed by Ca and Fe, but lowest levels of Cr. Moreover, the root extracts of Phytolacca dodecandra in general contained relatively higher amounts of total polyphenols and furnished higher antioxidant and antibacterial activities compared to its Croton macrostachyus counterpart