Seven commonly known medicinal plants from Zimbabwe were analysed for their antioxidant activity as well as their total phenolic content. The plant samples used in this study were Albizia amara, Elionurus muticus, Heteropyxis natalensis, Hoslundia opposita, Lippia javanica, Ocimum urticifolia and Warburgia salutaris. The plant samples were extracted using 70% ethanol. The 2,2-diphenyl-1-picrylhydrazyl radical assay was used to determine the antioxidant activity of the plant extracts, while the Folin-Ciocalteu method was used to determine the total phenolic content. The antioxidant activities of the plant extracts ranged from 95.84 ± 0.50% for E. muticus to 5.31 ± 4.47% for H. opposita. Total phenolics in the plant extract estimated as tannic acid equivalent (TAE) ranged from 0.098 ± 0.005 mg per 100 g for H. natalensis to 0.024 ± 0.006 TAE for H. opposita. There was a poor correlation (R ¼ 0.522) between total phenolic content and antioxidant activity in the plant samples. The results indicate the presence of phenolic compounds as well as significant antioxidant activity.
Four wild fruits, Diospyros mespiliformis, Flacourtia indica, Uapaca kirkiana and Ziziphus mauritiana, were extracted with methanol and analysed for radical-scavenging effect of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, reducing power and anion radical effect on superoxide anion using colorimetric method. There was an increase in the radical-scavenging effect, reducing power and superoxide anion radical-scavenging effect as the concentration of sample increased. Diospyros mespiliformis had high DPPH radical-scavenging capacity. The peels of F. indica and U. kirkiana had higher DPPH radical-scavenging effects, reducing power and superoxide-scavenging effects compared with the pulp while the pulp of Z. mauritiana had high DPPH radical-scavenging effects, reducing power and superoxide-scavenging effects compared with the peel.
SummaryThe phenolic compound content and profiles of three wild fruits found in Zimbabwe were tentatively identified using the traditional colorimetric methods and high-performance liquid chromatography (HPLC). The fruits assayed were: Ximenia caffra, Artobotrys brachypetalus and Syzygium cordatum. Ximenia caffra fruit peels contained the highest amounts of total phenolics amounting to 1205 lg g)1 in fresh weight, flavonols amounting to 27 lg g )1 and phenolic acids on HPLC tentative identification showed higher concentrations compared with the profiles of the other fruits. Syzygium cordatum fruit peels contained the least amounts of phenolics amounting to 20 lg g)1, flavonols amounting to 8 lg g )1 and phenolic acids' HPLC profiles showed low concentrations. Comparing the peels and pulps of all the fruits, we detected more total phenolics in the peels of X. caffra as high as 1205 lg g )1 and the pulps had 228 lg g)1, more flavonols and phenolic acids while the peels of S. cordatum fruits contained the least with a total phenolic acid content of 20 lg g )1, and had more flavonols in the pulps than the peels, 11 lg g)1 and 8 lg g)1, respectively. Ximenia caffra contained 1.2% and about 1% dry weight condensed tannins in peels and pulps, respectively. In S. cordatum we detected 0.2% and 0.3% dry weight condensed tannins in the peels and pulps, respectively.
Polyphenol oxidase (PPO), the enzyme responsible for the postharvest spoilage of fruits, was extracted and purified from Uapaca kirkiana peel and pulp by ammonium sulfate precipitation and dialysis. Further purification of peel PPO was carried out by gel filtration chromatography. Optimum pH values were 7 and 8 for peel and pulp PPO, respectively. The optimum temperatures for peel and pulp PPO were 45 and 35 • C, respectively. Inhibition studies of the PPO enzyme were performed using citric acid, sodium azide, sodium metabisulfite and thiourea. The most effective inhibitors were sodium azide and citric acid for both peel and pulp PPO. V max and K m values were 13.63 units min −1 and 4.923 mmol L −1 , respectively, for peel PPO and 14.03 units min −1 and 5.43 mmol L −1 , respectively, for pulp PPO. Three isoenzymes of Uapaca kirkiana PPO were detected by polyacrylamide gel electrophoresis. One of the isoenzymes could be identified as having a molecular weight of 26 625 Da.
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