Evaluating the Antioxidant Activity and Identifying Potent Compounds Using GC-MS Analysis of Allium cepa (Onion), Allium sativum (Garlic) and Zingiber officinale (Ginger) Methanol Extracts

Abstract

Background: Candidiasis caused by Candida albican species is one of the major health problems in immune-compromised patients in developing countries. Candida species are involved in the main opportunistic yeast infection in the world, but among the species of the genus, Candida albicans continues to be the most common. The in vitro antioxidant activity of methanol extracts of Alliumcepa (Onion), Alliumsativum (Garlic) and Zingiber officinale (Ginger) on Candidaalbicans was tested on the test drug Fluconazole. Aim: The study was carried out to assess the quality and quantity of the secondary metabolites present in Alliumcepa (Onion), Alliumsativum (Garlic) and Zingiber officinale (Ginger) plant extracts using standard methods. Method: The plant extract was subjected to thin-layer chromatography, and further subjected to column chromatography using standard methods and two fractions, F1 and F2 were obtained. The in vitro antioxidant activities of the plant extracts were determined using FRAP, DPPH and TBARS models, the antifungal activities and the minimal inhibitory concentration of plant extracts and its fractions using standard methods were assessed, and the combined plant extracts with the highest activity were also determined using a 2:2mg/ml ratio, and finally the phytoconstituents of the most active fraction was identified using GC-MS. Results: The secondary metabolites detected were tannins, reducing sugars, phenols, saponins, terpenoids, steroids, alkaloids and anthraquinones in both the aqueous and methanol extracts. However, flavonoids were absent in both aqueous and methanol extracts of Allium cepa, anthraquinones were absent in aqueous extract of Allium cepa and aqueous extracts of Zingiber officinale, terpenoids were found in the aqueous extracts of Allium cepa while steroids were absent in methanol extracts of Zingiber officinale and aqueous Allium sativum. The antioxidant powers of both fractions (F1 and F2) were dose-dependent. Significantly higher (p<0.05) antioxidant power was assessed at 100 mg/ml while the least antioxidant power was assessed at the lowest concentration (20mg/ml). No significant (p<0.05) difference was assessed in the antioxidant power of the fraction 1 and ascorbic acid at the concentrations of 20 and 40mg/ml. The fraction 2 significantly (p<0.05) exhibited a high radical scavenging activity at the different concentrations of (40, 60, 80 and 100mg/ml) compared to ascorbic acid at the same concentrations. Significantly higher (p<0.05) scavenging activity was assessed at the highest concentration of fraction 2 (100mg/ml) while the lowest activity was assessed at 20mg/ml of fraction 2. No significant (p<0.05) difference was assessed in the antioxidant power of the plant extract and ascorbic acid at the concentrations of 20mg/ml. Conclusion: The fractions were subjected to GC-MS analysis and they showed the presence of some important compounds which include oleic acid, cis-Vaccenic acid, pentadecanoic acid, octadec-9-enoic acid, 5-Eicosene, to mention a few.