Antioxidant Activity and Phytochemical Contents of Some Selected Nigerian Fruits and Vegetables

Abstract

Ten plants which are used as condiments, spices, herbs, and eaten raw in Nigeria were investigated for their antioxidant activities using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) method. Phytochemicals such as total phenols, flavonoids, β- Carotene, and lycopene were also determined. The results showed that the highest antioxidant activity was found in Lactuca sativa (92.62%) and Allium sativum had the lowest (4.32%). Lactuca sativa with the lowest IC50 (0.26mg/mL), is the most potent vegetable of the samples analyzed. Phenolic contents of fruits and vegetables ranged from 106mg quercetin/g of extract for Capsicum annuum to 360mg quercetin/g of extract for Lycopersicon esculentum (unripe) while flavonoid contents ranged from 64 mg quercetin/g of extract for Daucus carota to 482 mg quercetin/g of extract for Zingiber officinale. Ripe Lycopersicon esculentum and Capsicum frutescens have higher Phenolic and Flavonoid contents than the unripe ones. There was significant correlation (r = 0.63, p< 0.05) between antioxidant activity and flavonoid contents but phenolic contents poorly correlate with antioxidant activity (r = 0.31, p< 0.05) of samples analyzed. Zingiber officinale had the highest content of β-carotene (66.30µg/g of extract) and Allium sativum had the lowest (2.37µg/g of extract). Ripe Lycopersicon esculentum (22.73µg/g of extract) had the highest lycopene and Allium sativum had the lowest (1.23µg/g of extract). Ripe Lycopersicon esculentum has higher lycopene and β-carotene contents than the unripe ones, but a decrease was obtained for Capsicum frutescens upon ripening. Both β-carotene and lycopene poorly correlate with antioxidant activity but significantly correlate with each other. These fruits and vegetables can be considered as good sources of antioxidants as shown by the values obtained for antioxidant activity, phenolic, flavonoid, β-carotene and lycopene contents.