Antioxidant properties of chlorophyll-enriched and chlorophyll-depleted polyphenolic fractions from leaves of Vernonia amygdalina and Gongronema latifolium

This study investigated the optimum polyphenol extraction conditions for two Nigerian green leafy vegetables, Vernonia amygdalina (VA) and Gongronema latifolium (GL) that are widely used for food and medicinal purposes. Seven different solvents were used to extract the total phenolic contents of the leaves; 100% acetone, 80% acetone, 50% acetone, 100% ethanol, 70% ethanol, 100% methanol and 70% methanol and their total phenolic contents were determined. The results showed that the 80% acetone was significantly (p < 0.05) the most effective for polyphenol extraction from the leaves and generally the acetone-containing solvents were more effective than alcohol-containing solvents. The 80% acetone extract was fractionated on a silicic acid-packed column to give two main fractions: acetone eluted chlorophyll-enriched (flow-through) and ethanol eluted chlorophyll-depleted (column-bound). The ethanol fractions of VA and GL were significantly better (p < 0.05) DPPH radical scavengers than the acetone fractions. In contrast, the acetone fraction was a significantly better (p < 0.05) scavenger of hydroxyl radicals when compared to the ethanol fraction. Both acetone and ethanol fractions significantly (p < 0.05) and dose-dependently inhibited linoleic acid oxidation, though duration of inhibition was less at lower concentrations (10 and 25 μg/ml) than at the highest concentration (50 μg/ml).