Seasonal monitoring of the antioxidant activity of Erythroxylum suberosum A. St.-Hil. leaves: Correlation with hyperoside and isoquercitrin contents

Abstract

This study evaluated the seasonal of two flavonoids, antioxidant activity, chromatographic profiles by Thin Layer Chromatography, and High-Performance Liquid Chromatography, in Erythroxylum suberosum A.St.-Hil. These variables were observed from August 2013 to May 2014 in correlation with climatic variables such as temperature, rainfall index and global radiation. The chromatographic profiles were similar in the aqueous and ethanol extracts, and the flavonoids hyperoside and isoquercitrin were identified and quantified. In the inhibition of the DPPH^• radical, the most active was the aqueous extract from the 2^nd collection (IC₅₀: 4.45 μg/mL).  For the phosphomolybdenum complex reduction method, ethanol extract from the 1^st collection was active (206.39 μg/mL equivalent ascorbic acid). Regarding the environmental correlations, it was observed that the higher global radiation index has a strong influence on the concentrations of hyperoside and contributes to the antioxidant activity. On the other hand, higher temperatures contributed to higher isoquercitrin content in aqueous extracts. Therefore, the results indicated that August is the best collection period for Erythroxylum suberosum A.St.-Hil. leaves, in order to obtain higher isoquercitrin and hyperoside contents and, consequently, higher antioxidant activity.