Seasonal variation in the phytoconstituents and antioxidant activity in Moringa oleifera Lam. leaves of North India.

Moringa oleifera Lam., commonly known as drumstick tree or horseradish tree, is a draught tolerant economically valuable species native to India. M. oleifera leaves are useful in treating hyperglycaemia and dyslipidaemia and the leaf extract is a potential cognitive enhancer and neuroprotectant. The dried leaves of M. oleifera are rich in polyphenols such as flavonoids and phenolic acids which are known for their antioxidant potential. It is also well known that seasonal changes expose plants to different environmental conditions that have an effect on their phytochemical compositions. Studies were thus carried out on different extracts of leaf samples collected in five seasons to analyse the seasonal effects on the phytoconstituents. HPTLC was used to quantify seven polyphenolic compounds viz. chlorogenic acid, rutin, gallic acid, ellagic acid, caffeic acid, ferulic acid and quercetin. Variation in total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activity using DPPH assay, Nitric Oxide scavenging, Super Oxide scavenging and phosphomolybdate assay were also studied vis a vis seasonal variations. Chlorogenic acid and rutin were found to be present in maximum quantity in the methanolic extracts of the January (winter) samples while all the rest of the compounds viz. gallic acid, ellagic acid, caffeic acid, ferulic acid and quercetin were present in the highest amount in the methanolic extracts of the leaf samples collected in the month of August (monsoon season). Besides this, the lowest amounts of chlorogenic acid, rutin, gallic acid, ellagic acid and caffeic acid were detected in the aqueous extracts of summer (June) samples. Ferulic acid and quercetin were not detected in the aqueous extracts but their lowest amounts were detected in the aqueous methanolic extracts (L50 %) of the summer (June) samples. Overall, the trend for both TPC and TFC with respect to the seasons was winter > spring > rainy > autumn > summer. Similar to their TPC and TFC, the sequence of the antioxidant capacity by all methods was winter > spring > rainy > autumn > summer, with the highest oxidative quenching activity being observed for the samples collected in winter. As is evident from the results of the present study, the secondary metabolites composition is strongly affected by the seasonal variations. Thus, the best season for harvesting the leaves is winter followed by spring. [Display omitted] • Seasons have marked effects on the phenolic phytoconstituents and antioxidant activity of the leaves of Moringa oleifera Lam. • Leaves collected in the winter season contain the highest TPC and TFC. • Chlorogenic acid and rutin are the most abundant phenolic constituents present in the winter samples. • Methanolic extract of the leaves collected in the winter season exhibit the best radical scavenging activity. • Best season for harvesting the leaves is winter followed by spring. [ABSTRACT FROM AUTHOR]