Determination of flavonoids, polyphenols and antioxidant activity of Tephrosia purpurea: a seasonal study.

Objective: Tephrosia purpurea (Linn) Pers. is widely used in traditional medicine to treat liver disorders, febrile attacks, enlargement and obstruction of liver, spleen, and kidney. In the present study, investigations were carried out to determine the seasonal impact on the content of flavonoid glycosides and on antioxidant activities so as to identify the optimal time of harvesting.

Methods: The plant materials were collected in different seasons during 2013-2014. Air-dried, powdered plant materials were extracted with 95% ethanol and ethanol: water (1:1) by ultrasound-assisted extraction process. Their chemical composition in terms of total polyphenol and flavonoid contents (TPCs and TFCs) was determined using modified colorimetric Folin-Ciocalteu method and aluminum chloride colorimetric assay respectively. To determine the in vitro antioxidant activity, diphenyl-picryl hydrazyl (DPPH) radical-scavenging assay and total antioxidant capacity by phosphomolybdate antioxidant assay were carried out. High-performance liquid chromatography (HPLC)/photo-diode array (PDA) analysis was used to quantify the flavonoid glycosides in the samples collected in different seasons. Correlation studies were also carried out between antioxidant activities and TPCs.

Results: The highest TPC and TFC were found to be in the 95% ethanolic extract of the August sample and the lowest in the 50% hydro-alcoholic extract of the plant sample collected in winter season. It was observed that in both the assays used to determine the antioxidant activity, the 95% ethanolic extracts in all the seasons showed a higher activity than their respective 50% hydro-alcoholic extracts with an increase in activity as we go from cold to hot to rainy seasons. Based on correlation analysis, DPPH radical-scavenging activities as well as the spectrophotometrically measured phosphomolybdenum complex were also strongly correlated with TPC of the extracts. The most abundant flavonoid glycoside was quercetin-3-O-rhamnoglucoside in all the seasons. The content of all flavonoids was observed highest in the 95% ethanolic extract of the plant collected in August (TP-3). The 50% hydro-alcoholic extract of the plant collected in December (TP-6) showed the lowest amount of flavonoids and antioxidant activity.

Conclusion: The findings of this study confirmed that the metabolism and production of flavonoids in T. purpurea are vigorously affected by seasonal factors. Significant differences were observed in the TPC, TFC and flavonoid glycoside composition in the 95% ethanolic as well as 50% hydro-alcoholic extracts of T purpurea collected in different seasons. Since the 95% ethanolic extract of the August sample (TP-3), which also happens to be its flowering season, exhibited the highest TPC, TFC and antioxidant activities in both DPPH and phosphomolybdate assays as well as contained the highest content of all flavonoids, it could be recommended as the optimal season of harvesting T purpurea with respect to its pharmaceutically important constituents, i.e., flavonoids.