Effect of drying temperatures on antioxidant properties of Napier grass (Pennisetum purpureum)

This study was carried out to determine the effect of oven drying temperatures on antioxidant properties of Napier grass. Fresh samples of Napier grass were oven dried at 50, 60, 70, 80 and 90 °C for 7 h. Fresh and dried samples were extracted with water (95 °C, 30 min) and the extracts were analysed for total phenolic content (TPC) assay, total flavonoid content (TFC) assay, diphenyl-picryl-hydrazyl (DPPH) assay, Ferric reducing antioxidant potential (FRAP) assay, ferric thiocyanate (FTC) method and thiobarbituric acid (TBA) method. The data show significant changes in TPC and TFC of Napier grass. DPPH radical scavenging activity of all the samples were significantly increased after drying. Ferric reducing potential of fresh Napier grass extract (71.31 ± 1.30) and samples dried at 50 °C (66.62 ± 2.77) and 90 °C (65.58 ± 5.98) were not significant. Sample dried at 50 °C showed no significant difference with that of fresh Napier grass extract in FTC and TBA assay indicating it is a recommended drying temperature in preserving antioxidants. The results suggested that Napier grass extract possess high antioxidant properties and it can be potent natural antioxidants. It also shows that sample dried at 50 °C have the greatest antioxidant properties.