Antioxidant activities of tea prepared from kenaf (Hibiscus cannabinus L. KR9) leaves at different maturity stages

Kenaf (Hibiscus cannabinus L.) is a fast-growing herbaceous plant that received great attention in Malaysia as a valuable fibre crop. Yet, different maturity of plants’ leaves could affect the antioxidant capacities of the tea prepared. Therefore, the aim of this study was to determine the physical properties of KR9 kenaf leaves and antioxidant activities of tea prepared from KR9 kenaf leaves at four different maturity stages, which were 60, 90, 120 and 150 days after sowing (DAS). The analysis that carried out were DPPH (2-2-diphenyl-1-picrylhydrazyl) radical scavenging assay, ABTS (3-ethylbenzothiazoline-6-sulphonic acid) radical scavenging assay, ferric reducing antioxidant power assay, total phenolic content assay, total flavonoid content assay, and chromatographic analysis of phenolic compounds. Results demonstrated that the kenaf leaves at 150 DAS were able to retain the most colour after drying. It also revealed that the tea prepared from kenaf leaves at 120 DAS showed the highest antioxidant activity in all antioxidant analysis tested. Kenaf leaves tea contained mainly kaempferol, tannic acid, chlorogenic acid, caffeic acid and catechin hydrate. Hence, it was deduced that the antioxidant activity in kenaf leaves increased until 120 DAS and dropped at 150 DAS. There was a strong positive correlation relationship among all the antioxidant analysis and the phenolic compounds presented in the kenaf leaves tea. Thus, the phenolic compounds detected contributed significantly to the antioxidant activities of the kenaf leaves tea. The 120 DAS kenaf leaves was recommended for tea preparation since it possessed high antioxidant activities.