Effect of different drying methods on the physical properties and antioxidant activities of Hibiscus cannabinus leaves

Abstract

Kenaf (Hibiscus cannabinus L.) has become a valuable industrial crop in Malaysia as a source of natural fibrous stem. Recently, the leaves has been also considered as a source of industrial products. Besides, the kenaf leaves can make into tea. Being a perishable, storage is challenging, hence the aim of this study was to evaluate the effects of different drying methods on the physical properties and antioxidant activities of kenaf leaves. Analysis of total flavonoid content (TFC) and total phenolic content (TPC) were also carried out. The sample retained the highest antioxidant activities was then subjected to high performance liquid chromatography (HPLC) to quantify the phenolic and flavonoid compounds. Freeze dried sample was found to have the best quality in terms of color retention and antioxidant activities compared with those subjected to room, microwave, vacuum oven and oven drying. Freeze dried sample retained the highest antioxidant activities as shown by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity assay, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical scavenging assay, and ferric reducing antioxidant power (FRAP) assay. Kenaf leaves tea (KLT) contained kaempferol, caffeic acid, tannic acid, catechin hydrate and chlorogenic acid, which can be used as sources of alternative antioxidant in food and biopharmaceuticals industry. There were positive correlation relationship between all antioxidant analysis, phenolic and flavonoid compounds presented in the KLT. Microwave drying, which is low in operating cost and time saving can be the alternative to freeze drying. Further studied can be undertaken to optimize the condition of different drying methods.