Abstract

The kenaf (Hibiscus cannabinus L.) leaf tea was prepared by subjecting kenaf leaf in far infrared roaster at different time and temperature. Further, the effect of far infrared (FIR) irradiation on the total polyphenol, total flavonoid, antioxidant activity and angiotensin I-converting enzyme (ACE) inhibition ability were investigated in kenaf leaf tea. The data revealed that the FIR irradiation at 60°C increased the total polyphenol (TP) contents and total flavonoids (TF) content as the treatment time increased, and the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity and lipid peroxidation inhibition activity were also increased by FIR irradiation. The ACE inhibition activity also altered after FIR treatment. Likewise, the quantification analysis of kaempferitrin by use of HPLC showed an increase in the content in time and temperature dependent manner. Overall, this research showed that kenaf leaf treated with FIR at 60°C for 30 min is an optimal condition in processing to make a functional healthy kenaf leaf tea with higher phenolic content and higher biological (antioxidant and ACE inhibitory) activity.

Key words: Angiotensin I-converting enzyme (ACE) inhibition, antioxidant, far infrared, kaempferitrin, kenaf.