Effect of brewing time and temperature on the physical properties, antioxidant activities and sensory of the kenaf leaves tea

Kenaf (Hibiscus cannabinus L.), an annual herbaceous plant in the Malvaceae family, has become a multifunctional crop in Malaysia due to its large number of industrial applications for its fibrous stem. Recently, its kenaf leaves that have high antioxidant properties are getting more attention to be developed into tea. Therefore, this research aims to determine the best brewing time and temperature based on the physical properties, antioxidant activities and sensory of kenaf leaves tea (KLT). The kenaf leaves powder which was infused in hot (80 °C or 100 °C; 5 min or 10 min) or cold water (room temperature; 60 min or 120 min) were analysed. Results demonstrated that the KLT brewed at 80 °C for 10 min and 100 °C for 10 min showed the highest antioxidant activities in most of the antioxidant analysis conducted. Moreover, the colour of cold-brewed KLT was much lighter than the hot-brewed KLT and the cold-brewed KLT (room temperature; 120 min) can likely be a new trend for the consumer since it contained high antioxidising capabilities. However, the pH, greenness, yellowness, sensory results in KLT were not affected significantly by both brewing time and temperature (p > 0.05). The antioxidant test was correlated positively with the phytochemical contents but insignificant relationship with most of the colour parameters. Overall, the optimum temperature and time for brewing KLT was 80 °C at 10 min because it saved energy and extracted the highest amount of antioxidants while retaining similar sensory taste with other brewing conditions.