Extraction of tannic acid and kaempferol compounds from kenaf (Hibiscus Cannabinus L.) using ultrasound-assisted extraction

Hibiscus Cannabinus L. or kenaf plant is studied for its high content of natural antioxidants and abundance of bioactive compounds especially phenolic and flavonoid compounds. In this study, optimum methods for the extraction of tannic acid and kaempferol compounds from kenaf plants were obtained using the non-conventional method, ultrasound-assisted extraction (UAE). Kenaf leaves and bast fibres were used with different type of extraction solvents which were ethanol and water and different extraction times using UAE which were 10, 20, 30, 40, and 50 minutes. Meanwhile, the constant parameter is 50% duty cycle of UAE, the power of UAE used was 60% and the temperature set was 40◦C for ethanol and 50◦C for water. After the extraction process, phytochemical screening test was performed on each sample to identify the presence of phenolic and flavonoid compounds. The results showed that ferric chloride test gave dark green colour to leaves samples which indicated the presence of phenolic compounds. Meanwhile, 10% NaOH test gave yellow colour for both types of samples indicating the presence of flavonoid compounds. High-Performance Liquid Chromatography (HPLC) analysis was used to analyse the concentrations of tannic acid (phenolic compounds) and kaempferol (flavonoids compounds) from all samples. Results from HPLC analysis gave the concentrations of compounds from each sample. It was found that the optimum parameters were achieved by using kenaf leaves extracted with water as a solvent, with an extraction time of 10 minutes, resulting in the highest concentrations of tannic acid, which were 3141.89 ± 2.59 ppm. For kaempferol compound, the optimum parameters was also kenaf leaves using water as solvents extracted in 30 minutes producing 7.47 ± 0.05 ppm concentration. Fourier Transform Infrared-Attenuated Total Reflectance (FTIR-ATR) analysis showed O-H, C-H and C-O bond that indicated tannic acid and kaempferol compounds in samples. Lastly, Field Emission Scanning Electron Microscopy (FESEM) analysis confirmed the efficiency of UAE methods extractions by showing the changes in surface structure of samples by perforations and cells ruptured. From these study, it is concluded that the extraction of kenaf leaves and bast fibres using UAE for tannic acid and kaempferol compounds are effectives with the methods that have been obtained in this experiment.