Effect of various solvents on the pulsed ultrasonic assisted extraction of phenolic compounds from Hibiscus cannabinus L. leaves

This work aimed to assess the effect of different extraction solvents (water, methanol, ethanol, and acetone) on the pulsed ultrasonic assisted extraction of Hibiscus cannabinus L. (kenaf) leaves extract (KLE), including extraction yield, antioxidation evaluation, antimicrobial analysis, tyrosinase inhibitory, Fourier transform infrared spectroscopy (FTIR) and ultra high performances liquid chromatography (UPLC) study. Results showed that the ethanol extracted KLE exhibited the highest content of total phenolic content (98.17 mg/g KLE). The ethanol extracted KLE also presented a good performances on 2,2-diphenyl-1- picrylhydrazyl (DPPH) radical scavenging capacity assay, 2,2'- azino- bis (3- ethylbenzo thiazoline- 6-sulphonic acid) (ARTS) radical scavenging assay, ferric reducing antioxidant power (FRAP) assay, and antimicrobial activity. Good correlation was obtained between the antioxidant activities analysis and total phenolic contents. Additionally, the ethanol extracted KLE showed the strong tyrosinase inhibitory (70.42%), although it was lower than the water extracted KLE (77.50%). Three phenolic compounds (caffeic acid, catechin hydrate, and tannic acid) were identified in the ethanol extracted ICLE by UPLC. These findings clearly indicate that ethanol was the most effective solvent for extraction of phenolic and flavonoid compounds from kenaf leaves. The results suggest that the kenaf leaves can be a promising source of natural antioxidant, antimicrobial, and antityrosinase constituent for application in the food, cosmetic and pharmaceutical industries.