Brönsted acidic ionic liquid based ultrasound-microwave synergistic extraction of pectin from pomelo peels

3-Methyl-1-(4-sulfonylbutyl) imidazolium hydrogensulfate, [HO3S(CH2)4mim]HSO4, was applied as an extractant in an ultrasound-microwave synergistic extraction approach to substitute conventional solvent for the extraction of pectin from the albedo part of pomelo peels. The analysis of variance (ANOVA) test and response surface method were employed for the optimization of the extraction conditions. A pectin yield of 328.64 ± 4.19 mg/g was achieved using the obtained optimal conditions, which was significantly higher than yields of conventional methods with reference solvents. Pectin samples extracted with [HO3S(CH2)4mim]HSO4 and hydrochloric acid solutions were tested by ANOVA and showed no significant differences in total carbohydrate content and degree of esterification; while galacturonic acid content was significantly different for the pectin from each extraction solvents. The differences revealed from images of atomic force microscopy and scanning electron microscope, Fourier transform infrared spectroscopy, and thermogravimetric analysis suggested the physiochemical properties of pectin could be affected by the extraction solvent. The [HO3S(CH2)4mim]HSO4 proved to be a promising alternative to conventional solvents and the proposed method is efficient for the extraction of pectin from the albedo of pomelo peels.