Ultrasound-microwave assisted extraction of pectin from fig (Ficus carica L.) skin: Optimization, characterization and bioactivity.

Four operating parameters in ultrasound-microwave assisted extraction (UMAE) process including sonication time (ST, 10-30 min), microwave power (MP, 300-600 W), irradiation time (IT, 5-15 min), and the liquid to solid ratio (LSR, 10-30 mL/g) on the extraction yield of pectin from fig skin were optimized. The yield (13.97%) of pectin with an average molecular mass of 6.89 × 103 kDa was maximized at 21.35 min ST, 580.9 W MP, 11.67 min IT, and 24.66 mL/g LSR based on a second-order polynomial model (R2 = 0.986) with a high level of significance (p < 0.0001). Field emission-scanning electron microscopy (FE-SEM) imaging and Fourier transform-infrared (FTIR) spectra of the pectin extracted under optimal conditions exhibited a disintegrated network in structural morphology and the main functional groups, respectively. The extracted low-methoxyl pectin (DE = 33.65%) with high lightness contained considerable amounts of uronic acids and neutral monosaccharides (glucose, fucose, arabinose, galactose, rhamnose, and mannose). A strong dose-depended behavior for antioxidant functions and cytotoxic inhibitory activities of pectin against HepG2 and A549 cells was found.