Optimizing, characterizing, and unveiling of functional properties and structure of grape pomace pectin obtained by a sequential ultrasound-microwave extraction

An ultrasound-microwave-assisted extraction (UMAE) approach was optimized using response surface methodology (RSM) to attain the maximum extraction yield (13.1%) of grape pomace pectin (GPP) by integrating 28.58 min sonication time, 600 W microwave power, 12.67 min irradiation time, and a liquid-to-solid ratio of 21.71 mL/g. The esterification degree, galacturonic acid (GalA) content, and molecular weight of the purified GPP were 72.5%, 67.9%, and 6.108 × 10⁵ Da, respectively. The most abundant monosaccharides in the structure of GPP after GalA were glucose, galactose, arabinose, and rhamnose, respectively. FTIR and ¹H NMR spectra identified the main chemo-functional and structural groups of GPP. The XRD, FE-SEM, and DSC results showed the GPP's amorphous structure with some scattered particles and high thermo-stability potential. The GPP at higher doses showed a pseudoplastic flow behavior with remarkable emulsifying, foaming, antiradical, and antioxidant properties for industrial applications.