Extraction and Characterization of Pectins from Ripe Grape Pomace Using Both Ultrasound Assisted and Conventional Techniques

Abstract

Ripe grape pomace is a waste of grape juice processing that can be considered a valuable source for pectin extraction. The pectin was extracted via optimization using both ultrasound-assisted procedure (UAE-PRGP) and conventional extraction procedure (CE-PRGP). The pH values were 1.0, 2.0, and 3.0 for both techniques, the temperatures were set at 50, 60, and 70 °C for UAE, and 60, 75, and 90 °C for CE. The process time levels of the selected techniques were also different as 10, 20, and 30 min for UAE and 60, 90, and 120 min for CE. The yield (EY) of pectin extraction, the esterification degree (DE), and galacturonic acid (GA) were determined for optimization. The optimum values of pH, temperature, and time for UAE were 2.99, 58.82 °C, and 30 min, respectively, and for CE were 2.99, 66.42 °C, and 120 min, respectively. The optimum values (w/w %) for EY, DE, and GA were 16.45%, 42.97%, and 52.05%, respectively, in CE, and 24.25%, 27.78%, 61.39%, respectively, for UAE. Fourier transform infrared spectroscopy (FTIR) showed that UAE-PRGP had lower DE than CE-PRGP. Differential scanning calorimetry (DSC) revealed that UAE-PRGP had slightly greater thermal stability than CE-PRGP while commercial pectins (apple and citrus) had higher thermal stability than both extracted pectins. The apparent viscosity values of commercial pectins were higher than those of CE-PRGP and UAE-PRGP while all pectins indicated pseudoplastic manner. The UAE-PRGP showed higher stability and emulsifying activity than CE-PRGP, while lower than commercial pectins. UAE-PRGP with more GA and EY and less DE can be potentially used in various dairy foods.

Graphical Abstract