Effect of microwave drying pretreatment on extraction of pectin from apple pomace

In order to develop a new method for drying apple pomace and improve the quality of pectin which was extracted from dried apple pomace, effect of microwave drying pretreatment(MDP) on extraction of apple pectin from apple pomace was investigated. With increasing the microwave energy of MDP, more rupture in the tissue of apple pomace was observed using scanning electron microscope, and the rehydration capacity of apple pomace decreased. However, the color of apple pomace didn’t change significantly. The pectin yield extracted from apple pomace was significantly increased after MDP (p＜0.05), an about 50% increase of pectin yield was obtained at 300W for 15 min (7.5×10-2 kW?h) or at 500 W for 10 min (8.3×10-2 kW?h), but the microwave energy for MDP greater than 8.3×10-2 kW?h led to the degradation of pectin in apple pomace. The degree of esterification (DE, %), intrinsic viscosity (ηi) and the viscosity-average molecular weight (Mw,ave) of apple pectin obtained from apple pomace using MDP were significantly increased, while its galacturonic acid (GA, %) was not changed significantly.