Physicochemical properties of pectin extracted from navel orange peel dried by vacuum microwave.

Vacuum microwave drying (VMD) technique was applied for drying fresh navel orange peel (NOP) under different vacuum degrees including 0, 25, 45, 65, and 85 kPa. Compared with the traditional hot-air drying (HAD), the drying time of VMD was remarkably reduced by 90.7–94.7%. In addition, the drying time had a negative correlation to the vacuum degree, the drying time at 85 kPa was only 5.3% of HAD. The extraction yield of VMD pectin was significantly higher than that of HAD. Comparing to HAD, the extracted pectin by VMD exhibited an increase in the degree of methoxylation, but a decline in the average molecular weight and apparent viscosity. Moreover, the VMD can promote pectin adsorption capacities to the Pb2+ with the adsorption mechanism of the pseudo-second-order kinetic model. These findings indicated that VMD is a powerful, efficient, time-saving technology for drying fresh NOP and assisting extraction of pectin from NOP. • VMD significantly improved the drying efficiency of navel orange peel (NOP). • VMD with higher vacuum was an effective way to save drying time. • NOP tissue treated by VMD was more loose and porous than HAD. • VMD-treated pectin exhibited the lower molecular weight and apparent viscosity. • VMD-treated pectin had a larger DM and stronger Pb2+ removal rate than HAD. [ABSTRACT FROM AUTHOR]