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, timesaving technology for drying fresh NOP and assisting extraction of pectin from NOP.