The extraction of water-soluble dietary fiber (SDF) from apple pomace (AP) by cellulase, microwave- and ultrasound-assisted methods was studied in comparison with conventional acid method. The functional properties of extracted SDFs were further evaluated, and the speciality of each method was clarified in order to suggest the right method to adopt for practice. Results indicated that AP is rich in SDF, which is significantly potential to be applied in food processing. Acid hydrolysis of AP gave 10.3% of SDF, whereas ultrasound-assisted extraction (UAE) provided a yield of 16.4% after 40 min of sonication. Microwave-assisted extraction (MAE) gave a slightly lower yield (14.9%) than UAE, but it showed a drastic efficiency, wherein the yield was achieved after 2 min of irradiation. The hydrolysis of AP by cellulase occurred with the highest SDF yield (18.7%) among all the methods used. The functional properties of SDF were improved by UAE, MAE and cellulase extraction, wherein the water retention and swelling capacities were increased more considerably than the oil retention capacity. Especially, cellulase showed a remarkable performance in improving the hydration property.
A large amount of apple pomace (AP) was produced as the by-product of apple processing in China. Its disposal is of significance in consideration of resource utilization and environmental protection. Therefore, the results of this study can promote the full use of AP and similar industrial wastes, and also help to avoid possible pollution. In addition, the comparison of acid, cellulase, microwave- and ultrasound-assisted methods suggests the right method to adopt SDF extraction method for practice.