Abstract: The optimization of process parameters for ultrasonic-aided aqueous extraction and ultrasonic-aided enzymatic extraction of water-soluble dietary fiber (SDF) from ginger was developed using one-factor-at-a-time followed by orthogonal array designs. The extraction yield of SDF was investigated with respect to material-to-liquid ratio, ultrasonic treatment time, ultrasonic power and acid cellulase dosage. The optimal ultrasonic-aided aqueous extraction conditions were 25 min ultrasonic treatment at 100 W power and 1:30 material-to-liquid ratio, resulting in an SDF yield of 10.02%. The optimal ultrasonic-aided enzymatic extraction conditions were 3% acid cellulase dosage, 1:25 material-to-liquid ratio and 25 min ultrasonic treatment at 100 W power, and the resulting SDF yield was 13.86%, which was 38.2% higher than that obtained by the former method. SDF from ginger revealed strong scavenging activity against hydroxyl and superoxide anion radicals with an IC50 of 2.58 mg/mL and 0.42 mg/mL, respectively. Moreover, DPPH radicals also could be scavenged by the SDF with a scavenging rate exceeding 40%. Its water-holding capacity and swelling power were 359% and 2.86 mL/g, respectively.

Key words: ginger, water-soluble dietary fiber, ultrasonic treatment, acidic cellulase, functional properties