## 3 Results and Discussion  
### Results of One-Way Test for Ultrasound-Assisted Enzymatic Extraction of SDF  
It can be seen from Figure 1a that with the decrease in the ratio of cellulase and hemicellulose, the extraction rate of SDF firstly increased and then decreased, and when the ratio was \(1/1\), the extraction rate was the highest. Therefore, the \(1/1\) ratio of cellulase and hemicellulose was selected for subsequent experiments. As can be seen from Figure 1b, the extraction rate of SDF first increased and then decreased with the increase in the amount of enzyme added. [PERSON] et al. (2018) extracted polysaccharides handles from _Schisandra chinensis_ with cellulase, finding that the polysaccharide extraction rate showed first an increasing and then a decreasing trend with the increase in cellulase concentration, which was similar to the results of this experiment. With a low amount of enzymes added, the substrate could not be completely hydrolyzed and the slow dissolution rate of the enzyme and substances also led to a low extraction rate. With an increase in enzyme concentration, the reaction rate was accelerated, and the enzyme degraded some of the IDF into SDF ([PERSON] et al., 2019), which significantly increased the SDF extraction rate. However, excessive enzyme addition reduced the polymerization degree of SDF, which was not conducive to subsequent alcohol precipitation and thereby reduced the extraction rate of SDF ([PERSON] et al., 2019). Therefore, the appropriate enzyme addition amount was 5%. It can be seen from Figure 1c that the extraction rate of SDF first increased and then slightly decreased with an increase in the extraction solution volume. [PERSON] et al. (2019) extracted Se-polysaccharides from Se-enriched _Lentinus edodes_ and found that the effect of the liquid-solid ratio on the Se-polysaccharides yield also showed a similar trend of first increasing and then decreasing, reaching the maximum value at 20/1 mL/g. A different material-liquid ratio might affect the dissolution of SDF into the liquid. When the extraction solution was insufficient, the viscosity of the reaction system was high, and SDF could not be quickly dissolved--a part of the SDF remained in the raw material, resulting in a low SDF extraction rate. An appropriate increase in solvent volume could increase the contact area of SDF and the extraction solution. After the enzyme and substrate adequately contacted, the continued increase in solvent volume resulted in a decrease in the SDF extraction rate. It was likely that the increase in solvent volume affected the transfer of ultrasonic energy, and the reduction in enzyme concentration led to insufficient contact between the enzyme and substrate, resulting in a low reaction efficiency ([PERSON] et al., 2019). In addition, an increase in solvent  
Figure 1: Effects of enzyme ratio (**a**), enzyme addition amount (**b**), material–liquid ratio (**c**), and reaction time (**d**) on the extraction rate of soluble dietary fiber (SDF). volume would increase the subsequent amount of anhydrous ethanol, resulting in a waste of resources [38]. Therefore, the material-liquid ratio of 1/20 g/mL was appropriate. As can be seen from Figure 1d, the extraction rate of SDF first increased and then decreased, and it reached a maximum value at 30 min. [PERSON] et al. [26] obtained SDF from _Hericium erinaceus_ using ultrasound-assisted enzymatic extraction, finding that the SDF extraction rate increased with an increase in time, reaching the highest value at 35 min, and then significantly decreased, which was similar to the results of this experiment. The increase in the SDF extraction rate might be due to the fact that, when the extraction time was too short, the residue and the solvent could not fully react; however, with an increase in time, the SDF gradually dissolved, and the expansion of the material hydration was also conducive to the ultrasonic crushing of the tissue structure, which promoted the release of SDF.