## 3 Results and Discussion
### Enzymatic Activities  
It is known that chitosan has the potential for inducing defense-related enzymes [41], so the enzymatic activities, including catalase and peroxidase, in soybean sprouts after treatments of chitooligosaccharide were studied. Results showing catalase activity of soybean sprouts in different treatments were presented in Figure 6. In general, the treatments of chitooligosaccharide depicted higher catalase activity, among which, the highest increase was treatment with 0.01% of 1 kDa chitooligosacacharide, and resulted with 185.55 U/g fresh weight. Treatments with 2 kDa and 3 kDa chitooligosacacharide had similar stimulation effects on the activity of catalase, and at a concentration of 0.01%, they improved the activity of catalase to 156.67 U/g fresh weight and 159.64 U/g fresh weight, respectively. Regardless of the molecular weight, chitooligosacacharide with a concentration higher or lower than 0.01% has less elicitor activity. Catalase can detoxify H\({}_{2}\)O\({}_{2}\) to water, thereby reducing the damage of reactive oxygen species to plants. The increase in the activity of catalase was most likely a response to the increased generation of reactive oxygen species and indicative of oxidative stress [42].  
Figure 5: Hydroxyl radical scavenging activity of soybean sprouts under different chitooligosacacharide treatments. The treatments were conducted with chitooligosaccharides of three molecular weights (1, 2, and 3 kDa) at four different concentrations (0.001 to 1%). The control treatment (0%) included the same solutions without chitooligosaccharides. Vertical bars represent the standard error of three replicates. Different letters indicate statistically significant difference (\(p<0.05\)).  
Peroxidase is involved in a variety of physiological functions in plants, and because of its importance in coloration, flavor development, nutritional properties, and texture of fruits and vegetables, it can change the consumer's acceptability of plant-based foods [19]. In the current study, soybean sprouts treated with chitoligosaccharide had higher levels of peroxidase than the control, which coincided with the trend of catalase (Figure 7). Regardless of the molecular weight, peroxidase activity first increased and then decreased with the concentration increase in chitoligosaccharide, and the best concentration of chitoligosaccharide was 0.01%. Among them, the highest peroxidase activity was shown in the soybean sprouts when they were soaked in 0.01% of 1 kDa chitoligosaccharide--this resulted in 2183.76 U/g fresh weight. Peroxidase activity in soybean sprouts treated with 0.01% of 2 kDa and 3 kDa chitoligosaccharide increased significantly as well.  
Therefore, chitoligosaccharide treatment could enhance resistance to oxidative stress. Moreover, it also suggested that chitoligosaccharide could be recognized as an effective biotic elicitor, triggering a specific induction of catalase and peroxidase [43].  
Figure 6: Catalase activity of soybean sprouts under different chitoligosaccharide treatments. The treatments were conducted with chitoligosaccharides of three molecular weights (1, 2, and 3 kDa) at four different concentrations (0.001 to 1%). The control treatment (0%) included the same solutions without chitoligosaccharides. Vertical bars represent the standard error of three replicates. Different letters indicate statistically significant difference (\(p<0.05\)).