## 3 Results and Discussion
### Antioxidant Activity Evaluation  
It is believed that free radicals are directly related to various diseases, and dietary antioxidants, which are able to scavenge free radicals, may be used to reduce the risk of these diseases. Therefore, it is important to investigate the radical scavenging effect of antioxidants in soybean sprouts [2]. The most commonly used method is based upon the stable free radical DPPH [36]. In the present study, antioxidant activity was evaluated by scavenging capability of DPPH (Figure 4). Regardless of molecular weight and concentration, antioxidant activity in thiotoligosaccharide-treated soybean sprouts was higher than the control, which could be the result of high total phenolics accumulation observed in the preceding section [37]. Among them, the smallest molecular weight led to the highest DPPH radical scavenging activity under the same treatment concentration. DPPH radical scavenging activity increased gradually along with the increase in thiotoligosaccharide until 0.01%, and after that it gradually reduced. The soybean sprouts treated with 0.01% of 1 kDa chitololigosaccharide showed the strongest DPPH scavenging activity of 28.14%, which is about 1.83-fold compared with the control of 15.40%. The scavenging activity of soybean sprouts treated with 0.01% of 2 kDa and 3 kDa chitololigosaccharide were 23.71% and 21.83%, respectively. This clearly indicated that thiotoligosaccharide-treated soybean sprouts have better free radical scavenging ability to protect the plant from oxidative damage [38]. However, the antioxidant activity of soybean sprouts was continuously decreased when the concentration of chitololigosaccharide was higher than 0.01%. These changes in antioxidant activity may confirm that if the concentrations of chitololigosaccharides were too high and oxidative stress was too high, then its stimulatory effect was weakened.  
Because hydroxyl radicals are so reactive that they can cause potential damage to cells [39], the hydroxyl radicals scavenging activity in chitololigosaccharide-treated soybean sprouts was also investigated. As shown in Figure 5, the hydroxyl radical scavenging activity of soybean sprouts was similar to the changing trend of the DPPH radical scavenging  
Figure 4: DPPH radical scavenging activity of soybean sprouts under different chitololigosaccharide treatments. The treatments were conducted with chitololigosaccharides 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 chitololigosaccharides. Vertical bars represent the standard error of three replicates. Different letters indicate statistically significant difference (\(p<0.05\)).  
activity. An amount of 0.01% of 1 kDa chitooligosacacharide was the most effective one, which increased the hydroxyl radical scavenging activity of soybean sprouts to 64.33%, which is about 1.43-fold compared with the control. Treatments with 0.01% of 2 kDa and 3 kDa chitooligosacacharide also improved the hydroxyl radical scavenging activity of soybean sprouts, representing 33% and 28% increases, respectively. The enhancement in antioxidant activity of soybean sprouts treated with chitooligosacacharide demonstrated an improvement in their biological function, and these soybean sprouts may meet the needs of people looking for new drugs from food materials [40].