## 3 Results and Discussion
### Ultrasound-Assisted Extraction of TPC, TSC and DPPH Antioxidant Activity from COG Rhizomes  
Based on the validated optimal extraction conditions for maceration extraction, an ultrasound-assisted extraction technique was designed using the optimal parameters (temperature of 40 \({}^{\circ}\)C and solvent-to-material ratio of 80 mL/g) in order to improve the extraction efficiency of the TPC, TSC and DPPH antioxidant activity from COG rhizomes.  
Figure 7A,B show that the recovery yields of both TPC and TSC from COG rhizomes using ultrasound-assisted extraction methods were very high after only 5 min of extraction and they increased significantly with each subsequent 5 min interval. The use of ultrasound to assist the extraction process can lead to high extraction efficiency in a short period, caused by the continuous creation and collapse of cavitation bubbles, which help to weaken or break down the plant cell walls, thereby increasing the mass transfer rate of solutes into the solvent [40]. However, according to the law of solute diffusion, UAE also requires a suitable extraction time to achieve the highest yields of the soluble compounds [41]. In this study, the extraction yields of TPC and TSC reached the maximum values after 15 and 10 min of extraction, respectively, and further extending the time did improve the recovery of these compounds. The data for the DPPH antioxidant capacity in Figure 7C show a similar changing trend to the two groups of TPC and TSC. The extract reached very high DPPH antioxidant activity (128.20 uM TE/g DW) after just 5 min of extraction, increasing to 141.85 uM TE/g DW after 10 min of extraction before decreasing with the extended time.  
This result is consistent with previous studies on the impact of ultrasound-assisted extraction (UAE) on bioactive compounds from grapes [42], rosemary leaves [43] and white mushrooms [44]. These studies indicate that the amounts of the compounds and the antioxidant activity obtained from UAE extracts reach the highest levels after relatively short periods (usually between 10 and 20 min) and then decrease when the extraction time  
Figure 7: Influence of ultrasound-assisted extraction on the extraction efficiency of TPC (**A**), TSC (**B**) and DPPH antioxidant activity (**C**). Different letters represent statistically significant differences among the values (\(p<0.05\)).  
is extended. The decline is explained by the increased degradation of the compounds in the liquid phase, while the extraction rate decreases due to the concentration gradient of the solutes between the material and the solvent approaching equilibrium.  
As shown in Table 5, there was no statistically significant difference in the yields of the TPC, TSC and DPPH antioxidant activity obtained from the two different extraction methods. However, in terms of production efficiency, the UAE extraction showed a great advantage in reducing the extraction time while maintaining the recovery efficiency of the bioactive compounds. Specifically, to recover comparable yields of TPC and TSC, UAE required only approximately one-eighteenth and one-fourth of the extraction duration compared to maceration extraction, respectively.  
A previous study comparing the impact of extraction methods on the compound recovery efficiency reported that UAE improved the TPC recovery from sorghum by 22% compared to the conventional solvent extraction technique [45]. Regarding the extraction of compounds from several herbal materials by various methods, [PERSON] et al. (2019) [46] found that UAE was the most suitable method to maximize the recovery of bioactive compounds. Studies on the extraction of compounds from Gac fruit also showed that the required extraction duration was shortened by five times when using UAE, while achieving significantly higher antioxidant activity recovery compared to the conventional solvent extraction [47; 48]. The results from this study indicate that UAE is a promising method for the extraction of saponins, polyphenols and antioxidant activity from COG rhizomes.