## 3 Results and Discussion  
### Effects of Solvents on Extraction Yield  
The extraction process of the desired compounds from plant materials can be influenced by several factors, including the nature of the raw material, the properties of the desired compounds, the extraction methods, the properties of the solvents and other process conditions, such as the temperature, time and pH. Under similar temperatures and extraction times, the selection of an appropriate solvent is considered as the crucial factor affecting the recovery of the desired compounds [7]. In general, the selection of an appropriate solvent to extract a target group of compounds from a material principally depends on the solubility of these compounds relative to the solvent's polarity [8]. However, with extraction for further applications in food or pharmaceuticals, the choice of an appropriate solvent is limited by the toxicity of the solvents [14]. Therefore, this study only focused on investigating solvents that pose minimal health risks while still ensuring diversity in solvent polarity.  
Figure 1 clearly demonstrates significant differences in the recovery of the TPC, TSC and DPPH antioxidant activity among the three extracts obtained from different solvents including ethyl acetate, ethanol 96%, ethanol 80%, acetone and distilled water. While ethyl acetate and ethanol 80% resulted in the highest TPC yields, the greatest recovery of TSC was attributed to the water and 80% ethanol extracts. The extraction of chemical compounds from plant materials depends on their chemical nature, the polarity of the solvent and other factors. Solvents like water and acetone are inefficient in extracting total polyphenols from plants because polyphenols are often bound to other biopolymers, such as proteins and polysaccharides. The difference in the polyphenol recovery efficiency between 80% ethanol and 96% ethanol in the study aligns with previous findings indicating that diluted ethanol is more effective than absolute alcohol in extracting phenolic compounds due to its ability to dissolve both polar and non-polar compounds [15; 16; 17]. Previous studies have indicated that most saponins are polar compounds, so the use of highly polarized solvents such as ethanol and distilled water could achieve higher extraction efficiency compared to other solvents [6; 9; 18].  
The evaluation of the antioxidant activity revealed that water, acetone and ethanol 96% were the extracts with the lowest DPPH radical scavenging activity, and the ethanol 80% extract possessed significantly higher antioxidant activity compared to the others. The strong antioxidant activity of the 80% ethanol extract can be explained by the excellent extraction capabilities of this solvent for both saponins and phenolic compounds. These groups of compounds have been proven to be the main contributors to the antioxidant capacity of plant extracts [17; 19]. Several previous studies have also suggested that combining solvents or using diluted solvents leads to higher extraction efficiency and antioxidant activity because ethanol cannot extract all compounds in plants. Thus, the use of diluted ethanol can improve the extraction efficiency of water-soluble antioxidant compounds [20]. In addition, ethanol has been commonly used in the extraction of natural compounds because it is considered a low-risk solvent for human health, and its reasonable cost makes it suitable for applications in industrial production [17]. Based on the obtained results, 80% ethanol was selected as the solvent for further experiments to simultaneously extract the TPC, TSC and antioxidant activity from COG rhizomes.