## 3 Results and Discussion
### Single-Factor Investigation of Extraction Conditions
#### 3.2.2 Effects of Extraction Temperature on Extraction Yield  
In conventional extraction techniques, it is generally observed that increasing the extraction temperature within the range of 20 to 80 \({}^{\circ}\)C enhances the recovery efficiency of  
Figure 2: Influence of extraction time on extraction efficiency of TPC (**A**), TSC (**B**) and antioxidant activity (**C**). Different characters indicate statistically significant differences among the values (\(p<0.05\)). plant compounds, particularly polyphenols [8; 30]. Because the boiling point of ethanol is 78.3 \({}^{\circ}\)C, the investigated temperature in this study was limited to 70 \({}^{\circ}\)C to avoid the excessive evaporation of ethanol, which may cause unexpected issues during extraction [31]. Figure 3A reveals significant variations in the TPC yield obtained at 30, 40 and 50 \({}^{\circ}\)C but no significant differences were found between the temperatures of 50 and 60 \({}^{\circ}\)C. There are two mechanisms that may be involved in the higher diffusion rate of phenolic compounds at elevated temperatures. Firstly, the bonds between lignins and various phenolic acids are cleaved, thereby releasing phenolic compounds. Secondly, lignins may undergo self-decomposition at high temperatures, leading to the liberation of a greater number of phenolic compounds [32]. The data in Figure 3B show that the TSC extracted from COG rhizomes also reached the highest level at the temperature of 50 \({}^{\circ}\)C but then decreased when higher extraction temperatures were applied. Theoretically, elevated temperatures can soften plant tissue and weaken the bonds between various plant components, such as phenol-protein or phenol-polysaccharide linkages, facilitating the release of phytochemicals into the liquid phase. Furthermore, the viscosity and surface tension of the solvent decrease at higher temperatures, creating favorable conditions for enhanced solvent interactions with the solid sample [18]. However, excessive heating can accelerate the oxidation and degradation of the desired bioactive compounds. Moreover, unwanted components such as proteins and polysaccharides from the raw material may penetrate into the solvent at high temperatures and form gel networks, which can hinder the extraction process of the desired compounds [33; 34]. A similar changing trend in the DPPH antioxidant activity to those of the TPC and TSC was observed, as shown in Figure 3C, where the peak of the antioxidant activity belonged to the extract obtained at 50 \({}^{\circ}\)C. A previous study on COG rhizomes reported that polyphenol compounds play a major role in contributing to the antioxidant activity of COG rhizomes [35]. The literature shows that the temperature can affect reactions involving antioxidants or may alter their structures and properties [36], and various studies have also recommended that temperatures above 70 \({}^{\circ}\)C should not be used to extract bioactive compounds from plant materials like grape pomace [27], _Clinacanthus mutans_ Lindau leaves [34] and _Polyscias frutiosa_ roots [29] as they may lead to a reduction in the antioxidant activity of the obtained extracts. 2.3 Influence of Solvent-to-Material Ratio on Extraction Yields of TPC, TSC and Antioxidant Activity  
Figure 4A,B show an increasing trend in the TPC and TSC with an increasing solvent-to-material ratio, respectively. This trend is predictable because, according to the diffusion law, increasing the amount of solvent enhances the concentration gradient of the solutes, thereby accelerating the diffusion rate of soluble compounds from the material into the  
Figure 3: Influence of extraction temperature on the extraction efficiency of TPC (**A**), TSC (**B**) and antioxidant activity (**C**). Different characters indicate statistically significant differences among the values (\(p<0.05\)). solvent. Although the TSC yield was not significantly improved (\(p<0.05\)) from the ratios of 40/1 to 80/1 (mL/g), the yield of TPC continued to rise at the ratio of 80/1 (mL/g).