## 4 Discussion
In their study, the optimal ratio for the tested parameter was 30:1 [34]. Our optimisation showed that, regardless of the response function, the optimal ethanol concentration is 47% \(v/v\). Ethanol is an effective solvent for the extraction of compounds with antioxidant potential, such as polyphenols and flavonoids, as well as tannins, terpenoids, and alkaloids. Water is used, among other substances, for the extraction of tannins, anthocyanins, terpenoids, and saponins [35]. [PERSON] et al. (2024) also optimised the ethanol concentration (in the range of 25-75% \(v/v\)) used for the extraction of _Rheum ribes_ flowers in terms of phytochemical (the total polyphenol and flavonoid content) and antioxidant activity (the FRAP method). In their study, the optimal ethanol concentration was 53.14% [36]. [PERSON] et al. (2015), in their study on the optimization of UEA of _Zizyplus lotus_ fruits for antioxidants, found an optimal ethanol concentration of 50%. They optimised the ethanol concentration in the range of 0 to 100% [37]. A significant effect of the ethanol concentration on the antioxidant potential, including the total phenolic content, is postulated by [PERSON] and [PERSON] (2016). In their studies, extraction with a binary solvent (alcohol and water) was more efficient in obtaining phenolic compounds compared to the process using pure ethanol. This is probably related to the polarity of both solvents [38]. Ethanol and water mixtures are more polar than absolute ethanol, which may positively influence the extraction efficiency of phenolic compounds from plant material [39]. [PERSON] et al. (2007) made interesting observations about the content of phenolic compounds in grape marc extracts, depending on the ethanol concentration. Researchers observed an increase in the yield of phenols at a water content in ethanol from 10% to 30% and their constant levels at a water content of 30% to 60%. When the water content exceeded 50%, the phenol concentration decreased [30]. [PERSON] et al. (2021) compared the antioxidant activity (TAC, FRAP, DPPH, ABTS, and SRSA) as well as the polyphenol and flavonoid content of _S. officinalis_ root extracts prepared in water and 20, 40, 80, and 100% ethanol. The lowest content of polyphenols (TPC) and flavonoids (TFC) was noted in aqueous extracts, while the highest was in 40% (TPC) and 80% (TPC and TFC) ethanol. The concentration of these compounds was almost twice as high in extracts prepared in the above-mentioned alcohol concentrations, compared to aqueous extracts. A similar relationship between the lowest antioxidant activity in water extracts and in ethanol extracts was observed in the case of the TAC, FRAP, and SRAS methods, in which the highest results were observed after using 80% (TAC, SRAS) and 40% (FRAP) alcohol. The highest activity assessed by the DPPH technique was noted for the extract in pure ethanol and the lowest for the sample in 40% solvent. The opposite relationship was observed in the ABTS method. These observations led the authors to choose 80% ethanol as the most efficient solvent for extracting compounds with antioxidant potential. However, it is crucial to note that these studies did not optimise the ethanol concentration as a solvent [40]. In the aforementioned work by [PERSON] et al. (2024), compounds with antioxidant potential were extracted more efficiently after using ethanol at concentrations of 40% and 70% \(v/v\) compared to concentrated ethanol [4]. The extraction time was the third independent variable in the optimization process. As already mentioned, one of the main advantages of UAE is the reduction in the processing time while maintaining or even increasing the efficiency compared to conventional techniques [41]. In the case of the DPPH method, it was noticed that extending the extraction time above 11 min and shortening it below 7 min resulted in a decrease in the antioxidant activity of the extract below 11 mmol Trolox/L.