## 3 Results and Discussion
### Determination of Polyphenolic Content  
Polyphenolic compounds are a group of health-promoting compounds that are widely represented in plants. As a result, these secondary metabolites, often used in medicines, nutraceuticals, food additives, and fine chemicals, are responsible for the therapeutic effects of plants. Among them are compounds with different properties from the point of view of physicochemistry and biological activity. Hence, the spectrum of their beneficial effects on the human body is very wide. Many of them determine the antioxidant activity of plant extracts. Figure 4: Antioxidant activity determined using FRAP method for extracts obtained from Japanese knotweed at 25 and 50 \({}^{\circ}\)C using UASE under the following extraction conditions: (**a**) extraction time of 10 min and a frequency of 37 kHz; (**b**) extraction time of 20 min and a frequency of 37 kHz; (**c**) extraction time of 10 min and a frequency of 80 kHz; (**d**) extraction time of 20 min and a frequency of 80 kHz. Using methanol, methanol/water mixture (50/50%, \(\
icefrac{{v}}{{v}}\)), and water as reaction solvents. The same letters indicate data for which the results are not statistically significant. Figure 6 compares the content of polyphenic compounds in extracts obtained from Japanese knotweed using methanol, water and a mixture of these two liquids as an extraction medium at temperatures of 25 \({}^{\circ}\)C and 50 \({}^{\circ}\)C and different extraction times (10 min and 20 min) and at different ultrasound frequencies, i.e., 37 kHz and 80 kHz. Based on the presented results, it can be concluded that the most polyphenic compounds are contained in methanol-water extracts (orange bars), and the lowest content is characteristic of water extracts (gray bars). This fact is related to the better solubility of this class of compounds in alcohol-water mixtures, which directly translates into the antioxidant properties of the extracts. As for the effect of UASE conditions, the use of a higher ultrasound frequency results in weaker isolation of polyphenic compounds (compare the heights of the bars for a given extractant and temperature in Figure 6a,b with those in Figure 6c,d). In general, an increase in temperature to 50 \({}^{\circ}\)C leads to lower efficiency of polyphenol isolation as a result of their very probable degradation. As is known, during the thermal isolation of natural substances, two competitive processes take place--extraction and degradation/transformation of the released substances into others. The validity of this statement is confirmed by the data  
Figure 5: Antioxidant activity determined using CUPRAC method for extracts obtained from Japanese knotweed at 25 and 50 \({}^{\circ}\)C using UASE under the following extraction conditions: (**a**) extraction time of 10 min and a frequency of 37 kHz; (**b**) extraction time of 20 min and a frequency of 37 kHz; (**c**) extraction time of 10 min and a frequency of 80 kHz; (**d**) extraction time of 20 min and a frequency of 80 kHz. Using methanol, methanol/water mixture (50/50%, \(v/v\)), and water as reaction solvents. The same letters indicate data for which the results are not statistically significant. in Figure 6d, which shows that at a less effective ultrasound frequency in isolation, an increase in temperature reveals a higher yield of polyphenols. In summary, the highest content of these compounds is observed in extracts obtained using a methanol/water mixture at a temperature of 25 \({}^{\circ}\)C, a longer extraction time (20 min), and a lower frequency (37 kHz). It should be noted here that the content of polyphenols obtained by us for the given conditions (31.28 mg/g) is consistent with the literature. [PERSON] et al. [30] determined the content of polyphenic compounds in various medicinal plants, including knotweed, giving a value of 34.91 mg/g. In the literature, one can also find papers in which the authors obtained higher contents of polyphenic compounds [24; 25; 31].