## 3 Results and Discussion  
### Total Flavonoid Content  
The total flavonoid content extracted from the hemp ranged from 3.02 to 9.35 mg QE \(\cdot\)g\({}^{-1}\), varying according to the experimental conditions (Figure 2). Similar results for the total flavonoid content, ranging from 1.83 to 11.20 mg QE \(\cdot\)g\({}^{-1}\) dw, were obtained in aerial studies on hemp parts from the Cannabis sativa L. variety, as carried out by [PERSON] et al. [15]. In the extracts obtained with 50% ethanol, the highest flavonoid content was 11.20 mg QE \(\cdot\)g\({}^{-1}\) dw for young plants and 5.21 mg QE \(\cdot\)g\({}^{-1}\) dw mature plants. Studies conducted by [PERSON] et al. [24] showed that the average flavonoid content in the inflorescences of cannabis cv. Carmagnola was about 0.62 mg \(\cdot\)g\({}^{-1}\) for samples with moisture content ranging from 8% to 12%. Based on the obtained results, the effects of the independent variables on the dependent variables are presented in Table 2.  
Figure 2: Response surfaces obtained with the Box–Behnken experimental design for the total flavonoid content (mg QE:g\({}^{-1}\)) in hep depending on the (**a**) intensity and time, (**b**) particle size and time, and (**c**) particle size and intensity. It was observed that the linear and quadratic terms of the particle size, extraction time, and ultrasound intensity significantly affected (\(p<0.05\)) the extraction of flavonoid compounds. However, the linear and quadratic term of the particle size, and the quadratic terms of the extraction time and ultrasound intensity demonstrated negative correlations, indicating that an increase in the magnitude of these variables may favor the extraction of flavonoid compounds only up to a certain value. This effect is very visible in the case of the disintegration degree, as the total flavonoid content initially increased with the rising particle size, from 0.25 to 0.75 mm, and then decreased as the particle size increased from 0.75 to 1.25 mm. The degree of fragmentation was the variable that most significantly influenced the extraction of flavonoid compounds. In general, the yield of flavonoids increased with an increased time of extraction. Above 14 min, a slight decrease in the total flavonoid content was visible, so a further extension of the extraction time may reduce the extraction of the target compound. Being exposed to ultrasound for too long causes structural damage in the solute and reduces the extraction efficiency, which was confirmed during the extraction of phenolic compounds from waste coffee grounds [25], phenolic compounds from black chokeberry waste [26], and flavonoids from hawthorn seeds [27]. The extraction time had the least influence on the total flavonoid content in the obtained extracts. The total flavonoid content increased with the intensity of the ultrasound. The growth in the intensity of the ultrasound from 1.6 to 8.6 W\(\cdot\)m\({}^{-2}\) increased the total flavonoid content by 47.7%. However, applying ultrasound intensity above the test range may reduce the extraction yield of the target compound. The different effects of ultrasound power on the content of phenolic compounds were observed by [PERSON] et al. [25]. They demonstrated an increase in the efficiency of phenolic compound extraction from coffee-ground waste when the ultrasound power increased from 100 to 244 W, as well as a decrease in efficiency when the ultrasound power exceeded 250 W. In the work of [PERSON] et al. [25], a statistically significant negative interaction was found between the extraction time and the intensity of the ultrasound, which means that the effect of the combined action of the two predictors is less than the sum of the individual effects. The parameters presented in Table 2 were re-estimated considering only the significant terms (\(p<0.05\)).