## 3 Results  
### Total Phenolic Content (TPC)  
The studies conducted by the authors showed the content of polyphenols in infloresences ranged from 6.69 to 15.29 mg GAE\(\cdot\)g\({}^{-1}\), depending on the experimental conditions (Figure 2). This is consistent with the values obtained by other authors. There are numerous reports in the literature concerning the content of polyphenols in hemps. However, they most often concern the content of these compounds in seeds, oil and flour [39; 40; 41; 42; 43]. The number of studies on the content of polyphenols in infloresences is limited. [PERSON]'s research showed a significantly higher polyphenol content in infloresences than in other parts of the plant. The total polyphenol content (TPC) in the infloresences ranges from 26.2 to 33.2 mg GAE\(\cdot\)g\({}^{-1}\) (10.5-48.9 mg GAE\(\cdot\)g\({}^{-1}\)) depending on the variety [44].  
Figure 2: _Cont._In the aerial parts of the cannabis studied by [PERSON] [45], the TPC value ranged from 5.85 to 17.05 mg GAE:g\({}^{-1}\)d.w. depending on the solvent concentration (30-90%), and the maturity of the plant. The (50%) ethanol was recognized as the best solvent for the extraction of polyphenols from both young and mature cannabis samples. In the extracts obtained with 50% ethanol, the highest content of TPC was found for both young (17.05 mg GAE:g\({}^{-1}\)d.w.) and mature (9.25 mg GAE:g\({}^{-1}\)d.w.) plants. On the other hand, TPC in flowers alone ranges from 4.7 to 8.1 mg GAE:g\({}^{-1}\)[46].  
The results of ANOVA analysis showed that the linear and quadratic terms of particle size and time and intensity of ultrasonic treatment significantly affected the yield of total phenolic content. However, the quadratic terms of all variables had negative coefficients, which indicates the existence of a local extreme in the studied area. This extreme is very clearly visible in the case of particle size where the value of TPC initially increases with the increase of particle size and then decreases. Based on the values of the probabilities listed in Table 1, it can also be concluded that particle size was the variable that had the greatest impact on the extraction efficiency of polyphenols from hemp. The highest content of polyphenols of 15.89 mg GAE:g\({}^{-1}\) was obtained during the extraction with the particles of 0.75 mm at a time of 10 min and ultrasound intensity of 5.1 W\(\cdot\)cm\({}^{-2}\), while the lowest value was noticed at 6.69 mg GAE:g\({}^{-1}\) for the particle size of 1.25 mm at time of 10 min and ultrasound intensity of 1.6 W\(\cdot\)cm\({}^{-2}\).  
Figure 2: Response surfaces for the total polyphenol content (mg GAE:g\({}^{-1}\)) in hemp showing the effect of (**a**) particle size and time, (**b**) particle size and intensity, (**c**) intensity and time.  
Based on the regression analysis, the model was adjusted to the experimental data, as shown in Equation (3):  
\[TPC=-9.59+20.94X_{1}+1.77X_{2}+2.66X_{3}-0.08X_{2}X_{3}-16.25X_{1}^{2}-0.06X_{2}^ {2}-0.12X_{3}^{2} \tag{3}\]  
Equation (3) was tested with an analysis of variance, and it supplied an excellent fit to the empirical data. \(p\)-values of the model less than 0.05 and \(p\)-value of lack of fit higher than 0.1 indicate that the model predicted data well to actual experimental response results. This was also confirmed by the high values of the determination coefficients R\({}^{2}\) (0.9822) and the adjusted coefficient R\({}^{2}\) (0.9643) and the low value of the coefficient of variation (5.32%). Adequate precision was found to be 20.6375, which testified to an acceptable proportion of signal-to-noise ratio because a value greater than 4 was required for model discrimination.  
The model was also validated by residual analysis, as presented in Figure 11 (Appendix A). The result shows a good correlation between the experimental and predicted values of the response and that the errors are independent and normally distributed. This demonstrates that the selected model is appropriate and can be deployed for the optimization of total phenolic content.