## 4 Conclusions  
In this study, the influence of pulsed ultrasound-assisted extraction parameters on the yield of bioactive substances applying the response surface method was investigated. The Box-Behnken plan was successfully used to optimize the effects of process variables such as particle size, time, and ultrasonic intensity on the yield of the total polyphenic content, their antioxidant activities and unit energy consumption. The statistical analysis pointed out that, the four developed models were accurate and well-fitted to empirical data The optimal conditions for the extraction of polyphenols from cannabis were found to be 0.65 mm for particle size, 13.14 min for extraction time and 6.92 for ultrasound intensity, which resulted in the maximum value of 15.24 mg GAE\(\cdot\)g\({}^{-1}\). Taking into account the antioxidant activity of the extracts the optimal conditions were found in the range particle size of about 0.6 mm; extraction time, 12.30-15 min; and ultrasound intensity, 8-8.60 W\(\cdot\)cm\({}^{-2}\). These parameters  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Optimized** & \multicolumn{3}{c}{**Extraction Variables**} & \multicolumn{3}{c}{**Yield of Extraction**} \\
**Condition** & \(\mathbf{X_{1}}\) & \(\mathbf{X_{2}}\) & \(\mathbf{X_{3}}\) & **Response** & **Predicted** & **Experimental \({}^{\mathbf{a}}\)** & **Predictive Capacity (\%)** \\ \hline TPC & 0.65 & 13.14 & 6.92 & TPC & 15.90 & 15.24 \(\pm\) 0.42 & 95.82 \(\pm\) 2.62 \\ DPPH & 0.59 & 12.35 & 8.07 & DPPH & 71.96 & 66.90 \(\pm\) 3.61 & 92.96 \(\pm\) 5.02 \\ FRAP & 0.63 & 15 & 8.6 & FRAP & 106.98 & 100.40 \(\pm\) 8.25 & 93.84 \(\pm\) 7.71 \\ Unit Energy Consumption & 0.48 & 7.69 & 1.84 & UEC & 0.38 & 0.36 \(\pm\) 0.01 & 94.74 \(\pm\) 3.72 \\ \hline \end{tabular} \(X_{1}\)—particle size (mm); \(X_{2}\)—processing time (min); \(X_{3}\)—ultrasonic intensity (W-cm\({}^{-2}\)); \({}^{\mathbf{a}}\)—mean \(\pm\) standard deviation of the three experiments.  
\end{table}
Table 5: Comparison between the empirical and estimated values of total phenolic content, DPPH, FRAP and unit energy consumption determined in the optimized conditions.  
were close to the optimal parameters of polyphenol extraction. By optimizing the process in terms of unit energy consumption, the best conditions were obtained in the range of the particle size of approx. 0.5 mm, the extraction time of 7.7 min and the intensity of ultrasounds of 1.8 W-cm\({}^{-2}\). The best agreement between numerical values of optimization variables under contrary demands (low energy consumption-high efficiency) was obtained for the size of the raw material particles, and the lowest for the intensity of ultrasound. Under the optimum conditions for unit energy consumption, the amount of predicted total phenolic was 10.14 mg GAE-g\({}^{-1}\). Under the optimum conditions for a yield of polyphenols, the amount of predicted unit energy consumption was 1.61 kJ-mg\({}^{-1}\) GAE-g\({}^{-1}\) dry matter. The developed models of pulsed ultrasound-assisted extraction proved to be efficient for obtaining polyphones from Cannabis sativa L. at low unit energy consumption.  
Conceptualization, Z.K.; methodology, Z.K.; software, J.K.; validation, P.F. and S.K., formal analysis, Z.K.; investigation, A.P., A.B. and Z.K.; resources, J.K.; writing--original draft preparation, Z.K., A.P. and A.B.; writing--review and editing, Z.K., A.P. and A.B.; visualization, J.K.; supervision, Z.K.; project administration, J.K.; funding acquisition, P.F. and S.K. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.