## 3 Results and Discussion
### Determination of the Significant Factors Affecting the Extraction Process
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Run**} & \multicolumn{1}{c}{**Solvent**} & \multicolumn{1}{c}{**Extraction**} & \multirow{2}{*}{**SMR**} & \multicolumn{1}{c}{**Ultrasound**} & \multicolumn{1}{c}{**Solvent**} & \multirow{2}{*}{**ABTS**} & \multirow{2}{*}{**TPC**} \\  & **Concentration** & & **Time** & & **Assistance** & & & \\ \cline{2-7}  & **A** & **B** & **C** & **D** & **E** & & \\ \hline
1 & 60 (\(-\)) & 30 (\(-\)) & 40 (\(+\)) & Yes (\(-\)) & Ethanol (\(-\)) & 70.02 \(\pm\) 4.85 & 39.34 \(\pm\) 2.69 \\
2 & 60 (\(-\)) & 90 (\(+\)) & 10 (\(-\)) & No (\(+\)) & Methanol (\(+\)) & 47.80 \(\pm\) 3.21 & 17.28 \(\pm\) 1.18 \\
3 & 100 (\(+\)) & 30 (\(-\)) & 10 (\(-\)) & Yes (\(-\)) & Ethanol (\(-\)) & 25.97 \(\pm\) 1.82 & 20.94 \(\pm\) 1.63 \\
4 & 100 (\(+\)) & 90 (\(+\)) & 10 (\(-\)) & No (\(+\)) & Ethanol (\(-\)) & 35.71 \(\pm\) 2.45 & 13.54 \(\pm\) 0.99 \\
5 & 60 (\(-\)) & 30 (\(-\)) & 10 (\(-\)) & Yes (\(-\)) & Methanol (\(+\)) & 35.15 \(\pm\) 2.51 & 18.72 \(\pm\) 1.27 \\
6 & 80 (0) & 60 (0) & 25 (0) & Yes (\(-\)) & Ethanol (\(-\)) & 37.15 \(\pm\) 2.42 & 23.58 \(\pm\) 1.52 \\
7 & 100 (\(+\)) & 30 (\(-\)) & 40 (\(+\)) & Yes (\(-\)) & Methanol (\(+\)) & 68.45 \(\pm\) 4.79 & 31.35 \(\pm\) 2.18 \\
8 & 100 (\(+\)) & 90 (\(+\)) & 10 (\(-\)) & Yes (\(-\)) & Methanol (\(+\)) & 21.80 \(\pm\) 1.45 & 16.26 \(\pm\) 1.18 \\
9 & 100 (\(+\)) & 90 (\(+\)) & 40 (\(+\)) & Yes (\(-\)) & Ethanol (\(-\)) & 62.37 \(\pm\) 4.28 & 30.13 \(\pm\) 2.06 \\
10 & 60 (\(-\)) & 30 (\(-\)) & 40 (\(+\)) & No (\(+\)) & Methanol (\(+\)) & 101.99 \(\pm\) 5.95 & 28.03 \(\pm\) 2.02 \\
11 & 100 (\(+\)) & 30 (\(-\)) & 40 (\(+\)) & No (\(+\)) & Ethanol (\(-\)) & 66.15 \(\pm\) 4.52 & 22.35 \(\pm\) 1.74 \\
12 & 60 (\(-\)) & 90 (\(+\)) & 10 (\(-\)) & Yes (\(-\)) & Ethanol (\(-\)) & 34.01 \(\pm\) 2.38 & 25.10 \(\pm\) 1.25 \\
13 & 80 (0) & 60 (0) & 25 (0) & Yes (\(-\)) & Methanol (\(+\)) & 55.83 \(\pm\) 3.23 & 27.71 \(\pm\) 1.84 \\
14 & 60 (\(-\)) & 90 (\(+\)) & 40 (\(+\)) & No (\(+\)) & Ethanol (\(-\)) & 97.16 \(\pm\) 6.52 & 33.07 \(\pm\) 2.09 \\
15 & 80 (0) & 60 (0) & 25 (0) & No (\(+\)) & Methanol (\(+\)) & 35.88 \(\pm\) 2.41 & 17.81 \(\pm\) 1.17 \\
16 & 100 (\(+\)) & 90 (\(+\)) & 40 (\(+\)) & No (\(+\)) & Methanol (\(+\)) & 68.68 \(\pm\) 4.63 & 29.37 \(\pm\) 1.91 \\
17 & 60 (\(-\)) & 30 (\(-\)) & 10 (\(-\)) & No (\(+\)) & Ethanol (\(-\)) & 41.70 \(\pm\) 2.82 & 15.35 \(\pm\) 0.92 \\
18 & 80 (0) & 60 (0) & 25 (0) & No (\(+\)) & Ethanol (\(-\)) & 79.01 \(\pm\) 5.55 & 25.69 \(\pm\) 1.80 \\
19 & 60 (\(-\)) & 90 (\(+\)) & 40 (\(+\)) & Yes (\(-\)) & Methanol (\(+\)) & 57.56 \(\pm\) 3.67 & 34.73 \(\pm\) 2.25 \\
20 & 100 (\(+\)) & 30 (\(-\)) & 10 (\(-\)) & No (\(+\)) & Methanol (\(+\)) & 34.38 \(\pm\) 2.41 & 12.70 \(\pm\) 0.99 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of the verified RSM responses in the first stage of the extraction optimization experimental design and the ABTS and TPC assay values for analyzed variants of spent coffee grounds extracts. Interestingly, for both ABTS and TPC, SMR proved to be the most crucial factor. Thus, finding the best solvent-matrix ratio is critical for optimization of the extraction process. The extracted compound recovery yield depends on the polarity of the solvent. During the extraction process, the solvent interacts with the matrix cells, causing the release of bioactive compounds. With the increase in the solvent to matrix ratio, the hydroxyl groups react with the phenolics and hydrophilic compounds, which negatively affects the extraction yield and leads to solvent wastage [36]. The extraction type has been shown to play a crucial role in the isolation process of most food components with bioactive potential. Techniques known as green technologies decrease the use of organic solvents and simultaneously reduce the risks associated with the toxicity of solvents and solvent residues in the extracts. According to the literature, an ultrasound-assisted extraction should be considered as a preferable method in the process of polyphenols extraction [37].