# Extraction of Antioxidants from Grape and Apple Pomace: Solvent Selection and Process Kinetics
## 3 Results and Discussion
### Kinetic Modeling of Extraction Process
In the case of acetone, the addition of water helps in the extraction slow phase, increasing two-fold the k\({}_{\text{d}}\) value: as this increase cannot be due to solvent viscosity (it is lower in the case of pure acetone), it should be due to the solvation power of the solvent for the phenolics extracted in this slow phase; this factor is key to explaining a higher solvent-solute interaction and, thus, the ability of the solvent to desorb the solute from the pore surface. The case of water is interesting: the relatively high value of q\({}_{0}\) indicates a mild solvation power for phenolics during washing (therefore, these phenolics should be \begin{table}
\begin{tabular}{c c c c c c} \hline
**Extraction** & **q\({}_{0}\)** & **q\({}_{1}\)** & **q\({}_{e}\)** & **k\({}_{d}\)** & **r\({}^{2}\)** \\ \hline Ethanol 70\% (\(\
u\)/\(\
u\)) 25 \({}^{\circ}\)C & 50 \(\pm\) 0.5 & 41 \(\pm\) 0.5 & 91 \(\pm\) 1.0 & 9 \(\times\) 10\({}^{-3}\)\(\pm\) 5\(\times\) 10\({}^{-4}\) & 0.99 \\ Ethanol 70\% (\(\
u\)/\(\
u\)) 50 \({}^{\circ}\)C & 70 \(\pm\) 8.2 & 38 \(\pm\) 7.7 & 108 \(\pm\) 16 & 0.015 \(\pm\) 5\(\times\) 10\({}^{-3}\) & 0.82 \\ Ethanol 70\% (\(\
u\)/\(\
u\)) 70 \({}^{\circ}\)C & 69 \(\pm\) 6.8 & 47 \(\pm\) 6.0 & 116 \(\pm\) 13 & 0.015 \(\pm\) 4\(\times\) 10\({}^{-3}\) & 0.95 \\ Ethanol 70\% (\(\
u\)/\(\
u\)) 90 \({}^{\circ}\)C & 73 \(\pm\) 1.8 & 48 \(\pm\) 1.4 & 121 \(\pm\) 3.2 & 6 \(\times\) 10\({}^{-3}\)\(\pm\) 1\(\times\) 10\({}^{-3}\) & 0.99 \\ Ethanol 96\% (\(\
u\)/\(\
u\)) 70 \({}^{\circ}\)C & 19 \(\pm\) 3.2 & 15 \(\pm\) 3.2 & 34 \(\pm\) 6.4 & 0.05 \(\pm\) 6 \(\times\) 10\({}^{-3}\) & 0.98 \\ Acetone 100\% (\(\
u\)/\(\
u\)) 25 \({}^{\circ}\)C & 2.6 \(\pm\) 0.2 & 6.2 \(\pm\) 0.7 & 8.8 \(\pm\) 0.9 & 5 \(\times\) 10\({}^{-3}\)\(\pm\) 2\(\times\) 10\({}^{-3}\) & 0.96 \\ Acetone 80\% (\(\
u\)/\(\
u\)) 25 \({}^{\circ}\)C & 28 \(\pm\) 8.8 & 69 \(\pm\) 21 & 98 \(\pm\) 30 & 0.030 \(\pm\) 0.011 & 0.95 \\ Water 25 \({}^{\circ}\)C & 8.8 \(\pm\) 0.4 & 3.2 \(\pm\) 0.4 & 12 \(\pm\) 0.8 & 0.23 \(\pm\) 0.023 & 0.98 \\ Ethylene glycol 90\% (\(\
u\)/\(\
u\)) 70 \({}^{\circ}\)C & 60 \(\pm\) 4.4 & 60 \(\pm\) 3.4 & 120 \(\pm\) 7.8 & 4 \(\times\) 10\({}^{-3}\)\(\pm\) 2\(\times\) 10\({}^{-3}\) & 0.95 \\ Propylene glycol 90\% (\(\
u\)/\(\
u\)) 70 \({}^{\circ}\)C & - & 75 \(\pm\) 21 & 75 \(\pm\) 21 & 0.025 \(\pm\) 9 \(\times\) 10\({}^{-3}\) & 0.90 \\ ChCl: EG (1:4) & 41 \(\pm\) 4.2 & 30 \(\pm\) 3.9 & 71 \(\pm\) 8.1 & 0.024 \(\pm\) 4 \(\times\) 10\({}^{-3}\) & 0.94 \\
90\% (\(\
u\)/\(\
u\)) 70 \({}^{\circ}\)C & & & & & \\ \hline \end{tabular}
\end{table} 
Table 4: Kinetic parameters from the extraction process of GP measuring antioxidant capacity by DPPH method; q\({}_{0}\), q\({}_{1}\), and q\({}_{e}\) are measured in TEAC/gds, while k\({}_{\text{d}}\) units are gds/(TEAC-min). notably polar in nature, for example, due to their glycosylation), while a high value for q\({}_{1}\) shows a good solvation power for those phenolics remaining in the porous structure at the beginning, compounds that are slowly extracted in the second extraction period, which can be expected when using a relatively viscous solvent (in comparison to the others here tested). The low value for k\({}_{\rm d}\), similar to that of pure acetone, can be explained, again, by the high viscosity of water, especially at 25 \({}^{\circ}\)C. Glycols are even better solvents from the TPC perspective in terms of q\({}_{0}\) and q\({}_{\rm e}\), and their high viscosity, as in the case of water, can be the reason for the low values of k\({}_{\rm d}\). Considering the results for TPC and AC values, as ethyleneglycol is toxic and due to economic and logistic reasons, for food and pharma applications, the ethanol 70%-water 30% mixture working at relatively high temperature (70 \({}^{\circ}\)C) is the best solvent to obtain active extracts from apple pomace, considering that a higher temperature, though it can be better for a fast extraction in the washing stage, in the end is deleterious for the antioxidant capacity of the extract.