## 3 Results and Discussion
### Acid-Catalyzed Treatment and Solvents Effects  
As mentioned above, aqueous mixtures of 40% of either 1- or 2-propanol were used to accomplish the organosolv treatment of PP by maintaining a temperature of 90 \({}^{\circ}\)C. The effect of acid catalysis on polyphenol recovery from PP was tested by switching sulfuric acid concentration (\(C_{\text{SuAc}}\)) to different levels and carrying out the organosolv treatment under variable time regimes. Assessment of the severity of each treatment was determined using Equations (4) and (5), and the results drawn are analytically given in Table 2. For the treatment with 1-propanol, statistically higher YTP was achieved with \(C_{\text{SuAc}}\) of 1% at 60 min and with \(C_{\text{SuAc}}\) of 1.5% at 60 min. These treatments were characterized by CSF values of 0.28 and 0.39, respectively, which were statistically different (\(p<0.05\)). The corresponding CSF values were 7.28 and 7.39, which were also statistically different. This finding suggested that the maximum YTP with minimal process severity may be attained with \(C_{\text{SuAc}}\) of 1% at 60 min. Regarding the process with 2-propanol, significantly higher YTP was obtained with \(C_{\text{SuAc}}\) of 1% at 300 min, and \(C_{\text{SuAc}}\) of 1.5% at 300 min. The corresponding CSF values for these treatments were 0.82 and 0.95, which had no statistical difference (\(p>0.05\)). Similarly, the corresponding CSF values were 7.82 and 7.95, which were not significantly different (\(p>0.05\)). Thus, with 2-propanol treatment, maximum performance with minimal severity could be obtained with \(C_{\text{SuAc}}\) of 1% at 300 min. Considering the above set of conditions, the treatment with 1-propanol would afford a YTP of 18.85 mg CGAE g\({}^{-1}\) DM, which was almost 20% higher compared to the 15.00 mg CGAE g\({}^{-1}\) DM obtained with the 2-propanol treatment. Process severity with 1-propanol was also lower compared to that performed with 2-propanol. This outcome strongly pointed to the superiority of 1- over 2-propanol in recovering PP polyphenols. Figure 1: Testing of water mixtures with 1- and 2-propanol for total polyphenol recovery efficiency. Extractions were carried out at 70 \({}^{\circ}\)C for 210 min. Columns designated with different letters (a, b, c) represent statistically different total polyphenol yield (YTP) values. Bars indicate standard deviation. To have a deeper insight into the effect of both 1- and 2-propanol on process severity and efficiency, empirical models relating Y\({}_{\rm TP}\) with either CSF or CFS were also established, as depicted in Figure 2. In the case of 1-propanol treatment, the quadratic models linking Y\({}_{\rm TP}\) with CSF and CFS were as follows:  
\[\rm Y_{TP}=-6.91 CSF^{2}+7.09 CSF+16.91\ (R^{2}=0.78,\ p=0.0109) \tag{6}\]  
\[\rm Y_{TP}=-6.91 CSF^{2}+103.77 CSF^{\prime}-371.10\ (R^{2}=0.78,\ p=0.0109) \tag{7}\]  
Thus, considering Model (6), the maximum Y\({}_{\rm TP(max)}\) may be determined by the following equation:  
\[\rm Y_{TP(max)}=\frac{D}{4\times(-6.91)} \tag{8}\]  
where D = 7.09\({}^{2}\) - 4 \(\times\) (\(-6.91\)) \(\times\) 16.91. Using Equation (8), the maximum Y\({}_{\rm TP}\) was determined to be 18.25 mg CGAE g\({}^{-1}\) DM. This was in accordance with the experimental value 18.85 mg CGAE g\({}^{-1}\) DM, which was achieved with \(C_{\rm SuAc}\) = 1%, at 60 min, as shown in Table 2. Likewise, when the model (7) was considered, the theoretical maximum Y\({}_{\rm TP}\) determined was 18.48 mg CGAE g\({}^{-1}\) DM. Therefore, both models provided accurate predictions. On the other hand, for the treatments carried out with 2-propanol, the correlations between Y\({}_{\rm TP}\) with CSF and CFS were adequately described by linear models:  
\[\rm Y_{TP}=5.68 CSF+10.34\ (R^{2}=0.88,\ p=0.0002) \tag{9}\]  
\[\rm Y_{TP}=5.68 CSF^{\prime}-29.45\ (R^{2}=0.88,\ p=0.0002) \tag{10}\]  
Thus, Y\({}_{\rm TP(max)}\) could be determined by using the maximum CSF and CFS, which were 0.95 and 7.95, respectively (Table 2).