## 2 Results and Discussion
### Recovery of Polyphenols from mPEG-Grafted Silica Particles
Increasing the citric acid concentration to 40% increased desorption ratio by \(\sim\)2-fold in comparison to 10 and 20% citric acid in ethanol with a final desorption ratio of 29%. It was concluded that addition of citric acid was not sufficient to release most of the polyphenols adsorbed onto mPEG-modified silica particles,  
Figure 3: Adsorption capacities of bare, mPEG-2000-, and mPEG-5000-grafted silica particles for total polyphenols as determined by Folin–Ciocalteu method. Adsorption experiments were performed with 25 mg of adsorbents. A statistically significant difference between all the capacity values was observed (\(p<0.05\)). Error bars indicate a standard deviation observed for duplicates. GAE: Gallic acid equivalents. yet achieved comparable desorption ratios that were observed in 100 mM + 200 mM sorbitol in 70% aqueous ethanol (Figure 4). 3.2 Screening PEG Cosolvent Systems for the Recovery of Polypphenols from mPEG-Grafted Silica Particles: Developing PEG-Water and PEG-Ethanol Cosolvent Systems  
Due to the limited polyphenol desorption abilities of the solvents discussed above, an alternative solvent system capable of releasing the majority of polyphenols from silica particles was needed. Cosolvent systems are widely used in the pharmaceutical industry to solubilize poorly water-soluble drugs [46]. Propylene glycol (PG), ethanol, glycerin, and PEG-400 are commonly used and the Food and Drug Administration (FDA) approved the cosolvents [47]. A system using PEG-200 or PEG-400 as a cosolvent was developed in this study for the effective release of polyphenols from mPEG-modified silica particles. It is hypothesized that the interactions between polyphenols and mPEG-grafted surfaces are unusually strong [48] and are likely due to the hydrogen bonding network. Therefore, solvents behaving like PEG can possibly break this network effectively. It was intended to create a competition between mPEG on the silica surface and PEG-200 or PEG-400 in the cosolvent and achieve complete recovery of polyphenols from silica particles. Effect of PEG Concentration on Polyphenol Recovery  
Figure 4 shows the desorption ratios of PEG-water and PEG-ethanol cosolvent systems with variable PEG concentrations (_r/v_). The slight addition of PEG-400 (10%) to ethanol increased the desorption ratio by \(\sim\)- and 14-fold in comparison to 70% and 30% aqueous ethanol, respectively (Figure 4). A similar trend was observed when only 10% PEG-400 was added to water, where an increase in the desorption ratio of \(\sim\)- and 14-fold in comparison to 70% and 30% aqueous ethanol,  
Figure 4: Desorption of total polyphenols from mPEG-5000 grafted silica particles using various solvents. Ethanol is abbreviated as EtOH. A 1 mL desorption solvent was used for recovery of grape pomace polyphenols adsorbed on 25 mg mPEG-5000-grafted silica particles. Error bars indicate a standard deviation observed for duplicates. was determined, respectively. When the PEG-400 concentration was increased from 10% to 30 and 50% (_v/v_) in ethanol, 3- and 4-fold increases in the desorption ratios compared to the 10% solution were observed, respectively. With that, \(\sim\)99.9% of the adsorbed polyphenols was recovered using 50% PEG-400-ethanol. These high desorption ratios observed in PEG-400-ethanol cosolvent systems are attributed to the ability of PEG to break the strong hydrogen bond network between mPEG-grafted silica particles and polyphenols. It is likely that adding more PEG introduces competition at the polyphenols' binding sites and induces the release of more polyphenols. Previous research showed that PEG-400 has remarkable polyphenol solubility in comparison to traditional solvents such as alcohol, castor oil, and water [30]. Therefore, polyphenols released in PEG solvent will be an ideal platform for the downstream use of polyphenols.