# High-Pressure Effects on Selected Properties of Pea and Soy Protein Isolates
## 3 Results
### Surface Hydrophobicity  
Figure 3 presents the relative effects of HPP (200-600 MPa for 5-15 min) at different pH values (6-8) on the surface hydrophobicity (H\({}_{0}\)) of pea and soy solubilized proteins. For  
Figure 2: Effects of high-pressure processing, 200, 400 and 600 MPa for 5, 10 and 15 min on the content of free sulfhydryl groups of pea ((**A**)—pH 6, (**B**)—pH 7, (**C**)—pH 8) and soy ((**D**)—pH 6, (**E**)—pH 7, (**F**)—pH 8) protein isolates at different pH values. The columns with diagonal stripes represent control samples (0.1 MPa). Blank, gray and black filled columns denote 5-, 10- and 15-min processing times, respectively. Different letters indicate significant differences (\(p\) < 0.05) between samples represented in each figure.  
unprocessed PP, the highest value of H\({}_{0}\) was found at pH 7 (H\({}_{0}\) = 1735), followed by pH 8 and 6. It is worth to note that a higher amount of free SH groups was also observed at pH 7, probably related to a net balance favoring more expanded protein conformations at this pH, thus exposing more hydrophobic zones and free SH groups. Unprocessed SP samples showed higher H\({}_{0}\) values (H\({}_{0}\) = 2103-2209) than for PP, but a much lower pH effect.  
In general, all HPP conditions tested led to an increase in proteins' surface hydrophobicity, most probably related to protein partial unfolding and exposure of hydrophobic groups previously hindered inside the protein folded structures, or, in a few cases, to non-significant changes (\(p\) > 0.05) in this parameter [16; 17]. HPP effects were more pronounced for PP than for SP samples, similar to what has already been observed for the HPP effects on free SH groups (Section 3.2). Higher pressures and/or higher processing times seem to originate more pronounced increases in protein surface hydrophobicity. As observed for the HPP effects on free SH groups, also, in this case, the influence of pH on the magnitude of the effects of HPP on protein hydrophobicity was much more pronounced for PP (Figure 3A-C) than for SP (Figure 3D-F). It is interesting to note the effects observed for  
Figure 3: Relative variation (%) of protein surface hydrophobicity for the HPP-treated samples, having as reference the surface hydrophobicity measured for unprocessed samples. Results are shown for pea ((**A**)—pH 6, (**B**)—pH 7, (**C**)—pH 8) and soy ((**D**)—pH 6, (**E**)—pH 7, (**F**)—pH 8) protein samples. Different letters indicate significant hydrophobicity differences (\(p\) < 0.05) between samples at the same pH. Significant differences (\(p\) < 0.05) in relation to the unprocessed samples, at the same pH, were observed for all tested samples except those indicated by an asterisk (\(\text{\textdagger}\)\(p\) > 0.05).  
short pressurization times (5 min): for SP there were no significant differences compared to non-pressurized samples, for pH 6-8, while, for PP there was a clear dependence on pH, with samples at pH 6 (Figure 3A) not showing significant differences (\(p>0.05\)) comparatively to the control sample or among them, there was already a tendency towards an increase in H\({}_{0}\) at pH 7 (Figure 3B) and greater differences were observed at pH 8, with H\({}_{0}\) increasing significantly (\(p<0.05\)) comparatively to the control sample and with increasing pressure.