# High-Pressure Effects on Selected Properties of Pea and Soy Protein Isolates
## 3 Results
### Emulsifying Properties  
Since HPP can alter protein solubility, conformation and hydrophobicity, it is expected to affect proteins' influence on emulsion formation and stability, and, thus, the EAI and ESI values. However, the effect of HPP on the surface tension of PP and SP solutions was minor and, in most cases, not statistically significant, either in relation to the unprocessed control sample or in relation to the different processing conditions (results not shown; see Section S2 and Figure S3 as Supplementary Data). Among all HPP conditions studied, for both the PP and SP samples and the three different pH, the more pronounced effects of HPP (and those that lead to significant differences (\(p<0.05\)) in relation to the unprocessed samples) were observed mainly at pH 8, as shown in Figure 4 (the whole set of results is shown in Figures S4 and S5 as Supplementary Data). Figure 4: Emulsifying activity index (EAI) measured for O/W emulsions prepared with pea ((**A**)—total fraction, (**B**)—soluble fraction) and soy ((**C**)—total fraction, (**D**)—soluble fraction) protein dispersions (pH 8), previously subjected to different high-pressure processing treatments (200, 400 and 600 MPa for 5, 10 and 15 min). The columns with diagonal stripes represent unprocessed (0.1 MPa) control samples. 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. Since the EAI is calculated in relation to the protein concentration, and considering the relatively low solubility of the commercial protein isolates, one can expect that the amount of protein in the total PPI and SPI fractions that effectively will contribute to the interfacial activity will be relatively low. Therefore, not unexpected, the soluble protein fractions showed higher EAI values (Figures 4, S4 and S5). HPP seems to decrease the interfacial area coated by the protein [14], at least at pH 8 and for certain HPP conditions, as suggested by the reduced EAI values observed for the HPP-processed samples at this pH value. For the PP total fraction (Figure 4A), EAI was 52 \(\pm\) 4 m\({}^{2}\cdot\)g\({}^{-1}\) for the unprocessed samples and decreased by approximately 16-19% with HPP, whereas, for the emulsions prepared with the PP soluble fraction (Figure 4B), EAI was 179 \(\pm\) 5 m\({}^{2}\cdot\)g\({}^{-1}\) for the unprocessed samples, also decreasing by a similar order with HPP treatments. In both cases, there were negligible effects of pressure level or pressurizing times. There was also a reduced effect of HPP on EAI of emulsions prepared with the total SP fraction (Figure 4C), with a reduction of EAI up to 25% for certain HPP conditions (200 and 600 MPa/5 and 15 min). Emulsions prepared with HPP-treated SP soluble fraction showed a considerable reduction of EAI higher pressures (Figure 4D). Considering PP dispersions, significant effects (\(p<0.05\)) on ESI were only observed at pH 7, for certain HPP conditions, as shown in Figure 5. For greater clarity, only the results obtained for 15 min of processing by HPP are shown, although, qualitatively, the effect observed for other times was similar. In this case, there was a general tendency for ESI to increase with the HPP treatments, especially for the soluble protein fraction. For SP dispersions, a different behavior was observed for the total and soluble protein samples. Regarding the total SP, the HPP treatment resulted in a significant decline in ESI at pH 6 (\(p<0.05\)) (Figure 6A), while significant increases, though less pronounced, were observed at pH 8 for certain HPP conditions, and an intermediate behavior at pH 7.