# High-Pressure Effects on Selected Properties of Pea and Soy Protein Isolates
## 5 Conclusions  
HPP can lead to substantial changes in the structure of pea and soy proteins that may improve some of their techno-functional properties. Therefore, HPP increases, for instance, the solubility and surface hydrophobicity of protein isolates from both pea and soy, although the consequence on interfacial and emulsifying protein properties was dependent on the selected processing conditions, and often with a compromised positive effect due to further protein aggregation. In addition, similar HPP conditions can also lead to a decrease in free SH groups, which would point to protein folding and establishment of intermolecular interactions, corroborating again the complexity of the HPP effects on proteins' conformation and their propensity to interact. The effects of a different pH during the HPP treatment were previously studied, but mainly comparing the behavior above and below the proteins' isoelectric point. Here, we clearly showed that, even within a relatively short pH range, above pH, the degree of protein ionization does have a significant influence on the conformational changes undergone by proteins under pressure. In particular, the application of HPP to both PPI and SPI revealed an increase in the solubility of proteins in both isolates. Specifically, the solubility of SPI was significantly more pronounced at pH 7 and 8 and pressure above 400 MPa, with almost three times the percentage of soluble proteins in comparison to without HPP. Furthermore, the surface hydrophobicity of proteins from both sources increased with HPP, with the increase correlating to increasing pressure and holding time. Unlike the hydrophobicity, the content of free sulfhydryl groups in proteins from both sources decreased with HPP, particularly for PPI at pressures above 400 MPa, suggesting a balance between protein unfolding and further aggregation under certain conditions. Finally, the emulsifying properties of the protein isolates were found to be dependent on pH, pressure, holding time and the fraction of the protein isolates used. Overall, findings from this study reveal that HHP can be effectively used to improve and tailor pea or soy proteins to be used as technological ingredients in food formulations, however, additional studies are needed to fully understand, from a fundamental point of view, the digestibility issues related to the consumption of HPP-treated proteins and their effects on the human body. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app13042359/s1](https://www.mdpi.com/article/10.3390/app13042359/s1)]([https://www.mdpi.com/article/10.3390/app13042359/s1](https://www.mdpi.com/article/10.3390/app13042359/s1)), Figure S1. SDS-PAGE analysis of high pressure-treated (A) pea and (B) soy protein isolates at 0.1, 400 and 600 MPa for 15 min at pH 6 (lanes 2-4), pH 7 (lanes 5-7) and pH 8 (lanes 8-10). Lane 1--protein molecular weight markers. To the right are the most likely protein fractions based on the standards' molecular masses--LOX denotes for lipoxygenase, and PA2 for the major component of the albumin fraction; in (B) \(\alpha\)\(\alpha\), \(\alpha\) and \(\beta\) denote for the \(\beta\)-conglycinin subunits, A1, A2, A3, and A4 for the glycinin's acid subunits, B for the glycinin's basic subunit, and AB for acid-basic subunits pair. Figure S2. Relative amount of the main proteins and their subunits obtained from the SDS-PAGE electrophoretic analysis for the PPI (A,B) and SPI (C,D) samples. Results are shown for two different pH (pH 6, A and C; pH 8, B and D). Black filled columns denote for non-pressurized samples, dashed columns for samples treated at 400 MPa, 15 min, and blank filled columns denote for samples treated at 600 MPa for 15 min.