# High-Pressure Effects on Selected Properties of Pea and Soy Protein Isolates
## 1 Introduction  
In recent decades, there has been an increase in the pursuit of technologies and products that allow us to tailor the technological properties of macromolecules present in foods to improve nutritional and sensorial quality of food products. In this way, the use of vegetable proteins has been the focus of many research efforts to develop new products and to replace other sources of protein [1]. One of the most cultivated crops in the world is soybean, due to the global growing demand for its oil and protein content (ca. 35%). Soy proteins are among the most studied legume proteins and have several applications in food production, mainly due to their nutritional and functional properties. Similar to soy, pea has been increasingly exploited as a source of protein, largely due to its ability to grow worldwide. Peas contain approximately 25% of proteins that have several applications in the food industry, for instance, emulsification, gelation and texture improvement, which is increasing this pulse popularity [1, 2].  
The widespread applications of these proteins, particularly in food formulations processed by newer technologies, is restricted due to the limited knowledge concerning adequate processing parameters [3]. Since the structure, conformation and physicochemical properties of proteins can be affected by pressure, high-pressure processing (HPP) can be a useful tool to tailor the techno-functional properties of food proteins [4]. Under HPP, changes in protein conformation are expectable, related to a change from a high-volume conformation to a low-volume conformation, which usually follows a non-linear response to pressure and occurs predominantly at higher pressures, i.e., above 400 MPa. The collapse of molecular cavities due to water penetration, accompanied by their hydration, and theshortening of the hydrogen bonds are the most relevant consequences of pressure [5]. These effects promote intermolecular interactions that destabilize the tertiary structure and the eventual unfolding of the protein [6]. After the release of pressure, the structure of proteins will frequently be different from the native structures, leading to altered properties such as foaming, emulsification or gelation [7].  
Several studies using vegetable proteins have shown the advantages of HPP to modify the supramolecular structures of proteins, creating new structured systems and textures and improving their functionality [8; 9]. However, there is still a lack of information about the effect of HPP on proteins with different structures and macromolecular organization, namely for commercial protein isolates, which are often composed of proteins that are far from their original native state, and under different environment conditions and HPP processing. Therefore, the objectives of the present study were (i) to evaluate the effects of different HPP parameters, i.e., pressure and holding time, on selected structural and technological protein characteristics, e.g., solubility, content of free sulfhydryl groups, surface hydrophobicity and emulsifying properties; (ii) to assess these effects for commercial pea and soy protein isolates, which typically correspond to proteins with a high degree of denaturation; and (iii) to evaluate these effects for proteins with a different charge density, achieved by studying a relatively short pH range (6-8), slightly above the isoelectric point for most pea and soy proteins and with applied interest.