Ohmic Heating as a Strategy for the Processing of Soy Protein Isolates: Effects of Process Parameters on Thermal Efficiency and Protein Stability

Ohmic heating (OH) is an emerging technology used as an alternative to conventional thermal treatments. It is based on the passage of electric current through food, which acts as a resistor, generating heat rapidly and uniformly. Due to the growing demand for plant-based protein sources as substitutes for animal-derived proteins, analyzing the effects of OH on soy proteins is of significant scientific and technological relevance. In this context, this study aimed to evaluate the application parameters of this technology in soy protein isolates (SPI). Using an OH system, the electric field strength (0, 20, 30, 40, 45, and 50 V/cm), protein isolate concentration (1.5, 3, 4.5, 6, 7.5, and 9%), pH (2, 4, 6, 8, and 10), and ionic strength (0, 0.1, 0.2, 0.3, and 0.5 mol/L) were varied. It was observed that higher ionic strength resulted in increased electrical conductivity, promoting a faster temperature rise and consequently greater heat generation. Solutions with lower pH showed higher electrical conductivity, possibly due to the increased presence of free positive charges (H⁺ ions), which favored faster heating. However, under highly acidic conditions, a decrease in heat generation was observed, suggesting possible protein denaturation, which alters dielectric properties and compromises the efficiency of ohmic heating. Regarding the applied electric field, lower field intensities resulted in better electrical conduction in soy systems, although the temperature increase occurred more slowly. On the other hand, higher field intensities led to faster heating and greater heat generation in less time, although the process became less efficient in terms of thermal uniformity and may also have contributed to protein denaturation. The different concentrations of soy protein isolate also significantly influenced the process. Higher concentrations showed increased electrical conductivity due to the greater amount of ionic solids present. However, at concentrations of 7.5% and 9%, protein denaturation was observed, indicating a threshold for the safe application of OH without compromising protein integrity. In conclusion, ohmic heating is an efficient technique for application to soy proteins, provided that ionic strength, pH, electric field, and concentration parameters are properly controlled. The balance among these variables is essential to maximize electrical conductivity and heat generation while preventing protein denaturation and preserving the functional properties of the protein.