OHMIC HEATING AS A STRATEGY FOR THE FUNCTIONAL MODULATION OF SOY PROTEIN ISOLATE

Ohmic heating (OH) is an emerging technology capable of promoting structural changes in proteins, directly impacting their techno-functional properties. Modifying the functional properties of soy protein isolate (SPI) is a strategic approach to broaden its applicability in food systems. This study evaluated the effect of ohmic heating on both general and surface properties of SPI, including surface hydrophobicity, solubility, particle size, and Zeta potential, under varying electric field intensities (0–50 V·cm⁻¹), pH ranges (2–10), and NaCl concentrations (0–0.5%), in order to understand the interaction mechanisms induced by the treatment (OH-treated SPI, SPI-OH) compared to the untreated control (SPI). Surface hydrophobicity was determined through bromophenol blue dye binding. Protein solubility was assessed using the Bradford method, while Zeta potential and particle size were analyzed via dynamic light scattering (DLS). The results indicated that ohmic heating induced modifications in the protein surface organization. An increase in surface hydrophobicity was observed, especially at intermediate electric field intensities (around 30 V·cm⁻¹), followed by a slight reduction in the treated samples, suggesting hydrophobic residue masking or rearrangement. This effect was accompanied by an overall increase in protein solubility under alkaline conditions, while the presence of NaCl resulted in decreased solubility for SPI-OH, likely due to the formation of insoluble aggregates and structural changes that hinder interaction with the aqueous medium, even in the presence of salt ions, which typically enhance solubility. Particle size analysis revealed an oscillatory response to the electric field, with a trend toward reduced average size in SPI-OH across both pH variation and salt concentration gradients, suggesting induced disaggregation possibly due to partial protein denaturation. Zeta potential data showed similar charge profiles across specific pH ranges for both samples; however, an increase in negative surface charge was detected at intermediate electric field strength (30 V·cm⁻¹). In relation to salt concentration, SPI-OH exhibited a reduction in Zeta potential compared to SPI, suggesting lower surface negative charge density, possibly due to structural rearrangements induced by the process, which may affect colloidal stability and functional properties. These findings demonstrate that ohmic heating can modulate the interfacial properties of SPI in a medium-dependent manner and may serve as a promising technological strategy for the functional modulation of plant proteins, opening new perspectives for its use in protein engineering applications.