Accessing the thermal and electric effects in β-lactoglobulin denaturation and interaction with phenolic compounds

Protein-phenolic interactions have been on the spotlight in food research since they can change the structural, functional and nutritional properties of both compounds. Electric field processing technologies, such as ohmic heating (OHM), can contribute to improving food safety, quality and to tailor functionality of foods and ingredients. In this study, the potential of OHM processing in modifying protein-phenolic interactions was accessed. beta-lactoglobulin (beta-Lg) solutions were processed at 70 degrees C and 90 degrees C by conventional heating and OHM (26 V cm(-1) at 50 Hz and 20 kHz), followed by their association with different phenolic compounds - i.e., quercetin (Qu), malvidin-3-glucoside (M3G), trans-resveratrol (TR), p-coumaric acid (p-C) and tyrosol (Ty). The protein solutions and protein-phenolic complexes were characterized by UV-spectroscopy, fluorescence spectroscopy, circular dichroism, and antioxidant capacity. Protein-phenolic interactions were confirmed by changes in the UV-absorbance spectra, reduction of the surface hydrophobicity and changes in the secondary structure of the protein. The formation of stable complexes was established through fluorescence quenching analysis and the binding affinities were found to be in the order TR > Qu > p-C > M3G > Ty. Furthermore, the binding parameters and changes of the protein's structural features were impacted by the processing conditions, including those associated with OHM. This study demonstrates for the first time that OHM processing and the control of its variables can potentially be used to tune beta-Lg-PhCs interactions.