Interactions between isolated pea globulins and purified egg white proteins in solution

In the present work, the interactions and associations between low denatured pea globulins (PPI) and purified main egg white proteins (ovalbumin (OVA), ovotransferrin (OVT), and lysozyme (LYS)) were studied at pH 7.5 and 9.0 by using isothermal titration calorimetry (ITC), dynamic light scattering (DLS), laser granulometry and confocal laser scanning microscopy (CLSM). From ITC, we detected strong exothermic interactions between PPI and LYS at both pHs, which led to aggregation. At these pH values, the net positive charge of lysozyme favored electrostatic interactions with negative charges of pea proteins, and oligomers were formed during titration experiments. Furthermore, DLS, laser granulometry, and CLSM data showed that the particle size of the mixture increased with increasing LYS to PPI molar ratio (from 0.8 to 20). Large irregular aggregates up to 20–25 µm were formed at high molar ratios and no complex coacervate was observed. No or very weak interactions were detected between OVT or OVA and PPI whatever the pH. These results suggest the role of electrostatic interactions between LYS and PPI when considering protein mixtures.