INFLUENCE OF PROTEIN CHARGE ON THERMAL PROPERTIES AS WELL AS MICROSTRUCTURE AND RHEOLOGY OF HEAT INDUCED NETWORKS FOR OVALBUMIN AND VICILIN

Abstract

The storage modulus (G′) and loss modulus (G″) for both ovalbumin and vicilin exhibited bimodal responses with respect to pH; lower values were obtained around the isoelectric points (IEP) and at pH extremes. Around the IEP, protein networks were characterized as highly aggregated with high tan δ (G″/G′) values. At pH values away from the IEP, the microstructure appeared as well crosslinked networks with corresponding lower tan δ values. In most cases, (except ovalbumin in acid conditions) this trend was not reversed at pH extremes. Inclusion of sodium dodecylsulfate (SDS) at pH 8.5 had an effect similar to increasing pH. For both proteins, network deterioration at high SDS concentrations was associated with protein unfolding and increased protein solvent interactions. For networks with low tan δ values (e.g. ovalbumin in alkaline conditions) the G moduli in the final network were influenced by changes during the initial cooling phase, whereas for aggregated products and most vicilin networks, changes in the G moduli during the final cooling phase were prominent. The contribution of electrostatic interactions to well crosslinked networks from both vicilin and ovalbumin was as a repulsive force in the balance required for network formation. For vicilin, electrostatic interactions also appeared to serve as an attractive force even under conditions of reasonable network formation. This may account for the difference in network quality for the two proteins.