Effect of thermal treatments on large and small deformation properties of whey protein/pectin mixed gels

Real food systems are always a combination of structuring biopolymers with inclusions of different solutes such as water and lipids. A better understanding of mixed gelled systems is critical to gain a better control of formulated foods. Whey proteins and polysaccharides are two gelling biopolymers used by the food industry for their wide range of rheological and textural properties. Mixed gels containing more than one gelling agent are usually classified into three types: interpenetrating, coupled and phase-separated networks. Phase-separated networks are the most frequently observed as thermodynamic incompatibility is a common phenomena with mixtures of biopolymers. During gel formation, competition between phase separation and gel formation takes place. All factors that can affect this dynamic process will modify the final structure of the gels. Among these factors, heating and cooling kinetics should be considered as a key parameter in the modulation of phase-separated mixed gel structures. Large and small deformation behaviors of whey protein gels and whey proteins/pectin mixed gels have been studied for different heating and cooling rates at three pH values (6, 7 and 8). The structure of gels has been observed using confocal laser scanning microscopy. Fast heating and cooling kinetics were determined as critical to stop the phase separation process and to maintain optimum textural properties especially at pH 8. Heat treatment history could be identified as another effective tool (with relative concentration of polymers, ionic strength and pH) to modulate mixed gel microstructure and textural properties. On the other hand, obtained results are proving, once again, the high level of complexity of mixed systems and are underlying possible hurdles in the large scale used of these systems.