Gelation and structural characteristics of incompatible whey proteins/hydroxypropylmethylcellulose mixtures

The influence of hydroxypropylmethycellulose (HPMC) on whey protein (WPC) gelling properties was studied under thermodynamic incompatibility conditions at neutral pH and room temperature. The binodal curve characterizing phase separation was determined. Thermal transitions of mixed systems above the binodal curve showed two endothermic peaks corroborating phase separation. First of all the gelation process of single HPMC was studied by different techniques in order to interpret the behaviour of mixed systems. Gelation dynamics of mixed systems showed two competitive phenomena during heating, phase separation and gelation. The solid character of mixtures increased when WPC concentration was higher than 8% and the WPC/HPMC ratio was 4 or higher. The gelation temperature, determined by dynamic rheometry, was related to the relative amount of both components. The morphology of mixed gels after the heating/cooling cycle was of the type core–shell , where the core was constituted by HPMC gel. The elastic modulus of mixed gels was much higher than that of single WPC gels at the same concentration, while hardness and relative viscoelasticity were slightly decreased. Core–shell macrostructure results are very interesting because it could find applications in the design of microcapsules or in controlled delivery systems, in which an active component could be partitioned into separated phases or to develop new structures and food products.