Rheological properties of protein/polysaccharide blends as affected by time-dependent phase separation

FEDERICO JARA; PILOSOF, ANA M. R.

Atenas

Congreso; 11th INTERNATIONAL CONGRESS ON ENGINEERING AND FOOD 11th ICEF 2011; 2011

School of Chemical Engineering - National Technical University of Athens

The use of mixed protein/polysaccharide systems is gaining increasing importance due to their synergistic interactions, offer the possibility to control or improve the functional and structural properties of food products. Usually protein/polysaccharide blends tend to separate into two phases, one rich in polysaccharide and another rich in protein, due to the phenomenon of thermodynamic incompatibility. In the present work, we studied the rheological properties of gels prepared from a mixture of whey protein concentrate (WPC) and hydroxypropylmethylcellulose (HPMC) as affected by the degree of phase separation. In the first place, the phase separation kinetics of a mixed system containing 4% wt/wt of HPMC and 15% wt/wt of WPC was determined, measuring the change of the lower phase volume over time. After that, dynamic rheological tests were conducted in a controlled stress rheometer (Paar Physica MCR 300), on mixed gels with different degrees of phase separation (0, 7, 16, 34 and 70%) and single WPC and HPMC gels, determining the elastic modulus (G ´) and gelation temperature (Tgel). Tgel values for WPC and HPMC were 82.0 ± 1.0 º C and 54.0 ± 2.0 º C, respectively. The homogeneous system (0% of phase separation) presented a Tgel of 76.3 ± 2.0 º C, which tends to the average value of the Tgel of individual components affected by their concentrations (76 º C) (Jara, Pérez & Pilosof, 2010). Moreover, at low phase separation degrees (7 or 16%) the Tgel was determined by the HPMC rich-phase, indicating that the mixed gel microscopic morphology could be determining its macroscopic properties (Jara & Pilosof, 2009). Finally, when the system reaches a 70% of phase separation, it presented a Tgel of 79.4 ± 4.0 ° C, similar to that obtained for single WPC (80 º C). On the other hand, the elastic modulus (G ´) of mixed gels did not show any correlation with the degree of phase separation, although there was a synergistic effect due to concentration of the components during the separation process. Thus, controlling the degree of phase separation before gelling a mixed WPC/HPMC system allows to obtain gels with specific gelation temperature or elastic properties Keywords: thermodynamic incompatibility, gelling, hydroxypropyl methylcellulose, whey proteins, dynamic rheology. Jara, F. L., Pérez, O. E., & Pilosof, A. M. R. (2010). Impact of phase separation of whey proteins/hydroxypropylmethylcellulose mixtures on gelation dynamics and gels properties. Food Hydrocolloids, 24, 641-651. Jara, F. L., & Pilosof, A. M. R. (2009). Glass transition temperature of protein/polysaccharide co-dried mixtures as affected by the extent and morphology of phase separation. Thermochimica Acta, 487(1-2), 65-73.