Evaluating the effect of protein composition on gelation and viscoelastic characteristics of acid-induced whey protein gels

The effects of protein composition on the gelation and rheological characteristics of acid-induced whey protein gels were studied. Gels composed of mixtures containing β-Lactoglobulin (β-Lg), α-Lactalbumin (α-La) and glycomacropeptide (GMP) were rheologically investigated using a mixture design and analyzed by response surface methodology. All mixtures evaluated gelled and self-supported gels were obtained, except for the gel containing the highest GMP concentration. Gelation was monitored by oscillatory time sweep and the viscoelastic properties were determined by creep-recovery and stress relaxation measurements with the simplified Burgers model and the Peleg equation fitted to the data, respectively. The results showed that a higher elastic modulus was found in gels containing greater proportions of β-Lg. Addition of α-La and/or GMP reduced the elastic character the gels. The gelling time increased as the proportion of α-La of the mixture was increased, and as a consequence the pH of gelation was reduced. On the other hand, the effect of GMP addition presented the opposite effect. Considering the creep-recovery test, there was a decrease in the simplified Burgers model parameters with the increased proportion of α-La and/or GMP in the mixture. For all gels, the main deformation was caused by the retarded elastic strain, and the reversible deformation was higher than the irreversible deformation. It was also observed that the stress relaxation process was more pronounced in mixtures with lower proportion of β-Lg. Mixed gels were structurally more fragile, and β-Lg was the main component responsible for strengthening the network.