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Stress Relaxation of Acid-induced Milk Gels

Sabadini, Edméia, Hubinger, Míriam D., Cunha, Rosiane L.
Food and bioprocess technology 2012 v.5 no.2 pp. 508-518
biopolymers, carrageenan, caseinates, denaturation, differential scanning calorimetry, experimental design, gels, ionic strength, milk, mixtures, networks, potassium chloride, protein concentrates, response surface methodology, sodium chloride, solutes, stress relaxation, sucrose, temperature, viscoelasticity, whey protein
The effects of the addition of sugar (sucrose) or salt (KCl/NaCl mixture) on the rheological properties of acid milk gels formed under different process and composition conditions were studied using an experimental design and surface response analysis. The variables evaluated were: sodium caseinate, whey protein concentrate, carrageenan, sucrose or KCl/NaCl concentration, and the mixing temperature of the components. The stress relaxation measurements were made within the linear viscoelasticity domain, and the data obtained were fitted to the generalized Maxwell model. Five parameters were obtained from the fitting: three elastic elements and two viscous elements. In addition, the denaturation process of whey protein with different solute concentrations was evaluated using differential scanning calorimetry. Denaturation temperature increased with increases in the solute concentrations, but enthalpy values did not change independent of solute type and concentration. The results showed that the elastic and viscous moduli increased with sucrose concentration, i.e., the gel network was reinforced, while the opposite occurred with the addition of the saline mixture. Increasing ionic strength of saline mixture and the process temperature were the more important effects with respect to the rheological properties of gels with added saline mixture. On the other hand, the biopolymer concentrations showed the most significant effects on the properties of gels with added sugar.