Influence of protein concentration on rheological properties of carrageenan gels in milk

The influence of milk protein concentration on the rheological properties of carrageenan (0.1-0.5%) in permeate (0% casein) and in retentate (2.7-8.3% casein) was studied. The permeate and retentate were prepared via ultrafiltration of homogenized milk (amount of fat 1.6%). The viscoelastic properties were determined by dynamic oscillating rheometry, and by measuring fracture gel strength and fracture depth of formed gels by penetration. Low concentrations of carrageenan in permeate formed very weak gels with low storage modulus G' and high phase shift angle delta. Storage modulus G' showed a linear dependence on the concentration of carrageenan and a quadratic dependence on the protein concentration, with some deviation at the highest casein and carrageenan content, respectively. Phase shift angle decreased in the presence of milk proteins (to tan delta similar to 0.12). The fracture gel strength increased and fracture depth decreased as the concentration of carrageenan was increased. (C) 2003 Elsevier Ltd. All rights reserved.