κ-carrageenan -: Protein interactions:: Effect of proteins on polysaccharide gelling and textural properties

Gelation and melting processes of kappa-carrageenan (K-C) in the presence of beta-lactoglobulin (beta-lg), native and denatured soy protein (NSP and DSP) isolates were investigated by dynamic rheological techniques, apparent viscosity measurements and DSC. In the presence of proteins, large increases in gelation temperatures and storage moduli of the mixed gels compared to single kappa-C gel were observed. Differences between the proteins in the first steps of the gelation process were revealed by apparent viscosity measurements. Although little changes in melting temperatures were observed in the presence of proteins by dynamic rheology, the DSC analysis showed a large increase in these temperatures. Synergistic effects were also observed on textural properties and water absorption of the gels. The addition of proteins increased gel hardness, cohesiveness, gumminess, springiness and reduced syneresis. These results might be due to excluded volume effects that increased the effective concentration of the hydrocolloid and electrostatic interactions between both biopolymers in solution. The different behaviours observed with the three proteins would be related to their water absorption capacity, molecular size, flexibility and superficial charge under the experimental conditions described. (C) 2002 Published by Elsevier Science Ltd.