Carrageenan Gels in Skim Milk: Formation and Rheological Properties

Abstract

Phase behavior and mechanical properties of gels of three (kappa-, iota-, and lambda-) carrageenans in skim milk are thoroughly studied. The measurements were performed with the aid of a dynamic rheology in different regimes including determination of frequency dependences of rheological parameters, creep, and critical strain and stress at which the gelled systems are destroyed. Temperature dependences of the rheological parameters were also measured. A set of obtained data allowed to quantitatively characterize the mechanical properties of milk gels and compare the gel-forming properties of various carrageenans. In addition to gels of individual polysaccharides, their mixed gels were studied for the first time. It is shown that kappa-carrageenan formed the most stiff and brittle gels. Its mixing with iota- or lambda-carrageenans made gels softer. This effect is observed when the degree of substitution of kappa-carrageenan was higher than 50% that indicates its prevalent role in the mixed systems. The gelation is explained by the formation of crosslinked structure where the nodes are the casein micelles connected by polysaccharide chains. Their binding occurs due to electrostatic interactions between the sulfo groups of carrageenans and amino groups of kappa-casein. In the case of kappa- or iota-carrageenans, network structure is additionally stabilized due to crosslinking of segments of their molecular chains by the double helices at the gaps between casein micelles.