Does the branching degree of galactomannans influence their effect on whey protein gelation?

Abstract

The influence of the degree of branching of galactomannans on the heat-induced gelation of whey proteins was investigated, using oscillatory rheological measurements at low strain amplitude and microstructural analysis by confocal laser scanning microscopy. Galactomannans were from different origins and/or enzymatically modified, with mannose-to-galactose ratios ranging from 1.5 to 3.7. Whey protein gels were formed at 13% protein, pH 7 and low ionic strength. Galactomannan concentration ranged from 0 to 0.6%. Within the range of concentrations used, the presence of the galactomannan decreased the gelling temperature and had a positive effect on the gel strength of the whey protein gel. These effects are more pronounced as the degree of branching decreases. The effect of the original guar sample was quite different from all the other samples, either in terms of rheology or microstructure, particularly for the higher galactomannan concentration. The mixed gels appeared as biphasic systems, with the polysaccharide enriched phase dispersed on the protein matrix at low polysaccharide concentrations, but progressing to a phase inversion at higher polysaccharide concentrations, especially for the lower branched samples. The linear viscoelasticity seems to be insensitive to some of the microstructural changes observed within the mixed gels. The branching degree of the galactomannan does have an effect on microstructure and viscoelasticity of the WPI gels, but this effect is limited to a short range of mannose-to-galactose ratios, above which this effect is insignificant.