Heat-induced phase behavior of β-lactoglobulin/polysaccharide mixtures

The influence of polysaccharides on the thermal stability of β-lactoglobulin at pH 6.8 was investigated regarding polysaccharide type, concentration and size. Two kinds of polysaccharides, sulfate-containing polysaccharides (carrageenans and dextran sulfate with different molecular mass) and neutral polysaccharides (dextran with different molecular mass), were investigated. At low ratios of sulfate-containing polysaccharide to β-lactoglobulin, heat-induced aggregation was decreased as shown by lower turbidity. Increasing the ratio induced a significant increase in turbidity, leading to segregative phase separation. Phase diagrams were established by centrifugation, chemical assays and visual observation for β-lactoglobulin/kappa-carrageenan and β-lactoglobulin/dextran sulfates. Significant phases (stable, separated and gel) were found, indicating the varieties of phase behavior and a strong competition between phase separation and gelation caused by thermal treatment. Moreover, gelation was reversible in β-lactoglobulin/dextran sulfate systems depending on the polysaccharide concentration.