Binding Interactions Between alpha-glucans from Lactobacillus reuteri and Milk Proteins Characterised by Surface Plasmon Resonance

Interactions between milk proteins and alpha-glucans at pH 4.0-5.5 were investigated by use of surface plasmon resonance. The alpha-glucans were synthesised with glucansucrase enzymes from Lactobacillus reuteri strains ATCC-55730, 180, ML1 and 121. Variations in the molecular characteristics of the alpha-glucans, such as molecular weight, linkage type and degree of branching, influenced the interactions with native and denatured beta-lactoglobulin and kappa-casein. The highest overall binding levels were reached with alpha-(1,4) compared to alpha-(1,3) linked glucans. Glucans with many alpha-(1,6) linkages demonstrated the highest binding levels to kappa-casein, whereas the interaction with native beta-lactoglobulin was suppressed by alpha-(1,6) linkages. Glucans with a higher degree of branching generally displayed lower protein binding levels whereas a higher molecular weight resulted in increased binding to kappa-casein. The interactions with kappa-casein were not pH dependent, whereas binding to denatured beta-lactoglobulin was highest at pH 4.0 and binding to native beta-lactoglobulin was optimal at pH 4.5-5.0. This study shows that molecular weight, linkage type and degree of branching of alpha-glucans highly influence the binding interactions with milk proteins.