Influences of mannosylerythritol lipid-A on the self-assembling structure formation and functional properties of heat-induced β-lactoglobulin aggregates

beta-lactoglobulin dominates the behaviors of whey aggregates in food products. Interactions between beta-lactoglobulins and surfactants are greatly diverse and have aroused much attention due to their benefits to the food functionality. The influences of the glycolipid biosurfactant mannosylerythritol lipid-A (MEL-A) on the heat-induced beta-lactoglobulin aggregates were investigated by measuring the aggregate structure, the binding nature of MEL-A toward beta-lactoglobulin, and the interface behaviors as well as the foaming and emulsifying property. The results showed that MEL-A with a concentration above CMC reduced the random beta-lactoglobulin aggregation after heat treatment, facilitating the formation of self-assembling core-shell particles composed of a core of beta-lactoglobulin aggregates covered by a shell of MEL-A vesicles with diameters less than 2 mu m. In the presence of MEL-A, beta-lactoglobulin aggregates gave rise to a decreased surface tension at the air-water interface, viscoelasticity and foaming capacity, whereas there was increased foaming stability and emulsifying properties after heat treatment for less than 3 h. Moreover, the excessively heat-induced aggregation was not conducive to the enhancement of both of the functional properties in the current model, while MEL-A effectively prevented the aggregation from proceeding based on the existing molecular interactions. The comprehensive results of infrared spectroscopy, circular dichroism spectroscopy, fluorescence spectroscopy and isothermal titration calorimetry confirmed that the interaction forces between MEL-A and beta-lactoglobulin were driven by hydrophobic interactions between the hydrophobic groups exposed from the protein and the fatty acid chain or acetyl groups of MEL-A as well as the hydrogen bonding between the mannosyl-D-erythritol group of MEL-A and amino acid.