Improvement in emulsifying properties of whey protein-Rhamnolipid conjugates through short-time heat treatment

Whey protein-rhamnolipid (WP-rhamnolipid) conjugates were prepared via Maillard reaction by heating in liquid systems. Protein-saccharide conjugates generally exhibit better technical functional properties. To optimize the reaction conditions, mixtures of whey protein and rhamnolipid at varying weight ratios, 8:1, 4:1, 2:1, 1:1, 1:2, 1:4 and 1:8, were heated at 80 degrees C for 10, 20, 40 and 60 min. Emulsifying properties, zeta potential and interfacial activity of the conjugates were evaluated, and results showed that conjugates prepared in some conditions showed significantly improved emulsifying activity, the 1:1 conjugates heated for 10 min had the highest emulsifying activity; the zeta potential decreased significantly in the early stage of heat treatment and then stabilized, indicating that the colloidal stability and electrostatic repulsion were enhanced; an increase in the rhamnolipid component could increase the interfacial activity of conjugates. The formation of conjugates and changes in reaction process were studied by browning value, free amino analysis, fourier transform infrared spectroscopy (FTIR), high performance liquid chromatography (HPLC) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). WP-rhamnolipid conjugates formed by short-time heat treatment have great potential as highly efficient bioemulsifiers.