Interactions of Whey Proteins during Heat Treatment of Oil-in-Water Emulsions Formed with Whey Protein Isolate and Hydroxylated Lecithin

 California Polytechnic State University.

 Massey University.

 To whom correspondence should be addressed:  Riddet Centre, Massey University, Private Bag 11 222, Palmerston North, New Zealand. Telephone:  (64) 6 350 4401. Fax:  (64) 6 350 5655. E-mail:  h.singh@ massey.ac.nz.

The interactions of proteins during the heat treatment of whey-protein-isolate (WPI)-based oil-in-water emulsions with and without added hydroxylated lecithin were studied by examining the changes in droplet size distribution and the quantity and type of adsorbed and unadsorbed proteins. Heat treatment at 90 °C of WPI emulsions resulted in an increase in total adsorbed protein; unadsorbed β-lactoglobulin (β-lg) was the main protein interacting with the adsorbed proteins during the first 10 min of heating, but after this time, unadsorbed α-lactalbumin (α-la) also associated with the adsorbed protein. In emulsions containing hydroxylated lecithin, the increase in total adsorbed protein during heat treatment was much lower and the unadsorbed β-lg did not appear to interact with the adsorbed proteins during heating. However, the behavior of α-la during heat treatment of these emulsions was similar to that observed in the emulsions containing no hydroxylated lecithin. In the presence of NaCl, the particle size of the emulsion droplets and the quantities of adsorbed protein increased markedly during heating. Emulsions containing hydroxylated lecithin were less sensitive to the addition of NaCl. These results suggest that the binding of hydroxylated lecithin to unfolded monomers or intermediate products of β-lg reduces the extent of heat-induced aggregation of β-lg and consequently decreases the interactions between unadsorbed β-lg and adsorbed protein. This was confirmed by sodium dodecyl sulfate−polyacrylamide gel electrophoresis (SDS−PAGE) of heated whey protein and hydroxylated lecithin solutions.

Keywords: Whey protein; hydroxylated lecithin; emulsion; heat treatment