The Effect of Whey Protein Isolate-Dextran Conjugates on the Freeze-Thaw Stability of Oil-in-Water Emulsions

This study examines the impact of Maillard-type conjugates formed between whey protein isolate (WPI) and the nonionic polysaccharide dextran by dry heating at 80 degrees C for 2 hours (conjugate 1) and at 60 degrees C for 5 days (conjugate 2) on the freeze-thaw stability of oil-in-water emulsions. Emulsions stabilized with WPI, WPI-dextran mixture, conjugates 1 and 2, were prepared using microfluidizer, respectively, and then subjected to from one to three freeze-thaw cycles (-18 degrees C for 22 hours, +40 degrees C for 2 hours). The emulsion stability to freeze-thaw processing was assessed by zeta potential, average particle size, polydispersity index (PDI) and backscattering profile by a recently developed optical analyzer (Turbiscan). Results demonstrated that WPI-dextran conjugates brought about a remarkable improvement in freeze-thaw stabilizing properties when compared with WPI or WPI-dextran mixture which can be attributed to the enhancement of repulsive steric forces between the oil droplets as a result of dextran overlapping the thicker interfacial coatings surrounding the oil droplets. The conjugate 2 stabilized emulsion showed much better stability after freeze-thaw cycling than the conjugate 1 probably due to the higher extent of conjugation.