Viscoelastic properties of protein-stabilized emulsions: Effect of protein-surfactant interactions

Viscoelastic properties of whey protein isolate-stabilized emulsions have been investigated by determining storage and loss moduli of both fresh emulsions and heat-set emulsion gels. Gel strength increases with the increase of protein concentration in the system. The flocculated protein-covered oil droplets behave as active fillers and hence dramatically enhance the gel strength. The presence of water-soluble surfactant Tween 20 induces a dramatic reduction in emulsion gel strength, which is attributable to protein displacement from the oil-water interface. Oil droplets that are fully covered with Tween 20 do not adhere to protein gel matrix and do not contribute to gel strength. The presence of oil-soluble monopalmitin increases the viscous character of fresh emulsions and substantially reduces the modulus of heat-set emulsion gels. The viscoelastic properties of heat-set emulsion gels containing monopalmitin are only slightly frequency-dependent, and these gels can be classified as "strong gels".