VISCOELASTIC PROPERTIES OF MIXED DAIRY GELS

Pure and mixed gels prepared from a whey protein isolate (WPI) and skim milk powder (SMP) by heating to 90-degrees-C at pH 4.3-4.6, with or without fat globules, were studied by mechanical testing. The testing involved compression to 20% deformation and oscillatory rheometry (storage and loss moduli, G' and G'', respectively). Compressive stresses of mixed gels varied between 0.7 and 1.9 kPa. Gels containing WPI reached higher G' values and had shorter gel-set times than those containing SMP. SMP based gels were more elastic than WPI based gels as revealed by the lower loss tangent (tan delta = G''/G') values achieved after 17 min (0.18-0.23 versus approx. 0.38, respectively). Addition of fat resulted in higher compressive stresses and shorter gel-set times but did not affect the initial gelation rate. Gels with different viscoelastic and mechanical properties were prepared with varying amounts of WPI, SMP and emulsified fat.