EFFECTS OF STARTER CULTURES ON SMALL DEFORMATION RHEOLOGY OF STIRRED YOGURT

Stirred yoghurt produced from UHT milk enriched with skim milk powder and by using 11 commercial starter cultures was subjected to dynamic r heological measurements with a cone and plate device. Independent of t he starter type used, yoghurt exhibited linear viscoelastic behaviour up to a shear strain amplitude (y(o)) of similar to 0.02 and a showed cross-over of storage and loss modulus at y(o) similar to 0.2-0.3. Pha se shift (tan delta) and storage moduli (G) proved to be inversely int errelated with standard yoghurt showing higher G values and lower tan delta. Coefficients of the power law relation between complex viscosi ty G and shear strain rate amplitude indicate that the increase of G* with increasing frequency is less pronounced in viscous yoghurt, whic h can be attributed to cross-linking effects of extraneous polysacchar ides.