INFLUENCE OF DRY-MATTER FORTIFICATION ON FLOW PROPERTIES OF YOGURT .1. EVALUATION OF FLOW CURVES

Yogurt was produced in laboratory scale by using 4 enrichment substrates and 3 commercial starter cultures. Flow curves of the stirred products were evaluated by a step-shear technique and fitted to the Herschel-Bulkley (HB) model. Generally, increasing protein levels resulted in a significant increase of HB yield values and consistency indices whereas HB exponents decreased. Calculated HB yield values were closely related to experimentally determined static yield values. As compared to skim milk powder and milk protein powder but at similar protein levels, yogurt enriched with Na-caseinate showed highest viscosities, especially at low shear rates. This behaviour was found to be independent of the type of starter used. On the other hand, specific properties of the starter cultures affected the flow curves. Their typical shape was influenced neither by type nor by amount of protein fortification.