RHEOLOGY AND SURFACE-TENSION OF SELECTED PROCESSED DAIRY FLUIDS - INFLUENCE OF TEMPERATURE

The effects of temperature on the rheological behavior and surface ten sion of commercial samples of skim milk, 3.5% milk, 38% cream, two dif ferent cultured buttermilk products, and buttermilk powder solution we re studied using a controlled stress rheometer and the Wilhelmy plate method, respectively. The rheology of the dairy fluids was greatly inf luenced by temperature but to varying degrees depending on the product tested. The rheological data for skim milk, 3.5% milk, buttermilk pow der solution, and 38% cream could be fitted to the Bingham model at al l temperatures, and the cultured buttermilk products could be fitted t o the power law model. For the uncultured products, viscosity and yiel d stress decreased as temperature increased. The dairy products exhibi ted great variation in surface tension, which also was strongly depend ent on temperature. For 38% cream, the measurements of surface tension indicated a high degree of instability as temperatures varied, which suggests that the milk fat globule membrane was destabilized at the in terface between air and water. This study demonstrates the effect of t emperature on bulk and interfacial properties of dairy fluids as fat c ontent and milk fat globule fragments vary.