A novel technique for determining glass–rubber transition in dairy powders

A novel rheological technique is described, for determining the glass–rubber transition temperature (Tgr) of spray dried dairy powders. The approach involves constant rate heating of powder under compression and measurement of changes in either gap distance (Method 1) or normal force (Method 2). Significant increases in the rate of change of these parameters was shown to correspond with Tgr. The techniques were applied to skim milk, micellar casein and whey permeate powders and a range of fat-enriched micellar casein powders. Tgr temperatures, so obtained, were compared with glass transition temperatures (Tg) determined by Differential Scanning Calorimetry (DSC). Methods 1 and 2 gave predictions for non-fat dairy powders of Tg endset (Tge) with SEP of 8.8 and 4.4 °C, respectively. These novel techniques provide an accurate means of determining glass transitions in dairy powders, including high protein and fat-containing powders, whose relaxation properties can be difficult to measure by DSC.