Influence of milk proteins on the development of lactose-induced stickiness in dairy powders

The stickiness behaviour of a range of spray dried dairy powders differing in protein/lactose ratio was determined using a fluidised bed apparatus. Powders with higher protein/lactose ratios were less susceptible to sticking. Stickiness was related to both the glass transition temperature (Tg) and the temperature increment by which Tg must be exceeded before sticking occurred (T−Tg). T−Tg values of approximately 10, 22, 29, 45 and 90 °C were found for powders containing 15.5, 26.9, 39.5, 55.7 and 83.4% protein respectively. Composition had different effects on Tg and T−Tg. The rate at which water was sorbed and desorbed by powders increased with protein content. With increasing protein content, preferential sorption of water by non-amorphous constituents delayed the rate at which lactose underwent the requisite change from the ‘glassy’ to the ‘rubbery’ form in order that powder particles became sticky.