Fluidisation of whey powders above the glass-transition temperature

The fluidisation of partially-crystallised whey powder above the glass-transition temperature of lactose has been investigated, with the intent of crystallising the amorphous-lactose fraction in order to reduce the propensity of the powder to cake during storage. Partially-crystallised whey powder can be fluidised in a vibrated fluidised bed at temperatures of 25 to 40 °C above the glass-transition point of lactose, depending on the relative humidity of the air, before the powder becomes too sticky to fluidise. This temperature difference can be increased up to 80 °C by fluidising the powder with fine, relatively non-sticky, fully-crystallised whey powder in order to coat and protect the sticky partially-crystallised whey particulates during fluidisation. Despite this temperature-difference increase, the time required to crystallise the amorphous-lactose fraction in partially-crystallised whey powder is not reduced sufficiently for this process to be viable in industry. An amorphous whey powder crystallisation process is likely to be more feasible, because the reduced salt and protein concentrations in this powder would ensure that lactose crystallisation is faster. Finally, this work has highlighted the potential of using the phenomenon of lactose plasticization above the glass-transition temperature and fines coating to improve the instant properties of milk-based powders.