Single droplet analysis for spray drying of foods
2013
Perdana, J.A.
Many food ingredients, such as enzymes and probiotics, are spray dried to provide shelf-life. Major hurdle to apply spray drying is the lack of scientific insight on the inactivation mechanisms of components and the extensive optimization required for formulation and drying conditions to obtain powders of acceptable quality. This thesis reports on the development of an alternative approach to study drying behaviour involving single droplet experimentation in combination with predictive modelling. During single droplet drying, conditions such as drying air temperature, drying time, air flow rate, and particle size could be well controlled, which enabled systematic investigation of inactivation kinetics of heat sensitive components. Experiments were carried out with the heat sensitive enzyme (b-galactosidase) and the probiotic microorganism (Lactobacillus plantarum WCFS1). A novel viability enumeration method was developed to measure survival of probiotic bacteria, involving rehydration of (semi-) dried particles on a micro-porous chip in combination with fluorescence-based viability enumeration. The drying history of single droplets was modelled using an effective diffusion model. The diffusivity in this model was measured and modelled as function of moisture content and temperature on the basis of gravimetric analysis of thin film drying in a dynamic vapour sorption analyser (DVS). Subsequently, models were developed to describe inactivation kinetics as function of particle drying history. Finally, the obtained insight and approach were validated by comparison of predictions to results obtained during lab-scale spray drying experiments. Moreover, the single droplet approach can be used as a tool for screening optimal spray drying conditions
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