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Abstract: Milk protein concentrate (MPC) is a newly developed dairy powder with wide range of applications as ingredients in the food industry, such as cheese, yogurt, and beverage. MPC has relatively poor solubility as a result of their high protein content (40–90wt%), with distinct dissolution behaviour in comparison to skim milk or whole milk powders. Here, a focused beam reflectance measurement (FBRM) was used to monitor the dissolution process of an MPC powder, with the data used to develop a kinetic dissolution model based on the Noyes–Whitney equation. The model was used to estimate the dissolution rate constant k and the final particle size in suspension d ∞, describing dynamic dissolution behaviours and final solubility respectively of a particular powder. In this work, the effects of dissolution temperature, storage duration and storage temperature on dissolution properties of an MPC powder were also investigated. A quantitative understanding of relationship between process and storage conditions with powder functionality could be achieved from k and d ∞ profiles. This approach can potentially be applied to predict the dissolution behaviour of specific dairy powders in a more robust manner than conventional solubility tests. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The surface structure of crystalline particles affects the functionality of the particles in drug delivery. Prediction of the final structure of particles that crystallize easily within the spray drying process is of interests for many applications. A theoretical framework was developed for the prediction of crystal structure precipitating on the surface of the particle. This model was based on the dimensionless Damkohler number (Da), to be an indicator of final particle morphology. Timescales of evaporation and reaction were required for calculation of the Damkohler number. The modified evaporation time scale was estimated based on the time that is available for the crystal to precipitate after supersaturation. The reaction time scale was estimated based on the time scale for induction time. Mannitol was produced under different processing conditions in order to validate the theoretical model. Results showed for the high Damkohler numbers, the surface structure of the particle was rough, while smaller Damkohler numbers led to relatively smooth particle surfaces. Additionally, although the beta polymorph was dominant in all of the experiments, alpha polymorph was precipitated in the experiments with a large Damkohler number. The theoretical framework developed will be a useful predictive tool to guide the manipulation of particle crystallization in spray dryers. [ABSTRACT FROM AUTHOR]

In-situ crystallization of particles in spray drying has several advantages particularly for product quality modification in the pharmaceutical industry. This process was investigated in a counter current spray dryer using lactose as a model material by manipulation of the local humidity within the drying chamber. Sample collection and humidity injection at different location of the dryer were carried out to better understand the mechanism of particle formation and solidification which are essential components of in-situ crystallization. They revealed that particle formation can be delayed by local humidity elevation. Differential scanning calorimetry and XRD of the yields showed that humidity manipulation was capable to produce semi crystalline lactose of up to 90% crystallinity. The results confirmed that there is a critical period for crystallization such that extending this period would significantly increase the degree of crystallization. Comparison on different requirements of crystallization indicated that extending the time for nucleation and the growth at the critical period via humidity manipulation has the most significant effect on the in-situ crystallization process. [ABSTRACT FROM AUTHOR]

Abstract: A low velocity spray tower was built in Monash which allows the production of mono-dispersed particles. As part of a larger project in controlling the functionality of the particles produced, the computational fluid dynamics technique (CFD) was used to gain more insights into the drying characteristics of the mono-dispersed droplets. Introduction of droplet and mass transfer did not significantly alter the flow field. Analysis revealed that the wet bulb region was significant in this tower. Varying the inlet air temperature from 100°C to 180°C resulted in contrasting drying history. These drying kinetics were then extended to assess the in-situ crystallization phenomenon. For this spray drying tower, it was found that lower inlet temperature condition favoured a higher degree of crystallinity. [Copyright &y& Elsevier]

Mixing surfactants with whole milk feed before spray drying could be a commercially favorable approach to produce instant whole milk powders in a single step. Pure whole milk powders obtained directly from spray drying often have a high surface fat coverage (up to 98%), rendering them less stable during storage and less wettable upon reconstitution. Dairy industries often coat these powders with lecithin, a food-grade surfactant, in a secondary fluidized-bed drying stage to produce instant powders. This study investigated the changes in wetting behavior on the surface of a whole milk particle caused by the addition of surfactants before drying. Fresh whole milk was mixed with 0.1% (wt/wt) Tween 80 or 1% (wt/wt) lecithin (total solids), and the wetting behavior of the shell formed by each sample was captured using a single-droplet drying device at intermediate drying stages as the shell was forming. The addition of surfactants improved shell wettability from the beginning of shell formation, producing more wettable milk particles after drying. The increase in surfactant loading by 10 times reduced the wetting time from around 30 s to <5 s. At the same loading of 1% (wt/wt; total solids), milk particles with Tween 80 were much more wettable than those with lecithin (<5 s compared with >30 s). We proposed that Tween 80 could adsorb at the oil-water interface of fat globules, making the surface fat more wettable, whereas lecithin tends to combine with milk proteins to form a complex, which then competes for the air-water surface with fat globules. Spray-drying experiments confirmed the greatly improved wettability of whole milk powders by the addition of either 0.1% (wt/wt) Tween 80 or 1% (wt/wt) lecithin; wetting time was reduced from 35 ± 4 s to <15 s. To the best of our knowledge, this is the first time that a dynamic droplet drying system has been used to elucidate the complex interactions between ionic or nonionic surfactants and milk components (both proteins and fat), as well as the resultant effect on the development of milk particle functionality during drying. [ABSTRACT FROM AUTHOR]