(13f) Understanding the Dispersion of Powders in Liquids

Understanding the dispersion of powders in liquids

G.M.H. Meesters*^#, M.L.M. Oostveen*^#, E.M. Bosma*, S. Khodadadi*, J.R. van Ommen*

*Product and Process Engineering, Department of Chemical Engineering, Delft University of Technology, The Netherlands

^#DSM Biotechnology center, Delft, The Netherlands

Powdered ingredients are common in food formulations, such as milk powder, coffee, soup mixes and cacao drinks. They are usually intended for rehydration in water and their reconstitution should be rapid and complete (D. W. Mimouni 2009). Currently, methods that quantify the overall solubility of powders are available, but do not provide insight into the actual reconstitution properties and are relatively crude (Fang, Selomulya and Chen 2008). In order for a powder or agglomerate to fully dissolve it has to overcome four different stages which are: wetting of the powder, sinking of the powder through the liquid-air interphase, followed by dispersion and finally dissolution. These four stages together are often described as the solubilisation of powders. Depending on the properties of the powder, one or more of the four phases may determine the rate in the whole process of dissolution of powders. It is important for product development to be able to distinguish between the four stages. Each stage may require a different approach in increasing the rate of the stage, thus increasing the overall solubility of a powder. This research presented here describes the wetting and dispersing behaviour of powders with a range of porosities and particle sizes.

The wettability is measured as penetration time of a single droplet of liquid placed on loosely packed powder bed with different porosities. The drop penetration time is recorded by a digital microscope camera. Drop penetration times are compared to the theory proposed by Hapgood (Hapgood, et al. 2002). The internal structure of miniature powder beds is characterized using  micro computed tomography (microCT) scanner (Oostveen et al., 2015).

The dispersability of the powder is measured by following the particle size distribution in time, using a forward light scattering device and by measuring the obscuration (optical density) of the liquid as the powder disperses in the liquid.

The increased insight in the subsequent steps contributes to a better understanding of powder rehydration and can be used in future for the design of food powders with improved performance

Fang, Y., C. Selomulya, and X.D. Chen. “On measurement of food powder reconstitution properties.” Drying technology 26 (2008): 3-14.

Hapgood, K.P., J.D. Litster, S.R. Biggs, and T. Howes. “Drop penetration into porous powder beds.” Journal of colloid and interface science 253 (2002): 353-366.

Mimouni, A., H.C. Deeth, A.K. Whittaker, M.J. Gidley, and B.H. Bhandari. “Rehydration process of milk protein concentrate powder monitored by static light scattering.” Food Hydrocolloids 23 (2009): 1958-1965.

Oostveen, M.L.M,  Meesters, G.M.H., Ommen-van, J.R., “Quantification of powder wetting by drop penetration time” , Powder Technol. 274 (2015), 62-66