(748g) Elucidation of the Rehydration Behaviour of Food Powders

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 (Mimouni, et al. 2009). Currently, methods that quantify the overall reconstitution behaviour of powders are available, but do not provide insight into the actual reconstitution properties and are relatively crude (Fang, Selomulya and Chen 2008). This research aims to quantify the wetting of food powders during their rehydration process.

A single droplet is placed on loosely packed powder beds of a range of porosities and drop penetration time is recorded by a digital microscope camera. Drop penetration times for corn starch, potato starch and rice starch, as well as maltodextrin and instant starch are reported and compared to the theory proposed by Hapgood (Hapgood, et al. 2002). Characterization of the internal structure of miniature powder beds is performed using a micro computed tomography (microCT) scanner.

Although the presence of macrovoids within loosely packed beds is confirmed and recorded drop penetration time are within one order of magnitude for all powders, the current model is unable to calculate drop penetration times for starches a priori.  The effect of moisture content, internal porosity are investigated and several adaptions to the model are suggested. Most promising results are obtained by replacement of the effective pore radius predicted by Carman- Kozeny equation, by the experimentally observed pore radius in microCT imaging. Theoretical drop penetration times predicted by this semi-empirical model  are in good agreement with experimental results.

Drop penetration time measurements on maltodextrin and instant starch correctly reflect that the wetting time of heterogeneous powder beds can be dominated by one of the components. This is promising for the application of the current method to various food powders, to control quality, optimize properties or tackle problems during production.

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.