‘Consider instant soup, powdered milk and cocoa powder’, explains Dr Ruud van Ommen in his office in the old test factory at TU Delft. Instant coffee and Nesquik have been pre-treated to dissolve easily. In order to improve their understanding of the process, the researchers preferred to start with simpler powders, like starch from potatoes, wheat or corn.
If you watch closely as a scoop of powder gradually dissolves in water, you can distinguish four phases. First, the water must penetrate the powder (which is difficult with cocoa, due to its fat content). The wet powder then sinks into the liquid, after which the powder particles disintegrate into smaller granules, which subsequently dissolve in the liquid. Further investigation into these steps will enhance our understanding of this process, and it could eventually lead to the development of more easily dissolved powders for food or medication.
For example, the first graduate, Merel Oostveen MSc, discovered that when she poured a drop of water onto a layer of starch, the drop was absorbed into the powder ten times faster than predicted by the theory, based on the size and shape of
the granules. Microscopic examination of the starch revealed considerable variation in the open space between the powder particles, such that the large pores accelerated the humidification process by a factor of ten. Oostveen published this finding, which led to an invitation to present at a conference in Beijing.When she heard that the founder of the theory of dissolution would also be in the hall, she began to worry. How would Professor Karen Hapgood from Monash University in Australia react? Van Ommen explained that refuting and refining theories through experimentation is the essence of science. Fortunately, Hapgood held the same view.The team consisting of Van Ommen, Dr Gabrie Meesters and Dr Sheila Khodadadi expects to supervise several more final-year students on this topic in the future. For example, final-year student Erik Bosma is using laser diffraction to investigate how granules disintegrate while sinking. This method has already proved useful for water soluble substances. He is now trying it with fatty substances, which do not disintegrate as easily.