The chemistry of desiccant properties of carbohydrates is attributed to the OH groups in the molecules of carbohydrates. However, the process of adsorption of water molecules by the carbohydrate molecules differ depending on the three dimensional structure and hence the amount of water adsorbed by these molecules.
Oligosaccharides such as maltose, maltotriose, maltopentose, maltohexose and polysaccharide such as amylose were exposed to air after heating and evacuating at 120oC and the evolving changes on the surface of the samples were followed by near infrared spectroscopy. The adsorption effectivity of these molecules was also followed by gravimetry. The combination frequency of water molecules in the region 5300-5100 cm-1was followed during the adsorption evolution of water on these molecules. This region of the spectrum reveals the adsorption of water molecules and the variation in the absorption bands reflect the change in the environment of the water molecules on the surface of the saccharides.
These investigations gave insight into the understanding the way the OH groups on the saccharide molecules adsorb water molecules. The results clearly reveal that the adsorption of water increases with the increase in the number of monomer units in oligosaccharides. The adsorption of water is highest with polysaccharide amylose. In the oligosaccharide maltotriose, the α-1,4-glycosidic bondings between the monomer glucose units start taking the shape of a spiral and it allows the water molecules form hydrogen bondings with OH groups across the monomer units. As the curvature increases the possibility for adorption also increases. One full circle in the spiral formed when the number of monomer units in the oligosaccharide reaches 7. This increase the adsorption possibilities for water molecules.
