Water Adsorption Characteristics of Acyclic Oligosaccharides of α-Gluose Studied by Near Infrared Spectroscopy

Abstract

The adsorption properties of water molecules on maltooligosaccharides are attributed to the OH groups of the glucose rings in maltooligosaccharides. The water molecules are adsorbed onto OH groups by hydrogen bond formation. Near infrared spectroscopic and gravimetric techniques were used in analysing the adsorption characteristics of maltooligosaccharides. Near infrared spectra of the dry maltooligosaccharides were acquired during the adsorption of wa- ter molecules at a relative humidity of 50%. The amounts of water adsorbed by the samples were also recorded by an ana- lytical balance. Second derivative techniques were used in decomposing the OH combination frequency of the adsorbed water molecules in the region 5300-5000 cm -1 . The results indicate that the water molecules are adsorbed on to C2 and C3-OH groups at a higher rate compared to the adsorption onto C1-OH groups in the molecules. Adsorption also takes place onto the ethereal oxygen atoms in the glucose rings. The gravimetric results show that the adsorption of water molecules increases with the number of glucose units in the maltooligosaccharides except maltotriose which has the highest adsorption over a period of 75 minutes.