Abstract
Lactose is a disaccharide of importance in humans dietary, food products, and the pharmaceutical industry. From the existing isomeric forms, β-lactose is rarely found in nature. Thus, in this work, a simple methodology to obtain anhydrous β-lactose (βL) from α-lactose monohydrate (αL·H2O) is presented. The αL·H2O powder was dispersed into a basic alcoholic solution (72 hours), at controlled conditions of temperature (27, 29, 31, and 32°C), without stirring. The slurry was dried at room temperature and characterized. Fourier transform infrared spectroscopy showed the formation of βL for the samples prepared at 29 and 32°C. Raman spectroscopy confirmed this result and suggested the occurrence of crystalline βL. Rietveld refinement of the X-ray diffraction patterns was employed to identify and quantify the composition of the isomers. The samples prepared at 29 and 31°C showed the formation of pure βL, while those at 27 and 32°C showed the presence of αL·H2O and a mixture of the two isomers, respectively. The morphology of the powders was studied by scanning electron microscopy, observing the formation of irregular shape αL·H2O particles and axe-like βL particles. Clearly, with this methodology, it was possible to obtain pure, crystalline, and anhydrous βL at mild temperature.
Highlights
Lactose (4-O-β-D-galactopyranosyl-D-glucopyranose) is found exclusively in the milk of mammals and is composed of molecules of galactose and glucose, linked by a β-glycosidic bond (1,4)
Samples prepared at different temperatures were analyzed using the Fourier transform infrared spectrometry (FTIR), to elucidate the formation of the polymorph
According to Listiohadi et al (2009) the bands located at 3600–3200 cm−1 correspond to the stretching of the OH groups of the lactose molecule, while the vibrations at 1650 cm−1 are related to the flexion of the OH groups of the crystallized water molecules [18]
Summary
Lactose (4-O-β-D-galactopyranosyl-D-glucopyranose) is found exclusively in the milk of mammals and is composed of molecules of galactose and glucose, linked by a β-glycosidic bond (1,4). Since the anomeric carbon of glucose is free, this disaccharide exhibits the features of reducing sugars; that is, the chain configuration is opened by the formation of an aldehyde group [1]. In the food industry, it is used as a commercial additive because of its texture, flavor, and adhesive properties [2]. When used as excipient in drugs, lactose is the substance where the active ingredient is dispersed and preserved in a stable state [4, 5]. This disaccharide exists in two isomeric forms, α-lactose, and β-lactose, which shows the phenomenon of mutarotation, that is, the interconversion of the stereocenters [6]. Lactose exhibits three polymorphs (anhydrous forms) and a solvate (hydrated form): anhydrous β-lactose (βL), International Journal of Polymer Science
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