The use of near infra-red spectroscopy to detect changes in the form of amorphous and crystalline lactose

Abstract

The suitability of near infra-red spectroscopy (NIR) to follow changes in both the amorphous and crystalline state of lactose at room temperature was investigated. Amorphous lactose samples were stored in sealed glass jars with saturated salt solutions to control the relative humidity. NIR spectra were recorded after various periods of storage and the data related to calorimetric and thermo-gravimetric assessments of the physical form of the material. Differentiation between crystalline and amorphous states of lactose was found possible by studying the shape and magnitude of regions of the near infra-red spectrum corresponding to combination and first overtone stretching frequencies of water. It was possible to follow changes in the amorphous, the onset of crystallisation and the solid state transition from β- to α-lactose. NIR with benefits of being non-invasive, non-destructive and operating at room temperature, has been shown to be a valuable tool with which to assess changes in the physical form of lactose.