DVS Determination of Amorphous Lactose

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Ingredients, such as sugars, can be present in an amorphous or a crystalline state. The amorphous state is either specifically adjusted to benefit from the special product structures and properties, or it is caused process-related, e.g. during spray- and freeze drying, grinding, compaction, extrusion, evaporation or baking.

A characteristic of amorphous products is their hygroscopicity. The associated high water-binding capacity leads to a reduction of the product viscosity and to an increased mobility of the molecules. By exceeding a critical moisture content uncontrolled recrystallization is favored. In consequence, product changes such as caking, reduced solubility, increase of Maillard reactions and fat oxidation as well as a rougher mouthfeel affect the physical and chemical stability, the acceptance and the quality of the product.

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To estimate the stability of such products and formulations, the knowledge about the amorphous content and the recrystallization kinetics is crucial.

In literature, several methods have been described to determine the amorphous content of powdered products. However, the detection limits of these methods are often limited to amorphous contents above 10 % for X-ray diffraction and Differential Scanning Calorimetry or 1 % for FT-Raman spectroscopy, NIR-spectroscopy, and solution calorimetry. Lower detection limits could be achieved using isothermal microcalorimetry (0.2 %) and solid-state NMR (0.5 %) [8].

Besides these methods gravimetric dynamic water vapor sorption (DVS) was successfully applied for determining amorphous contents. Compared to the above-mentioned methods, DVS is an easy and sensitive method with a detection limit down to 0.1 %.