Crystallization Kinetics and X‐ray Diffraction of Crystals Formed in Amorphous Lactose, Trehalose, and Lactose/Trehalose Mixtures

Abstract

ABSTRACT: Effects of storage time and relative humidity on crystallization kinetics and crystal forms produced from freeze‐dried amorphous lactose, trehalose, and a lactose/trehalose mixture were compared. Samples were exposed to 4 different relative water vapor pressure (RVP) (44.1%, 54.5%, 65.6%, 76.1%) environments at room temperature. Crystallization was observed from time‐dependent loss of sorbed water and increasing intensities of peaks in X‐ray diffraction patterns. The rate of crystallization increased with increasing storage humidity. Lactose crystallized as α‐lactose monohydrate, β‐anhydrous, and anhydrous forms of α‐ and β‐lactose in molar ratios of 5:3 and 4:1 in lactose and lactose/trehalose systems. Trehalose seemed to crystallize as a mixture of trehalose dihydrate and anhydrate in trehalose and lactose/trehalose systems. The crystal forms in a mixture of lactose and trehalose did not seem to be affected by the component sugars, but crystallization of the component sugars was delayed. Time‐dependent crystallization of lactose and trehalose in the lactose‐trehalose mixture could be modeled using the Avrami equation. The results indicated that crystallization data are important in modeling of crystallization phenomena and predicting stability of lactose and trehalose‐containing food and pharmaceutical materials. Keywords: crystallization, lactose, trehalose, crystal form, X‐ray diffraction