Crystallization and X‐ray Diffraction of Crystals Formed in Water‐Plasticized Amorphous Spray‐dried and Freeze‐dried Lactose/Protein Mixtures
2005
Haque, Md Kamrul | Roos, Yrjö H.
Effects of proteins (whey protein isolate [WPI], Na‐caseinate, and gelatin), drying method, storage relative vapor pressure (RVP), and time on lactose crystallization and crystals formed were investigated using x‐ray diffraction (XRD). Crystallization was observed from increasing peak intensities of XRD patterns. Lactose in lactose/protein (5:1,3:1) mixtures crystallized in samples stored at RVP of 44.1% and above in both spray‐dried and freeze‐dried materials, except in freeze‐dried lactose/Na‐caseinate and lactose/gelatin mixtures, which showed lactose crystallization at 54.5% RVP and above. The rate of crystallization increased with increasing RVP and storage time. The rate of crystallization in spray‐dried materials was higher than in freeze‐dried materials, and the crystallization rate decreased with increasing protein content. Lactose crystallized mainly as α‐lactose monohydrate in spray‐dried lactose/WPI and lactose/gelatin mixtures. Crystals formed in freeze‐dried lactose/WPI and lactose/gelatin mixtures were anhydrous β‐lactose and α‐lactose monohydrate crystals. Lactose crystallized as a‐lactose monohydrate in both spray‐dried and freeze‐dried lactose/Na‐caseinate mixtures. Trace amounts of anhydrous β‐lactose were present in spray‐dried lactose/WPI (5:1) and lactose/gelatin (5:1) mixtures. Peak intensities of XRD patterns for anhydrous β‐lactose decreased with increasing protein content and storage time. The crystallization data were successfully modeled using Avrami equation at an RVP of 65.6% and above. These data are important in understanding and predicting storage stability of lactose‐ and protein‐containing food and pharmaceutical materials.
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