Crystallization Kinetics of Amorphous Lactose as a Function of Moisture Content Using Isothermal Differential Scanning Calorimetry

Abstract

Isothermal differential scanning calorimetry (DSC) was used to study the crystallization kinetics of amorphous lactose at 3 moisture contents. Each sample was heated to several temperatures between Tg and Tm. After subtraction of an induction time, the Avrami equation was used to model the data and a Lauritzen-Hoffman like expression used to fit the crystallization rates between Tg and Tm. The highest Tm/Tg ratio and crystallization rate were observed for the sample containing the most moisture. Conversely the lowest Tm/Tg ratio and crystallization rate were observed for the sample containing the least moisture. Evidence for multiple transitions was seen. The Avrami equation may not be the best way to model such data.

State diagrams for improving processing and storage of foods, biological materials, and pharmaceuticals (IUPAC Technical Report)

“…Crystallization in starch-containing foods is often referred to with the term retrogradation, which is time-dependent and has been suggested to be kinetically controlled by the glass transition of starch [2]. The Avrami equation has been successfully fitted to kinetic crystallization data for lactose [88,211]; trehalose and sucrose [92] and starch gels [209,212,217,218]. The value of the Avrami exponent, n, was found to be higher at lower storage temperatures and at conditions with small T-T g values.…”

“…• Crystallization kinetics at constant relative humidity can be investigated by monitoring timedependent changes in sorbed water contents during storage and observed differences resulting from crystallization [88,[207][208][209][210][211]]. …”

Untersuchung der Kristallisation amorpher Lactose in Milchpulver anhand Dynamischer Wasserdampfsorption

“…So ist die Sandigkeit kristalliner Lactose in Speiseeis unerwünscht [6,7]. Flüssig im Tank gelagerte Milchschokoladenmassen können unkontrolliert verdicken oder sich festsetzen, wenn amorphe Lactose kristallisiert [8].…”

“…Verschiedene Verfahren wurden für den Nachweis amorpher Anteile in Lactose angewandt: Röntgendiffraktometrie, Differential Scanning Calorimetry (DSC), isotherme Mikrokalorimetrie, Lösungskalorimetrie, Raman Spektrometrie, Kernresonanz und Wasserdampfsorption [7,22,23,25,26]. Anhand DSC ließen sich kürzlich die Glasübergangstempe-raturen und Induktionszeiten der Kristallisation von amorpher Lactose in Lactosepulver und Molkenpulver messen [2].…”

“…Sie wurde bereits herangezogen, um die Kristallisation von amorphem Lactosepulver [7] oder von amorpher Lactose in Magermilchpulver zu modellieren [17]. Die Anwendung der Avrami-Gleichung auf DVS-Daten ist allerdings neu.…”