Evaluation of Lactose Crystalline Forms by Nondestructive Analysis

Four methods of quantification of solid lactose using X-ray diffraction were tested. The diffracted peak areas of the two crystalline forms of lactose (α-lactose monohydrate and β-lactose) were compared. Linear and logarithmic relationships between these areas and the quantity of lactose forms were established; correlation coefficients were greater than 0.99. Three methods were applied successfully during hydration of amorphous lactose. However, the fourth method, which considered the peak of α-lactose monohydrate corresponding to a diffraction angle of 2Θ = 12.4° as a reference, gave excessive values. Three of these methods were therefore applied to the hydration of skimmed milk powder. The weak excessive values observed may be the presence of mixed crystals of α-and β-lactose in milk powders. Gravimetry and X-ray diffraction of amorphous lactose, during water uptake under relative humidity of 53%, enhanced three periods: progressive water adsorption by amorphous lactose, water release because of crystallization of amorphous lactose, and water constant level with crystallized α-lactose monohydrate and β-lactose. Differential scanning calorimetry of the different forms of lactose (amorphous, partially crystallized and crystallized forms) were also done during the same period.