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Quantitative X-Ray Diffraction Determination of α-Lactose Monohydrate and β-Lactose in Chocolate



ABSTRACT:  Lactose is a constituent of milk chocolate. During processing and cooling, lactose may precipitate as α-lactose monohydrate and β-lactose. The presence of α-lactose monohydrate has a deleterious effect on the quality of milk chocolate. A quantitative X-ray diffraction method for determination of α-lactose monohydrate and β-lactose in chocolate is described. The α-lactose monohydrate signal at 19.9°2θ with Cu-Kα X-rays is a cubic function of concentration. The β-lactose signal at 20.9°2θ is a linear function of concentration. α-Lactose monohydrate is detectible at about 0.1 weight% and can be quantified at >0.5 weight%. β-Lactose is detectible at about 1 weight% and can be quantified at >3 weight%. About 10 min is required to prepare and run a sample.

Practical Application: The crystalline form of lactose affects the quality of chocolate. A rapid method for quantifying crystalline forms of lactose in chocolate is described. The method can be used for quality control and for improving chocolate quality.