Lactose is a constituent of milk chocolate. During processing and cooling, lactose may precipitate as alpha-lactose monohydrate and beta-lactose. The presence of alpha-lactose monohydrate has a deleterious effect on the quality of milk chocolate. A quantitative X-ray diffraction method for determination of alpha-lactose monohydrate and beta-lactose in chocolate is described. The alpha-lactose monohydrate signal at 19.9 degrees 2theta with Cu-Kalpha X-rays is a cubic function of concentration. The beta-lactose signal at 20.9 degrees 2theta is a linear function of concentration. alpha-Lactose monohydrate is detectible at about 0.1 weight% and can be quantified at >0.5 weight%. beta-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.