Lactose crystallization: determination of alpha-lactose monohydrate in spray-dried dairy products

摘要

A new method was used to determine the amount of alpha-lactose monohydrate present in spray-dried milk products. During the manufacture of spray-dried milk products, the lactose may crystallize (a process during which the alpha-lactose picks up a molecule of water), while the hygroscopicity and caking properties decrease. In order to determine the degree of crystallization of alpha-lactose monohydrate, the water bound to the crystals (water of crystallization or hydrate water) is calculated as the difference between total moisture and free moisture or non-hydrate water. The free moisture content is determined in a drying oven at 87 or 105 degreesC at constant weight. The total moisture is determined by a new method using a vacuum-drying desiccator with dried zeolite powder as a function of temperature, vacuum and time. This new method is then compared to the Karl Fisher method. Results on the percentage of alpha-lactose monohydrate are also presented for various milk, whey and lactose powders with degrees of crystallinity of alpha-lactose monohydrate ranging from 0 to 100%. Combining the method for total moisture content using a vacuum-drying oven, and the method for free moisture content makes it easy to determine the amount of alpha-lactose monohydrate in spray-dried dairy products.