Can the water content of dairy products be determined accurately by microwave drying?

Abstract

 Oven drying is the most frequently used moisture determination method. To obtain results faster than heating by convection in classic drying ovens, more rapid heating techniques are used. One of these is drying by microwaves. The result of all drying methods is mass loss under the conditions applied. Only in a few cases does the mass lost correspond exactly to the water content. Mass loss is caused by the evaporation of all volatile matter during the drying process, i.e. not only by the loss of water. Foodstuffs in particular risk decomposition reactions and the formation of volatile substances at higher temperatures. The results of drying processes depend on the drying parameters and are variable, whereas the water content is a specific property of the sample. If the water content is to be determined accurately by a drying process, the drying parameters must be adjusted in a way that the results equal those obtained by a specific method, e.g. the Karl Fischer titration. The dependence on the drying parameters varies for different products. In many cases the levels of a set of parameters can be determined so that the mass lost equals the analysed water content; in other situations a differing but reproducible result can be multiplied by a constant factor to give the reference value. This study shows that, for some dairy products, the water contents found by microwave drying are very close to those determined by Karl Fischer titration.