Сomparative evaluation of vacuum and air oven moisture content determination methods for some varieties of dried fruits and vegetables

Abstract

Drying methods are the most widely used techniques. Drying techniques with convective heating principle comprise ordinary oven drying and vacuum oven drying. It is important to be aware that drying techniques do not measure the water content as such. The result is a mass loss under the conditions applied or “moisture” is often used instead. These conditions can principally be freely chosen and the results are, consequently, variable. Drying to a constant mass is often required, but a real constancy is only achieved in rare cases. The mass loss is not only caused by water but by all the substances volatile under the drying conditions, either already contained in the original sample or produced by the heating process. The application of low pressure in vacuum ovens reduces the danger of producing volatile decomposition compounds but does not allow a distinction to be made between water and other volatile substances already present in the product. To shorten the long determination times, more intensive heating is used. The results can vary in a very broad range depending on the drying parameters applied. Mass-loss results can, however, be matched with the results of another method, particularly a reference method, by adjusting the parameters in an appropriate way. In these cases the most suitable calibration must be established for every type of product in a specific way [1].