Abstract
The paper presents water diffusion coefficients as providing a significant contribution to the creation of a comprehensive database and knowledge of weight variation during the drying process of raw plant materials that is used for modelling the technological process and designing innovative products. Dehydration is one of the most widely used methods for improving the stability and durability of fruit and vegetables because it reduces water activity and microbial activity, and minimises the physical and chemical changes during storage. The considerable impact of pressure on heat exchange and weight during the convection drying process of osmotically pretreated apples is demonstrated. The course of the drying curves and the drying rate is determined by the use of pressures of 0.02 and 500 MPa. Varied pressure applied during osmotic impregnation significantly influences the value of the diffusion coefficient: the average determined for the entire course of the drying curve and the average determined in the intervals of the reduced water content. The lowest values of the average water diffusion coefficient are obtained for apples preboiled under overpressure conditions and, at the same time, the determined diffusion coefficients in the water content are characterised on the drying curve by a clearly decreasing course until the reduced water content reaches approximately 0.2.
Highlights
To determine the quality of foods of plant origin, especially processed as a result of water removal, the following characteristics are most often used: structure, including density, porosity and consistency, optical—colour, general appearance, sensory—taste, smell, rehydration ability and nutritional value
The osmotic dehydration affected the course of the process by changing its mechanism and the value of the diffusion coefficient of water in the sample
It was found that the use of osmotic dehydration under varied pressures influenced the achievement of a different level of dehydration and, a different value of the initial water content after osmotic dehydration of the samples
Summary
To determine the quality of foods of plant origin, especially processed as a result of water removal, the following characteristics are most often used: structure, including density, porosity and consistency, optical—colour, general appearance, sensory—taste, smell, rehydration ability and nutritional value. They depend on many process factors, but, most of all, they depend on the properties of the raw material [1,2]. The preservation of the smell, and in many cases its intensification compared to the material obtained only by convection, is associated with the formation of a layer of osmotic substance on the surface of the plant material. In addition to the many advantages mentioned above, the material treated with this method is characterised by a porous structure, smooth surface, and almost unchanged shape and size, which affects the visual impression of the potential consumer and facilitates its rehydration in water [9,10,11]
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