The study objects were the Republic of Kazakhstan selection apple sorts: “Baiterek”, “Sarkyt” and “Saya”, also pear sorts: “Syilyk”, “Zhazdyk” and “Nagima”. Study of the process of moisture evaporation within vacuum drying of the fruits has essential value in the nutritional value saving. Basically, the product evaporative capacity is characterized by the evaporation resistance coefficient ‒ µ. Also during moisture removal, thermodynamic state of moisture changes that is described by water activity indicator ‒ aw. Experimental determination of these parameters allows for the analyzing moisture evaporation during vacuum drying process. Studies have established the following evaporation resistance coefficients: µ=2.03±0.07 for apple sorts and µ=2.3±0.05 for pear sorts. Either water activity decreases from 1.0 to 0.62±0.01 for apple sorts and from 1.0 to 0.65±0.04 for pear sorts. Two drying periods are discovered. The first drying period: 5.45–6.10 h for apple sorts; and 6.12–6.25 h. for pear sorts. The second drying period duration: 4.15–3.50 h for apple sorts; and 4.35–4.48 h for pear sorts. The critical humidity value: 27.1±2.1 % for apple sorts; and 30.1±2.5 % for pear sorts. Comparative analysis of calculated and experimental data shows maximum deviations 22.5 % for apple sorts and 23 % for pear sorts. The proposed equation for the calculating a moisture evaporation rate, considering the product properties and the hygroscopic parameters of air, can be used in practice to study the moisture evaporation dynamics from the product surface. The study results allow for the selecting an optimal mode for vacuum drying of apples and pears sorts in order to safe nutritional value and to produce biologically active additives for the food industry

The aim of the present study was to analyse and compare camel milk powder quality and functional properties produced with spray-drying and freeze-drying techniques. Freeze-drying is recognized as an advanced method for the production of high-quality dried products, but it has been a costly process for production of camel milk powder. Spray-drying and freeze-drying of camel’s milk demonstrated that the nutritional characteristics of this product basically remained unchanged compared to fresh milk. The differences were found analysing flowability, solubility and hygroscopicity of camel milk powder samples obtained with freeze-drying and spray-drying technique. Analysed quality indices of camel milk demonstrated that spray-drying has lower impact on camel milk powder physical properties in comparison with freeze-drying.

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In the dairy technology, for the preserving of initial nutritional properties of whole milk commonly a vacuum freeze-drying approach is used. However, a significant impact on the quality indicators of the resulting products within vacuum freeze-drying has a temperature of the product sublimation in the freeze-drying chamber. From the point of view of energy savings and maximum preservation of the initial qualities, the optimal sublimation temperature value is recommended at the t = -15 °C within vacuum freeze-drying process. The physicochemical indicators of whole and reconstituted camel milk have similar values within acceptable limits. Nevertheless, partial denaturation of amino acids that leading to the decreasing in the content of low molecular weight protein fractions and for the increasing of protein fractions with higher molecular weight are occurred. Thermolabile whey protein compounds, such as Albumin and Globulin fractions are especially susceptible to denaturation changes, due to the hydration membrane of proteins present on the surface is destroyed, leading to minor changes in the amino acid composition.

The article develops a methodology for conducting experimental studies on vacuum drying of varieties of apples, pears and raspberries growing in the southern regions of the Republic of Kazakhstan. Experimental studies and analysis of the influence of regime parameters on the drying process of selected products have been carried out, depending on the height of the layer of the dried material, the degree of grinding of raw materials, the degree of heating of the dried material and the pressure of the medium in the evacuated chamber.The analysis of the obtained drying curves for apples, pears and raspberries, in the initial state having a liquid paste-like mass, at the pressure in the vacuum chamber of 0.008 MPa, the loading height of 3, 4 and 5 mm, the degree of heating of the dried material - about 40 ° C, previously selected for research, shows that they have a similar character - all drying curves have quite clearly defined segments: the period of establishing regime parameters or the period of the beginning of drying, the period of constant drying rate and the period of decreasing drying rate.The results of experimental studies are generalized and based on them, equations describing the dynamics of moisture evaporation from the surface of products in the form of fourth-degree polynomial equations are obtained.

Studies have established that various drying periods are observed during the drying process: for example, for apple varieties, the first drying period is 5.45...6.10 hours, and for pear varieties 6.12 ...6.25 hours. The duration of the second drying period for apple varieties is 4.15...3.50 hours, and for pear varieties 4.35...4.48 hours. The analysis of the drying curve showed that the boundary between the periods of constant and falling land velocity, i.e. the critical humidity for apple varieties is on average 27 ± 2.1%, and for pear 30.1 ± 2.5%. An analysis of the kinetics of moisture evaporation shows that in an apple during the first four hours of drying, on average, 2.71 g evaporates, and for the next two hours it decreases monotonically to 2.31 g. The same picture of moisture evaporation dynamics is also observed for pears: for the first four hours, on average, 3.41 g evaporates, and for the next two hours, the evaporation dynamics decreases to 2.78 g. Studies have established that the coefficient of evaporation resistance for apple varieties: Baiterek, Sarkyt and Saya is µ = 2.03 ± 0.07, for pear varieties: Sylyk, Zhazdyk and Nagima is µ = 2.3± 0.05.

The article studied the patterns of changes in water activity during vacuum drying of apple varieties: Baiterek, Sarkyt and Saya and pear varieties: Syilyk, Zhazdyk and Nagima. Studies have established that in all the studied varieties of apple and pear, the following pattern is observed: in the first four hours of the drying time, the water activity indicator decreases monotonously, and the subsequent drying time drops sharply. This pattern is explained by the fact that after four hours of drying time, part of the remaining weakly bound moisture is gradually removed from the product, and then the bound moisture. Studies have shown that dehydration of fruits, the water activity characterizing the qualitative properties of the product decreases: for apple varieties from 1.0 to 0.62 ± 0.01, for pear varieties this indicator decreases from 1.0 to 0.65 ± 0.04. On the basis of mathematical processing of experimental data, a power-law dependence of water activity on the duration of drying was established. The established pattern of changes in water activity from the duration of drying in subsequent works will be used to determine the optimal drying mode for apples and pears in order to produce high-quality dry powders for the food industry.

As the drying zone deepens, outer surface layer of the product does not have time to be moistened, due to a small amount of moisture coming from the inside. It becomes dry, its temperature rises. The intensity of moisture transfer from the inner layers of the product depends on many parameters, including a moisture diffusion coefficient. The study aim is to create a methodology for determining the moisture diffusion coefficient within vacuum drying of fruits, by taking into account cracks, channels and capillaries formed in the dry layer of the product through the resistance coefficient to evaporation. The work essence consists in the determining of the moisture diffusion coefficient as a driving force, a difference between water activity and air humidity, by considering the resistance coefficient to evaporation, characterizing the effect of hydrodynamic resistance of the dried dry layer of the product. This approach was used to determine the moisture diffusion coefficient during vacuum drying of the Baiterek apple sort and the Zhazdyk pear sort of Kazakhstani selection. It was established that in the first period of drying the moisture diffusion coefficient decreases on average from 24,4∙10‒7 m2/s to 13,2∙10‒7 m2/s. The critical humidity for pear is 37.4 %, and for apple 35.1 %. As result of the formation of dry layer on the surface and subsequent layers, the moisture diffusion coefficient gradually decreases. In the second drying period, the moisture diffusion coefficient decreases from 5,42∙10-8 m2/s to 2,12∙10‒8 m2/s. The work practical significance is related with the application of the obtained results in the determination of the optimal drying regime with maximum preservation of the product original quality. The proposed methodology can be used in the practice to study the moisture diffusion coefficient within vacuum drying of fruits, by considering the product properties and the hygroscopic parameters of the drying matter