Introduction: The crystallization of lactose to separate it from the liquid fraction is a fundamental process in the production of an innovative product - partially delactosed demineralized whey. The technology of its production implies obtaining two valuable products, namely, milk sugar and the most partially delactosed demineralized whey, which has a composition close to the composition of milk and can be used by the enterprise for food purposes, which solves the problem of whey utilization at small and medium-sized milk processing enterprises (20 - 50 tons of whey per day). Most of the scientific works aimed at investigating the crystallization process of lactose rely on the traditional crystallization method. 

Purpose: Theoretical and experimental substantiation of the intensification of the process of crystallization of lactose from condensed NF concentrate of curd whey using cyclic temperature regimes to increase the yield of milk sugar.

Materials and Methods: Тhe initial NF concentrate had a degree of demineralization (48±2)%, contained a mass fraction of solids (55±0.5)%, lactose – 79.6%, protein – 13.2%, ash – 3.7% and other 3.5% in terms of dry matter; the initial temperature was 68 ° C. The experimental sample was subjected to cyclic temperature treatment, which included three sixty-minute cooling to temperatures of 6-8 °C and two fifteen-minute heating to temperatures of 67 °C and 60 °C, respectively. In the control sample, crystallization was carried out in the traditional way. The total duration of the processes for the experimental and control samples was 3.5 hours. During the experiment, the temperature of crystallizate, dry matter content in the intercrystalline solution and crystallizate mass were determined by standardized methods. Analysis, differentiation method and mathematical modeling were used for theoretical study. 

Results: By analyzing the processes of heat transfer, evaporation and crystallization of lactose under cyclic temperature regime, with accompanying evaporation of moisture by air bubbling, mathematical dependencies between the amount of crystallized lactose, the percentage of solids in the intercrystalline liquid and physical and chemical parameters of crystallizate, which in turn depend on temperature, were obtained. The adequacy of analytical dependencies was confirmed experimentally. The results of analytical and experimental studies are presented in the form of graphical dependences of temperature and dry matter content in the intercrystalline solution on the time of the process at cyclic and traditional modes of lactose crystallization.  As a result of experimental studies it is established that at cyclic temperature mode of crystallization the average crystal size increases 4 times and the percentage of crystallized lactose - 1.5 times in comparison with the control sample for which the traditional mode of crystallization was used. This effect is explained by the intensification of the crystallization process due to an increase in the concentration of dissolved lactose during moisture evaporation.

Conclusion: The value of the presented results lies in the possibility of using a cyclic temperature regime of lactose crystallization to increase the percentage of crystallized lactose and the average crystal size. The proposed crystallization regime makes it possible to effectively separate crystallized lactose and simultaneously obtain concentrated partially delactosed demineralized whey.  This solves the problem of whey utilization for food purposes at small and medium-sized milk processing enterprises. The most expedient directions of further research are optimization of temperature regimes of cyclic crystallization process, duration of cycles and search of ways of intensification of this process. The obtained analytical dependences allow to reduce the number of labor-intensive and lengthy experimental studies necessary for the optimization of the process.