A BST R ACTThe results of studies of physical changes of the structure of milk ice cream at fat content of 4.0 % -6.0 % and frozen whipped fruit desserts at different degree of overrun with/without addition of whey and whey protein concentrate are given in the paper. It is shown that the storage temperature affects the dispersion of structural elements of frozen whipped fruit desserts. An average size of air bubbles of frozen whipped desserts stored at minus 18 °C is 1.2 -1.4 times larger than the size of the bubbles of the samples stored at minus 25 °С. The average size of ice crystals increased 1.4 times after 9 months of storage at minus 18 °C. The average size of air bubbles of ice cream at 4 % fat content increased 1.5 times after 6 months of storage, and the ice crystals size increased 1.1 times. It is recommended to use the storage temperature below minus 25 °С to keep the quality of ice cream and frozen whipped desserts. Milk ice cream and frozen fruit desserts are recommended to be stored at minus 18 °С during not more than 6 months.FOR CITATION: Sitnikova P.B., Tvorogova A.A. Physical changes in the structure of ice cream and frozen fruit desserts during storage. Food systems. 2019; 2(2): 31-35.

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In the transportation and sale of ice cream, fluctuations in air temperature are possible with an excess of the recommended temperature minus 18 ° C. During subsequent storage, this leads to a change in the dispersion of structural elements (ice crystals and air bubbles) and the appearance of organoleptic defects. The article presents the results of studying the effect of temperature fluctuations on the dispersion of structural elements using the example of ice cream with the most effective stabilization system under conditions of realistically possible temperature fluctuations. The object of the study was ice cream with a mass fraction of fat 10%, dry fat-free milk residue 10%, sucrose 14%, and with a complex stabilizer-emulsifier containing 0.35% of an emulsifier with a high demulsifying effect (mono- and diglycerides with a high content of unsaturated fats) and a synergistic composition of hydrocolloids (0.15%) (locust bean gum and guar and carrageenan). It was found that a threefold change in the product temperature in the range of minus 18 ° C – minus 12 ° C – minus 18 ° C and subsequent storage for six months leads to an increase in the average size of ice crystals by 35%, and in the control sample only by 6%. In this case, for three months of storage, the angles with a larger base of the crystal increase by at least 10 ° C. During the same period, the average diameter of the air bubble increased by 61%. In the control sample, the air bubble increased by 26%. Frozen should not be stored until sale for a long time, for example, more than one month. This recommendation is to avoid a decrease in the fineness of structural elements ice cream subjected to a threefold increase in temperature from minus 18 ° C to minus 12 ° C with subsequent freezing to minus 18°C even when using an effective stabilizer.

In this research the results of analytical studies are presented, which prove the lack of data on influence of aging process on dispersion of structural elements in ice cream with fat mass fraction of 6% or less, and experimental studies on definition of dispersion of air phase and ice crystals in milk ice cream. It was found that the process of the mix aging doesn’t significantly affect the dispersion of air phase and ice crystals in ice cream with fat mass fraction of 3%. In ice cream with fat mass fraction of 6%, made from a mix, the dispersion of the air phase increased along with the aging process, and the size of almost all air bubbles were less than 50 microns. At the same time the dispersion of ice crystals increased by no more than 10%. The decrease in dispersion of the air phase during the storage period was observed, mostly in ice cream with a fat mass fraction of 6% produced of the cured mix. The research results have the practical importance as they justify the need for the aging process in the production of ice cream with a low mass fraction of fat and determine the necessity of further research in this area.

Nowadays the functional ice cream production keeps developing. Due to that the traditional composition of the ice cream is amended. In case of substitution of the low molecular weight nutrients (sucrose, lactose and mineral salts of dry skimmed milk residue) with technologically functional nutrients, it changes the cryoscopic temperature, which influences the parameters of production process, in particular the temperature of the ice cream getting from the freezer. In this regard, the problem of calculating the cryoscopic temperature of ice cream mixtures has become acute, since it is not possible to find this parameter experimentally at all food enterprises. While calculating the cryoscopic temperatures on the basis of existing reference data, in some cases the authors encountered a significant (more than 0.5 °C) deviation of the calculation results from the experimental data. In order to establish the cause of these deviations, the authors analyzed aqueous solutions of sucrose, fructose, trehalose, erythritol, maltodextrin, polydextrose, sorbitol, glucose-fructose syrup, dry glucose syrup, inulin in concentrations that provide for the cryoscopic temperatures of solutions within the range from 0 °C to minus 6 °C. The cryoscopic temperature of the solutions was measured by an osmometer-cryoscope, and the conventional molecular weight of the substances was calculated on the basis of Raoult ratio, taking into account the high molecular weight substances and admixed impurities. It was shown that the values of the conventional molecular weight for trehalose and sorbitol solutions differ by more than 15% from the values of chemically pure substances due to presence of low molecular weight monomers in their composition. The presented experimental data on the conventional molecular weight values can be used for calculation of cryoscopic temperature of various types of mixtures used for ice cream production. As an example of application of obtained clarified values of conventional molecular weights, this article provides a method for calculation of cryoscopic temperature of low sucrose and sucrose-free ice cream mixtures, as well as a comparison of the calculation results with experimentally obtained data.