KINETICS OF THERMAL INFLUENCE ON DRY MILK POWDERS

ABSTRACT

In this work, changes in the degree of decomposition under the influence of temperature were considered. Experimental data on changes in the degree of decomposition of the substance were also presented. Experimental studies of the reaction of thermal decomposition of milk powder over time can be represented as a change in the proportion of decomposed substance. The speed of these processes depends on the moisture content of the food product. Thermal effects may be increased or decreased by other components contained in the product. A distinctive feature is the recommendations for choosing the temperature regime for drying food products, for which drying is combined with subsidence of biochemical, chemical and other processes.

АННОТАЦИЯ

В данной работе были рассмотрены изменение степени разложения под действием температуры. А также были приведены экспериментальные данные по изменение степени разложения вещества. Экспериментальные исследования реакции термического разложения сухого молока с течением времени можно представить как изменение доли разложившегося вещества. Скорость данных процессов зависит о содержания влаги в пищевом продукте. Тепловое влияние может усиливаться или ослабляться другими компонентами, содержащимися в продукте. Отличительную особенность имеют рекомендации по выбору температурного режима сушки пищевых продуктов, для которых сушка совмещается с проседанием биохимических, химических и других процессов.

Keywords: milk powder, spray drying, chemical content, dairy materials.

Ключевые слова: сухое молоко, распылительная сушка, химический состав, молочные продукты.

Introduction. In fresh spray-dried milk powder, all the constituent components are fairly evenly distributed in the particle mass. In this case, the continuous phase is lactose, in which fat globules, protein particles and other components are dispersed. More recent studies have established that the continuous phase in the particles can be a protein, which is a porous system of interconnected protein micelles.

A significant proportion of milk powder particles, mainly, has a spherical shape and is in a free state. The bulk of the particles has a size of up to 50 microns. A small part of the powder forms agglomerates by combining individual particles with each other. The surface of the particles under the microscope at low magnification appears smooth, glossy and slightly melted. There are crater-like depressions on the surface of individual particles.

The size of the particles and the nature of their surface change under the influence of temperature. Thus, Zhilov S.N. [1] found that when the critical moisture content of the product is reached, depressions (craters) form on the surface of all dried particles, the size and number of which increases with increasing temperature. When the drop temperature reaches 100°The craters disappear and become round due to the water vapor formed inside the particles. In this case, the elasticity of water vapor becomes approximately equal to atmospheric pressure, and with a further increase in temperature exceeds it. This eliminates the deformation of the particles, leads to the stretching of their shells and an increase in the diameter of the particles. At high drying temperatures, these changes are more significant and their effects are noticeable. Thus, during spray drying in countercurrent dryers with an increase in temperature from 176°C to 248°C, with an increase in particle size and a simultaneous increase in the air content in them, the volume weight of the powder decreases by 36.5% [2].

In direct-flow dryers, with significant thermal exposure, relatively large voids arise in the initial period due to the rapid formation of a solid shell, and this also causes an increase in the air content in the particles and a decrease in bulk mass.

According to Kharitonov V.D., in dairy products dried by spray drying, the volume fraction of voids ranges from 4% to 60%, in dairy bases of baby food it averages 13.9% [3].

During the drying process, the components of milk powder undergo a number of changes, which affects the quality of the product. Changes in milk fat under the influence of temperature concern both its physical condition and chemical composition.

The fat in powdered milk is mostly fairly evenly distributed inside its particles. Electron microscopic studies show that the size of fat globules in the particles of powdered milk obtained from a homogenized product is 0.04 - 1 microns, and from non-homogenized milk - 5 microns [4].

During the drying process, the material must acquire the appropriate characteristics required by the standard and preserve several native properties to the maximum extent possible. Therefore, drying is considered not only as a heat and mass transfer, but also as a technological process in which it is necessary to form and control the appropriate technological properties. For a particular product, certain properties are the most important and determine the quality indicators for a food product set by the standard. Therefore, it is necessary that these properties be preserved and, if possible, improved during the drying process, while others will inevitably change [5-6].

Although food drying is often carried out in order to slow down the physico-chemical, biochemical and other processes that cause spoilage of products or reduce their quality, the drying process itself can contribute to irreversible changes in the product. These changes are mostly related to the thermal effect on the main components of food raw materials: proteins, fats, carbohydrates, vitamins. Therefore, it is extremely important to choose a temperature regime for drying food products. On the one hand, an increase in the temperature of the drying agent is a factor in the intensification of the process, on the other hand, excessive thermal exposure leads to a defective finished product.

From the above, the relevance of the problem of choosing criteria for evaluating acceptable drying temperature conditions for a particular product in a particular drying unit is obvious.

To substantiate these criteria, it is necessary to consider the physico-chemical essence of changes in the main components of food products that occur under the influence of heat.

Objects and Methods.

The objects of research at various stages of work were: - selected whole pasteurized milk with a fat mass fraction of 3.4-6.0%.

The method for identifying thermal destruction reaction products was carried out by absorption spectroscopy.

The composition of gases released during decomposition was determined by gas adsorption chromatography on a chromatograph with a thermal conductivity detector using aluminum oxide as a sorbent.

Results and Discussion. Under the influence of heat, protein denaturation and caramelization of lactose can occur, and at higher temperatures, chemical decomposition up to charring. The speed of these processes depends on the moisture content of the food product. The thermal effect may be enhanced or weakened by other components contained in the product [7].

A distinctive feature is the recommendations on the choice of the temperature regime for drying food products, for which drying is combined with subsidence of biochemical, chemical and other processes.

The weight loss in milk powder samples as a function of time at constant temperatures is shown in Table 1.

Table 1.

Change in the degree of decomposition of a substance

The nature of the change in the degree of decomposition depending on temperature is described by the equations shown in Table 2.

Table 2.

Kinetics of changes in the degree of decomposition depending on temperature

When calculating the regression equations: x₁ is the time of thermal exposure, x₂ is the temperature of thermal exposure, E is the residual term showing the intersection of the function with the ordinate axis at zero values.

Conclusion. Experimental studies of thermal effects have shown that the change in mass obeys chemical laws, which indicates the possibility of applying the laws of the kinetics of chemical reactions to the description of the kinetics of drying. The maximum value of the degree of decomposition is a function of the inverse value of the temperature of the drying agent and can be considered as a criterion for the thermal effect on the dairy product during the drying process. To determine the empirical coefficients, it is necessary to study the changes in the qualitative indicators of the product. It is impossible to estimate the permissible loss of mass, or rather, the magnitude of the temperature effect on the product, since there is no such indicator in existing standards. Therefore, the assessment was carried out according to physico-chemical indicators characterizing the change in product quality.

References:

1. Colella, A. P., Prakash, A., & Miklavcic, J. J. (2023). Homogenization and thermal processing reduce the concentration of extracellular vesicles in bovine milk. Food Science & Nutrition, 00, 1–10. https://doi.org/10.1002/fsn3.3749
2. Tetra Pak. (1995). Dairy Processing Handbook. Tetra Pak Processing Systems, G3.
3. Dmitrichenko, M.I. Examination of the quality and detection of falsification of food products: textbook/M.I. Dmitrichenko. – St. Petersburg: Peter. – 2003. -160 p.
4. Zakharova, L.A. Technology of milk and dairy products. functional products: textbook / L.A. Zakharova, I.A. Mazeeva. - Electron. Dan. – Kemerovo: KemSU, 2014. – 107 p. - Access mode: https://e.lanbook.com/book/60194
5. Zolotin, A.Yu. Classification of fermented milk products for baby food/A.Yu. Zolotin, N.P. Androsova // Dairy industry. – 2001. – No. 12. – P. 23-25.
6. Dairy Processing Handbook. Lausanne, Tetrapak, 2015.
7. Colella, A. P., Prakash, A., & Miklavcic, J. J. (2023). Homogenization and thermal processing reduce the concentration of extracellular vesicles in bovine milk. Food Science & Nutrition, 00, 1–10. https://doi.org/10.1002/fsn3.3749