EFFECT OF 137CS ON FATTY ACID COMPOSITION IN COW`S MILK

Abstract

Lipid composition of raw milk is a key factor determining the nutritional value and technological suitability of the milk. Monitoring the level of contamination of cow’s milk is often not available for farmers, living in the zone of radioactive contamination. ¹³⁷Cs activity concentration was higher than permissible level of 100 Bq/kg in all the studied milk samples from all the experimental groups of animals from the studied settlements. The highest value of the ¹³⁷Cs activity concentration of 600 Bk/kg in cow’s milk was found in Stare Selo village of Rokytne district. According to our study, local animals have partially adapted to the seasonal increase in background radiation, and the milk of these cows, in accordance with existing quality standards, is conditionally suitable for consumption. The only factor prohibiting the consumption of this milk is the level of cesium-137 contamination. An increase in the ¹³⁷Cs activity concentration of more than 100 Bq/kg in cow’s milk causes a sharp decrease in the relative content of polyunsaturated fatty acids (mostly of omega-6 fatty acids) and changes in the omega-3/omega-6 ratio downward omega-3 relative content. Relative adaptation of the lactating cows to the contamination was revealed; however, metabolism of lipids in the mammary gland and the level of lipids secretion are found to be sensitive to the level of ¹³⁷Cs contamination of milk. Thus, a violation of the secretory function of the mammary gland was revealed, in particular, metabolism of lipids with 18 carbon atoms in the chain. Relative content of linoleic acid immediately decreases by several times with the increasing the contamination level. Concentration of the stearic acid immediately exceeds the physiological limits at the value of ¹³⁷Cs activity concentration in milk about 110–130 Bq/kg. It gradually increases with the increasing the ¹³⁷Cs activity concentration up to 270–330 Bq/kg. And then it is being plateaued with the increasing the ¹³⁷Cs activity concentration up to 600 Bq/kg. On the base of the study of effect of ¹³⁷Cs on fatty acid ratio in cow’s milk, the C18-coefficient is being proposed to be used as the parameter of damage to the mammary gland of cows in response to a high level of ¹³⁷Cs contamination, which is calculated as follows: C18c = (C18:0–C18:2)/100). Determination of the C18-coefficient indicates the dose-dependent effect of the ¹³⁷Cs contamination on lipid metabolism in the mammary gland and catabolism of polyunsaturated fatty acids, particularly linoleic acid. Duration of the affecting contamination is obviously decisive factor of damage effect to the mammary gland, defining the level of biochemical transformations and initiating of peroxide processes.