INTRODUCTION
The oxidation of lipids degree has a considerable influence on the formation of sensory, functional characteristics, nutritional value and safety of meat products. As a result of lipid oxidation, firstly, the accumulation of peroxides occurs, and also that of aldehydes and ketones, the presence of which adversely affects the security of raw materials; secondly, the degree of digestibility and protein content of essential fatty acids, amino acids, vitamins is reduced, affecting biological value; thirdly, the decrease of protein solubility, change of color, taste and odor is stated [1, 2, 6].
Peroxidation is the result of interaction of organic compounds, and molecular oxygen to form hydroperoxides and reactive free radicals. In muscle tissue polar and nonpolar lipids are subjected to oxidation and to a greater extent - phospholipids in membranes of muscle fibers, the composition of which contains the polyunsaturated fatty acids. The process of lipid oxidation begins immediately after slaughter and it is the result of the imbalance between pro-oxidant and antioxidant systems of raw meat [3, 4, 5, 8].
The proper antioxidant meat system includes enzymatic and non-enzymatic systems. Catalase, glutathione peroxidase, superoxide dismutase are distinguished from endogenous antioxidant enzymes. Their activity depends on the presence of antioxidants such as tocopherols, ascorbic acid, ubiquinone, glutathione, etc. [6].
Endogenous antioxidant enzymes, especially catalase and glutathione peroxidase can potentially inhibit the development of oxidation processes during storage of raw meat. Glutathione peroxidase selenium-containing enzyme is able to recover almost all types of organic hydroperoxides, as well as to prevent the accumulation of secondary peroxidation products [17, 18]. Catalase - heme-containing enzyme - is able to use one molecule as an electron donor, and another one - as an oxidizer, i.e. electron acceptor. It is a basic primary antioxidant, which catalyzes the decomposition of hydrogen peroxide to water, by combining this function with glutathione peroxidase. Protoheme is presented in peroxidase prosthetic group that, unlike most of the hemeproteins of heme groups is very weakly bound to the apo-enzyme. In the reaction catalyzed by peroxidase, hydrogen peroxide is restored by the compounds serving as electron donors, such as ascorbate, or quinines or cytochrome C. This enzyme has a high specificity and effectively neutralizes several hydroperoxide compounds: methyl and etilgidroperoxide, methyl, ethyl and other aliphatic alcohols. The mechanism of peroxidase and Glutathione peroxidase action is to supplement each other, providing protection from the effects of lipid peroxidation at the stage of chain reactions branching and the formation of secondary peroxide products [18]. Both enzymes implement detoxification of enzyme active oxygen radicals, the formation of hydrogen peroxide from superoxide being catalyzed. In addition to differences in their substrate specificity, these two enzymes differ in substrate affinity. At low concentrations of hydrogen peroxide, organic peroxides are preferably catalyzed by peroxidase, whereas at high concentrations catalases work [19].
