[Comparative characteristics of oxidative modification intensity of proteins in infant milk formulas].

Cow's milk is mainly used in the production of infant milk formulas. However, the protein composition of cow's milk differs significantly from the proteome of breast milk. In addition, various technological factors significantly affect the properties and structure of proteins, susceptibility to oxidative processes. This article uses a method of complex evaluation of the products of oxidative modification of proteins to characterize the total level of carbonyl compounds with the analysis of the ratio of aldehyde-dinitrophenylhydrazones (ADNPH) and ketone-dinitrophenylhydrazones (CDNPH), which increases the possibility of determining the severity of protein damage. The purpose of the study was to compare the level of indicators of oxidative modification of proteins in adapted milk infant formulas. Material and methods. The research objects were 4 dry adapted milk infant formulas, as well as ultra-pasteurized cow's milk. The intensity of oxidative modification of milk proteins was determined spectrophotometrically by the reaction of carbonyl compounds with dinitrophenylhydrazine (DNFG). Results. With spontaneous oxidation in infant formula, the total area of carbonyl derivatives of proteins (Sомб) was increased compared to the indicators of ultra-pasteurized cow's milk. The greatest change occurred in relation to ADNFG indicators (SАДНФГ), the level of which increased in 3 formulas by 48.6-59.4%. The content of ketone derivatives (SКДНФГ) did not differ significantly in the studied mixtures from milk indicators. The level of carbonyl derivatives of proteins in milk infant formulas was even more elevated during the induction of oxidation by the addition of iron ions and hydrogen peroxide to the incubation medium. The content of both total and various fractions of carbonyl compounds exceeded the corresponding indicators of cow's milk by 2.0-2.6 times. Conclusion. The results of the study indicate a greater susceptibility to oxidative damage of proteins in milk infant formulas, compared with cow's milk.

[Intensity of processes of oxidative modification of proteins in women's and cow's milk].

Breast milk is a source of all the essential nutritional components necessary for the full growth and development of the child, therefore, it is necessary to study its composition and physical and chemical properties in order to adapt human milk substitutes. Adapted infant milk formulas are produced mainly from cow's milk, bringing formula nutrient composition closer to the composition of women's milk, adapting it in accordance with the requirements of the infant body. However, technological processes for the production of dairy products contribute to the activation of oxidative reactions, the violation of protein conformation. The purpose of the study was to compare the intensity of formation of carbonyl derivatives of human and cow's milk proteins during spontaneous and metal-catalyzed oxidation. Material and methods. The object of the study were samples of mature milk of healthy nursing mothers (n=12), and samples of drinking ultra-pasteurized milk for baby nutrition (n=8) which were used as a comparison material. The intensity of oxidative modification of milk proteins was determined spectrophotometrically by the interaction of carbonyl derivatives of amino acid residues with 2.4-dinitrophenylhydrazine to form 2.4-dinitrophenylhydrazone derivatives in a native sample of biological material and under induction of protein oxidation in vitro by the Fenton reaction by adding FeSO4 and hydrogen peroxide solutions. The content of nonprotein sulfhydryl groups was determined after protein precipitation spectrophotometrically with 5.5'-dithio-bis-2-nitrobenzoic acid. Results. The intensity of spontaneous (basic) oxidation doesn't have significant differences between the indicators of breast and cow's milk. Significant differences were established in the content of carbonyl derivatives of amino acid residues of human and cow's milk proteins during metal-catalyzed oxidation. Incubation with iron ions caused 1.5-2.5 fold more formation of both aldehyde and ketone derivatives of cow's milk proteins, recorded in the visible and ultraviolet spectrum. In cow's milk during spontaneous oxidation and induction of oxidation by a metal, the percentage of aldehyde-dinitrophenylhydrazones was lower than in breast milk and, conversely, the proportion of ketone-dinitrophenylhydrazones, late markers of oxidative degradation of proteins, was significantly higher. The content of non-protein sulfhydryl groups in cow's milk was 2 times less than in fresh human milk. A significant excessive content of aldehyde-dinitrophenylhydrazones (2 times) and ketone-dinitrophenylhydrazones (2.6 times) undet metal-catalyzed protein oxidation of cow's milk in comparison with breast milk indicates a lower level of antioxidant reserves of cow's milk. This is confirmed by the reduced level of non-protein sulfhydryl groups. The results obtained indicate the need to improve the antioxidant status of dairy products for infant nutrition.