Antioxidant Capacity and Quality of Human Milk and Infant Formula Determined by Direct Current Polarography

Antioxidants present in infant food contribute to its nutritive value and provide protection from oxidative damage. Here, a direct current polarographic method, based on a decrease of anodic current from the hydroxoperhydroxo-mercury(II) complex (HPMC) formed at a mercury dropping electrode at its potential of dissolution, was used to determine the total antioxidant capacity (TAC) of infant formulas, human milk collected from mothers of full-term and preterm infants, human milk supplemented with fortifier, and cow milk. TAC of milk samples and infant formula correlated with protein content measured by the Bradford method (Pearson correlation coefficient 0.605, p <0.001), while TAC of human milk correlated with content of free thiol groups measured by the Ellman method (0.779, p <0.001). The results obtained showed that, in contrast to the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, HPMC enables specific insight into the quality of infant milk food which reflects the amounts of free thiol groups and protein content. The significant contribution of milk proteins and the most prevalent amino acids, particularly cysteine, arginine, and phenylalanine, to TAC was shown. Thus, the HPMC method might be useful in monitoring the quality of infant formulas and human milk for preterm infants before and after supplementation with fortifier.