Determination of antioxidant potential of human milk peptides and amino acids and effects of tryptophan on bacterial growth in formula

Oxidative stress is associated with many infant diseases. Antioxidants have the ability to scavenge free radicals and reduce oxidative stress. Novel breast milk peptides demonstrated the ability to inhibit the formation of lipid peroxides using linoleic acid emulsion system and showed potential to scavenge free radicals using oxygen radical absorbance capacity assays. All peptides, except for 23-8-8, significantly reduced the generation of lipid hydroperoxides compared to control. Peptide 23-8-11 showed greatest antioxidant activity compared to other human milk peptides and was able to decrease hydroperoxides produced from autoxidation of linoleic acid. ORAC assay suggest that the most active peptides were 23-8-11(ISELGW [-NH2]) and 23-8-10 ([ACE]-ISELGW), followed by 23-8-5 (WISELG), 23-8-4 (ISELGW) AND 23-8-7 (ISELWG). The effects of two of peptides 23-7 and 23-8 on quality mother's milk and infant's milk formulas were evaluated using the electronic nose. There is no significant difference in quality between milk samples with and without peptides as graphs depicted a high amount of overlap of principle component analysis data points between all samples. Addition of peptides ISELGW and YGYTGA to human milk and Infant formula milk had no significant difference in odour profile. These results demonstrate potential in the involvement of human milk peptides and tryptophan as a means of reducing diseases related to oxidative stress, and may be included into infant formulas following further analysis. Resazurin tests do not suggest antimicrobial activity of peptides nor tryptophan, although further evaluation is necessary. One-way ANOVA on peptides analyzing Total Plate Count suggests 23-6, 23-7, and 23-8 show a significant difference. LSD test shows that peptides 23-6, 23-7, and 23-8 have antimicrobial properties of the same potency. Antioxidant properties of amino acids were evaluated using ORAC, where the amino acids showing highest antioxidant activity are cysteine (589 TE/mM +/- 22.1 TE/mM), tryptophan (193 TE/mM +/- 1.94 TE/mM), tyrosine (171 TE/mM +/- 2.11 TE/mM), methionine (111 TE/mM +/- 4.25 TE/mM), histidine (60.0 TE/mM +/- 1.80 TE/mM), and phenylalanine (8.72 TE/mM +/- 6.0 TE/mM); the remaining amino acids showed values close to zero. The stable free radical diphenylpicrylhydrazyl (DPPH) was used to evaluate scavenging of free radicals. Controls were Vitamin C and glutathione at 97 +/- 0.06% at 2 mg/ml and a 95 +/- at 6 mg/ml respectively. Tryptophan had 90+/- 11.1% at 6 mg/ml demonstrating that it is an effective at scavenging free radicals.