Characterisation and quantification of protein oxidative modifications and amino acid racemisation in powdered infant milk formula

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Zhifei Chen, Fabian Leinisch, Ines Greco, Wei Zhang, Nan Shu, Christine Y. Chuang, Marianne N. Lund, Michael J. Davies

Modification of proteins in infant milk formula (IF) is of major concern to the dairy industry and consumers. Thermal treatment is required for microbiological safety, but heat, light, metal-ions and other factors may induce oxidative damage, and be a health risk. In this study protein modifications in IFs were quantified. IFs contained both reducible (disulphide) and non-reducible (di-tyrosine, lanthionine, lysinoalanine) protein cross-links. Dehydroalanine and the cross-linked species lanthionine and lysinoalanine were detected. Protein carbonyls were detected predominantly on high molecular mass materials. Oxidation products of phenylalanine (m-tyrosine), tryptophan (N-formylkynurenine, kynurenine, 3-hydroxykynurenine), tyrosine (di-tyrosine) and methionine (methionine sulphoxide) were detected, consistent with amino acid modification. Higher levels of most of the markers of protein modification were present in the hydrolysed protein brand, when compared to the conventional IF samples, indicative of increased damage during additional processing. Significant levels of racemised (D-) amino acids were present. These data indicate that amino acids in proteins in IFs are modified to a significant extent during manufacture, with hydrolysed IF being particularly prone.
Original languageEnglish
JournalFree Radical Research
Volume53
Issue number1
Pages (from-to)68-81
ISSN1071-5762
DOIs
Publication statusPublished - 2019

    Research areas

  • Cross-links, di-tyrosine, infant milk formula, kynurenine, methionine sulphoxide, protein carbonyls, protein oxidation, racemisation

ID: 216204230