Characterizing the protein composition of term and preterm human milk

Claire Molinari

Research output: ThesisDoctoral Thesis

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Abstract

[Truncated] Human milk contains a wide variety of proteins that confer nutritional, protective and developmental advantages to breastfed infants. The intake of human milk proteins is particularly important for preterm infants, in that they are born with higher nutrient requirements than term infants and are more vulnerable to infection in the extra-uterine environment. Indeed, clinical studies have found the protein intake of preterm infants to be critical to their growth and development. Despite the importance of human milk proteins, the majority of studies into human milk protein composition have tended to be quite limited, focusing on a small number of proteins only.

The primary objective of this thesis was to investigate the protein composition of term and preterm milk over the first 2 months of lactation, focusing upon both proteins of high and low abundance in human milk. A secondary aim was to investigate compositional variability between different mothers and the relationships between the concentration of individual proteins, macronutrients, and milk production, particularly in preterm mothers.

Initially, the effect of milk storage on proteins was investigated to ensure that laboratory collection and storage protocols did not affect the integrity of the milk protein fraction. The degree of proteolysis in the skim milk and fat globule protein fractions, protein oxidation and the milk lipase activity were measured at regular intervals in human milk samples (n = 8) stored at 25°C. β-casein was rapidly hydrolyzed, with 38 ± 5 % (mean ± SEM) remaining after 72 hours. The immunological proteins were resistant to proteolysis, however the activity of lipase was reduced by 35% after 2 hours storage (p < 0.001). Protein oxidation was not observed. The addition of a protease inhibitor cocktail to milk samples prevented the majority of proteolysis and thus was included in all subsequent studies.

Original languageEnglish
QualificationDoctor of Philosophy
Publication statusUnpublished - 2012

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