Temporal changes of major protein concentrations in preterm and term human milk. A prospective cohort study

Background: Proteins are major contributors to the beneficial effects of human milk (HM) on preterm infant health and development. Alpha-lactalbumin, lactoferrin, serum albumin and caseins represent approximately 85% of the total HM protein. The temporal changes of these proteins in preterm (PT) HM and its comparison with term (T) HM is poorly characterized. Aims: To quantify and compare the temporal changes of the major proteins in PT HM and T HM. Methods: HM was collected for 4 months postpartum at 12 time points for PT HM (gestational age 28 0/7 -32 6/7 weeks; 280 samples) and for 2 months postpartum at 8 time points for T HM (gestational age 37 0/7-41 6/7 weeks; 220 samples). Proteins were measured with a micro-fluidic LabChip system. Results: Casein, alpha-lactalbumin and lactoferrin decreased with advancing stages of lactation in PT and T HM, whereas serum albumin remained stable. Only marginal differences between PT and T HM were observed for alpha-lactalbumin during postpartum weeks 3-5 and for serum albumin at the first week. However, a comparison of HM provided to preterm and term infants at the same postmenstrual ages revealed that alpha-lactalbumin contents were significantly lower in PT HM than in T HM during the 39 48 postmenstrual weeks. Conclusions: This study provides comprehensive information of the longitudinal changes of major proteins in PT and T HM, and suggests limited availability of alpha-lactalbumin, a nutritionally important protein, in breastfed PT infants after reaching the term corrected age. This information may be important to optimize HM protein fortification, although its biological relevance needs to be confirmed by intervention studies. Clinical trial registry: ClinicalTrials.gov (NCT02052245), https://clinicaltrials.gov/ct2/show/NCT02052245. (C) 2018 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.