Human milk (HM) is the gold standard for infant nutrition, as it has the optimum composition of nutritional elements needed for growth and development, providing numerous short and long-term benefits for infants. Early infant nutrition is very important for improving clinical outcomes and, based on all its benefits, HM is the first choice for feeding preterm infants.

When not enough own mother’s milk (OMM) is available, pasteurized donor human milk (DHM) is currently the preferred alternative for preterm infants rather than premature infant formula. The use of DHM in comparison to the use of formula milk is linked to the lower incidence of different diseases and complications, such as necrotizing enterocolitis. Also, other benefits have been recently reported, e.g. the composition of the gut microbiome from infants receiving DHM appears to be more similar to the one of infants consuming OMM than those feeding with infant formula.

To avoid newborn infection through transmission of pathogens that might be present in HM, holder pasteurization (HoP) is routinely employed at HM banks, as it destroys or inactivates most bacteria and viruses16. During HoP, HM is heated at 62.5 ᵒC for 30 min followed by rapid cooling to room temperature. It is known that HM composition is affected by this procedure and that some compounds degrade. While total carbohydrates and protein contents remain relatively stable, the total fat content seems to be affected noticeably. Furthermore, several bioactive components, such as enzymes, immunoglobulins or immune cells are compromised or destroyed during this process .

One of our currently on-going studies provides the first comprehensive assessment of the impact of pasteurization on the HM lipidome and metabolome. The combination of screening methods allowed to identify that the main affected metabolic pathways were related to hormones (e.g., steroids) and fatty acids. We also found that HoP may have an impact not only on the composition, but also on physico-chemical properties, cellular components, and the functionality of lipids. This has not yet been reported. Furthermore, the analysis of total fatty acids in HM showed that concentrations of 76% of the analyzed fatty acids were altered during pasteurization, with a median decrease in the relative concentration of 10%. The biological relevance and impact of the observed changes in composition and functionality of HM components should be addressed in future studies.

With the aim of a better preservation of the composition of DHM, the use of softer alternatives has been in the spotlight of on-going investigations. However, to date, none of these techniques has yet been implemented for the routine processing of DHM at HM banks.