Nutritional, trace element and heavy metal stability in human milk during standard milk bank processing

Human milk (HM) is the optimal source of nutrition for neonates; however, mothers of preterm infants may experience insufficient milk production. Donor HM from human milk banks (HMB) undergoes freezing and Holder pasteurisation (HoP) to ensure safety, but these processes can alter nutrient and mineral composition. Heavy metals in HM also require monitoring due to neonatal vulnerability. We analysed eighty-eight HM samples from twenty-two donors at four processing stages: fresh, frozen at -20°C, post-HoP and frozen at -80°C. Macronutrients were measured using a MIRIS® HM analyser. Cu, Zn, Se, iodine, As, Cd, Hg and Pb were quantified via ICP-MS. Statistical analyses included repeated-measures ANOVA and paired t tests. Macronutrient concentrations remained largely stable across processing stages. Cu and iodine exhibited significant stage-specific reductions, particularly following HoP and -20°C freezing (p < 0·05). Se and Zn were minimally affected. Hg and As were detectable in some samples but remained below safety thresholds, while Cd and Pb were undetectable at all stages. Notably, carbohydrate levels increased after -80°C freezing, likely due to sample homogenisation variability. Routine HMB processing effectively preserves the nutritional profile of HM while ensuring microbiological safety. Stage-dependent reductions in Cu and iodine suggest that careful monitoring is warranted, especially for preterm infants. Importantly, heavy metal contamination was negligible, confirming the safety of donor HM for neonatal feeding.