Objective and methods: We measured the contents of fat, protein, lactose, calcium, phosphorus, zinc, iron, copper, and vitamin A in processed mature milk samples (individual, n = 60, and pooled, n = 10) from a reference human milk bank in Brazil and assessed the effect of pasteurization followed by freezing on the nutrient composition and the pattern of zinc distribution in fractions (fat, whey, and casein) of milk samples (n = 15).
Results: Mean nutrient concentrations were within expected ranges in mature milk from healthy women, except fat, which was lower. Interindividual variability of nutrient concentrations was high (coefficient of variation, 21-62%) but reduced overall in pooled samples. Processing of milk samples did not affect the nutrient contents but did cause a significant shift (P < 0.04) in the relative distribution of zinc, with a decrease in the whey fraction and an increase in the fat fraction.
Conclusions: Redistribution and possible alterations in the zinc-binding pattern during processing in human milk banks may reduce zinc bioavailability to the infant.