Impact of pasteurization on the antibacterial properties of human milk

Growing evidence favours the use of human milk for the feeding of preterm newborns based on its many beneficial effects. Despite the many benefits, human milk has been associated as a possible vehicle of transmission for a number of infections. Although pasteurization of human milk can diminish the risk of neonatal infection, it also significantly reduces the concentrations of immunological components in human milk due to thermal damage. In order to evaluate the impact of pasteurization on the antibacterial properties of human milk, we aimed to compare the capacity of raw and pasteurized human milk to inhibit bacterial proliferation. Therefore, a single milk sample was collected from ten healthy lactating mothers. Each sample was divided into two aliquots; one aliquot was pasteurized, while the other was kept raw. Both aliquots were inoculated either with Escherichia coli or Staphylococcus aureus and incubated at 37 °C during 8 h. Viable colony counts from the inoculated samples were performed at regular time points to compare the bacterial growth in both forms of breast milk. Relative to the tryptic soy broth control sample, both raw and pasteurized milk samples exhibited an inhibitory effect on the growth of E. coli and S. aureus. Compared with the raw portion, growth inhibition was significantly lower in the pasteurized milk at every time point beyond T0 (after 2, 4 and 8 h of incubation) (p = 0.0003 for E. coli and p < 0.0001 for S. aureus).

Our study shows that pasteurization adversely affects the antibacterial properties of human milk.