Human

milk exerts inhibitory action on the growth of pathogenic microorganisms such as Staphylococcus aureus,1 Escherichia coli,2 Candida,3 Shigella, and Klebsiella pneumonia,4 reducing the incidence and severity of gastrointestinal and respiratory infections in breastfed infants.5-7 This protective effect, among other benefits, defines breast milk as a preferential food in the first 6 months of life—particularly among low-weight infants or those with immune deficiencies. As a result, human milk is frequently used in hospitals to feed low birth weight and premature infants. In these cases, human milk must be collected, stored, and transported to the neonatal unit, and donor milk must be thermally processed before feeding to infants to eliminate possible contamination8 and avoid the transmission of infective microorganisms.9,10 However, the thermal treatment applied may have undesirable effects on the nutrients and biocomponents of milk. The intensity of such effects in turn depends on the condi-tions applied. Pasteurization treatments at 63°C for 30 minutes (low pasteurization) and at 75°C for 15 sec-onds (high pasteurization) are the conventional meth-ods used in the milk industry to hygienize milk. Different authors have examined the effect of human milk pasteurization on its different nutrients11-15 and other components with antimicrobial activity, such as lactoferrin or immunoglobulins.16,17 These studies show that pasteurization results in thermal damage that can reduce and eliminate properties of interest for the nursing infant. On the other hand, it has been seen that the bactericidal capacity of human milk is lost if refrigerated storage is prolonged for 72 hours or more.2,18 In view of the interest of the bactericidal capacity of human milk as protection for infants, and considering the few studies found in the literature on the stability of this property of milk during manipulation, we decided to explore the stability of such bactericidal action after subjecting human milk to thermal hygienization under different conditions of time and temperature, as well as to examine the evolution of this property of pasteurized milk during refrigerated storage