Microbiological safety and immunoglobulin A retention in bottle-agitated Holder pasteurization of human milk

National guidelines for donor human milk pasteurization in Peru and most low to middle income countries use Holder Pasteurization (HoP; 62.5 °C, 30 min) and indicate that the bottles containing milk should be agitated manually every 5 min during the 62.5 °C plateau. The guidelines also assume indirect control of the temperature inside the bottles through adjustments in the setpoint temperature of the water bath. Automatic agitation of the bottles could improve the dynamic temperature patterns to be closer to the target temperature. The aim of this study was to describe the implementation of a pasteurizer with a particular automatic bottle-agitation method and compare it to manual HoP in terms of temperature patterns, control interventions, bacterial load reduction and immunoglobulin A retention. Human milk was collected from healthy donor mothers at the Hospital Regional Cusco’s milk bank. Sixteen samples were mature milk pools, and fourteen samples were from individual mothers (three colostrum, seven transitional and four mature). An automatic shaking system using a low-power direct current (DC) motor with a velocity reduction gear was designed to provide azimuthal and vertical oscillations to a plexiglass rack holding the bottles submerged in the water bath. Bacterial load reduction was determined by inoculating the samples with known concentrations of Escherichia coli and Staphylococcus aureus and determining the concentrations of surviving bacteria after pasteurization. The concentrations of IgA before and after pasteurization were determined by IgA enzyme linked immunoassay. The automatic shaking vibration consisted of 50-degree peak-to-peak azimuthal rotation with short 14-millisecond vertical acceleration spikes of 3.6 m/s2. For E. coli, the logarithmic reduction factors were not significantly different between the automatic and manual bottle shaking pasteurization groups (5.247 versus 5.667, respectively, with p = 0.292). The IgA retention percentages for mature milk were 58.31% (SD = 9.2%) in the automated group and 37.33% (SD = 9.28%) in the manual group, and the difference was significant (P = 0.0001). These results show that compared with pasteurization with automatic bottle agitation, manual bottle agitation causes a greater reduction in immunoglobulin A levels and requires more control interventions from users. Not applicable.