PC2031: The Effect of Holder's Pasteurization and Freeze Drying on Human Milk Foodborne Pathogens

Background: Human milk is fundamentally important in the growth and development of neonates and suboptimal breastfeeding contributes significantly to the societal cost of health care. Consumption of human milk has a protective effect not duplicated by breastmilk substitutes. Mothers in the United States commonly express and freeze human milk for personal use in feeding their infants. Ironically, the characterization and methods of preservation applied to many other human foods is more represented in the literature than this first food.

Freeze-drying (lyophilization) of human milk, exhibits nutrient retention during ambient storage >12 months at levels similar to fortified bovine milk-based powder infant formula produced at the commercial scale using tall-form spray dryers. Both powders are considered high-hygiene non-sterile powders appropriate for consumption by healthy infants.

For human milk used in clinical settings, Holder’s pasteurization (HoP, 62.5ºC, 30 min) is practiced in clinical settings including human milk banks, globally. In North America, the use of unpasteurized donor human milk is not endorsed. Adequate processing via HoP however, is designed to address the potential risks associated with bacterial contamination of human milk. Pasteurized human milk provides superior benefits that commercial formulas, despite using human milk composition as the standard, struggle to fully emulate.

Methods: This study confirmed the adequacy of Holder’s pasteurization (HoP; 62.5C, 30 min) for human milk prior to lyophilization using Cronobacter sakazakii, Escherichia coli O157:H7, Staphylococcus aureus, and Enterococcus faecium NRRL B-2354 (a Salmonella surrogate). Samples of human milk from 10 screened donors were pooled and inoculated at artificially high bacterial concentrations. The two treatments of HoP followed by lyophilization (HoP + L) and lyophilization only (LO) were run side-by-side. Samples were enumerated on tryptic soy agar with 0.6% yeast extract before and after each of the treatments.

Results: This study concluded that HoP treated samples demonstrated > 5-log reduction on each of the bacterial strains tested.

Conclusion: This work confirms the established adequacy of this fundamental thermal process reduced to practice as a preventive control against bacterial pathogens in donor human milk. The control LO samples showed, in the absence of the HoP heat treatment, minimal bacterial reductions occur during freezing and lyophilization. The combined use of HoP and lyophilization processing in sequence can result in a shelf-stable human milk powder of high hygienic quality.