Human milk is the optimal nutrition source for infants, providing a dynamic mix of energy, growth factors, and protective elements. When a mother’s own milk is unavailable, banked donor milk is the recommended alternative, especially for vulnerable infants. To make this donated milk safe, it must undergo pasteurization, a heat treatment process that kills potentially harmful bacteria and viruses. This heating introduces a conflict between pathogen safety and preserving biological quality. The process alters milk components, and the degree of change varies significantly across different nutrients and bioactive molecules.
Understanding Breast Milk Pasteurization
The standard method used globally by human milk banks is Holder Pasteurization (HoP). This thermal process involves heating the milk to 62.5°C for 30 minutes, followed by rapid cooling. The primary goal of HoP is to inactivate a wide range of pathogens, including bacteria, fungi, and viruses like HIV, which can be transmitted through raw milk. This time and temperature combination is effective because it sterilizes the milk while retaining many of its beneficial properties.
HoP transforms raw donated milk into a clinically safe product suitable for distribution. The heat treatment ensures that the milk meets the stringent safety standards required for feeding fragile, premature infants.
Effect on Macronutrients and Essential Vitamins
The macronutrients that provide energy and bulk growth material—fats, proteins, and carbohydrates—are generally the most stable components during pasteurization. The total concentration of protein remains largely unaffected by the HoP process, with non-protein nitrogen content showing minimal losses, typically less than 15%. Lactose, the primary carbohydrate, is highly heat-stable and its concentration is consistently unchanged following pasteurization. Fat content, which supplies the majority of calories, is also relatively stable in terms of overall concentration, though some studies suggest a small decrease of about 3.5%. More significant is the heat-induced inactivation of the enzyme lipase, which normally aids in fat digestion.
The impact on vitamins is highly dependent on their heat sensitivity. Water-soluble Vitamin C, which is sensitive to heat and oxidation, is unambiguously reduced by Holder Pasteurization. Certain B vitamins, like thiamine, may experience minimal losses. Conversely, fat-soluble vitamins such as Vitamin A and Vitamin E are often better retained, showing stability or only modest reductions. Vitamin D compounds may experience losses in the range of 10% to 20% due to the heat exposure.
Degradation of Immune Factors and Bioactive Proteins
The primary drawback of pasteurization is the degradation of the milk’s protective, non-nutritive components, which are crucial for infant immunity and gut health. These bioactive proteins are structurally complex and highly susceptible to heat denaturation. The heat treatment also inactivates maternal cells, such as white blood cells, and diminishes the activity of growth factors and anti-inflammatory cytokines necessary for gut maturation.
The most significant losses occur in specific immune factors:
- Lactoferrin, a protein that binds iron and plays a substantial role in pathogen defense and gut flora regulation, is extensively reduced, often by more than 80%.
- Secretory IgA, the most abundant antibody in milk, shows moderate losses, typically around 35% of its concentration.
- More heat-sensitive immunoglobulins, such as IgM and IgG, can be significantly decreased or completely degraded.
- Protective enzymes, including lysozyme, show variable reductions in activity, with reported losses ranging from 20% to 85%.
The Safety Trade-Off: When Pasteurized Milk is Necessary
Despite the losses to certain vitamins and protective proteins, pasteurized donor human milk remains an invaluable medical intervention and is considered the second-best option to a mother’s own milk. The process is a calculated safety trade-off, where the reduction in bioactive factors is accepted to eliminate the severe risk of transmitting infectious diseases to fragile infants. This risk is particularly acute in Neonatal Intensive Care Units (NICUs), where infants are already critically vulnerable due to prematurity.
The most compelling clinical justification for using pasteurized donor milk is its capacity to significantly reduce the incidence of Necrotizing Enterocolitis (NEC), a devastating and life-threatening intestinal disease common in preterm babies. For these medically fragile infants, a diet of pasteurized human milk is superior to formula, which has been associated with a higher risk of developing NEC. Donor milk serves a life-saving function by providing a safe, digestible, human-specific nutritional base when the mother’s own raw milk is unavailable or insufficient.