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Bacterial Content of Raw and Processed Human Milk 1
E N Agel1, B A Friend1, C A Long1
1Department of Food Service and Technology, University of Nebraska, Lincoln, Nebraska 68583.
Abstract:
Mature human milk samples were manually expressed into sterile containers and examined for their bacterial content. No other special precautions were taken to ensure asepsis. The total counts of seven individual samples ranged from 1.5 × 103 to 1.9 × 107 CFU/ml; the counts of pooled samples used for further processing ranged from 4.2 × 106 to 5.7 × 107 CFU/ml. Freezing had no significant effect on the counts. Although freeze-drying reduced the mean count by one log cycle, the decrease was not significant and the level of contamination was above the level considered safe for human consumption. Pasteurization at 62.5°C for 30 min reduced the load 4-5 log cycles and the reduction continued during subsequent storage at -25°C. Although heating at 75°C for 15 min reduced the load 6-7 log cycles, the microbial counts tended to increase during subsequent storage at 4°C.
Insights
Human milk contains significant bacterial contamination, with levels often exceeding safety standards. While freezing and freeze-drying had minimal impact, pasteurization effectively reduced bacterial load, though some regrowth occurred during storage.
Area of Science:
- Microbiology
- Food Science
- Public Health
Background:
- Human milk is a primary source of nutrition for infants.
- Understanding the microbial content of human milk is crucial for infant health and safety.
- Bacterial contamination levels in human milk can vary significantly.
Purpose of the Study:
- To quantify the bacterial load in mature human milk samples.
- To evaluate the impact of storage and processing methods (freezing, freeze-drying, pasteurization) on bacterial counts.
- To assess the safety of human milk based on microbial contamination levels.
Main Methods:
- Manual expression of mature human milk samples into sterile containers.
- Total bacterial counts determined using colony-forming units per milliliter (CFU/ml).
- Assessment of bacterial load after freezing, freeze-drying, and pasteurization (62.5°C for 30 min; 75°C for 15 min), with subsequent storage analysis.
Main Results:
- Total bacterial counts in individual samples ranged from 1.5 × 10^3 to 1.9 × 10^7 CFU/ml.
- Freezing did not significantly affect bacterial counts; freeze-drying caused a minor, non-significant reduction.
- Pasteurization at 62.5°C for 30 min reduced bacterial load by 4-5 log cycles, with continued reduction during cold storage. Heating at 75°C for 15 min reduced load by 6-7 log cycles, but microbial counts increased during subsequent refrigerated storage.
Conclusions:
- Mature human milk can harbor substantial bacterial contamination, often exceeding safe consumption levels.
- Standard freezing and freeze-drying methods are insufficient for significant bacterial reduction.
- Pasteurization is effective in reducing bacterial load, but post-processing storage conditions are critical to prevent microbial regrowth.
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