Human milk has been recommended as the preferred food for preterm babies. Its unique immunological factors would be beneficial for these infants. The presence of possible microbial contamination raises the question of whether or not the mother's or donated milk should be used raw. Pasteurization would eliminate the need for costly and time consuming screening for potential pathogenic microorganisms prior to the use of raw human milk. However, heat treatment has been shown to destroy some of the immune factors in human milk. This study was designed to compare four treatments of frozen human milk and their effects on the bacteria count and on the level of immunoglobulin A (IgA).

Twenty women volunteered to express 150 ml of their milk by following standard collection techniques. The milk was tested raw. Tryptone glucose extract agar and MacConkey agar were used to obtain total plate count and coliform count, respectively. Low level IgA end point radial immunodiffusion plates were used to obtain IgA levels. Four-30 ml portions of each sample were placed in sterile plastic containers, covered and frozen for 34 days. One 30 ml portion of each frozen sample was treated in one of the following ways: (1) thawed overnight in a refrigerator, (2) thawed under running water (44-49°C) , (3) thawed in a 62.5°C water bath for 30 minutes (holder pasteurization), and (4) thawed in a microwave oven for 50 seconds at 700 watts. The mean percentage of IgA loss for the running water, holder pasteurization and microwaving methods were 2.6, 16.2 and 30.5 percent, respectively. There was a slight increase (1.2 per cent) in IgA content in the samples thawed in the refrigerator.

If the dairy industry standard for clean cow milk (less than 10,000 colonies/ml) is applied to human milk, the holder pasteurization and microwave methods are 99.9 percent effective. Nineteen of the 20 samples (90 percent) thawed overnight in the refrigerator and 19 of the 20 samples (90 percent) thawed under running water showed effective destruction of bacteria. The one sample where there was still a high count for both of these methods had an initial count greater than 3 x 106.

The microwave method may be an unreliable treatment as it results in inconsistency of the end point internal temperature. Freezing itself may aid in both bacteria destruction and IgA retention in human milk.

LLU Discipline





Graduate School

First Advisor

Kenneth I. Burke

Second Advisor

U. D. Register

Third Advisor

O. Ward Swarner

Fourth Advisor

Patricia K. Johnson

Fifth Advisor

Gerald W. Shavlik

Degree Name

Master of Science (MS)

Degree Level


Year Degree Awarded


Date (Title Page)




Library of Congress/MESH Subject Headings

Milk, Human; Infant, Premature; Immunoglobulins



Page Count

vii; 57

Digital Format


Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.


Loma Linda University Electronic Theses and Dissertations

Collection Website



Loma Linda University. Del E. Webb Memorial Library. University Archives

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Nutrition Commons