Effects of different thawing methods on the immune and nutritional contents of expressed breast milk

The present study aimed to investigate, through measurement of immunological and nutritional contents, of differences in various methods of thawing frozen breast milk expressed from puerperal women approximately 1 month postpartum. The specimens examined were those of expressed milk (n = 20) obtained from 20 women 3 to 5 weeks postpartum who attended an outpatient breastfeeding clinic at The Jikei University Daisan Hospital in Tokyo from November 2010 through January 2011 and of 2 brands of milk formula (n = 2). Levels of the immunological markers immunoglobulin A (IgA) and lipase and levels of the nutritional markers glucose, total protein, total fat, and total cholesterol were compared among fresh specimens immediately following expression and specimens frozen for 1 month and thawed under running water at room temperature, in a microwave oven at 500 W, or in hot water (70°C) (n = 1 per group). The study was approved by the ethics committee of our university and by the clinical review board of the hospital. Analysis was performed with the software package SPSS 16.0J, and statistical comparison was performed with Wilcoxon's signed-rank test. Most of the women who provided expressed milk specimens were primiparous (n = 14), with a mean age of 32.8 years and a mean gestational period of 39 weeks; the mean time between parturition and specimen sampling was 22.7 days. Levels of IgA after hot-water thawing were significantly increased (p < 0.01). However, lipase levels after microwave-oven thawing or hot-water thawing were significantly decreased, to levels approximately 1% of those in fresh specimens immediately after expression (p < 0.01), and suggest that lipases are heat sensitive. Glucose levels were not affected by the thawing method, whereas total protein levels after microwave-oven thawing or hot-water thawing were higher significantly than those in fresh specimens (p = 0.01). Levels of total fat and cholesterol were significantly decreased after microwave-oven or hot-water thawing (p < 0.01) and indicate that the decrease in fat levels depends on the application of heat during thawing. In contrast, no decrease in immunological or nutritional markers was observed for either milk formula specimen regardless of the thawing method. Although water and lukewarm water are already recommended for thawing expressed breast milk, incorrect thawing methods might be used in homes where convenience is prioritized. Puerperal women should be informed of the risk of both immunological and nutritional damage to frozen expressed breast milk depending on the thawing method.