Breast Milk

Human breast milk should be stored at refrigerator temperatures for no longer than two days, according to the results of a small trial published in the October issue of the Archives of Diseases in Childhood, Fetal and Neonatal Edition.

Storage for longer periods or at colder temperatures causes the milk to lose antioxidant activity. "Human milk, which contains compounds beneficial to infants, is often expressed and stored before use. Changes in its antioxidant activity with storage have not [previously] been studied," write N. Hanna, from the UMDNJ–Robert Wood Johnson Medical School in New Brunswick, New Jersey, and colleagues.

"Preterm infants are born relatively deficient in antioxidant defences, and ingesting human milk rapidly increases antioxidant concentrations," according to Dr. Hanna and colleagues. "This may partly explain the protection afforded by human milk in the development of necrotising enterocolitis and retinopathy of prematurity."Within 24 hours of delivery, 16 breast milk samples from mothers of term and preterm infants were divided into aliquots. Fresh samples were immediately tested for antioxidant activity based on their ability to inhibit the oxidation of 2,29-azino-di-3-(ethylbenzthiazolinesulphonate) to its radical cation compared with Trolox, a strong antioxidant that is a derivative of vitamin E. The remaining aliquots were stored at –20°C (freezer temperature) or 4°C (refrigerator temperature) for analysis at 48 hours and at seven days. Both refrigeration and freezing significantly decreased antioxidant activity, but freezing resulted in a greater decrease than refrigeration.

Storage for seven days decreased antioxidant activity in breast milk more than did storage for 48 hours. Although there was no difference in antioxidant activity in milk from mothers who delivered prematurely or at term, formula milk had significantly lower antioxidant activity than did fresh human milk.Study limitations include small sample size and inability to ascertain which components of milk are affected by storage."Fresh human milk has the highest antioxidant capacity, which decreases with storage over time.

To preserve antioxidant capacity, milk should only be stored for a short time at refrigerator temperature and not frozen," the authors write. "The antioxidant capacity of infant formula did not change with storage, which is consistent with previous studies suggesting stability of fat soluble vitamins with storage. Thus it is likely that antioxidant enzyme activity of human milk degraded with storage."

Arch Dis Child Fetal Neonatal Ed. 2004;89:F518-F520 Reviewed by Gary D. Vogin, MD