Changing patterns of free fatty acids in breast milk during storage.

Milk was collected from eight mothers. Total lipid and free fatty acids were determined on collection. The samples were divided into aliquots and stored at 25, 4, or -11 degrees C for 6, 12, 24, or 48 h. Additional samples were stored at -11 or -70 degrees C for 1, 2, 4, 6, or 8 weeks. The effect of temperature, length of storage, and total milk lipid on the release of individual fatty acids during storage was determined. There was no measurable lipolysis in milk stored at -70 degrees C. In the other samples both storage temperature and length of storage significantly affected lipolysis of milk lipids. The accumulation of free fatty acids in the milk increased with the length of storage and with increased storage temperature. Total lipid was not a significant factor in the release of fatty acids during the initial 48 h of storage. In samples stored for greater than 48 h at -11 degrees C, total lipid was positively correlated with the release of fatty acids. The pattern of free fatty acids in milk changed as storage progressed with an increase in the proportion of free 18:2, 20:4, and the other long-chain polyenoic acids. This may have implications for infant nutrition as these fatty acids are required for normal growth and development of the neonate.