Effect of temperature and length of storage on serum-stimulated and serum-independent lipolytic activities in human milk.

Milk was collected from five mothers. Upon collection, serum-stimulated and serum-independent lipolytic activities were determined. The milk samples were aliquoted and stored at 25, 4, -20, and -70 degrees C. After storage for 3, 6, 12, and 24 h, serum-stimulated and -independent activities were again determined and compared with the initial activities. Storage at 25 degrees C resulted in a significant (p less than 0.05) decrease in lipolytic activity. Serum-stimulated activity decreased 83.4% and serum-independent activity decreased 66.9% over the 24-h period. Storage at 4 degrees C resulted in a significant (p less than 0.05) decrease of 22.6% in serum-stimulated activity and a 7.2% decrease in serum-independent activity. No significant changes were observed in milk stored for 24 h at -20 and -70 degrees C. Milk was stored at -20 and -70 degrees C for an additional 1, 2, and 4 weeks. Serum-stimulated lipolysis did not change significantly over the 4-week period. Serum-independent lipolysis increased significantly (p less than 0.05) with storage time. Storage at -20 degrees C resulted in an increase of 20% and storage at -70 degrees C resulted in an increase of 36% over the 4 weeks.