Digestive enzymes in human milk: stability at suboptimal storage temperatures.

BACKGROUND: Women who return to work outside of the home while still breastfeeding must often store the expressed milk at less than optimal temperatures. Human milk provides digestive enzymes (amylase and lipase) that compensate in the newborn for immature pancreatic function.
METHODS: We have assessed the stability of amylase and bile salt-dependent lipase after storage for 1-24 h at 15, 25, and 38 degrees C.
RESULTS: Both enzymes were stable at 15 and 25 degrees C for 24 h, whereas at 38 degrees C there was a 15 and 20% decrease in lipase and amylase activity, respectively. The stability of milk lipoprotein lipase was also tested. This very labile enzyme was more stable in milk than previously reported for blood and tissues, i.e., 20 and 50% decrease in activity after storage at 15 or 25 degrees C for 24 h, respectively. A two-unit drop in milk pH by 24 h of storage would not affect the activity of digestive enzymes, which are stable at pH > 3.5.
CONCLUSIONS: We conclude that milk provides the same compensatory digestive activity after short-term storage, even at relatively high temperature, as when fed fresh to the infant.