Effect of prolonged refrigeration on the lipid profile, lipase activity and oxidation status of human milk.

Objective: The study was aimed at evaluating the effect of prolonged refrigeration of fresh human milk (HM) on its fatty acid profile, free fatty acid content, lipase activities and oxidative status. Methods: Human milk from mothers of pre-term newborns was collected, pooled and placed in the Neonatal Intensive Care Unit (NICU) refrigerator. Pooled milk was aliquoted and analyzed within 3 hours of collection, and after 24, 48, 72, and 96 hours of storage. The milk samples were analysed for pH, total and free fatty acid profile, lipase activity at room temperature and at 4°C, lipase activity at room temperature in presence of sodium cholate (BSDL), total antioxidant capacity, thiobarbituric acid reactive species, malondialdehyde and conjugated diene concentration. The experiment was replicated in three independent trials. Results: Prolonged refrigeration did not affect the fatty acid composition of breast milk, and preserved both its overall oxidative status and the activity of HM lipolytic enzymes. In particular, BSDL activity, LC-PUFAs and medium chain saturated fatty acid concentrations were unaffected for up to 96h of refrigerated storage. Conclusion: Prolonged refrigeration of fresh human milk for 96 hours maintained its overall lipid composition. The limited lipolysis during storage should be ascribed to the activity of lipoprotein lipase, responsible for the decrease in pH. Our study demonstrates that infants who receive expressed milk stored for up to 96h receive essentially the same supply of fatty acids and active lipases as do infants fed directly at the breast.