Comparison of lactoferrin activity in fresh and stored human milk

OBJECTIVE: Lactoferrin (Lf), the dominant protein in human milk (HM), has been shown to have anti-inflammatory and anti-microbial activity in the neonatal gut. Previous studies indicate that freezing significantly decreases the concentration of Lf in HM. The objective of our study was to compare the activity of Lf in fresh and frozen HM over time. STUDY DESIGN: HM samples were examined fresh and after storage at -20 degrees C for 3 and 6 months. Lf concentration was determined by enzyme-linked immunoassay, and the activity was measured by examination of nitric oxide (NO) production and tumor necrosis factor-alpha secretion from rat macrophages exposed to HM samples. RESULT: After 3 and 6 months at -20 degrees C, the average decrease in Lf concentrations was 55% and 65%, respectively. The bioactivity of Lf also decreased significantly over 6 months. CONCLUSION: Freezing HM for 3 or more months significantly decreases Lf levels and activity. Periodically providing fresh HM may benefit vulnerable preterm neonates.