Major losses of fat, carbohydrates and energy content of preterm human milk frozen at −80°C

Long-term storage of human milk (HM) requires freezing at low temperatures, the consequences of which upon macronutrients are unclear. To test the null hypothesis that HM freezing and storage for a range of 1 to 10 weeks at −80 °C does not affect HM fat, protein, lactose and energy contents. Samples of HM were obtained from 20 mothers (60 samples) of preterm infants (25 to 35 weeks gestation), who routinely expressed their milk, every 3 h, using an electric pump, from the second to the seventh week after delivery. All samples were frozen at −80 °C for 8 to 83 days (43.8 days average). After thawing and homogenization, energy and macronutrient contents were measured using an HM analyzer. Fat, carbohydrates and energy contents were significantly lower in thawed HM than in fresh HM (fat, fresh vs thawed: 3.72±1.17 vs 3.36±1.19 g/100 ml, P