Human milk properties and nutrient fortification

The effects of nutrient fortification and storage on human milk properties are important considerations when feeding premature infants. We hypothesized that milk total bacterial colony count (TBCC) and IgA concentration were not affected by the addition of nutrient fortifier or storage duration and that milk osmolality does not increase with storage. TBCC were measured in 10 frozen and 5 fresh milk samples from mothers of premature infants. The milk was divided into unfortified and fortified milk, and then stored for 0 to 72h at room or refrigerator temperature. Aliquots were obtained at 0 to 72h for TBCC, total IgA (ELISA), and osmolality (vapor pressure osmometer), and analyzed by repeated measures ANOVA. Log ,0TBCC were significantly greater in fortified (4.9,6.3,6.8,7.8) vs unfortified milk (4.8,5.6,6.2,7.5) at 0, 24, 48, and 72h, respectively, p=0.017; both increased with storage, p<0.001. IgA was similar between milks and with storage. Milk osmolality was greater in fortified than unfortified milk; both increased similarly, by ≈4%, from 0 to 72h, p=0.012. The differences between fortified and unfortified milk in TBCC but not in osmolality were observed by 24h. These findings may warrant consideration when human milk is used in the neonatal nursery and support the recommendation to use prepared milk within 24h.