Prolonged refrigerated storage of human milk: effects on nutritive and non-nutritive characteristics.

Due to the limited knowledge on which common advice on human milk storage is based, current recommendations concerning safe human milk conservation are far from being univocal. In an attempt to clarify some of the uncertainties existing on the storage of HM, we designed a comprehensive study to investigate the effects of prolonged refrigeration on the nutritive and non-nutritive characteristics of human milk, and on its microbiological composition. Human milk was collected and divided into 5 aliquots. One aliquot underwent analyses immediately, while the other aliquots were stored in the refrigerator for 24, 48, 72, and 96 hours before analysis. The temperature was constantly monitored. The samples were analysed for pH, free fatty acid (FFA) content, bile salt-dependent lipase (BSDL) activity, oxidative status, and bacterial profile. The experiment was replicated three times. The continuous temperature monitoring of the refrigerator showed a mean value of 6.8 ± 1.1°C. Limited lipolysis was seen during prolonged refrigerated storage, consistently with a slight decrease in milk pH. Refrigeration preserved milk overall oxidative status and the activity of BSDL. Moreover, the overall bacterial composition remained stable, with mean values for total bacteria, Enterobacteriaceae and coagulase positive Staphylococci counts under the recommended concentrations set for acceptability of milk in milk banks. In conclusion, refrigeration of expressed human milk in controlled conditions for 96 hours allowed to maintain its bioactivity and nutritional quality, without compromising its microbiological safety.