Effect of Thawing Time on Donor Human Milk Composition at 24 and 48 Hours

According to the human milk banking guidelines in Japan, issued in 2014, pasteurized donor human milk (PDHM) is discarded 24 hours after thawing. However, previous studies have suggested that PDHM remains safe for administration to preterm infants for up to 48 hours after thawing, potentially reducing unnecessary wastage.

This study aimed to assess the microbiological safety and the preservation of nutritional and immunological properties of PDHM stored under refrigeration for up to 48 hours after thawing.

This was a paired-sample experimental study evaluating the safety and composition of PDHM during refrigerated storage after thawing. Individual pasteurized milk samples from 40 donors were thawed overnight in a refrigerator and analyzed at 24 and 48 hours. Samples were cultured on sheep blood agar and incubated for 48 hours at 35 °C to assess bacterial growth. Macronutrients, micronutrients, and immune substances (sIgA and lactoferrin) were measured using specialized analyzers and ELISA kits. The pH of the samples was determined at 24 and 48 hours using a tabletop pH analyzer.

Small but statistically significant changes were observed in several components during 48 hours of storage. Fat, carbohydrates, calcium, inorganic phosphorus, sIgA, and lactoferrin showed slight variations, while protein and zinc remained stable. Fat decreased after 24 hours compared with immediately after pasteurization but did not decline further at 48 hours. The mean pH increased slightly from 7.047 to 7.102 (p = 0.003). No bacterial growth was detected at either 24 or 48 hours.

Although minor biochemical changes occurred, these were not clinically significant. Extending PDHM use to 48 hours after thawing maintained its nutritional and microbiological integrity and could inform revisions to current Japanese milk bank guidelines.