Effect of prolonged refrigeration on the protein quality of breast milk

In the past, several studies investigated the effects of different storage times and temperatures on different human milk components, including the abundance and/or the activity of single selected proteins. Nevertheless, extensive information on how prolonged refrigeration may modify the milk protein pattern is currently lacking. In the present study, skimmed breast milk was collected, aliquoted, and stored in a refrigerator for 24, 48, 72, and 96 hours before analysis. The experiment was independently replicated three times. The refrigerator temperature was constantly monitored. The resulting samples were then analysed for available lysine and secretory IgA contents, and their protein profile was obtained by monodimensional electrophoresis. Most abundant proteins were identified by MALDI TOF/TOF mass spectrometry. The refrigeration process did not affect either the total protein content or the HM protein profile. Markers of milk nutritional quality (dietary protein content and available lysine content), milk bioactive proteins (including the antimicrobial components lysozyme and lactoferrin) and immunological components (sIgAs, heavy chain of immunoglobulin and polymeric immunoglobulin receptor), were preserved up to 96h of refrigeration. In conclusion, refrigeration of expressed human milk in controlled conditions for 96 hours preserved protein bioactivity and nutritional quality.