Changes in Protein Levels during the Storage and Warming of Breast Milk in a Domestic Environment.

: Storage and warming can impact the protein concentration of breast milk (BM). This study aimed to explore the effects of routine BM handling, from storage to warming, on BM protein concentration. : Forty BM samples were collected from 40 mothers with full-term infants. Fresh BM samples were analyzed within 24 h of expression as a baseline. Additional samples were stored in a refrigerator for up to 4 days and in either a freezer compartment of a refrigerator with a separate door (refrigerator freezers) or a deep freezer for up to 6 months. We compared four warming techniques: rapid thawing in water at 25 °C and 37 °C immediately after freezer removal, and slow thawing in a refrigerator for 12 h, followed by warming in water at 25 °C and 37 °C. The protein concentration was measured using the Lowry method. : No significant decrease in BM protein concentration was observed across all storage conditions compared to baseline. BM with a higher protein content benefited more from storage in deep freezers than in refrigerator freezers. Thawing immediately after removal from the freezer at 25 °C preserved significantly higher total protein levels compared to alternative heating techniques. : Our findings support the recommendation for mothers to store BM in either type of freezer for up to 6 months. Our results suggest that rapid thawing at 25 °C is the most effective method for preserving protein levels compared to other thawing techniques used in our study.