Human milk that has been refrigerated, frozen and/or thawed may develop an odor that fresh milk doesn’t have due to a normal change in the fatty acids. This oxidation process is a lipase-mediated triglyceride breakdown process that prevents the growth of microorganisms in the expressed milk. The milk is safe to use and has not “soured” or “gone bad”. Many foods that humans eat have a strong smell that does not influence taste, such as hard boiled eggs, broccoli, cheeses and fish.
There is no evidence to suggest that infants will reject milk based on this odor. Heating milk to deactivate lipase is no longer recommended as many immunologically active factors in human milk are destroyed in the process. It is recommended to continue to feed this milk to the baby as any human milk would be. If it is perceived that the baby is refusing the milk, it could be mixed 50/50 with freshly expressed milk and offered to the baby.
• Fresh breast milk
• Frozen breast milk
Talk to your lactation professional or healthcare provider if your baby is rejecting milk for any reason.
ABM Clinical Protocol #8: Human Milk Storage Information for Home Use for Full-Term Infants, Revised 2017 Anne Eglash,1 Liliana Simon,2 and The Academy of Breastfeeding Medicine BREASTFEEDING MEDICINE Volume 12, Number 7, 2017 ª Mary Ann Liebert, Inc. DOI: 10.1089/bfm.2017.29047.aje
Spitzer J, Klos K, Buettner A. Monitoring aroma changes during human milk storage at +4°C by sensory and quantification experiments. Clin Nutr 2013;32:1036–1042.