Breast milk contains many antibacterial ingredients that are best within the first 48 to 72 hours of refrigeration. It contains white blood cells like leukocytes. In stored breast milk, some of the leukocytes are killed during freezing. Although it is safe to say that pumping milk is the better choice compared to formula, it is important to bear in mind that it does not offer as many health and immune system benefits as fresh milk.
Stored breast milk can change its properties, some of the changes are natural and can even help your baby’s digestion, like lipase activity that might be related to smell and taste. However, these changes can be very confusing and make it very hard to know if it is a “positive” or “negative” change, and decide whether the milk is still good for consumption. Another thing that happens to your breast milk when stored is degradation of some nutrients, for example, one of the first nutrients that decreases is Vitamin C, which is crucial for immune system development. Knowing that your milk has low levels of Vitamin C will allow you to manage your baby’s health better, the milk that has low Vitamin C is still good! and has many other beneficial ingredients, but knowledge is power – if you know you can add Vitamin C drops to your baby's daily routine, or add a few fresh breast milk meals during the week.