When breastmilk is stored, some parents notice a distinct change in its flavor and odor, which can lead to a baby refusing the bottle. This change is often due to the natural enzyme lipase becoming highly active, causing fat molecules to break down faster than usual. While this enzyme activity does not make the milk unsafe or less nutritious, the resulting taste can be unappealing to infants. Understanding this natural variation allows parents who pump and store milk to proactively identify the issue and implement strategies to ensure the milk remains palatable.
Understanding High Lipase Activity
Lipase is an enzyme naturally present in all human milk, playing a significant part in fat digestion. Its function is to break down triglycerides into glycerol and free fatty acids, helping the infant absorb fat-soluble vitamins and calories needed for growth. In some individuals, the activity level of lipase is unusually high, causing the fat breakdown process to accelerate rapidly once the milk is expressed and cooled.
The production of these free fatty acids alters the sensory characteristics of the milk over time. This change manifests as a “soapy,” “metallic,” or sometimes “rancid” smell and taste when the milk is stored. The exact reason why some mothers produce milk with significantly higher lipase activity is not understood, but it is considered a natural physiological variation. High lipase milk is completely safe and healthy for a baby to consume, even if they refuse the altered flavor.
Step-by-Step Guide to Testing for High Lipase
The most practical method to determine if high lipase activity is the cause of flavor changes is a simple sensory test at home. Begin by collecting a small sample of freshly expressed milk (one to two ounces) immediately after pumping. Taste and smell this fresh milk to establish a baseline, noting its characteristic mild sweetness and lack of strong odor.
Next, label this sample clearly with the date and time, and place it in the refrigerator for 12 to 24 hours. The duration of storage is crucial, as high lipase activity can sometimes become noticeable within a day. After the designated time, remove the stored sample, allow it to warm slightly, and then taste and smell it again.
If the stored milk has developed a noticeable soapy, metallic, or fishy flavor compared to the fresh sample, high lipase activity is likely the cause. This diagnostic step prevents a large volume of milk from being affected before a solution is implemented. If the milk remains unchanged after 24 hours, repeat the test with a sample stored for 48 to 72 hours, as the rate of lipase activity can vary.
Utilizing Milk Affected by High Lipase
Milk that has already developed the distinct soapy or metallic flavor is still safe and nutritionally sound, even if the infant refuses it. The primary strategy for using this affected milk is to mask or dilute the strong flavor to make it more palatable. One common approach is to mix a small amount of the high-lipase milk with a larger volume of freshly expressed milk, often starting with a 1:3 ratio and adjusting based on the baby’s acceptance.
For babies who have started solid foods, the affected milk can be incorporated into their meals to camouflage the taste. Try mixing it into infant oatmeal, pureed fruits, or vegetables. If the milk is consistently refused, use it for non-ingestion purposes, such as adding it to a milk bath, which can be soothing for the baby’s skin. The milk should never be discarded, as it retains beneficial components despite the flavor change.
Heat Treatment Strategies for Prevention
The most effective way to prevent the soapy or metallic taste in stored milk is to inactivate the lipase enzyme shortly after expression using scalding. This process requires heating the milk to a specific temperature high enough to deactivate the enzyme but low enough to preserve most beneficial properties. To perform this, pour freshly pumped milk into a clean saucepan and heat it gently on a stovetop.
The temperature must reach approximately 180°F (82°C) to stop the enzyme’s action. This is just below the boiling point; you will see small bubbles forming around the edges of the pan, but the milk should not come to a rolling boil. Using an instant-read food thermometer is the most accurate way to confirm the temperature. Once the milk reaches this target temperature, remove it from the heat immediately.
The treated milk must then be cooled rapidly to preserve its quality. Place the container of heated milk into a prepared ice bath, or transfer it to a heat-safe container and submerge it in ice water. Once cooled, the milk can be transferred to storage bags or bottles and frozen or refrigerated for later use without the risk of the flavor changing. Scalding should be done as soon as possible after pumping, ideally within an hour, to prevent the lipase from beginning its fat-breakdown process.