What is lipase? Kellymom has a comprehensive explanation on what it is:
A few mothers find that their refrigerated or frozen milk begins to smell or taste soapy, sour, or even rancid soon after it's stored, even though all storage guidelines have been followed closely. Per Lawrence & Lawrence (p. 781), the speculation is that these mothers have an excess of the enzyme lipase in their milk, which begins to break down the milk fat soon after the milk is expressed. Most babies do not mind a mild change in taste, and the milk is not harmful, but the stronger the taste the more likely that baby will reject it.
Lipase is an enzyme that is normally present in human milk and has several known beneficial functions:My own breastmilk was also high in the lipase enzyme. We noticed that when stored in the refrigerator, N didn't have any problems taking it. But when the milk was frozen then thawed, the milk smelled soapy. Luckily, I had enough refrigerated milk to last N the week and all of my frozen milk got donated and pasteurized.
- Lipases help keep milk fat well-mixed (emulsified) with the "whey" portion of the milk, and also keep the fat globules small so that they are easily digestible (Lawrence & Lawrence, p. 156).
- Lipases also help to break down fats in the milk, so that fat soluble nutrients (vitamins A & D, for example) and free fatty acids (which help to protect baby from illness) are easily available to baby (Lawrence & Lawrence, p. 156).
Per Lawrence & Lawrence (p. 158), the amount of BSSL in a particular mother's milk does not vary during a feed, and is not different at different times of day or different stages of lactation. There is evidence that there may be a decrease in lipase activity over time in mothers who are malnourished.
- The primary lipase in human milk, bile salt-stimulated lipase (BSSL), "has been found to be the major factor inactivating protozoans" (Lawrence & Lawrence, p. 203).
If your breastmilk has excess lipase, all is not lost! As stated in the quote above, "[m]ost babies do not mind a mild change in taste, and milk is not harmful, but the stronger the taste the more likely that baby will reject it." So if your baby does not mind the smell or taste of your breastmilk, then lucky you and there is no harm in feeding the baby breastmilk with excess lipase as long as baby takes it.
What can I do if my storage problem is due to excess lipase? Once the milk becomes sour or rancid smelling/tasting, there is no known way to salvage it. However, newly expressed milk can be stored by heating the milk to a scald to inactivate the lipase and stop the process of fat digestion. Scald the milk as soon after expression as possible.To scald milk:
- Heat milk to about 180 F (82 C), or until you see little bubbles around the edge of the pan (not to a full, rolling boil).
Scalding the milk will destroy some of the antiinfective properties of the milk and may lower some nutrient levels, but this is not likely to be an issue unless all of the milk that baby is receiving has been heat-treated.Per Lawrence & Lawrence, bile salt-stimulated lipase can also be destroyed by heating the milk at 144.5 F (62.5 C) for one minute (p. 205), or at 163 F (72 C) for up to 15 seconds (p. 771).
- Quickly cool and store the milk.
Here's a video on how to scald milk:
You can also check this FORUM THREAD from La Leche League on actual experiences of moms in scalding their breastmilk. Scalding breastmilk is a trial and error process and varies with each mom. Some moms find that they don't have to scald immediately after expression to get rid of lipase. Some moms need to use their scalded breastmilk within a couple of days while for others moms, putting the scalded breastmilk in deep freeze didn't cause any problems.
One problem for working moms would be how to scald breastmilk in the office since most working moms do not have access to a stove or time to scald the milk right after expression. Some moms have shared that they MICROWAVE their milk at the office. Please note that microwaving breastmilk is not recommended but neither is heating it on a stove. According to this article the reason is as follows:
"Microwaving breastmilk, or heating it on the stove, can cause a loss of Vitamin C content, along with loss of some of the milk's special anti-infective properties. The higher the temperature, the more pronounced the effect."
As explained in this FORUM, the purpose of heating over a stove is to de-activate the lipase enzyme, so microwaving shouldn't be an issue:
I did find that the easiest way to deal with my problem was to microwave the milk briefly before freezing. Not to boiling, just until it's hot to the touch. This is effectively the same treament as stovetop scalding, but a lot more convenient. For my very wimpy microwave, this was about 1 min. for 4 oz. of breastmilk. I know that ''do not microwave breastmilk'' is a mantra out there because you will damage or destroy the beneficial antibodies. However, in this situation, the purpose is exactly to heat-inactivate the lipase enzyme (too bad we can't selectively inactivate only some enzymes). In any case, scalded breastmilk still retains all the wonderful nutritional qualities even if some of the immunological benefits are diminished, and it's better than having baby refuse to drink the breastmilk at all.However, La Leche League and several breastfeeding experts do not recommend microwave scalding because aside from inactivating the lipase enzyme, it also destroys milk molecules as microwave cooking is different from conventional cooking. Some moms still scald their milk through microwave at the office because they would rather feed their babies microwaved breastmilk over formula.
*Note also, however, that sometimes, excess lipase may not be the culprit. It is possible that your milk may smell or taste funny after a certain expression time because of something you ate. I know someone who ate at a tocino buffet and her milk had red stuff (probably from the tocino nitrates) when she pumped shortly after.
It is also possible that the funny taste or smell of milk is due to improper storage. Remember, your other food stuff in the refrigerator CAN contribute the smell and taste of breastmilk. So make sure that your breastmilk is stored properly and your other food are stored in sealed and covered containers as well. Check HERE for milk storage tips.