Is it okay to mix formula into puree? Why or why not? Thanks!

It is okay to add formula to puree to "thin" out the fruit or vegetable mixture. Some moms use breastmilk, some use formula. However, I read that if you intend to freeze the purees for future use, adding formula might not be a good idea because the fat in the milk might separate during freezing and this is not good or palatable for the baby. If you do add formula, then best to feed baby immediately and not freeze it.