What happens to overheated proteins is that they uncurl, or denature.
Proteins do not usually refold properly after cooling.  Since the
activity of the protein is usually directly related to it's special
folded shape, denaturing destroys the protein's ability to do it's job.
THerefore overheating human milk destroys some of the important
protections.  In cow's milk formula, this is actually a benefit, as the
proteins in it are not appropriate for human babies, and denaturing them
can render them less allergenic.
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Catherine Watson Genna, IBCLC  NYC  mailto:[log in to unmask]