I asked an immunologist to weigh in on the denaturation of protein question
and also asked him to address whether any cells would be damaged. Note that
he addresses cell damage apart from protein denaturation. They are two
different questions.  Arly Helm, MS, IBCLC



Proteins
As in many biological situations one must consider the degree of the action
in question. A simple example is bumping one's arm against a doorknob as you
walk into the house. If the bump is a mild one, some pain is felt but there
is no visible damage to the living tissue in the area.  If the bump is
severe then blood vessels will be broken and cells damaged, resulting in a
visible bruise. This same concept applies to shaking a bottle of milk. If
the motion is moderate and the time short, the effects on proteins and cells
is minimal. If the bottle is vigorously shaken for a long time then you can
expect proteins and cells to be more severely affected.  Have you ever
whipped an egg white?  The white is primarily albumin, which is a protein.
The whipping action breaks the tertiary structure of the protein apart which
creates "sticky ends" that clump together.  Air is trapped in the clumps,
creating a wonderful meringue.  If you were to drop an egg into a jar of
water, close the lid and gently shake, the egg will slosh back and forth but
you will not see any effect on the proteins. Vigorously shaking is another
matter. 

Gently sloshing a bottle of milk to resuspend the cream will not damage any
proteins.  

Cells
The cells in breast milk are white blood cells or leukocytes, such as
macrophages and neutrophils, with a few lymphocytes included.  These cells
are found in human blood and survive a violent mixing action every time they
pass through the heart.  In the lab, we routinely process the cells by
centrifugation, pipetting up and down, vortexing and shaking with no ill
affects. The bottom line is that shaking will not kill these cells.  

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