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My wife just came back from a breastfeeding clinic where the health visitor admonished mothers for shaking their breastmilk rather than stirring it when preparing a bottle. Apparently it "denatures the proteins". This reeks of pseudoscience, but a five minute Google yielded a startling number of references that claim the same. Here are a couple of examples:

http://www.bflrc.com/ljs/breastfeeding/shakenot.htm

http://www.breastfeedingplace.com/breast-milk-handling-stirred-not-shaken/

Is there any science to back this up, or is it just a myth?

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Quoting from the "Effect of Shaking on Lipolysis of Cow's Milk" Journal of Dairy Science Volume 21, Issue 11, November 1938, Pages 671–682 (emphasis added):

Eufinger (10) showed that the titratable acidity of human milk increased several fold upon shaking for a few hours, and that the increase was associated with the presence of fat since the acidity did not increase when skimmilk was shaken

Goes on to explain that two other "investigators observed a marked increase in surface tension as a result of shaking human milk".

So this confirms that a chemical change occurs due to shaking; however, it does not confirm that protein denaturation occurs.

Instead, lipolysis is the hydrolysis of triglycerides into glycerol and fatty acids.

However, generally speaking, proteins can be denatured by shaking. For example, Cell Culture Technology for Pharmaceutical and Cell-Based Therapies (2005) explains at page 486:

shaking increases the air/liquid interface ... and often leads to protein denaturation. Several proteins are susceptible to denaturation by shaking, including human growth hormone (hGH) and recombinant factor XIII, both of which form insoluble complexes after shaking

Solution Behavior of Surfactants: Theoretical and Applied Aspects, Volume 2 (1982)at page 1501:

Indeed it is likely that all proteins may be affected by shaking although not to the same extent

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    What is the effect of shaking for, say, five seconds, which is a more likely length of shaking time than a few hours? May 1 '15 at 20:19
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    @iamnotmaynard exactly my thoughts after reading this, "shaking for a few hours" were talking about a 5-10 second max, immediate consumption.
    – Himarm
    May 1 '15 at 21:22
  • @iamnotmaynard "many enzyme solutions may be inactivated by mere shaking; a rennet solution, for instance, need be violently shaken only two minutes in a test tube in order largely to deprive it of its capacity to coagulate milk" Colloids in Medicine and Biology, page 189. Each different protein/enzyme in milk will have a different sensitivity to shaking. All I can say is that some proteins can be denatured on a short timescale. I don't have data for human milk proteins specifically.
    – DavePhD
    May 3 '15 at 15:21
  • @DavePhD did you see this one?biomarkersandmilk.blogspot.co.uk/2014/08/…
    – ninesided
    May 4 '15 at 6:07
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    @ninesided yes, I looked at that several times over the last few days. I think anthropology professor Quinn is making a couple mistakes. First, as one of the comments on her blog points out, she is not considering lipolysis, which the first article I cite is discussing. Secondly, she is assuming that shearing is the only mechanism for protein denaturation. According to "Bioseparations of Proteins: Unfolding/Folding and Validations" at page 110 "shear is a factor but a minor" and goes to explain that shaking continously brings new molecules to the air/liquid interface (continued below).
    – DavePhD
    May 4 '15 at 11:00

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