Andrew wrote:
> IGFs are peptides, hence proteinous/nitrogenous compounds.
> having said that, I am now no longer sure whether i merely assumed, or
read
> an authoritative
> opinion, that the culturing process definitely denatures the IGFs along
with
> the caseins.

Here are a couple of links that indicate that IGF-1 in humans is increased
by drinking milk, but not by yogurt, cheese, or ice cream:
http://www.mercola.com/2002/sep/28/milk_hormone.htm
http://www.organicconsumers.org/rbgh/womenigf1.cfm
They are probably both referring to the same study. While searching out
these links I read that IGF in milk would be broken down in the stomach (if
it's a peptide it should be broken down by pepsin), except that it is
protected by casein and ends up surviving to get absorbed later in the small
intestine. Perhaps the denaturing of casein by cooking or fermentation
alters the casein to such an extent (coagulates it) that it is no longer
protective and the IGF gets broken. Denatured means it's more
digestible--the protein backbone is more exposed to enzymes. Pasteurization
doesn't denature the proteins very much, if at all. Raw-dairy promoters say
that it is altered in some significant way, but it's obviously not
coagulated--it's still milk, and still coagulable. So pasteurization may
alter the casein somehow, but the IGF probably gets the protection whether
the milk is pasteurized or not, but loses it when the milk is more fully
denatured. This all seems more likely than that the IGF itself is denatured
in culturing. Denaturing is more a structural change than a chemical one,
altering secondary bonds, but not actually breaking the proteins. Since
peptides are simpler molecules I wouldn't think they are as affected as more
complex proteins by the same denaturing agents (such as lactic acid).