Jim wrote:
> 
> My understanding is that betacellulin is most heavily 
> concentrated in dairy fat.  Here's a little bit of a blurb 
> from Max Muscle website that I believe supports this: 
> 
> "Growth factors are contained within the fat globule membrane 
> in whey. They can also be found in colostrum, the pre-milk 
> breast fluid produced in the first 48 hours after giving 
> birth. Because whey concentrates are higher in fat than whey 
> isolates, growth factors are usually found at higher levels 
> in concentrates."

Good sleuthing, Jim. I didn't know that whey contained fat globules, but I
confirmed it here:

Carotenoids for ruminants: From forages to dairy products
http://www.aseanfood.info/Articles/11017271.pdf

"Kon et al. (1944) have reported that whey fat was richer in carotenoids
than the original milk fat (+50%), which could be explained by the lower
size of the fat globules in whey versus milk and the higher proportion of
carotenoids in the milk fat globule membrane versus in the globule core. In
contrast, these authors observed that retinol concentration was similar
between milk fat and whey fat...."

I guess that would put betacellulin in every dairy product except possibly
nonfat milk?

William wrote: 
> It seems curious that betacellulin is tested in the less common components

of dairy.
Hmmm.

Betacellulin has been found in tests to be in milk (the most common dairy
food), colostrum, and cheese whey. It has been mentioned as being in the fat
globules of whey and it has been advertised as being in whey protein powders
(as a selling point!). It has also been found in the serum (blood) of
bovines and humans.

Here again is one of the studies that found it in milk and other dairy
products:

Measurement of betacellulin levels in bovine serum, colostrum and milk 
SE Bastian, AJ Dunbar, IK Priebe, PC Owens, and C Goddard 
Journal of Endocrinology, Vol 168, Issue 1, 203-212
http://joe.endocrinology-journals.org/cgi/content/abstract/168/1/203

The presence of betacellulin in bovine colostrum and milk suggests that it
plays a role in the growth and development of the neonate and/or mammary
gland function. ... The high levels of betacellulin detected in FBS relative
to newborn and adult serum suggests a possible endocrine role for this
growth factor in the bovine foetus.