Hi Alan,

rennin is indeed a proteolytic enzyme that digests casein and
coagulates milk. The effect is a longer retaining in the stomach, and
enhanced digestion (since enzymes have more time to act). But even in
the absence of rennin, casein can still be digested by other
proteolytic enzymes (pepsin and trypsin). I am not saying that
digestion is 100% efficient, but that rennin is not absolutely
necessary. In the article I cited, it was said that 25% of the calcium
in milk is absorbed (figure obtained by radioisotope labeling), so
calcium in milk is indeed bioavailable (but milk might increase bone
loss for other reasons).

In the past, rennin (extracted from calves' stomachs) was used to make
cheese. Now, manufacturers use other enzymes that have the same effect
on casein. Thus, pre-digested forms of milk (like cheese) are more
digestible than milk itself.


--Jean-Louis Tu <[log in to unmask]>