Feed International - October/November 2017 - 26
26 ❙ FeedInternational
CHEMISTRY OF ORGANIC ACIDS
have been just weaned from an allmilk diet. It is important, then, to
understand how organic acids fare
in these two stomach pH values,
and this will lead us to select the
right acids for the right purpose.
For that, let us consider first
lactic acid (a weak organic acid)
with a pKa of 3.86. At stomach pH
2 (mature animals), the majority of
acetic acid will remain intact (undissociated and thus ineffective in
reducing stomach pH). In contrast,
at a stomach pH of 4 (young animals), the majority of lactic acid will
split to its components releasing
hydrogen protons, which drop pH,
and the conjugate base. Thus, in its
IT IS COMMON PRACTICE today
to use mixes of organic acids
that cover a broad pH spectrum
for different locations in the gut.
dissociated form, lactic acid at pH4
will be effective in reducing stomach pH, at least until pH is reduced
to below its pKa, but not suitable as
an antibacterial agent in the small
intestine since the majority of it will
be consumed in the stomach.
Next, let us consider acetic acid
(an even weaker organic acid) with
a pKa value of 4.75. It is evident
that this acid will remain largely
intact, and thus ineffective in reduc-
ing stomach pH, in both young and
mature animals as its pKa is higher
than any of the expected stomach
pH values. This is not important, of
course, for mature animals, but it
demonstrates that in young animals
acetic acid is a rather poor choice to
reduce stomach pH.
Finally, there is the case of organic
acids with more than one pKa value,
such as citric acid with three pKa
values as it has three protons to give in
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www.WATTAgNet.com ❙ October/November 2017