Pig International - November 2017 - 22

22 ❙ PigInternational
CHEMISTRY OF ORGANIC ACIDS
Second, organic acids in their intact (un-dissociated) form are believed
to penetrate the bacterial outer membrane entering its cytoplasm where
they dissociate under a neutral pH.
This drops internal pH, and bacteria
eventually die while trying to overcome the problem. Only weak acids
remain intact in the stomach, entering
into the small intestine where they can
attack bacteria. Such action also occurs in the stomach, but it is of limited
significance because feed does not
stay long in there. In contrast, in the
small intestine, bacterial populations
are substantial, and this is where a
general reduction in good and bad
bacteria usually ends up improving
feed conversion efficiency. However,
the action of organic acids can be curtailed by the overpowering ability of
the organism to maintain neutral pH
in the intestines, causing organic acids
to dissociate sooner or later. Only covered or otherwise protected organic
acids can reach the large intestine.

What is the importance of
pKa in the stomach?
We usually pick organic acids
to act in the small intestine, ignoring the importance of having a low
pH barrier in the stomach, but this
requires some explanation. In the
stomach of animals, there is water
and hydrochloric acid, with the
resulting pH being about 2, which

The pKa values of
several common
acids used in
animal feeds
Acid

pKa

Propionic

4.88

Butyric

4.82

Sorbic

4.76

Acetic

4.75

Benzoic

4.20

Lactic

3.83

Formic

3.75

Citric

3.13

Fumaric

3.02

Phosphoric

2.16

Hydrochloric

-6.30

It is evident that hydrochloric
acid is a most potent acid as
it dissociates completely and
instantly in water solutions.
is very acidic - as needed to bar
entrance to most pathogens. In
young animals, with a still developing digestive system, pH is often
closer to 4, especially in animals
that have been just weaned from an
all-milk 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
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 reducing 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
solution: 3.13, 4.76, 6.40. It is evident
that the first dissociation of protons
will occur in the stomach of young
animals, whereas the other two will
have to wait until they reach the small

Read more: 6 questions concerning organic acids, www.WATTAgNet.com/
articles/17510

www.WATTAgNet.com ❙ November/December 2017


http://www.WATTAgNet.com/articles/17510 http://www.WATTAgNet.com/articles/17510 http://www.WATTAgNet.com

Table of Contents for the Digital Edition of Pig International - November 2017

Pig International - November 2017
Contents
Pigs and Money
Industry Happenings
What you should know about gastric ulcers in pigs
Business, science behind phytogenics in pig feeds
Mastitis in sows: A perennial problem
Understanding chemistry of organic acids in antibiotic-free diets
How piglet gastric pH development affects gut health
Debunking trace mineral myths in animal nutrition
Animal feed formulation: Fiber matrix secrets revealed
World’s top 40 pork processors
World’s top 40 pork producers
5 programs pig producers don’t want to miss at IPPE 2018
Products
Marketplace
Advertisers’ Index
Pig International - November 2017 - BB1
Pig International - November 2017 - BB2
Pig International - November 2017 - Pig International - November 2017
Pig International - November 2017 - Cover2
Pig International - November 2017 - Contents
Pig International - November 2017 - Pigs and Money
Pig International - November 2017 - Industry Happenings
Pig International - November 2017 - What you should know about gastric ulcers in pigs
Pig International - November 2017 - 5
Pig International - November 2017 - 6
Pig International - November 2017 - 7
Pig International - November 2017 - Business, science behind phytogenics in pig feeds
Pig International - November 2017 - 9
Pig International - November 2017 - 10
Pig International - November 2017 - 11
Pig International - November 2017 - 12
Pig International - November 2017 - 13
Pig International - November 2017 - Mastitis in sows: A perennial problem
Pig International - November 2017 - 15
Pig International - November 2017 - 16
Pig International - November 2017 - 17
Pig International - November 2017 - 18
Pig International - November 2017 - 19
Pig International - November 2017 - Understanding chemistry of organic acids in antibiotic-free diets
Pig International - November 2017 - 21
Pig International - November 2017 - 22
Pig International - November 2017 - 23
Pig International - November 2017 - How piglet gastric pH development affects gut health
Pig International - November 2017 - 25
Pig International - November 2017 - 26
Pig International - November 2017 - 27
Pig International - November 2017 - Debunking trace mineral myths in animal nutrition
Pig International - November 2017 - 29
Pig International - November 2017 - 30
Pig International - November 2017 - 31
Pig International - November 2017 - Animal feed formulation: Fiber matrix secrets revealed
Pig International - November 2017 - 33
Pig International - November 2017 - 34
Pig International - November 2017 - 35
Pig International - November 2017 - World’s top 40 pork processors
Pig International - November 2017 - World’s top 40 pork producers
Pig International - November 2017 - 5 programs pig producers don’t want to miss at IPPE 2018
Pig International - November 2017 - Products
Pig International - November 2017 - Advertisers’ Index
Pig International - November 2017 - Cover3
Pig International - November 2017 - Cover4
http://www.piginternational-digital.com/201711
http://www.piginternational-digital.com/201710
http://www.piginternational-digital.com/201709
http://www.piginternational-digital.com/201707
http://www.piginternational-digital.com/201705
http://www.piginternational-digital.com/201703
http://www.piginternational-digital.com/201701
http://www.piginternational-digital.com/201611
http://www.piginternational-digital.com/201610
http://www.nxtbook.com/nxtbooks/watt/pigi_201609
http://www.piginternational-digital.com/201607
http://www.piginternational-digital.com/201605
http://www.piginternational-digital.com/201603
http://www.piginternational-digital.com/201601
http://www.piginternational-digital.com/201511
http://www.piginternational-digital.com/201510
http://www.nxtbook.com/nxtbooks/watt/pigi_201509
http://www.piginternational-digital.com/201507
http://www.piginternational-digital.com/201505
http://www.piginternational-digital.com/201503
http://www.piginternational-digital.com/201501
http://www.piginternational-digital.com/201411
http://www.piginternational-digital.com/201410
http://www.piginternational-digital.com/201409
http://www.piginternational-digital.com/201407
http://www.piginternational-digital.com/201405
http://www.piginternational-digital.com/201403
http://www.piginternational-digital.com/201401
http://www.nxtbook.com/nxtbooks/watt/pigi_201311
http://www.piginternational-digital.com/201310
http://www.piginternational-digital.com/201309
http://www.piginternational-digital.com/201307
http://www.piginternational-digital.com/201305
http://www.piginternational-digital.com/201303
http://www.piginternational-digital.com/201301
http://www.piginternational-digital.com/201211
http://www.piginternational-digital.com/201210
http://www.piginternational-digital.com/201209
http://www.piginternational-digital.com/201207
http://www.piginternational-digital.com/201205
http://www.piginternational-digital.com/201203
http://www.piginternational-digital.com/201201
http://www.nxtbookMEDIA.com