Found it:
Me:
>Thanks. I guess I'm wondering more about the specifics of nitrites.
>Do they act directly on the bacteria and spores? Do they affect the
>meat which then prevents C bot growth? Do they kill vegetative C bot.
>and spores or just kill veg-state? Or are they only preventives/inhibitors?
Bob LaBudde:
1. Nitrate does not work by itself. First it must be converted to
nitrite via microbial action, e.g., by micrococci.
2. Nitrite functions to tie up iron in the muscle tissue and
sarcoplasma by forming a stable complex under heat. When nitrite
complexed to myoglobin is heated to, e.g., 160 F, the bond formed is
reasonably stable. This is why ham is pink and so are hot dogs and
bologna. It is also responsible for the special flavor. Other
compounds that form more or less stable compounds with meat iron are
carbon monoxide, sulfite and cyanide. Oxygen forms only a weak
complex, as hemoglobin and myoglobin were designed to exchange it.
3. In an anaerobic environment, bacteria need transition metals as
catalysts to perform their metabolism, which is more difficult in the
absence of oxygen. Consequently the nutrient iron is a key one for
determining metabolic rate.
4. Clostridia are either microaerophilic (e.g., perfringens) or
strictly anaerobic (e.g., botulinum). They are highly dependent upon
a source of iron to attain fast growth rates. Many other genera are
also limited by iron availability.
5. Clostridia must break down the bonds between nitrite and iron in
order to get at the meat iron source. This defines a period of
limited metabolic rate described by microbiologists as the "lag
phase" of growth. Once the iron has been released, Clostridia goes
into the maximum metabolic rate, or "exponential phase", of growth.
6. The more iron present, the shorter the lag phase for Clostridia.
This is why beef is at higher risk with respect to Clostridia than,
say, chicken breast.
7. If you apply nitrite without heating to above 150 F, the effect is
very minor, similar to salt in affecting Aw, but the quantity is so
low as to not matter much. The effect on ORP would also be minor at
the levels used.
8. I suspect sodium cyanide would be much better than sodium nitrite
as a Clostridium-static compound, because of its stronger bond to iron.
9. In a similar manner, nitrite will reduce the nutrient availability
of iron to humans. One of the reasons cured meats are implicated in
colon cancer may be that the nitrite preserves the iron against
microbial action until the colon, where Clostridia can then release
it over time and foster their subsequent growth.
These ideas about nitrite are mostly my own, and are not well known
or understood by food microbiologists who have researched Clostridia.
So you may find them somewhat at odds with conjectures made in papers
you might come across.
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