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Pathogens thrive when three basic
living conditions are readily available. They are protein, water and
appropriate pH. A large percentage of foods typically contain these three
elements in ratios favorable to the rapid growth of pathogens. The greater
the abundance of protein and water and the more favorable the pH, the
higher the likelihood that foods will become contaminated.
In addition, some bacteria do best
with a good supply of oxygen, others when oxygen is absent, Some can get
along either way. The handling procedures on cooling, reheating and
thawing help to prevent any single condition from becoming so predominant
that it will favor the pathogen's growth and reproduction.
Protein
Most foods contain some protein.
Meats, fish, poultry and eggs are among the foods with the greatest
percentage of protein, making them and prepared foods containing them,
highly susceptible to food poisoning and intoxication. But, grains and
legumes also contain protein in significant quantities. They become
especially vulnerable once cooked. Rice and potatoes are among the most
likely carriers of disease. Vegetables contain very small amounts of
protein, and fruit contain very little if any protein at all.
Water
Foods that are moist enough to be soft
and easy to chew are also moist enough to support the growth of many types
of pathogens. There are some foods that are naturally 'dry' and have a
lesser chance of becoming infected; example certain root vegetables have a
relatively low moisture content. Other foods, once processed, lose much of
their moisture; very hard cheeses such as Romano or Parmesan cheeses;
dried, salted, or preserved foods such as olives and hams; nuts and seeds,
and uncooked grains, cereals, and meals. These are the foods that we treat
as "non-perishables", a recognition of the fact that they can be stored at
room temperature without fear of immediate loss of quality or
wholesomeness.
Moderate pH
The pH of most foods falls within a
range considered "moderate'; a state that makes foods attractive for the
growth and reproduction of many different types of micro-organisms. A
substance that is extremely acid (example lemon juice) will be closer to a
value of zero. Those that are extremely alkaline (example baking soda)
will measure closer to 14. Most foods tend to fall within range of about 4
to 10. Foods that are either more acidic or more alkaline than that will
generally no longer be susceptible to micro-organisms. Vinegar, lemon or
lime juice, and other very tart and sour-tasting foods are acid; baking
soda, alum, cream of tartar are bitter tasting and cause the mouth to
pucker, these items are alkaline. We use this general principle to
preserve foods when we pickle, salt, or brine them in order to change
their pH level to above 10 or below 4, increasing the shelf life of the
food.
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