Date: Fri Oct 29 08:47:51 1999
Posted By: Charlene Wolf-Hall, Faculty, Food Science
Area of science: Microbiology
When we talk about any type of microbial growth in foods there are several
factors involved. The main ones are the nutrient content of the food needs
to be enough to support growth - this is usually high in any food, the pH
or acidity of the food, the temperature of the food needs to be within the
gorwth range of the particular microorganism of interest, enough time at
the proper temperature to allow growth to commence, the correct amount of
oxygen for the particular microorganism, and enough water content.
For the foods you chose:
Molds grow much slower than bacteria if the conditions are very good as in
the turkey meat. Molds are, however, much more resistant to things like
low pH and low moisture, so they can grow without much competition from the
faster growing bacteria.
- Cheese - nutrient rich, acidic pH, inner portions don't have much
oxygen - but outer portions do, and moisture level depends on the type of
cheese. Soft cheeses, like cream cheese, have a much higher water content than
hard cheeses, such as Cheddar. May contain preservatives to prevent mold
- Apples - plenty of nutrients for molds, acidic pH, fairly high
oxygen content, and high moisture content.
- Bread - plenty of nutrients for molds, slightly acidic pH, high in
oxygen, fairly high in moisture. May contain preservatives to prevent mold
- Cake - plenty of nutritents, fairly neutral pH, high in oxygen, high
in moisture content - but water may be bound to solutes such as sugar and not
available for microbial growth as readily. May contain preservatives.
- Brocolli - similar to apple, but less acidic pH
- Turkey - excellent growth medium for almost any microorganism. The
bacteria naturally on the turkey will usually out compete molds and take
To get back to your question about temperature. Most molds will grow quite
well if all conditions are right - at about room temperature. Depending on
the species of mold involved, some can grow very well at refrigeration
temperatueres. Not many foodborne-molds grow at freezer temperature
though. Certain species of molds have heat resistant spores
that can survive some cooking processes and then germinate and grow when
the food is cooled. These species can be a problem in processed fruit products.
As for the food group, all the food groups contain many nutrients that
would support the growth of molds. The best ways to prevent mold growth
are to keep cold foods cold and hot foods hot, not to keep foods for too
long - especially at temperatures that would allow growth, possibly use
preservatives, and use proper sanitation methods when preparing foods.
I hope that answers your question.
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