NFS 220 Lecture Notes - Lecture 4: Foodborne Illness, Aerobic Organism
11 Jun 2018
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Factors that Affect Bacterial Growth
Food
Like any living organism, bacteria require food to survive. While some bacteria only need
simple nutrients, others require a more complex diet, including protein. Moist foods that
are rich in protein such as meat, milk, eggs and fish, are good food sources to support the
growth of pathogenic bacteria.
Acid
Bacteria do not grow in an acidic environment, so acidic foods such as lemons and lemon
juice vinegar, and some berries and fruits do not support the growth of bacteria. However,
when low acid foods such as vegetables, eggs, meats and soft cheese are prepared, special
care needs to be taken to ensure that bacteria cannot grow. Acidity in foods and other
substances is measured on a pH scale of 0 to 14, with neutral acidity being 7. The more
acidic the food, the lower its number on the pH scale.
Temperature
The temperature range from 4 and 60 degrees Celsius (40 to 140 Fahrenheit) is referred to
as the danger zone, when harmful bacteria can multiply rapidly. Temperatures below or
above will slow or stop bacteria growth. Temperature control is one of the best ways to
reduce the risk of foodborne illness caused by bacteria.
Time
Bacteria grow by multiplying. When a small number of pathogens are present in food, the
risk is usually low. However, when higher risk foods are left in the danger zone those
pathogens multiply rapidly. Restricting the amount of time that foods are left in the danger
zone will help to reduce the risk.
Oxygen
Aerobic bacteria require oxygen to grow. Anaerobic bacteria grow only when no oxygen is
present. Most bacteria that can cause food borne illness are aerobic, however some very
dangerous bacteria thrive only in anaerobic, oxygen-free environments.
When foods are improperly processed and then stores at room temperature in air tight
conditions such as cans, bottles, vacuum packaging or immersed in oil, anaerobic spores
may survive and grow.
Vacuum packaging can help to extend the shelf life and quality of food by removing oxygen,
but it is important to remember that some bacteria do not require oxygen for growth.
Therefore, vacuum packaging does not eliminate the need for food to be kept at proper
storage temperatures. Most vacuum packed food must be kept out of the danger zone. This
is particularly critical for foods such as luncheon meats and smoked fish that are often
served without additional cooking.
Moisture
Bacteria need moisture to survive. Bacteria, yeast and moulds grow rapidly in food with a
high moisture content such as meat, produce and soft cheese. Dry, sweet or salty foods
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Document Summary
Like any living organism, bacteria require food to survive. While some bacteria only need simple nutrients, others require a more complex diet, including protein. Moist foods that are rich in protein such as meat, milk, eggs and fish, are good food sources to support the growth of pathogenic bacteria. Bacteria do not grow in an acidic environment, so acidic foods such as lemons and lemon juice vinegar, and some berries and fruits do not support the growth of bacteria. However, when low acid foods such as vegetables, eggs, meats and soft cheese are prepared, special care needs to be taken to ensure that bacteria cannot grow. Acidity in foods and other substances is measured on a ph scale of 0 to 14, with neutral acidity being 7. The more acidic the food, the lower its number on the ph scale.
