MIB151S: Food Microbiology (Microbiology 1)
Cape Peninsula University of Technology
Lecture 13 Notes
Microbiology 1
13.1 Microorganism growth in food
13.2 Microbial growth and food spoilage
13.3 Controlling food spoilage
13.4 Food-borne diseases
13.5 Microbiology of fermented foods
13.6 Microorganisms as foods and food amendments
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Food Microbiology
Foods are not only of nutritional value to those that consume them, but often are
ideal culture media for microbial growth;
Microorganisms can be used to transform raw foods into chocolate, cheeses,
pickles, sausages and soy sauce;
In addition, wines, beers and other alcoholic beverages are produced through
microbial activity;
On the other hand, microorganisms can also degrade food quality and lead to
food spoilage;
Foods may also serve as vehicles for disease transmission;
The detection and control of pathogens and food spoilage microorganisms are
important in food microbiology;
It is important to realise that during the entire sequence of food handling, from
the producer to the final consumer, microorganisms can affect food quality and
human health.
13.1 Microorganism growth in food
Nutrient-rich foods are excellent environments for the growth of microorganisms;
Microbial growth is controlled by factors related to the food itself, i.e. intrinsic
factors, and to the environment where the food is stored, i.e. extrinsic factors;
a) Intrinsic factors: Intrinsic factors or food-related factors include pH, moisture
content, water activity or availability, oxidation-reduction potential, physical
, MIB151S: Food Microbiology (Microbiology 1)
Cape Peninsula University of Technology
Lecture 13 Notes
structure of the food, available nutrients and the possible presence of natural
antimicrobial agents;
b) Extrinsic factors: Extrinsic or environmental factors include temperature,
relative humidity, gases (CO2, O2) present, and the types and numbers of
microorganisms present in the food.
13.2 Microbial growth and food spoilage
Because foods are excellent source of nutrients, and if the intrinsic and extrinsic
conditions are ideal, microorganisms grow rapidly and may convert an attractive
and appealing food into sour, foul-smelling or fungus-covered mass;
Microbial growth in and on foods can lead to visible changes, including a variety
of colours caused by spoilage microorganisms;
Meat and dairy products, with their high nutritional value and presence of easily
metabolised carbohydrates, fats and proteins, provide ideal environments for food
spoilage; Proteolysis and putrefaction are results of microbial spoilage of such
high protein foods;
In comparison to meat and dairy products, fruits and vegetables have a much
lower protein and fat content, and thus undergo a different kind of food spoilage;
Bacteria do not seem important in the initial spoilage of whole fruits, instead
spoilage often is initiated by moulds;
13.3 Controlling food spoilage
With the beginning of agriculture, the need to preserve surplus foods became
essential to survival;
The use of salt as meat preservative and the production of cheeses and curdled
milks was introduced in Near Eastern civilisation as early as 3000 B.C.; the
production of wines and preservation of fish and meat by smoking also became
common by then;
