FNH 200 Lecture Notes - Lecture 5: Food Preservation, Food Browning, Foodborne Illness
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In this lesson you will learn about the chemical, enzymatic and microbiological factors
that are responsible for food deterioration and spoilage. We will discuss the important
environmental factors in food that affect the growth of disease-causing and spoilage-
causing microorganisms in food. You will also learn about various types of chemical
spoilage, such as enzymatic browning of fruit and vegetable tissues. Finally, as an
introduction to food preservation, you will learn the principles upon which food
preservation techniques are based. Upon completing this lesson you will have the
fundamental knowledge required to fully appreciate the concepts of food preservation
to be covered in Lessons 6 through 10.
After completing this lesson, you will be able to describe:
the factors (chemical, enzymatic, microbiological) that commonly contribute to
food deterioration and spoilage;
possible mechanisms for inhibiting those factors that promote deterioration of
quality in food systems
FOOD DETERIORATION: THE NEED FOR FOOD PRESERVATION
About 10-20 % of all agricultural commodities are lost each year (pre-harvest
deterioration) due to: weeds, insects, microorganisms, rodents and birds.
All foods (agricultural & aquatic products) undergo varying degrees of
deterioration after harvest (post-harvest) and during storage.
Losses occur in the nutritional value, safety, and aesthetic appeal (colour, texture,
Food is subject to physical, chemical and biological deterioration.
Biological deterioration involves:
heat, cold, light, oxygen, moisture, dryness, food enzymes, microorganisms and
macroorganisms (see figure below).
The objective of food preservation technologies is to delay the onset of spoilage and to
enable the creation of new food products from the resource commodities.The different
factors that can lead to deterioration of food indicated in Figure 5.1 are described in
more detail below.
Fig. 5.1 Food deterioration
Microorganisms are ubiquitous. Almost all food materials that arrive at food
processing plants, retail stores, food service receiving docks, and even your
kitchen, are contaminated with a variety of microorganisms.
Microorganisms cause a great deal of food spoilage throughout the world. This
has major economic consequences and as well as loss of potential sources of
nutrients, since the spoiled food typically is discarded.
Take a moment to brace yourself before you consider the types
of microbial spoilage that have transpired in your kitchen or
Perhaps bread or cheese has become spoiled by moulds.
Yogurt or fruit may have spoiled because of yeast or mould
growth. Meat, fresh or processed, may have become spoiled by
bacteria growing in the surface or within the product.
Microorganisms can be classified into 3 general categories as shown in Figure 5.2.
Fig. 5.2 The good, the bad, and the ugly microorganisms
From Fig 5.2., we note that microorganisms can be put to good use for the production
of fermented foods, but that they can also be the causes of spoilage and food borne
diseases. Bacteria, yeasts and moulds may contribute to fermented foods, as well as
food spoilage and food borne disease. Viruses can be agents of food borne disease
but do not cause food spoilage, nor are they used to produce fermented foods.
In this lesson, we will focus primarily on obtaining a general understanding of the role of
microorganisms in the deterioration or spoilage of food. The importance of
microorganisms in fermented foods and food borne diseases will be discussed in more
depth in lessons 9 and 12, respectively.
Some important characteristics of microorganisms in foods causing food spoilage are
Bacteria are the microorganisms that
grow the fastest in food.
They reproduce by cell division,
whereby one cell divides into two, and