A variety of microorganisms can use food as a growth medium. End products they produce can be desirable (fermented foods), undesirable (spoilage), or harmful (foodborne illness).
■ Name three foods that rely on microbial metabolism for their production.
■ Differentiate between fermentation and spoilage.
■ Which end products of fermentation might inhibit other microorganisms?
Figure 32.1 Fermented Foods Fermented foods have been intentionally altered in their production by carefully controlling the growth and activity of microorganisms.
Biochemical changes in foods, when perceived as undesirable, are called spoilage (figure 32.2). The processes that cause spoilage are often the same ones involved in fermentation of foods. In fact, a food product considered by one cultural population to be fermented may be considered spoiled by another. Sour milk and moldy bread are examples of foods considered spoiled as a result of microbial growth. The souring of milk, however, involves micro-bial processes analogous to those that cause the agreeable acidic flavor of sour cream, and the mold growing on bread may be related to the one that causes the blue veining in Gorgonzola cheese.
Growth of pathogens such as Clostridium botulinum, Staphylococcus aureus, Salmonella species, and E. coli O157:H7 can result in foodborne illness but generally does not result in perceptible changes in quality of a food. Depending on the type of pathogen, the illness may result from consuming either the living organisms or the toxins they have produced during growth.
Limiting microbial growth can preserve the quality of foods and prevent foodborne illnesses. Foods can be canned, pasteur-
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