CHAPTER
25
Applied and Industrial
Microbiology
Chapter Outline
Food Microbiology (pp. 778–785)
The Roles of Microorganisms in Food Production
The Causes and Prevention of Food Spoilage
Foodborne Illnesses
Industrial Microbiology (pp. 785–795)
Chapter Summary
Applied microbiology is the commercial use of microorganisms. There are two types: food mi-
crobiology and industrial microbiology.
Food Microbiology (pp. 778–785)
Food microbiology encompasses the use of microorganisms in food production and prevention
of food spoilage and food-related illnesses. Many of our favorite foods and beverages are pro-
duced by microbes.
The Roles of Microorganisms in Food Production
A classic example of microorganisms in food production is leavened bread, which utilizes the
aerobic metabolism of the yeast Saccharomyces cerevisiae, which produces CO2 bubbles, caus-
ing the dough to rise. Sourdough breads use starter cultures made of yeast and lactic acid bacte-
ria to give it a characteristic flavor. Biochemical fermentation refers to the partial oxidation of
sugars using organic molecules as electron acceptors. In contrast, spoilage is unwanted changes
Chapter 25 Applied and Industrial Microbiology
times in combination with smoking or drying, to preserve meats and fish. Many dairy prod-
ucts—including buttermilk, yogurt, and cheese—utilize starter cultures of lactic acid bacteria
real grains, and vodka is often made from potatoes. Beer and sake (rice beer) are made from bar-
ley and hops, and utilizes either bottom-fermenting yeast S. carlsbergensis to produce lagers or
top-fermenting yeast S. cerevisiae to produce ales. Sake is made similarly to beer but uses rice
starch converted to sugar by Aspergillus oryzae as a base. Vinegar is produced when the ethanol
from fermentation is further oxidized to acetic acid by the action of acetic acid bacteria.
The Causes and Prevention of Food Spoilage
Food spoilage may occur because of intrinsic factors or extrinsic factors.
Intrinsic factors include the nutritional content, water activity, pH, physical structure, and mi-
crobial competition. Some foods contain natural antimicrobial agents, while others, such as for-
tified foods, may facilitate the growth of microorganisms by providing more nutrients. Water
activity refers to the water content of foods available to microbes. Moist foods are more suscep-
tible to spoilage than dry foods. Addition of salt or sugar can reduce water activity, while a low
pH supports little microbial growth. Physical structure like rinds or skins protect some fruits and
vegetables; damaging these coverings or grinding foods allows access to the moist interior and
provides more surfaces for microbes to grow. Ground meat spoils faster because it has more sur-
face area and more oxygen, and microbes may be mixed in during the grinding process. Micro–
bial competition in fermented foods also retards spoilage.
Extrinsic factors include how food is processed, handled, and stored.
Foods may be perishable, semiperishable, or nonperishable.
A variety of methods are used to prevent spoilage. Industrial canning is a major food packag-
rials and sealing foods inside to preserve freshness.
Preservatives can also be used to prevent spoilage. Salt and sugar in high concentrations can
kill microbes present during food processing and retard further microbial growth. Other natural
preservatives include garlic, cranberries, cloves, cinnamon, oregano, and thyme, which contain
compounds that inhibit microbial metabolism. Wood smoke introduces growth inhibitors that
help preserve some foods. Other chemicals are purposely added to foods as preservatives, in-
cluding organic acids and gases. These are typically germistatic—that is, they inhibit microbes’
Instructor’s Manual for Microbiology with Diseases by Body System, 5e
Foodborne Illnesses
Consuming spoiled food can cause illness, but not all foodborne illnesses result from food spoil-
age. Foodborne illness (food poisoning) can be divided into two types: food infections are
Industrial Microbiology (pp. 785–795)
Diverse applications of microbes for producing useful materials or carrying out useful processes
make industrial microbiology an important field.
The Roles of Microbes in Industrial Fermentations
Industrial fermentations involve the large-scale growth of particular microbes for producing
beneficial compounds, such as amino acids or vitamins. The process is performed in huge, steri-
lizable vats, often using waste products from other industrial or food processes. In batch produc-
tion, organisms ferment their substrate until it is exhausted, and then the end product is
Industrial Products of Microorganisms
Microbes produce an incredible array of useful products, and recombinant organisms add to this
diversity.
Enzymes are one of the most important industrial products produced by microorganisms.
Most are naturally occurring substances for which people have devised a particular use. They
include amylase, produced by Aspergillus oryzae, used as a spot remover; pectinase, obtained
from Clostridium spp., which releases fibers from flax to produce linen; proteases, used as meat
tenderizers, spot removers, and in cheese production; as well as streptokinases and hyaluroni-
dase used to dissolve blood clots and enhance the absorption of injected fluids, respectively. En-
Chapter 25 Applied and Industrial Microbiology
Microbes also produce dyes, cellulose fibers, and biodegradable plastics. Some microorgan-
isms can convert organic materials into biofuels. This process can create ethanol, methane, and
hydrogen, which can be used as alternative fuels for heating, cooking, or powering vehicles.
Water Treatment
Water may become polluted physically, chemically, or biologically. In polluted waters, the pol-
lutant is obvious; in contaminated waters, pollutants may not be visible. The presence of biolog-
ical contaminants can result in waterborne illness, usually diarrheal disease. Consuming
contaminated water can cause bacterial, viral, or protozoal diseases or intoxication from micro-
bial toxins. Outbreaks are often due to point-source infections. In marine environments, red
tides (eutrophic blooms of dinoflagellates) produce toxins that can contaminate shellfish.
Potable water is water that is safe to drink but may not be devoid of all microorganisms and
chemicals. Water that is not potable is polluted. Permissible levels of microbes and chemicals
vary from state to state. Drinking water should have a coliform count of 0 (zero) per 100 ml of
water. Water treatment occurs in four stages: sedimentation, during which particles are allowed
are detected using DNA “fingerprinting” techniques.
Wastewater or sewage treatment removes or reduces contaminants in wastewater—the water
that leaves homes or businesses after being used for washing or flushing toilets. Effective
wastewater treatment reduces the biochemical oxygen demand (BOD) to levels too low to
support microbial growth, thus reducing the likelihood that pathogens will survive. Municipal
sewage systems collect wastewater in larger towns and cities and deliver it to treatment plants
for processing, which occurs in four stages:
Instructor’s Manual for Microbiology with Diseases by Body System, 5e