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Microbes in Food Science
MICROBES are microorganisms that are ever pres-
ent in the world around us. Whenever a plant
or animal dies, microbes begin to break down the
once-living organism into usable energy for
themselves. In the process, the organism
decays and degrades. This is what happens in
food spoilage. However, some microbes are
beneficial in food science.
Objective:
� Describe the different microbes that affect
food quality and spoilage.
Key Terms:
� aerobic
anaerobic
asexual reproduction
binary fission
budding
food microbiology
heterotrophic
mesophiles
molds
psychrophiles
thermophiles
E-unit: Microbes in Food Science � Page 1 � AgEdLibrary.com
Copyright © 2006 by CAERT, Inc. — Reproduction by subscription only. 070078
Microbes That Affect Food
Food producers and consumers are constantly fighting the battle of food spoilage. The race
from producer to consumer, which was a sprint decades ago, has now become more of a mara-
thon. Microbes are still present to begin the spoiling process, but because of the use of new
technology and age-old tech-
niques, food is safer and stays
fresh longer for consumers to
enjoy. There are three main
microbes that are the focus of
food microbiology, the study
of microorganisms and their
effect on the food industry.
Molds, yeast, and bacteria are the
main causes of most food spoil-
age, yet some of these microbes
actually benefit food production
and are used to create some of our
favorite foods.
MOLDS
If you have ever left a loaf of
bread on the counter for too long,
you may have noticed a fuzzy
growth beginning to spread across
the surface of the bread. Molds
are part of the fungus family and
feed on decaying organisms for
energy. Fungi are adaptable
enough to live nearly anywhere,
provided they have air and mois-
ture. Inside the bread bag, on a
warm countertop, surrounded by
moist bread, is a perfect place for
mold to begin growing.
Molds, like other fungi, reproduce asexually. Asexual reproduction is the forming of
offspring by simple cell division (mitosis) rather than by the union of sperm and egg. Male and
female organisms are not needed for asexual reproduction because the offspring grows and
splits directly from the parent. Molds have the ability to produce spores, which are released
into the air and carried to new locations. Mold spores fill our air supply but will only grow into
mold colonies when the spores land where conditions are favorable. When we open a bag of
E-unit: Microbes in Food Science � Page 2 � AgEdLibrary.com
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FIGURE 1. Microbes are an ever-present threat to the food industry.
(Courtesy, Agricultural Research Service, USDA)
FIGURE 2. Molds will grow wherever conditions are favorable. (Courtesy,
Agricultural Research Service, USDA)
bread, the air that enters the bag will carry enough mold spores to cause the fungus to spread if
given enough time.
Molds grow by the formation of filaments that extend above or below the food surface, giv-
ing the colonies a fuzzy appearance. In the process of consuming the food source for energy,
molds can produce byproducts known as mycotoxins. Mycotoxins, such as aflatoxin in corn,
can be deadly to humans or animals that consume the contaminated food.
Some forms of molds can actually be beneficial to food producers. Many types of cheese
rely on the action of molds to provide the colors and flavors that consumers want. Medicines,
such as penicillin and other antibiotics, are also produced through the action of molds.
Molds are unique in the way they are able to thrive in extremely high temperatures as well
as very low temperatures. Molds can be grouped into three categories based on their ability to
withstand temperature extremes. Mesophiles are those molds that grow best at room tem-
perature (between 50° and 110°F, 10° and 43.3°C). These molds are the type most commonly
found invading food products that are not refrigerated and usually left on countertops or
stored in pantries. Psychrophiles are a group of molds that grow best at temperatures of less
than 50°F (10°C). These molds can be present in a refrigerator and can be noticed on older
foods and sometimes around the door seal, which is seldom cleaned regularly. The final group,
thermophiles, consists of molds that thrive at high temperatures, between 110° and 140°F
(43.3° and 60°C). These molds are less common in our homes and kitchens because of the lack
of a constant high temperature. They could develop inside a sealed, clear container (think of
the bread bag) that is being exposed to sunlight on a countertop. The container could act as
sort of a “mini-greenhouse,” trapping heat and raising the temperature inside.
Although molds may need different temperature ranges in which to thrive, one thing all
molds need to survive is oxygen. Molds require an environment that is aerobic, or has oxy-
gen present. One of the best ways
to control mold growth is to
remove the source of oxygen,
producing an anaerobic envi-
ronment. Food packagers are con-
stantly researching ways to
remove oxygen from inside food
packages and keep it out for the
duration of the food storage. Even
our tightest-sealing containers at
home still allow oxygen to enter
when they are opened and then
sealed again. Only vacuum-sealed
food is able to withstand long
periods without the threat of
mold growth.
E-unit: Microbes in Food Science � Page 3 � AgEdLibrary.com
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FIGURE 3. Sealed jars of vegetables have no oxygen present inside the
containers, thus halting the growth of any molds without the need for
refrigeration.
YEAST
Another microbe that is both friend and foe to the food industry is yeast. Yeasts are unicel-
lular (single-celled) organisms that are actually part of the fungi family. Yeasts survive by con-
verting sugars and starches to usable energy. Reproduction for yeasts comes in the form of
budding. Budding is a process of asexual reproduction in which a small knob forms on the
parent organism. This “bud” will grow and eventually split away from the parent, creating a
new organism identical to the parent.
If asked for the main contribution of yeast, most of us would think of bread making. In that
process, yeast converts the sugars and starches present in the bread dough into carbon dioxide
and water. The carbon dioxide released is trapped in small bubbles in the sticky dough. This
causes the mixture to “rise,” Without yeast in our bread, we would have very flat, hard loaves
after baking.
Yeasts are also commonly used in processes that require fermentation. Yeasts are added to a
variety of food products, including wines, beers, and soy sauce to begin the fermentation pro-
cess. As the sugars in grapes (in
the case of wine) are consumed,
alcohol is produced as a byprod-
uct. The longer the mixture is
allowed to ferment, the stronger
the alcohol content of the final
liquid will be.
Not all contributions of yeasts
are beneficial, though. Yeasts are
also responsible for food spoilage
and sickness in some cases. Yeasts
can survive in either aerobic or
anaerobic environments, in high
or low pH conditions, and at a
variety of temperatures. These
qualities make yeasts tough com-
petitors when it comes to the
fight against food spoilage.
BACTERIA
If molds and yeasts were soldiers for food spoilage, bacteria would be commandos. Bacteria
are the most difficult of all microbes to control when it comes to food spoilage because of their
ability to adapt to nearly any condition on Earth. Bacteria can and will be found everywhere on
the planet. These microorganisms can live with or without oxygen, survive at any temperature
extreme, and use anything as a food source. Bacteria have even been found on hot-water vents
deep in the ocean where no other organisms can survive.
E-unit: Microbes in Food Science � Page 4 � AgEdLibrary.com
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FIGURE 4. Yeasts are both friends and foes when it comes to food
preservation. (Courtesy, Agricultural Research Service, USDA)
Bacteria come in a variety of shapes, but they
are all single-celled organisms. Some bacteria
may be able to create their own food source,
much like plants. However, the bacteria com-
monly responsible for food spoilage are
heterotrophic; that is, they require the intake
of food and nutrients to survive.
Bacteria reproduce by a process of binary
fission, in which the DNA in the bacterial cell
is replicated and the cell splits into two identical
cells. Under the correct conditions, some bacte-
ria are able to reproduce every 20 minutes. With
that schedule, a single bacterial cell could pro-
duce 17 million offspring in only eight hours!
Think of that the next time you reach for left-
overs that have been sitting out all afternoon at a
family picnic.
Because of their high reproductive rates, abil-
ity to adapt, and variety of food sources, bacteria
are the most difficult (and most dangerous) of all
microbes associated with food spoilage. Proper
cooking and refrigeration can slow the growth of
bacteria but not stop them completely.
Summary:
� Microbes are ever present in our environment. Molds, yeast, and bacteria are themain causes of most food spoilage, yet some of these microbes actually benefit foodproduction and are used to create some of our favorite foods. Scientists, food pro-cessors, and food packagers are all working to use the best possible methods forcontrolling and inhibiting undesirable microbial growth in our food.
Checking Your Knowledge:
� 1. List and briefly define the three common microbes that cause food spoilage.
2. What is the process of budding in yeast cells?
3. List the three types of molds and give the optimal temperature for each group.
E-unit: Microbes in Food Science � Page 5 � AgEdLibrary.com
Copyright © 2006 by CAERT, Inc. — Reproduction by subscription only. 070078
FIGURE 5. Bacteria can be found anywhere and
everywhere on Earth. (Courtesy, Agricultural Research
Service, USDA)
Expanding Your Knowledge:
� Expose a variety of food items to different environmental conditions and observethe growth of mold or the deterioration of the products. Conclude which environ-mental conditions favor the growth of microbes.
Web Links:
� National Restaurant Association—Reducing Food Spoilage
http://www.restaurant.org/foodsafety/how_to_spoilage.cfm
FoodService.com—Food Spoilage
http://www.foodservice.com/food_safety/fb6.cfm
Agricultural Career Profiles
http://www.mycaert.com/career-profiles
E-unit: Microbes in Food Science � Page 6 � AgEdLibrary.com
Copyright © 2006 by CAERT, Inc. — Reproduction by subscription only. 070078