Microbes in Food Science - Elmwood...

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



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.



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.



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.



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



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