Download science of food spoilage

SCIENCE OF
FOOD
SPOILAGE:
CAUSES,
CONSEQUENCES
AND
PREVENTION
SCIENCE OF FOOD SPOILAGE
Ewetoye Ibrahim
Sat, 5 Jan 2014
SCIENCE OF FOOD SPOILAGE: CAUSES, CONSEQUENCES AND
PREVENTION
Introduction:
Spoilage is the process in which food deteriorates to the point in which it is not edible to
humans or its quality of edibility becomes reduced. Various external forces are
responsible for the spoilage of food. Food that is capable of spoiling is referred to as
perishable food.
Food spoilage is due to a number of reasons -- air and oxygen, moisture, light, microbial
growth, and temperature. Each is briefly explained below.
Air and Oxygen
One important cause of food spoilage and spoilage is air and oxygen. Because air is
colourless, odorless, and tasteless, it is often taken for granted and sometimes forgotten as
a means to cause food to spoil.
Air consists of 78% nitrogen, 21% oxygen, and a 1% mixture of other gases. While
oxygen is essential for life, it can have deteriorative effects on fats, food colors, vitamins,
flavors, and other food constituents. Basically, oxygen can cause food spoilage in several
ways. It can provide conditions that will enhance the growth of microorganisms; it can
cause damage to foods with the help of enzymes; and it can cause oxidation.
Microorganisms: Oxygen can provide conditions that enhance the growth of
microorganisms. Some bacteria require oxygen for growth (aerobes) while others can
grow only in the absence of oxygen (anaerobes). Many bacteria can grow under either
condition and are called facultative anaerobes. Molds and most yeast that cause food to
spoil require oxygen to grow. They can often be found growing on the surface of foods
when air is present.
Enzymes: Certain enzymes that are naturally present in food are known as oxidizing
enzymes. These enzymes catalyze (speed up) chemical reactions between oxygen and
food components, and this leads to food spoilage. Although there are many oxidizing
enzymes, two that can cause darkening in diced and sliced vegetables are catalase and
peroxidase. The browning of vegetables caused by these enzymes is often accompanied
by off-flavors and odors. A simple heat treatment (blanching) is used to inactivate these
enzymes.
Oxygen: Oxygen can also cause spoilage of foods spontaneously, by itself. Oxidative
spoilage is the chief cause of quality loss in fats and fatty portions of foods. When lipids
oxidize, short chain carbon compounds are formed; these compounds have very strong
odors and flavors and are very undesirable and unacceptable. The off-odors resulting
from this type of spoilage are sharp and acrid and have been described as linseed oil-like,
tallowy, fishy or perfume-like.
Moisture
Water is one of the most common substances on earth. It is an essential component of all
foods. The amount of water in a food (known as percent water) influences the
appearance, texture, and flavor of the food. All living organisms as well as food contain
water. Water makes up about 70% or more of the weight of most fresh (unprocessed)
foods. Even "dry" foods like beans, flour and cereals contain some water. Fresh fruits and
vegetables contain the most water -- between 90% and 95% water. The amount of water
in some common foods is shown below.
Although the water content of a food is expressed as a percent, this number does not
reflect how the water exists in the food. Water in food is classified according to its
availability, or biological activity and is either "free" or "bound." Free water is not bound
to any components in a food; it can be used for microbial growth and is also available for
chemical reactions. Bound water is physically bound to large (molecules) components in
the food. It is not available to microorganisms for their growth and it cannot participate in
chemical reactions.
Water or moisture greatly affects the keeping qualities of food. Excessive moisture
pickup can result in product spoilage and spoilage by:
Microorganisms: microorganisms need water to dissolve the food they use. Water allows
the food to get into bacterial, yeast and mold cells where it is used for energy and growth.
Water also allows waste products to escape from the cells.
Chemical Reaction: the moisture in food also functions to allow chemical reactions to
occur between components in the product.
Food spoilage and spoilage can occur when there are slight changes in relative humidity.
Moisture can condense on the surface of a product and this can result in many common
food defects. The molding of grain, soggy cereals, and the caking and lumping of dry
products like powders and cake mixes can result from excessive moisture. Other defects
such as mottling, crystallization and stickiness have also been observed. Moisture
condensing on the surface of a food can also provide an environment for bacteria and
molds to grow and multiply. Physical defects such as cracking, splitting and crumbling
occur when excessive moisture is lost from foods.
Water is controlled in foods by:
Drying (dehydration), concentration and evaporation -- by removing water to a certain
level, deteriorative reactions can be reduced or prevented. Examples of products
preserved by these drying techniques include dry milk, potato flakes, drink mixes,
evaporated milk, and orange juice concentrate.
Freezing - the freezing of foods changes water from liquid to solid form and renders it
unavailable to microorganisms and chemical reactions.
Food Additives -- salt and sugar are used in many products to bind water and thereby
making it less available for microbial growth and biochemical reactions. Jams, jellies,
and cured hams are examples.
Light
Almost all foods are exposed to light from natural and/or artificial sources. The exposure
of foods to light can result in the photodegradation (or spoilage) of these products. This
photodegradation usually occurs in food constituents, such as pigments, fats, proteins,
and vitamins and results in discoloration, off-flavor development, and vitamin losses.
The light that is absorbed by the food can cause deteriorative reactions of the food
constituents. In most solid foods, the light only penetrates the outer layer of the product
and photodegradation occurs in this surface layer. Discoloration on the surface of foods
can certainly affect consumer acceptance of these products.
In liquid foods, light penetration can be greater and with mixing of the products due to
agitation, larger portions of food constituents may be deteriorated. The light sensitivity of
a food depends on many factors including the: light source strength and type of light that
it emits; distance of the light source form the food; length of exposure optical properties
of the packaging materials; oxygen concentration of the food; and the temperature.
Microbial Growth:
Microorganisms, specifically bacteria, mold, and yeasts, can cause food to spoil. For
example, microorganisms that break down fats in unsalted butter can cause it to become
rancid. Bacteria that breaks down protein in meat (proteolytic bacteria) and results in foul
odors. Also, if milk is kept too long or at improper temperatures, it will sour. Bacteria
that have survived pasteurization grow in the milk and produce acid from the lactose that
is naturally present in the milk.
The general sources of food spoilage microorganisms are the air, soil, sewage, and animal
wastes. Some microorganisms that are naturally present on the surface of foods grown in
the ground can also cause food spoilage. Bacteria from the animal's internal organs, skin,
and/or feet can contaminate meat and fish. Meat is rapidly contaminated when it is
ground for hamburger or sausage because the bacteria normally present on the outside of
the meat move into the chopped meat where there are many air pockets and rich supply of
moisture. Fish tissues are contaminated more readily than meat because they are more
delicate and so more easily penetrated.
Canned foods undergo a sterilization process to make them shelf-stable. If canned foods
are not properly processed, food spoilage (or food safety concerns) may occur. Swollen
cans usually contain gas produced by the bacteria Clostridium. Sour spoilage without gas
is commonly due to Bacillus. This type of spoilage is called flat-sour spoilage.
Lactobacilli are responsible for acid spoilage when they break down the carbohydrates in
foods and produce detectable amounts of acid.
Temperature:
When temperatures are not properly controlled, food can spoil. For example, for every
18°F rise in temperature within the moderate temperature range where most food is
handled (50°F to 100°F), the rate of chemical reaction is approximately doubled. As a
result, excessive heat will increase the rate of natural food enzyme reactions and the
reactions of other food constituents. As a result, protein will breakdown or denature;
emulsions will break; some vitamins will be destroyed; moisture will be lost and foods
will dry out; and the color, flavor and odor of some products may be affected
Exposing foods to uncontrolled cold temperatures will also cause physical spoilage.
Fruits and vegetables that accidentally freeze and thaw have their texture and appearance
affected. Skins and surfaces of these products will often crack, leaving them more
susceptible to microbial contamination. Some foods that become frozen may also be
adversely affected. For example, if mayonnaise freezes, the emulsion will break and the
components will separate.
Spoilage is caused in many foods by temperatures that are not extreme. Cold damage of
several fruits and vegetables can occur at common refrigerator temperatures (35-40°F).
Defects in produce exposed to cold temperatures include the development of off-colors,
surface pitting and a variety of decays. Uncut, fresh fruits and vegetables such as
bananas, lemons, squash and tomatoes are products that should be held at temperatures
no colder than 50°F for best quality.
Consequences:
Some spoiled foods are harmless to eat, and may simply be diminished in quality. But
foods exhibiting certain types of spoilage may be harmful to consume. Uncooked or
under-cooked animal flesh that spoils is typically quite toxic, and consumption can result
in serious illness or death. The toxic effects from consuming spoiled food are known
colloquially as "food poisoning", and more properly as "foodborne illness".
Prevention:
 A number of methods of prevention can be used that can either prevent, delay, or
otherwise reduce food spoilage.
 Preservatives can expand the shelf life of food and can lengthen the time long
enough for it to be harvested, processed, sold, and kept in the consumer's home
for a reasonable length of time.
 Refrigeration can increase the shelf life of certain foods and beverages, though
with most items, it does not indefinitely expand it. Freezing can preserve food
even longer, though even freezing has limitations.
 A high-quality vacuum flask (thermos) will keep coffee, soup, and other boiling-
hot foods above the danger zone (140F/58C) for over 24 hours.
 Canning of food can preserve food for a particularly long period of time, whether
canned at home or commercially. Canned food is vacuum packed in order to keep
oxygen out of the can that is needed to allow bacteria to break it down. Canning
does have limitations, and does not preserve the food indefinitely.
 Lactic acid fermentation also preserves food and prevents spoilage through
competitive exclusion, by reducing pH and preventing exposure to other sources
of nutritional degradation, such as oxidation, heat and sunlight.
Sources:
 "Beneficial Role of Lactic Acid Bacteria in Food Preservation and Human Health: A
Review". Scialert.net. Retrieved 2013-09-19.
 Fact sheet developed by: Dr. Robert B. Gravani Cornell University, Ithaca, NY July
1983
 "Food Safety Education | For Educators | Competencies | General | Spoilage |
Describe why food
spoils".www.foodsafetysite.com/educators/competencies/general/spoilage/spg1.html.
Retrieved 2014-01-04
 Jeanroy, Amelia; Ward, Karen. Canning & Preserving for Dummies.
 Wikipedia
Note: This article is protected by copyright law, but it may be cited as
“SCIENCE OF FOOD SPOILAGE: CAUSES, CONSEQUENCES AND
PREVENTION” Author: Ewetoye Ibrahim. www.facebook/scienceprodigy.
Retrieved 2014-01-04
Author:
Ewetoye Ibrahim is a research-minded
chemical engineering student at Ladoke
Akintola University of Technology,
Ogbomosho, Oyo State, Nigeria.