Food spoilage1

Food spoilage is the process where a food product becomes unsuitable to ingest by the
consumer. The cause of such a process is due to many outside factors as a side-effect of the
type of product it is, as well as how the product is packaged and stored.[1]
Due to food spoilage,
one-third of the worlds' food produced for the consumption of humans is lost every
year.[2]
Bacteria and various fungi are the cause of spoilage and can create serious
consequences for the consumers, but there are preventative measures that can be taken.
If food items are kept for a long period of time and not stored
properly, they get spoil such food items are bad for health. When
food items kept for a long time gets spoil as germs start growing on
it. Once the food is spoiled, it cannot be eaten and has to be thrown
away. Spoilage is a process in which food items deteriorate to the
point in which it is not edible to human.
Causes of Spoilage
The food and water may be infected by germs. Flies carry germs.
When they sit on our food, they pass on these germs to our food.
There are various factors which are responsible for food spoilage
such as bacteria, mould, yeast, moisture, light, temperature, and
chemical reaction.
1. Bacteria
They are the most abundant microorganisms found on the earth. They
are tiny in size and vary in shape. Some bacteria are useful also. They
help to convert milk into curd.
Bacteria growth (Source: femininetouchblog)
2. Protozoa

They are single-celled microorganisms that cause disease like food
poisoning etc.
3. Fungi
They are found in damp and warm places and grow on the dead and
rotting matter.
Fungi (Source: sciencedaily)
4. Temperature
Temperature is one of the major factors which is responsible for food
spoilage.
Signs of food spoilage
Signs of food spoilage include an appearance different from the fresh
food, such as a change in color, a change in texture, an unpleasant
odor or taste.
Food Preservation
Food is valuable. Preservingfood can help to avoid wasting of food.
Food preservationinvolves preventing the food from being spoilt.
Preservationof food is the process by which food is stored by special
methods. Cooked or uncooked food can be preserved in different
ways to be used later. Some methods of preservationare:

1. Freezing
Food kept in a refrigerator remains fresh for some days. Germs do
not grow easily in cool places. We preserve food items, like milk
fruit, vegetables and cooked food by keeping them in a refrigerator.
2. Boiling
By this method, we can preserve food for a short period of time.
Germs in milk are killed by pasteurization. It is done by boiling milk
for sometimes and then cooling it quickly.
3. Salting
We can add salt to preserve pickles and fish.
4. Sweetening
Excess sugar in food also acts as a preservative. We store food for a
long time in the form of jams, jellies, and murabbas by adding sugar.
5. Dehydration
In this method, the food items are dried in sun to stop the growth of
bacteria in them. Certain foods, like raw mangoes, fishes, potato
chips and papads are preserved by this method.

(Source: amazonaws)
6. Canning
In this method, air is removed from food and put in airtight cans so
that germs do not grow on them. Food items like vegetables, seafood,
dairy products etc. Are preserved through this method.
canning
Advantages and Disadvantages
 Advantages of food preservation: Germs do not grow easily in
preserved food and make it safe to eat. Preservation enables us to
enjoy seasonal fruits like strawberries and mangoes even during
the offseason.
 Disadvantages of food preservation: Excess salt and sugar are
used in the preservation of food which is not good for health. Some
methods of food preservation may lead to loss of nutrients.
Food preservationprevents the growth of microorganisms (such as yeasts),
or other microorganisms (although some methods work by introducing benign bacteria or fungi to
the food), as well as slowing the oxidation of fats that cause rancidity. Food preservation may

also include processes that inhibit visual deterioration, such as the enzymatic browningreaction
in apples after they are cut during food preparation.
Many processes designed to preserve food involve more than one food preservation method.
Preserving fruit by turning it into jam, for example, involves boiling (to reduce the fruit’s moisture
content and to kill bacteria, etc.), sugaring (to prevent their re-growth) and sealing within an
airtight jar (to prevent recontamination). Some traditional methods of preserving food have been
shown to have a lower energy input and carbon footprint, when compared to modern methods.[1]
Some methods of food preservation are known to create carcinogens. In 2015, the International
Agency for Research on Cancer of the World Health Organization classified processed meat, i.e.
meat that has undergone salting, curing, fermenting, and smoking, as "carcinogenic to
humans".[2][3][4]
Maintaining or creating nutritional value, texture and flavor is an important aspect of food
preservation.
Traditional techniques
New techniques of food preservation became available to the home chef from the dawn
of agriculture until the Industrial Revolution.
Curing
Bag of Prague powder#1, also known as "curing salt" or "pink salt". It is typically a combination of salt and
sodium nitrite, with the pink color added to distinguish it from ordinary salt.
Main article: Curing (food preservation)
The earliest form of curing was dehydration or drying, used as early as
12,000 BC. Smoking and salting techniques improve on the drying process and add antimicrobial
agents that aid in preservation. Smoke deposits a number of pyrolysis products onto the food,
including the phenols syringol, guaiacol and catechol.[5]
Salt accelerates the drying process
using osmosis and also inhibits the growth of several common strains of bacteria. More
recently nitrites have been used to cure meat, contributing a characteristic pink colour.[6]
Cooling
Main article: Refrigeration
Cooling preserves food by slowing down the growth and reproduction of microorganisms and the
action of enzymes that causes the food to rot. The introduction of commercial and domestic
refrigerators drastically improved the diets of many in the Western world by allowing food such as
fresh fruit, salads and dairy products to be stored safely for longer periods, particularly during
warm weather.
Before the era of mechanical refrigeration, cooling for food storage occurred in the forms of root
cellars and iceboxes. Rural people often did their own ice cutting, whereas town and city dwellers
often relied on the ice trade. Today, root cellaring remains popular among people who value
various goals, including local food, heirloom crops, traditional home cooking techniques, family
farming, frugality, self-sufficiency, organic farming, and others.
Freezing

Main article: Frozen food
Freezing is also one of the most commonly used processes, both commercially and domestically,
for preserving a very wide range of foods, including prepared foods that would not have required
freezing in their unprepared state. For example, potato waffles are stored in the freezer, but
potatoes themselves require only a cool dark place to ensure many months' storage. Cold stores
provide large-volume, long-term storage for strategic food stocks held in case of national
emergency in many countries.
Boiling
Main article: Boiling
Boiling liquid food items can kill any existing microbes. Milk and water are often boiled to kill any
harmful microbes that may be present in them.
Heating
Heating to temperatures which are sufficient to kill microorganisms inside the food is a method
used with perpetual stews. Milk is also boiled before storing to kill many microorganisms.
Sugaring
See also: Sugaring
The earliest cultures have used sugar as a preservative, and it was commonplace to
store fruit in honey. Similar to pickled foods, sugar cane was brought to Europe through the trade
routes. In northern climates without sufficient sun to dry foods, preserves are made by heating
the fruit with sugar.[7]
"Sugar tends to draw water from the microbes (plasmolysis). This process
leaves the microbial cells dehydrated, thus killing them. In this way, the food will remain safe
from microbial spoilage."[5]
Sugar is used to preserve fruits, either in an antimicrobial syrup with
fruit such as apples, pears, peaches, apricots, and plums, or in crystallized form where the
preserved material is cooked in sugar to the point of crystallization and the resultant product is
then stored dry. This method is used for the skins of citrus fruit (candied peel), angelica,
and ginger. Also, sugaring can be used in the production of jam and jelly.
Pickling
Main article: Pickling
Pickling is a method of preserving food in an edible, antimicrobial liquid. Pickling can be broadly
classified into two categories: chemical pickling and fermentation pickling.
In chemical pickling, the food is placed in an edible liquid that inhibits or kills bacteria and other
microorganisms. Typical pickling agents include brine (high in salt), vinegar, alcohol,
and vegetable oil. Many chemical pickling processes also involve heating or boiling so that the
food being preserved becomes saturated with the pickling agent. Common chemically pickled
foods include cucumbers, peppers, corned beef, herring, and eggs, as well as mixed vegetables
such as piccalilli.
In fermentation pickling, bacteria in the liquid produce organic acids as preservation agents,
typically by a process that produces lactic acid through the presence of lactobacillales.
Fermented pickles include sauerkraut, nukazuke, kimchi, and surströmming.
Lye
Main article: Sodium hydroxide § Food preparation
Sodium hydroxide (lye) makes food too alkaline for bacterial growth. Lye will saponify fats in the
food, which will change its flavor and texture. Lutefisk uses lye in its preparation, as do some
olive recipes. Modern recipes for century eggs also call for lye.
Canning

Preserved food
Main article: Canning
See also: Home canning
Canning involves cooking food, sealing it in sterilized cans or jars, and boiling the containers to
kill or weaken any remaining bacteria as a form of sterilization. It was invented by the French
confectioner Nicolas Appert.[8]
By 1806, this process was used by the French Navy to preserve
meat, fruit, vegetables, and even milk. Although Appert had discovered a new way of
preservation, it wasn't understood until 1864 when Louis Pasteur found the relationship between
microorganisms, food spoilage, and illness.[7]
Foods have varying degrees of natural protection against spoilage and may require that the final
step occur in a pressure cooker. High-acid fruits like strawberries require no preservatives to can
and only a short boiling cycle, whereas marginal vegetables such as carrots require longer
boiling and addition of other acidic elements. Low-acid foods, such as vegetables and meats,
require pressure canning. Food preserved by canning or bottling is at immediate risk of spoilage
once the can or bottle has been opened.
Lack of quality control in the canning process may allow ingress of water or micro-organisms.
Most such failures are rapidly detected as decomposition within the can causes gas production
and the can will swell or burst. However, there have been examples of poor manufacture
(underprocessing) and poor hygiene allowing contamination of canned food by the
obligate anaerobe Clostridium botulinum, which produces an acute toxin within the food, leading
to severe illness or death. This organism produces no gas or obvious taste and remains
undetected by taste or smell. Its toxin is denatured by cooking, however. Cooked mushrooms,
handled poorly and then canned, can support the growth of Staphylococcus aureus, which
produces a toxin that is not destroyed by canning or subsequent reheating.
Jellying
Main article: Aspic
See also: Potted shrimps and Confit
Food may be preserved by cooking in a material that solidifies to form a gel. Such materials
include gelatin, agar, maize flour, and arrowroot flour. Some foods naturally form a protein gel
when cooked, such as eels and elvers, and sipunculid worms, which are a delicacy in Xiamen, in
the Fujian province of the People's Republic of China. Jellied eels are a delicacy in the East End
of London, where they are eaten with mashed potatoes. Potted meats in aspic (a gel made from
gelatin and clarified meat broth) were a common way of serving meat off-cuts in the UK until the
1950s. Many jugged meats are also jellied.

A traditional British way of preserving meat (particularly shrimp) is by setting it in a pot and
sealing it with a layer of fat. Also common is potted chicken liver; jellying is one of the steps in
producing traditional pâtés.
Jugging
Main article: Jugging
Meat can be preserved by jugging. Jugging is the process of stewing the meat
(commonly game or fish) in a covered earthenware jug or casserole. The animal to be jugged is
usually cut into pieces, placed into a tightly-sealed jug with brine or gravy, and stewed. Red
wine and/or the animal's own blood is sometimes added to the cooking liquid. Jugging was a
popular method of preserving meat up until the middle of the 20th century.
Burial
Burial of food can preserve it due to a variety of factors: lack of light, lack of oxygen, cool
temperatures, pH level, or desiccants in the soil. Burial may be combined with other methods
such as salting or fermentation. Most foods can be preserved in soil that is very dry and salty
(thus a desiccant) such as sand, or soil that is frozen.
Many root vegetables are very resistant to spoilage and require no other preservation than
storage in cool dark conditions, for example by burial in the ground, such as in a storage
clamp. Century eggs are traditionally created by placing eggs in alkaline mud (or other alkaline
substance), resulting in their "inorganic" fermentation through raised pH instead of spoiling. The
fermentation preserves them and breaks down some of the complex, less flavorful proteins and
fats into simpler, more flavorful ones. Cabbage was traditionally buried during Autumn in northern
US farms for preservation. Some methods keep it crispy while other methods
produce sauerkraut.[citation needed]
A similar process is used in the traditional production of kimchi.
Sometimes meat is buried under conditions that cause preservation. If buried on hot coals or
ashes, the heat can kill pathogens, the dry ash can desiccate, and the earth can block oxygen
and further contamination. If buried where the earth is very cold, the earth acts like a refrigerator.
In Orissa, India, it is practical to store rice by burying it underground. This method helps to store
for three to six months during the dry season.
Butter and similar substances have been preserved as bog butter in Irish peat bogs for centuries.
Confit
Meat can be preserved by salting it, cooking it at or near 100 °C in some kind of fat (such
as lard or tallow), and then storing it immersed in the fat. These preparations were popular in
Europe before refrigerators became ubiquitous. They are still popular in France, where they are
called confit.[9][10]
The preparation will keep longer if stored in a cold cellar or buried in cold
ground.
Fermentation
See also: Fermentation (food)
Some foods, such as many cheeses, wines, and beers, use specific micro-organisms that
combat spoilage from other less-benign organisms. These micro-organisms keep pathogens in
check by creating an environment toxic for themselves and other micro-organisms by producing
acid or alcohol. Methods of fermentation include, but are not limited to, starter micro-organisms,
salt, hops, controlled (usually cool) temperatures and controlled (usually low) levels of oxygen.
These methods are used to create the specific controlled conditions that will support the
desirable organisms that produce food fit for human consumption.
Fermentation is the microbial conversion of starch and sugars into alcohol. Not only can
fermentation produce alcohol, but it can also be a valuable preservation technique. Fermentation
can also make foods more nutritious and palatable. For example, drinking water in the Middle
Ages was dangerous because it often contained pathogens that could spread disease. When the
water is made into beer, the boiling during the brewing process kills any bacteria in the water that

could make people sick. Additionally, the water now has the nutrients from the barley and other
ingredients, and the microorganisms can also produce vitamins as they ferment.[7]
Modern industrial techniques
Techniques of food preservation were developed in research laboratories for commercial
applications.
Pasteurization
Main article: Pasteurization
Pasteurization is a process for preservation of liquid food. It was originally applied to combat the
souring of young local wines. Today, the process is mainly applied to dairy products. In this
method, milk is heated at about 70 °C (158 °F) for 15–30 seconds to kill the bacteria present in it
and cooling it quickly to 10 °C (50 °F) to prevent the remaining bacteria from growing. The milk is
then stored in sterilized bottles or pouches in cold places. This method was invented by Louis
Pasteur, a French chemist, in 1862.
Vacuum packing
Main article: Vacuum packing
Vacuum-packing stores food in a vacuum environment, usually in an air-tight bag or bottle.
The vacuum environment strips bacteria of oxygen needed for survival. Vacuum-packing is
commonly used for storing nuts to reduce loss of flavor from oxidization. A major drawback to
vacuum packaging, at the consumer level, is that vacuum sealing can deform contents and rob
certain foods, such as cheese, of its flavor.
Freeze drying
This section needs
expansion. You can help
by adding to it.(September 2018)
Main article: Freeze drying
Artificial food additives
Main article: Preservatives
Preservative food additives can be antimicrobial—which inhibit the growth of bacteria or fungi,
including mold—or antioxidant, such as oxygen absorbers, which inhibit the oxidationof food
constituents. Common antimicrobial preservatives include calcium propionate, sodium
nitrate, sodium nitrite, sulfites (sulfur dioxide, sodium bisulfite, potassium hydrogen sulfite, etc.),
and EDTA. Antioxidants include butylated hydroxyanisole (BHA) and butylated
hydroxytoluene (BHT). Other preservatives include formaldehyde (usually in
solution), glutaraldehyde (insecticide), ethanol, and methylchloroisothiazolinone.
Irradiation
Main article: Food irradiation
Irradiation of food[11]
is the exposure of food to ionizing radiation. Multiple types of ionizing
radiation can be used, including beta particles (high-energy electrons) and gamma rays(emitted
from radioactive sources such as cobalt-60 or cesium-137). Irradiation can kill bacteria, molds,
and insect pests, reduce the ripening and spoiling of fruits, and at higher doses induce sterility.
The technology may be compared to pasteurization; it is sometimes called "cold pasteurization",
as the product is not heated. Irradiation may allow lower-quality or contaminated foods to be
rendered marketable.
National and international expert bodies have declared food irradiation as "wholesome";
organizations of the United Nations, such as the World Health Organization and Food and
Agriculture Organization, endorse food irradiation.[12][13]
Consumers may have a negative view of

irradiated food based on the misconception that such food is radioactive;[14]
in fact, irradiated food
does not and cannot become radioactive. Activists have also opposed food irradiation for other
reasons, for example, arguing that irradiation can be used to sterilize contaminated food without
resolving the underlying cause of the contamination.[15]
International legislation on whether food
may be irradiated or not varies worldwide from no regulation to a full ban.[16]
Approximately 500,000 tons of food items are irradiated per year worldwide in over 40 countries.
These are mainly spices and condiments, with an increasing segment of fresh fruit irradiated for
fruit fly quarantine.[17][18]
Pulsed electric field electroporation
Main article: Electroporation
Pulsed electric field (PEF) electroporation is a method for processing cells by means of brief
pulses of a strong electric field. PEF holds potential as a type of low-temperature alternative
pasteurization process for sterilizing food products. In PEF processing, a substance is placed
between two electrodes, then the pulsed electric field is applied. The electric field enlarges the
pores of the cell membranes, which kills the cells and releases their contents. PEF for food
processing is a developing technology still being researched. There have been limited industrial
applications of PEF processing for the pasteurization of fruit juices. To date, several PEF treated
juices are available on the market in Europe. Furthermore, for several years a juice
pasteurization application in the US has used PEF. For cell disintegration purposes especially
potato processors show great interest in PEF technology as an efficient alternative for their
preheaters. Potato applications are already operational in the US and Canada. There are also
commercial PEF potato applications in various countries in Europe, as well as in Australia, India,
and China.[19]
Modified atmosphere
Main article: Modified atmosphere
Modifying atmosphere is a way to preserve food by operating on the atmosphere around it. Salad
crops that are notoriously difficult to preserve are now being packaged in sealed bags with an
atmosphere modified to reduce the oxygen (O2) concentration and increase the carbon
dioxide (CO2) concentration. There is concern that, although salad vegetables retain their
appearance and texture in such conditions, this method of preservation may not retain nutrients,
especially vitamins. There are two methods for preserving grains with carbon dioxide. One
method is placing a block of dry ice in the bottom and filling the can with the grain. Another
method is purging the container from the bottom by gaseous carbon dioxide from a cylinder or
bulk supply vessel.
Carbon dioxide prevents insects and, depending on concentration, mold and oxidation from
damaging the grain. Grain stored in this way can remain edible for approximately five years.[20]
Nitrogen gas (N2) at concentrations of 98% or higher is also used effectively to kill insects in the
grain through hypoxia.[21]
However, carbon dioxide has an advantage in this respect, as it kills
organisms through hypercarbia and hypoxia (depending on concentration), but it requires
concentrations of above 35%,[22]
or so. This makes carbon dioxide preferable for fumigation in
situations where a hermetic seal cannot be maintained.
Controlled Atmospheric Storage (CA): "CA storage is a non-chemical process. Oxygen levels in
the sealed rooms are reduced, usually by the infusion of nitrogen gas, from the approximate 21
percent in the air we breathe to 1 percent or 2 percent. Temperatures are kept at a constant 0–
2 °C (32–36 °F). Humidity is maintained at 95 percent and carbon dioxide levels are also
controlled. Exact conditions in the rooms are set according to the apple variety. Researchers
develop specific regimens for each variety to achieve the best quality. Computers help keep
conditions constant." "Eastern Washington, where most of Washington’s apples are grown, has
enough warehouse storage for 181 million boxes of fruit, according to a report done in 1997 by
managers for the Washington State Department of Agriculture Plant Services Division. The
storage capacity study shows that 67 percent of that space—enough for 121,008,000 boxes of
apples—is CA storage." [23]

Air-tight storage of grains (sometimes called hermetic storage) relies on the respiration of grain,
insects, and fungi that can modify the enclosed atmosphere sufficiently to control insect pests.
This is a method of great antiquity,[24]
as well as having modern equivalents. The success of the
method relies on having the correct mix of sealing, grain moisture, and temperature.[25]
A patented process uses fuel cells to exhaust and automatically maintain the exhaustion
of oxygen in a shipping container, containing, for example, fresh fish.[26]
Nonthermal plasma
Main article: Nonthermal plasma
This process subjects the surface of food to a "flame" of ionized gas molecules, such as helium
or nitrogen. This causes micro-organisms to die off on the surface.[27]
High-pressure food preservation
Main article: Pascalization
High-pressure food preservation or pascalization refers to the use of a food preservation
technique that makes use of high pressure. "Pressed inside a vessel exerting 70,000 pounds per
square inch (480 MPa) or more, food can be processed so that it retains its fresh appearance,
flavor, texture and nutrients while disabling harmful microorganisms and slowing spoilage." By
2005, the process was being used for products ranging from orange juice to guacamole to deli
meats and widely sold.[28]
Biopreservation
3D stick model of nisin. Some lactic acid bacteria manufacture nisin. It is a particularly effective
preservative.
Main article: Biopreservation
Biopreservation is the use of natural or controlled microbiota or antimicrobials as a way of
preserving food and extending its shelf life.[29]
Beneficial bacteria or the fermentation products
produced by these bacteria are used in biopreservation to control spoilage and
render pathogens inactive in food.[30]
It is a benign ecological approach which is gaining
increasing attention.[29]
Of special interest are lactic acid bacteria (LAB). Lactic acid bacteria have antagonistic properties
that make them particularly useful as biopreservatives. When LABs compete for nutrients,
their metabolites often include active antimicrobials such as lactic acid, acetic acid, hydrogen
peroxide, and peptide bacteriocins. Some LABs produce the antimicrobial nisin, which is a
particularly effective preservative.[31][32]
These days, LAB bacteriocins are used as an integral part of hurdle technology. Using them in
combination with other preservative techniques can effectively control spoilage bacteria and
other pathogens, and can inhibit the activities of a wide spectrum of organisms, including
inherently resistant Gram-negative bacteria.[29]
Hurdle technology
Main article: Hurdle technology
Hurdle technology is a method of ensuring that pathogens in food products can be eliminated or
controlled by combining more than one approach. These approaches can be thought of as
"hurdles" the pathogen has to overcome if it is to remain active in the food. The right combination
of hurdles can ensure all pathogens are eliminated or rendered harmless in the final product.[33]

Hurdle technology has been defined by Leistner (2000) as an intelligent combination of hurdles
that secures the microbial safety and stability as well as the organoleptic and nutritional quality
and the economic viability of food products.[34]
The organoleptic quality of the food refers to its
sensory properties, that is its look, taste, smell, and texture.
Examples of hurdles in a food system are high temperature during processing, low temperature
during storage, increasing the acidity, lowering the water activity or redoxpotential, and the
presence of preservatives or biopreservatives. According to the type of pathogens and how risky
they are, the intensity of the hurdles can be adjusted individually to meet consumer preferences
in an economical way, without sacrificing the safety of the product.[33]
Principal hurdles used for food preservation (after Leistner, 1995)[35][36]
Parameter Symbol Application
High temperature F Heating
Low temperature T Chilling, freezing
Reduced water activity aw Drying, curing, conserving
Increased acidity pH Acid addition or formation
Reduced redox potential Eh Removal of oxygen or addition of ascorbate
Biopreservatives Competitive flora such as microbial fermentation
Other preservatives Sorbates, sulfites, nitrites
Foodspoilage microorganismsChemical reactionsthatcause offensive sensorychangesinfoodsare
mediatedbyavarietyof microbesthatuse foodas a carbon andenergysource. These organisms
include prokaryotes(bacteria),single-celledorganismslackingdefinednuclei andotherorganelles,
and eukaryotes,single-celled(yeasts) andmulticellular(molds) organismswithnucleiandother
organelles.Somemicrobesare commonlyfoundinmanytypesof spoiledfoodswhile othersare
more selective inthe foodstheyconsume;multiple speciesare oftenidentifiedinasingle spoiled
fooditembutthere may be one species(aspecificspoilage organism, SSO) primarilyresponsible for
productionof the compoundscausingoffodorsandflavors.Withinaspoilingfood,there isoftena
successionof differentpopulationsthatrise andfall asdifferentnutrientsbecome available orare
exhausted.Some microbes,suchaslactic acidbacteriaand molds,secrete compoundsthatinhibit
competitors[7].Spoilage microbesare oftencommoninhabitantsof soil,water,orthe intestinal
tracts of animalsandmay be dispersedthroughthe airandwaterand bythe activitiesof small

animals,particularlyinsects.Itshouldbe notedthatwiththe developmentof new moleculartyping
methods,the scientificnamesof some spoilage organisms,particularlythe bacteria,have changedin
recentyearsand some oldernamesare nolongerinuse.Many insectsandsmall mammalsalso
cause deteriorationof foodbutthese willnotbe consideredhere.YeastsYeastsare asubsetof a
large group of organismscalledfungi thatalsoincludesmoldsandmushrooms.Theyare generally
single-celledorganismsthatare adaptedforlife inspecialized,usuallyliquid,environmentsand,
unlike some moldsandmushrooms,donotproduce toxicsecondarymetabolites.Yeastscangrow
withor withoutoxygen(facultative) andare well knownfortheirbeneficial fermentationsthat
produce bread and alcoholicdrinks.Theyoftencolonizefoodswithahighsugaror saltcontentand
contribute tospoilage of maple syrup,pickles,andsauerkraut.Fruitsandjuiceswithalow pH are
anothertarget,and there are some yeaststhat grow on the surfacesof meat andcheese.There are
fourmain groupsof spoilage yeasts:Zygosaccharomycesandrelatedgeneratolerate highsugarand
highsaltconcentrationsandare the usual spoilage organismsinfoodssuchashoney,driedfruit,
jamsand soy sauce.Theyusuallygrowslowly,producingoff-odorsandflavorsandcarbondioxide
that may cause foodcontainerstoswell andburst.Debaryomyceshanseniicangrow at salt
concentrationsashighas 24%, accountingfor itsfrequentisolationfromsaltbrinesusedforcured
meats,cheeses,andolives.Thisgroupalsoincludesthe mostimportantspoilage organismsinsalad
dressings[8].Saccharomycesspp.are bestknownfortheirrole inproductionof breadand wine but
some strainsalsospoil winesandotheralcoholicbeveragesbyproducinggassiness,turbidityand
offflavorsassociatedwithhydrogensulfideandaceticacid.Some speciesgrow onfruits,including
yogurtcontainingfruit,andsome are resistanttoheat processing[9].Candidaandrelatedgenera
are a heterogeneousgroupof yeasts,some of whichalsocause humaninfections.Theyare involved
inspoilage of fruits,some vegetablesanddairyproducts[10].Dekkera/Brettanomycesare
principallyinvolvedinspoilage of fermentedfoods,includingalcoholicbeveragesandsome dairy
products.Theycan produce volatile phenoliccompoundsresponsible foroff-flavors[11].Molds
Moldsare filamentousfungi thatdonotproduce large fruitingbodieslike mushrooms.Moldsare
veryimportantforrecyclingdeadplantandanimal remainsinnature butalsoattack a wide variety
of foodsandothermaterialsuseful tohumans.Theyare well adaptedforgrowthonandthrough
solidsubstrates,generallyproduce airbornespores,andrequireoxygenfortheirmetabolic
processes.Mostmoldsgrowat a pH range of 3 to 8 and some can grow at verylow wateractivity
levels(0.7–0.8) ondriedfoods.Sporescantolerate harshenvironmental conditionsbutmostare
sensitivetoheattreatment.AnexceptionisByssochlammys,whose sporeshave a D value of 1–12
minutesat90ºC. Differentmoldspecieshave differentoptimalgrowthtemperatures,withsome
able to growin refrigerators.Theyhave adiverse secondarymetabolismproducinganumberof
toxicand carcinogenicmycotoxins.Some spoilagemoldsare toxigenicwhileothersare not[12].
Spoilage moldscanbe categorizedintofourmaingroups:Zygomycetesare consideredrelatively
primitive fungibutare widespreadinnature,growingrapidlyonsimple carbonsourcesinsoil and
plantdebris,and theirsporesare commonlypresentinindoorair.Generallytheyrequire highwater
activitiesforgrowthandare notoriousforcausingrotsina varietyof storedfruitsandvegetables,
includingstrawberriesandsweetpotatoes.Somecommonbreadmoldsalsoare zygomycetes.Some
zygomycetesare alsoutilizedforproductionof fermentedsoyproducts,enzymes,andorganic
chemicals.The mostcommonspoilage speciesare Mucorand Rhizopus.Zygomycetesare notknown
for producingmycotoxinsbutthere are some reportsof toxiccompoundsproducedbyafew
species.Penicilliumandrelatedgeneraare presentinsoilsandplantdebrisfrombothtropical and
Antarcticconditionsbuttendtodominate spoilage intemperate regions.Theyare distinguishedby
theirreproductive structuresthatproduce chainsof conidia.Althoughtheycanbe useful tohumans
inproducingantibioticsandblue cheese,manyspeciesare importantspoilage organisms,andsome
produce potentmycotoxins(patulin,ochratoxin,citreoviridin,penitrem).Penicilliumspp.cause

visible rotsoncitrus,pear,andapple fruitsandcause enormouslossesinthese crops.Theyalsospoil
otherfruitsand vegetables,includingcereals.Some speciescanattackrefrigeratedandprocessed
foodssuchas jams and margarine.A relatedgenus,Byssochlamys,isthe mostimportantorganism
causingspoilage of pasteurizedjuicesbecauseof the highheatresistance of itsspores.Aspergillus
and relatedmoldsgenerallygrowfasterandare more resistanttohightemperatures andlow water
activitythanPenicilliumspp.andtendtodominate spoilage inwarmerclimates.Manyaspergilla
produce mycotoxins:aflatoxins,ochratoxin,territrems,cyclopiazonicacid.Aspergilli spoilawide
varietyof foodand nonfooditems(paper,leather,etc.) butare probablybestknownforspoilageof
grains,driedbeans,peanuts,tree nuts,andsome spices.Othermolds,belongingtoseveral genera,
have beenisolatedfromspoiledfood.These generallyare notmajorcausesof spoilage butcan be a
problemforsome foods.Fusariumspp.cause plantdiseasesandproduce severalimportant
mycotoxinsbutare not importantspoilage organisms.However,theirmycotoxinsmaybe presentin
harvestedgrainsandpose a healthrisk.BacteriaSpore-formingbacteriaare usuallyassociatedwith
spoilage of heat-treatedfoodsbecause theirsporescansurvive highprocessingtemperatures.These
Gram-positive bacteriamaybe strictanaerobesorfacultative (capable of growthwithorwithout
oxygen).Some spore-formersare thermophilic,preferringgrowthathightemperatures(ashighas
55ºC). Some anaerobicthermophilesproduce hydrogensulphide (Desulfotomaculum)andothers
produce hydrogenandcarbon dioxide(Thermoanaerobacterium)duringgrowthoncanned/
hermeticallysealedfoodskeptathightemperatures,forexample,soupssoldinvendingmachines.
Otherthermophiles(BacillusandGeobacillusspp.) cause aflatsourspoilage of highor low pH
cannedfoodswithlittle ornogas production,andone speciescausesropinessinbreadheldathigh
ambienttemperatures[13].Mesophilicanaerobes,growingatambienttemperatures,cause several
typesof spoilage of vegetables(Bacillusspp.);putrefactionof cannedproducts,earlyblowingof
cheeses,andbutyricacidproductionincannedvegetablesandfruits(Clostridiumspp.);and
"medicinal"flavorsincannedlow-acidfoods(Alicyclobacillus) (Chang&Kang,2003). Psychrotolerant
sporeformersproduce gasandsicklyodorsinchilledmeatsandbrine-curedhams(Clostridium spp.)
while othersproduce off-odorsandgasinvacuum-packed,chilledfoodsandmilk(Bacillusspp.).
Lactic acid bacteria(LAB) are a groupof Gram-positive bacteria,includingspeciesof Lactobacillus,
Pediococcus,LeuconostocandOenococcus,some of whichare useful inproducingfermentedfoods
such as yogurtand pickles.However,underlow oxygen,low temperature,andacidicconditions,
these bacteriabecome the predominantspoilage organismsonavarietyof foods.Undesirable
changescausedby LAB include greeningof meatandgasformationincheeses(blowing),pickles
(bloaterdamage),andcannedorpackagedmeatand vegetables.Off-flavorsdescribedasmousy,
cheesy,malty,acidic,butteryorliver-likemaybe detectedinwine,meats,milk,orjuices spoiledby
these bacteria.LABmay alsoproduce large amountsof an exopolysaccharide thatcausesslimeon
meatsand ropyspoilage insome beverages.Pseudomonasandrelatedgeneraare aerobic,gram-
negative soil bacteria,someof whichcandegrade a wide varietyof unusual compounds.They
generallyrequire ahighwateractivityforgrowth(0.95 or higher) andare inhibitedbypHvaluesless
than 5.4. Some speciesgrowat refrigerationtemperatures(psychrophilic) while otherare adapted
for growthat warmer,ambienttemperatures.Fourspeciesof Pseudomonas(P.fluorescens,P.fragi,
P. lundensis,andP.viridiflava),Shewanellaputrefaciens,andXanthomonascampestrisare the main
foodspoilage organismsinthisgroup.Softrotsof plant-derivedfoodsoccurwhenpectinsthathold
adjacentplantcellstogetherare degradedbypecticlyase enzymessecretedbyX.campestris,P.
fluorescensandP.viridiflava.These twospeciesof Pseudomonascomprise upto40% of the
naturallyoccurringbacteriaonthe surface of fruitsandvegetablesandcause nearlyhalf of post-
harvestrot of freshproduce storedat coldtemperatures.P.fluorescens,P.fragi,P.lundensis,andS.
putrefacienscause spoilage of animal-derivedfoods(meat,fish,milk) bysecretinglipasesand
proteasesthatcause formationof sulfidesandtrimethylamine (off-odors) andbyformingbiofilms

(slime) onsurfaces(55;73).Some strainsare adaptedfor growthat coldtemperaturesandspoil
these foodsinthe refrigerator.Enterobacteriaceae are gram-negative,facultativelyanaerobic
bacteriathat include anumberof humanpathogens(Salmonella,E.coli,Shigella,Yersinia) andalsoa
large numberof spoilage organisms.Thesebacteriaare widespreadinnature insoil,onplant
surfacesandin digestivetractsof animalsandare therefore presentinmanyfoods.Erwinia
carotovora isone of the mostimportantbacteriacausingsoftrot of vegetablesinthe fieldorstored
at ambienttemperatures.Biogenicaminesare producedinmeatandfishbyseveral membersof this
groupwhile othersproduce off-odorsorcolorsinbeer(Obesumbacterium),baconandothercured
meats(Proteus,Serratia),cheeses(severalgenera),cole slaw (Klebsiella),andshell eggs(Proteus,
Enterobacter,Serratia).Temperature,saltconcentration,andpHare the mostimportantfactors
determiningwhich,if any,of these microbesspoil foods.ManyGram-negativebacteria,including
pseudomonadsandenterobacteriaceae,secreteacyl homoserine lactones(AHLs) toregulate the
expressionof certaingenes,suchasvirulence factors,asafunctionof cell density.TheseAHL
quorum-sensingsignalsmayregulate proteolyticenzyme productionandironchelationduring
spoilage of some foods[14] althoughthe role of these signalsinotherspoilage systemsisnotclear
[15]. Otherbacteriaare associatedwithspoilage of chilled,highproteinfoodssuchasmeat,fish,and
dairyproducts.Theymay not be the predominantspoilage organismsbutcontribute tothe
breakdownof foodcomponentsandmayproduce off-odors.Mostspeciesare aerobicalthoughsome
grow at lowoxygenlevelsandmaysurvive vacuumpackaging,andone (Brochothrix) isafacultative
anaerobe.Some examplesinclude:AcinetobacterandPsychrobacter,whichare predominant
bacteriaon poultrycarcassesonthe processingline andhave beenisolatedfromavarietyof spoiled
meatand fish.Acinetobactergrowsata pH as low as 3.3 and hasbeendetectedinspoiledsoft
drinks.These twogeneradonotproduce extracellularlipases,hydrogensulfide,ortrimethylamine
(fishyodor) andsoare consideredtohave a low spoilage potential.Alcaligenesisapotential
contaminantof dairyproductsand meatand has beenisolatedfromrancidbutterandmilkwithan
off-odor.These bacteriaoccurnaturally inthe digestive tractof some animalsandalsoinsoil and
water.Flavobacteriumisfoundwidelyinthe environmentandinchilledfoods,particularlydairy
products,fish,andmeat.It usesbothlipasesandproteasestoproduce disagreeableodorsinbutter,
margarine,cheese,cream,andotherproductswithdairyingredients.MoraxellaandPhotobacterium
are importantconstituentsof the microfloraonthe surface of fish.Photobacteriumcangrow and
produce trimethylamineinice-stored,vacuum-packagedfish.Brochothrix hasbeenisolatedfrom
meat,fish,dairyproductsandfrozenvegetables.Duringspoilage,itproducesodorsdescribedas
sour,musty,and sweaty[16].Spoilage of fruitsandvegetablesThe mainsourcesof microorganisms
invegetablesare soil,water,air,andotherenvironmental sources,andcaninclude some plant
pathogens.Freshvegetablesare fairlyrichincarbohydrates(5% or more),low inproteins(about1
to 2%),and, exceptfortomatoes,have highpH.Microorganismsgrow more rapidly indamagedor
cut vegetables.The presence of air,highhumidity,andhighertemperatureduringstorage increases
the chancesof spoilage.The commonspoilagedefectsare causedbymoldsbelongingtogenera
Penicillium,Phytophthora,Alternaria,Botrytis, andAspergillus.Amongthe bacterialgenera,species
fromPseudomonas,Erwinia,Bacillus,andClostridiumare important.Microbialvegetablespoilage is
generallydescribedbythe commontermrot,alongwiththe changesinthe appearance,suchas
blackrot, gray rot, pinkrot,soft rot,stem-endrot[17].Vegetablesare anothertemptingsource of
nutrientsforspoilage organismsbecause of theirnearneutral pHand highwateractivity.Although
vegetablesare exposedtoa multitude of soil microbes,notall of these canattack plantsandsome
spoilage microbesare notcommoninsoil,forexample,lacticacidbacteria.Mostspoilage lossesare
not due to microorganismsthatcause plantdiseasesbutrathertobacteriaand moldsthattake
advantage of mechanical andchillingdamage toplantsurfaces.Some microbesare foundinonlya
fewtypesof vegetableswhile othersare widespread.Erwiniacarotovoraisthe mostcommon

spoilage bacteriumandhasbeendetectedinvirtuallyeverykindof vegetable.Itcan even grow at
refrigerationtemperatures[18].Bacterial spoilage firstcausessofteningof tissuesaspectinsare
degradedandthe whole vegetable mayeventuallydegenerate intoaslimymass.Starchesand
sugars are metabolizednextandunpleasantodorsandflavorsdevelopalongwithlacticacidand
ethanol.BesidesE.carotovora,several Pseudomonasspp.andlacticacidbacteriaare important
spoilage bacteria.Moldsbelongingtoseveral genera,includingRhizopus,AlternariaandBotrytis,
cause a numberof vegetable rotsdescribedbytheircolor,texture,oracidicproducts.The higher
moisture contentof vegetablesascomparedtograinsallowsdifferentfungi toproliferate,butsome
speciesof Aspergillusattackonions.Intact,healthyfruitshave manymicrobesontheirsurfacesbut
can usuallyinhibittheirgrowthuntil afterharvest.Ripeningweakenscell wallsanddecreasesthe
amountsof antifungal chemicalsinfruits,andphysicaldamage duringharvestingcausesbreaksin
outerprotective layersof fruits thatspoilage organismscanexploit.Moldsare tolerantof acidic
conditionsandlowwateractivityandare involvedinspoilage of citrusfruits,apples,pears,and
otherfruits.Penicillium,Botrytis,andRhizopusare frequentlyisolatedfromspoiledfruits[19].
Yeastsand some bacteria,includingErwiniaandXanthomonas,canalsospoil some fruitsandthese
may particularlybe aproblemforfreshcut packagedfruits[20].Fruitsjuicesgenerallyhave
relativelyhighlevelsof sugarand a lowpH and thisfavorsgrowthof yeasts,moldsandsome acid-
tolerantbacteria.Spoilage maybe manifestedassurface pelliclesorfibrousmatsof molds,
cloudiness,andoff-flavors.Lackof oxygeninbottledandcanneddrinkslimitsmoldgrowth.
SaccharomycesandZygosaccharomycesare resistanttothermal processingandare foundinsome
spoiledjuices[21].Alicyclobacillusspp.,anacidophilicandthermophilicspore-formingbacteria,has
emergedasan importantspoilage microbe,causingasmokytaintandotheroff-flavorsin
pasteurizedjuices[22] Propionibacteriumcyclohexanicum,anacidtolerantnon-sporeforming
bacteriumalsosurvivesheatingandgrowsina varietyof fruitjuices[23].Lactic acid bacteriacan
spoil orange andtomatojuices,andsome pseudomonadsandenterobacteriaceaealsospoil juices.
These bacteriaare not as heattolerantbutmay be post-pasteurizationcontaminantscolonizationby
many,but notall,microbesandare the most importantfirststepindelayingthe spoilageprocess.
Microbesrequire certainconditionsforgrowth,andtherefore managementof the environmentof
foodscan change these factorsand delayspoilage:Many,butnot all,microbesgrow slowlyornotat
all at lowtemperatures,andrefrigerationcanprolongthe lagphase anddecrease growthrate of
microbes.Manymicrobesrequire ahighwateractivityandtherefore keepingfoodssuchasgrains
and cereal productsdrywill helptopreserve them.Some microbesrequire oxygen,othersare killed
by oxygen,andstill othersare facultative.Managingthe atmosphere duringstorage inpackagingcan
retard or preventthe growthof some microbes.Several typesof modifiedatmosphere packaging
(MAP) have beendevelopedtoretardgrowthof pathogenicandspoilage organisms.However,
microbes are endlesslyinnovative andeventuallyseemtocircumventthe barrierssetagainstthem.
Therefore furtherstrategiesandmultiplehurdlesare utilizedtoextendshelflife.These procedures
mustbe assessedforcompatibilitywithdifferentfoodssothat there are nosignificantorganoleptic
changesinthe foodscausedbythe treatmentor preservative.Thesemethodsforfoodpreservation
will notbe coveredindepthhere.Spoilageof dairyproductsMilkisan excellentmediumforgrowth
for a varietyof bacteria[24]. Spoilage bacteriamayoriginate onthe farmfromthe environmentor
milkingequipmentorinprocessingplantsfromequipment,employees,orthe air.LAB are usually
the predominantmicrobesinrawmilkandproliferate if milkisnotcooledadequately.When
populationsreachabout106 cfu/ml,off-flavorsdevelopinmilkdue toproductionof lacticacidand
othercompounds.Refrigerationsuppressesgrowthof LABandwithinone daypsychrophilicbacteria
(Pseudomonas,Enterobacter,Alcaligenesandsome spore-formers) grow andcan eventually
produce rancidodors throughthe actionof lipasesandbitterpeptidesfromproteaseaction[25].
Pasteurizationkillsthe psychrophilesandmesophilicbacteria(LAB),butheat-tolerantspecies

(Alcaligenes,Microbacterium,andthe sporeformersBacillusandClostridium) surviveandmaylater
cause spoilage inmilkorotherdairyproducts.Immediatelyfollowingpasteurization,bacterial
countsare usuallypHof 5.0–6.5 and a moisture contentof 50–80% maybe spoiledby
Pseudomonas,Alcaligenes,andFlavobacterium.Clostridiumsporogeneshasbeenfoundinspoiled
processedcheese,where itproducesgasholesandoff-flavors[28].Yeastsandmoldsare the main
spoilage organismsfoundinculturedmilks(yogurt,sour creamandbuttermilk) because the higher
acidityinthese productsinhibitsmanybacteria[29].Pseudomonas,yeastsandmoldscanspoil
butterand “light”butters.Since the lightbuttershave highermoisture contentthanbutter,theycan
supportmore microbial growth.Creammaybecome rancidwhenpopulationsof Pseudomonasand
Enterobacterproliferate.Preventionfromfoodspoilage microorganismManyfoodproductsare
perishable bynature andrequire protectionfromspoilage duringtheirpreparation,storage and
distributiontogive themdesiredshelf-life.Because foodproductsare now oftensoldinareasof the
worldfar distantfromtheirproductionsites,the needforextendedsafeshelf-lifeforthese products
has alsoexpanded.The developmentof food preservationprocesseshasbeendrivenbythe needto
extendthe shelf-life of foods.Foodpreservationisacontinuousfightagainstmicroorganisms
spoilingthe foodormakingitunsafe.Several foodpreservationsystemssuchasheating,
refrigerationandadditionof antimicrobial compoundscanbe usedto reduce the riskof outbreaksof
foodpoisoning;however,these techniquesfrequentlyhave associatedadverse changesin
organolepticcharacteristicsandlossof nutrients.Withinthe disposable arsenalof preservation
techniques,the foodindustryinvestigatesmore andmore the replacementof traditional food
preservationtechniquesbynewpreservationtechniquesdue tothe increasedconsumerdemandfor
tasty,nutritious,natural andeasy-to-handle foodproducts.Improvementsinthe colddistribution
chainhave made international trade of perishable foodspossible,butrefrigerationalone cannot
assure the qualityandsafetyof all perishable foods.The mostcommonclassical preservative agents
are the weakorganicacids,for example acetic,lactic,benzoicandsorbicacid.These molecules
inhibitthe outgrowthof bothbacterial andfungal cellsandsorbicacidisalsoreportedto inhibitthe
germinationandoutgrowthof bacterial spores.Inthe production of fooditiscrucial that proper
measuresare takento ensure the safetyandstabilityof the productduringitswhole shelf-life.In
particular,modernconsumertrendsandfoodlegislationhave made the successfulattainmentof
thisobjective muchmore of a challenge tothe foodindustry.Firstly,consumersrequire more high
quality,preservative-free,safebutmildlyprocessedfoodswithextendedshelf-life.Forexample,this
may meanthat foodshave tobe preservedathigherpHvaluesandhave to be treatedat mild-
pasteurizationratherthansterilizationtemperatures.Asacidityandsterilizationtreatmentsare two
crucial factors inthe control of outgrowthof pathogenicspore-formingbacteria,suchasClostridium
botulinum,addressingthisconsumerneedcallsforinnovative approachestoensure preservationof
products.Secondly,legislationhasrestrictedthe use andpermittedlevelsof some currently
acceptedpreservativesindifferentfoods.Thishascreatedproblemsforthe industrybecause the
susceptibilityof some microorganismstomostcurrentlyusedpreservativesisfalling.Anincreasing
numberof consumerspreferminimallyprocessedfoods,preparedwithoutchemical preservatives.
Many of these ready-to-eatandnovel foodtypesrepresentnew foodsystemswithrespecttohealth
risksand spoilage association.Againstthisbackground,andrelyingonimprovedunderstandingand
knowledge of the complexityof microbialinteractions,recentapproachesare increasinglydirected
towardspossibilitiesofferedbybiological preservation[30].The highsaltconcentrationinthe
serum-in-lipidemulsionof butterlimitsthe growthof contaminatingbacteriatothe small amountof
nutrientstrappedwithinthe dropletsthatcontainthe microbes.However,psychrotrophicbacteria
can grow and produce lipasesinrefrigeratedsaltedbutterif the moisture andsaltare not evenly
distributed[31].Whenusedinthe bulkform, concentrated(condensed) milkmustbe kept
refrigerateduntilused.Itcanbe preservedbyadditionof about44% sucrose and/orglucose to

lowerthe wateractivitybelowthatatwhichviable sporeswillgerminate (aw 0.95) [32]. Lactose,
whichconstitutesabout53%of the non fatmilksolids,contributestothe loweredwateractivity.
Whencanned as evaporatedmilkorsweetenedcondensedmilk,theseproductsare commercially
sterilizedinthe cans,andspoilage seldomoccurs.Microbial growthandenzyme activityare
preventedbyfreezing.Therefore,microbial degradationof frozendessertsoccursonlyinthe
ingredientsusedorinthe mixespriortofreezing.Chemical preservativesChemical preservativesare
substanceswhichare addedtofoodjust to retard,inhibitorarrestthe activityof microorganisms
such as fermentation,putrefactionanddecompositionof the food.Commonlyusedpreservatives
include,commonsalt,sugar,dextrose,spices,vinegar,ascorbicacid,benzoicacidanditssalt,SO2
and the saltsof sulphuricacid,nitrates,sorbicacidanditssalts,propionicacidanditssalts,lactic
acid andits salts.
The featuresof potassiummetabisulphateare:(1) It release the SO2andit isunstable;(2) It isused
for the fruitwhichhave nonwatersolventpigment(colourless);(3) Itcan not be usedinnaturally
colouredjuicessuchasphalsa,jamunbecause theyhave the anthocyninpigment;(4) Itcan not be
usedinthe product whichare packedin containerbecause itactson the tin containersandoil;(5)
Hyd
8.2 Factors affecting the growth of microorganisms infoods
You will learn more about food preservation methods in Study Session 10.
The growth of microorganisms in food products can be affected
by extrinsic factors and intrinsic factors, as you will see below. By understanding the
factors affecting the growth of microorganisms in food we can know how to keep
food safe to eat. This knowledge can also help us to work out how to preserve food
for longer.
8.2.1 Extrinsic factors
Extrinsic factors are factors in the environment external to the food, which affect
both the microorganisms and the food itself during processing and storage. Extrinsic
factors include temperature, humidity and oxygen.
Temperature
Different microorganisms grow over a wide range of temperatures. Some
microorganisms like to grow in the cold, some like to grow at room temperature and
others like to grow at high temperatures. This is of paramount importance in food
safety, because if you know the temperature growth ranges for dangerous
microorganisms it helps you to select the proper temperature for food storage to
make them less able to grow and reproduce.
Humidity
The humidity of the storage environment is an important factor for the growth of
microorganisms at the food surfaces. If you store food in a dry
atmosphere, microorganisms are less able to grow than if the food is stored in a
humid (moist) environment. Therefore, dry conditions are better for food storage than
moist conditions.

Oxygen
Many microorganisms need oxygen in order to develop and reproduce: these are
called aerobic microorganisms. A good example is Escherichia coli, a faecal
bacterium which grows readily on many foods. If you keep food in a low oxygen
environment, aerobic bacteria cannot grow and multiply. Conversely, there are some
microorganisms that grow without oxygen, called anaerobic microorganisms. An
example of this is Clostridium botulinum, the bacterium causing botulism, which can
survive in very low oxygen environments such as tinned foods.
8.2.2 Intrinsic factors
Intrinsic factors exist as part of the food product itself. For example, meat has
certain characteristics that may promote the growth of certain microorganisms. The
following common intrinsic factors affect the growth and multiplication of
microorganisms in foods.
pH
pH is pronounced ‘pee-aitch’.
The scientific term pH is a measure of how acidic or alkaline an environment is, on a
scale that has ‘neutral’ (neither acid nor alkaline) at pH7. Environments that are
acidic have pH values below 7; those that are alkaline have pH values above 7. Most
microorganisms grow best at close to the neutral pH value (pH 6.6 to 7.5). Only a
few microorganisms grow in very acid conditions below a pH of 4.0. Bacteria grow at
a fairly specific pH for each species, but fungi grow over a wider range of pH values.
For example, most meats naturally have a pH of about 5.6 or above. At this pH meat
is susceptible to spoilage by bacteria, moulds and yeasts; however the pH of meat
can be lowered by pickling, which makes it less favourable as an environment for
microorganisms to grow in.
Moisture content (water activity, aw)
Microorganisms need a moist environment to grow in. The water requirements of
microorganisms are described in terms of water activity (represented by the symbol
aW), a measure of how much water is present. The water activity of pure water is aW =
1.00. Most foodborne pathogenic bacteria require aW to be greater than 0.9 for
growth and multiplication; however, Staphylococcus aureus may grow with aW as low
as 0.86. But even Staphylococcus aureus cannot grow and multiply in drier food like
bread, which has aW = 0.7, although fungi can (Figure 8.1).

rogenSulphide (H2S) whichhasanunpleasantsmell andalsoformablack compoundwiththe base
plate of containers;(6) Bestto control mouldsthanbacteria;(7) 350 ppm KMS is mostlyusedinfruit
juice products.Featuresof sodiumbenzoate are:(1) Itis saltof benzoicacidandsoluble inwater;(2)
It delaysthe fermentationinthe juices;(3) Itis commonlyusedinthe productwhichare having
natural coloursuch as anthocyninpigment;(4) Itismore effective againstthe yeast;(5) 750 ppm
Sodiumbenzoate ismostlyusedinfruitjuices,squashesandcordials.
.3 Routes of microbial contamination of food
Bacteria are a major source of microbial contamination of food, i.e. the undesired
presence in food of harmful microorganisms or the harmful substances they produce.
Viruses, parasites and fungi are also able to contaminate food and cause foodborne
illnesses in humans. Microorganisms can enter food through different routes.
Look at Figure 8.3, which was introduced in Study Session 1, and notice that eating
contaminated food is a component of many transmission routes. The most common
routes of entry are discussed below.
View larger image
Figure 8.3 Routes of disease transmission. (Source: as Figure 1.2(a))
8.3.1 Air and dust

Microorganisms are found everywhere in our environment. Many types can be found
in air and dust, and can contaminate food at any time during food preparation or
when food is left uncovered (Figure 8.4). Imagine a kitchen where food is prepared
and stored in rural communities, and think how easily microorganisms in the air and
dust could contaminate the food.
Figure 8.4 Butter for sale in uncovered containers open to the air. (Photo: Janet
Haresnape)
8.3.2 Soil, water and plants
Many microorganisms present in soil and water may contaminate foods.
Microorganisms also grow on plants and can contaminate food if care is not taken to
remove them by washing or inactivate them by cooking. Soil is a particularly rich
source of Clostridium bacteria. Water may be contaminated by faeces. Plants may
also be contaminated by faeces if untreated sewage has been used as a fertiliser.
8.3.3 Gastrointestinal tract
The intestines of all humans and animals are full of microorganisms, some of which
are beneficial but others are pathogenic. Bacterial pathogens such as Salmonella,
Campylobacter and Escherichia coli (strain O157:H7) are common examples.
Contamination of foods by faecal material is the major cause of food poisoning
events. This includes indirect contamination, for example from people’s hands if they
prepare food without washing their hands after visiting the latrine/toilet (see below).

Escherichia coli (abbreviated to E.coli) exists in many harmless varieties or ‘strains’,
but some strains are pathogenic. The strain called E.coli O157:H7 causes a
potentially fatal foodborne disease in humans.
8.3.4 Animals
Many foodborne microorganisms are present in healthy animals raised for
food, usually in their intestines, hides, feathers, etc. Meat and poultry carcasses can
be contaminated during slaughter by contact with small amounts of intestinal
contents. For example, in animals slaughtered in rural communities without any
safety measures, microorganisms present in the animals’ intestines can easily
contaminate the meat.
Animal hides are an important source of contamination of the general environment,
the hands of meat workers, and skinned meat carcasses. Hides are a primary source
of E.coli O157:H7 and Salmonella species, both of which cause sickness and
diarrhoea. Hides become contaminated either because the outside of the hide is
dirty, or because once removed from the animal, the inside of the hide is a good
breeding place for microorganisms.
8.3.5 Animal feeds
Animal feeds are a source of microorganisms, especially Salmonella, which can
contaminate poultry and other farm animals. The organisms in dry animal feed
spread throughout the local environment and may get on to animal hides, hair and
feathers, as well as on people who handle the feeds.
8.3.6 Food handlers
The term food handler can be applied to anyone who touches or handles food, and
this includes people who process, transport, prepare, cook and serve food. The
presence of microorganisms on the hands and outer garments of food handlers
reflects the standard of hygiene in the environment and the individuals’ personal
hygiene (as you learned in earlier study sessions). The microorganisms transmitted
to foods by food handlers may come from the hides of animals, soil, water, dust,
gastrointestinal tracts and other environmental sources. In food preparation at home,
foodborne microorganisms can be introduced from the unwashed hands of people
who are infected by bacteria and viruses, and who cook and serve the food to family
members.
8.3.7 Food utensils
Food utensils are cutting boards, knives, spoons, bowls and other equipment used
in food preparation, which may become contaminated during food processing and
preparation. For example, in families where there is no access to running water, the
food utensils may not be properly cleaned, stored and handled, and may become a
major route of food contamination.

8.3.8 Cross-contamination
Cross-contamination of food is the transfer of harmful microorganisms between
food items and food contact surfaces. Prepared food, utensils and surfaces may
become contaminated by raw food products and microorganisms. These can be
transferred from one food to another by using the same knife, cutting board or other
utensil without washing it between uses. A food that is fully cooked can become re-
contaminated if it touches raw foods or contaminated surfaces or utensils that
contain pathogens. For example, you should never:
 allow raw meat to touch cooked meat
 put cooked meat on a cutting board that has just been used for raw meat
without cleaning it first (Figure 8.5)
 store raw meat on a shelf above cooked meat so that it could leak blood and
raw juices on to the cooked meat below.
Figure 8.5 Never put cooked meat on an unclean cutting board that has been used
to prepare raw meat. (Photo: Basiro Davey)
8.3.9 Unsafe temperature
An unsafe temperature for food storage is a major factor in food contamination.
Many microorganisms need to multiply to a very large number before enough are
present in food to cause disease in someone who eats it. However, if bacteria can
have warm, moist conditions and an ample supply of nutrients, one bacterium can
reproduce by dividing (on average) every half an hour and can produce 17 million
bacteria in 12 hours! So, if you leave lightly contaminated food out overnight, it will
be highly contaminated and infectious by the next day.
8.3.10 Poor personal hygiene
Poor personal hygiene of food handlers is another major factor in food
contamination. The most important contaminants of food are the microorganisms

excreted with faeces from the intestinal tract of humans. These pathogens are
transferred to the food from faecal matter present on the hands.
8.3.11 Pests
Foods can be damaged and also contaminated by pests. Many stored grains are lost
through the damage done by pests, including termites (mist), beetles, locusts,
cockroaches, flies and rodents such as rats and mice. Pests can damage and
contaminate foods in various ways, such as boring into and feeding on the insides of
grains, or tunnelling into stems and roots of food plants. For example, weevils cause
large losses of stored grains, especially in warm and humid conditions such as in
lowland areas of Ethiopia.
Pests also damage the protective skin of foods allowing microorganisms to get inside
the food and causing it to rot more quickly. Pests can pollute food with their excreta,
and with bodies and body fragments when they die. They also transfer
microorganisms on to food while walking on it (Figure 8.6). Flies and cockroaches
readily move between wastes and foods, transporting microorganisms with them as
they go.
Figure 8.6 Insects can leave dirt, excreta and possibly pathogenic microorganisms if
they are allowed to crawl on food. (Photo: Basiro Davey)
8.4 Avoiding food contamination
You now know that food can be contaminated from sources in the natural
environment, people, food preparation surfaces and utensils, raw and uncooked
food, animals, pests, and waste material. To prevent contamination, food production
and preparation operations need to be carefully controlled.
8.4.1 Microbial food contamination
Prevention of microbiological (often abbreviated to ‘microbial’) contamination is an
important function in food preparation, as summarised in Box 8.1.

Box 8.1 Avoiding microbial food contamination
Food handlers should follow these strategies:
 Thorough handwashing before and during food preparation, especially after
using the toilet, and handling raw food or waste.
 Soap/ash sanitiser and clean water should be available for handwashing at
convenient locations.
 Sick food handlers should not prepare food! One sick person can cause a
foodborne disease outbreak, particularly where people are in crowded or
unsanitary living conditions.
 Raw and cooked foods should be separated, because raw foods are a source of
microorganisms and can recontaminate prepared foods.
8.4.2 Chemical contamination of food
Attention also needs to be given to possible chemical contamination of food. Food
can be contaminated through the misuse or mistaken handling of chemicals,
including pesticides, bleach and other cleaning materials. All chemicals (detergent,
disinfectant, sanitiser) used in the food preparation area should be removed before
food preparation begins, to prevent any chemical contamination of the food.
Other possible sources of chemical contamination are:
 reusing containers which have been used for chemicals (Figure 8.7)
 using chemical sprays (e.g. to kill cockroaches) in areas where food is exposed
 accidentally adding chemicals which have a texture similar to table salt or sugar
during food preparation; they should always be stored separately.

Figure 8.7 The can that is being used to scoop salt from this sack has previously
been used for insecticide. (Photo: Pam Furniss)
8.4.3 Physical contamination of food
Physical contaminants include stones, pieces of glass, and metal. Physical
contamination can occur at any stage of the food chain: for example, stones, bones,
twigs, pieces of shell or foreign objects can enter food during handling and
preparation. These materials should be removed, if possible, for example by sieving
or picking out the items with clean fingers.
8.5 Food spoilage
Food spoilage is the process of change in the physical and chemical properties of
the food so that it becomes unfit for consumption. Food spoilage is any undesirable
change in food. Most natural foods have a limited life: for example, fish, meat, milk
and bread are perishable foods, which means they have a short storage life and they
easily spoil. Other foods also decompose eventually, even though they keep for a
considerably longer time. The main cause of food spoilage is invasion by
microorganisms such as fungi and bacteria.
8.5.1 Microbial spoilage
Microbial spoilage is caused by microorganisms like fungi (moulds, yeasts) and
bacteria. They spoil food by growing in it and producing substances that change the
colour, texture and odour of the food. Eventually the food will be unfit for human
consumption.
When food is covered with a furry growth and becomes soft and smells bad, the
spoilage is caused by the growth of moulds and yeasts (look back at Figure 8.1).
Microbial spoilage by moulds and yeasts includes souring of milk, growth of mould
on bread and rotting of fruit and vegetables. These organisms are rarely harmful to
humans, but bacterial contamination is often more dangerous because the food does
not always look bad, even if it is severely infected. When microorganisms get access
to food, they utilise the nutrients found in it and their numbers rapidly increase. They
change the food’s flavour and synthesise new compounds that can be harmful to
humans. Food spoilage directly affects the colour, taste, odour and consistency or
texture of food, and it may become dangerous to eat. The presence of a bad odour
or smell coming from food is an indication that it may be unsafe. But remember that
not all unsafe food smells bad.
 What is the difference between food contamination and food spoilage?
Reveal answer
The term contact spoilage is used when microbial spoilage is the result of direct
contact or touching between the food and any contaminated or unclean surface such
as shelves, food preparation boards or unwashed hands. It also includes food-to-
food contact, for example between cooked meat and raw meat or between rotting
fruit and sound fruit.

8.5.2 Physical spoilage
Physical spoilage is due to physical damage to food during harvesting, processing or
distribution. The damage increases the chance of chemical or microbial spoilage and
contamination because the protective outer layer of the food is bruised or broken and
microorganisms can enter the foodstuff more easily. For example you may have
noticed that when an apple skin is damaged, the apple rots more quickly.
8.5.3 Chemical spoilage
Chemical reactions in food are responsible for changes in the colour and flavour of
foods during processing and storage. Foods are of best quality when they are fresh,
but after fruits and vegetables are harvested, or animals are slaughtered, chemical
changes begin automatically within the foods and lead to deterioration in quality.
Fats break down and become rancid (smell bad), and naturally-occurring enzymes
promote major chemical changes in foods as they age.
Enzymic spoilage (autolysis)
Every living organism uses specialised proteins called enzymes to drive the
chemical reactions in its cells. After death, enzymes play a role in the decomposition
of once-living tissue, in a process called autolysis (self-destruction) or enzymic
spoilage. For example, some enzymes in a tomato help it to ripen, but other
enzymes cause it to decay (Figure 8.8). Once enzymic spoilage is under way, it
produces damage to the tomato skin, so moulds can begin to can attack it as well,
speeding the process of decay.
Figure 8.8 Role of enzymes in tomato spoilage: the tomato on the right has also
been attacked by fungi (moulds), speeding its decay.
Enzymic browning
When the cells of fruits and vegetables such as apples, potatoes, bananas and
avocado are cut and exposed to the air, enzymes present in the cells bring about a
chemical reaction in which colourless compounds are converted into brown-coloured
compounds. This is called enzymic browning. If the food is cooked very soon after
cutting, the enzymes are destroyed by heat and the browning does not occur. For
example, apples are prone to discolouration if cut open when raw, but when cooked
they do not go brown.
8.5.4 Appearance of spoiled food

Spoiled food is generally more a problem of appearance than a problem of disease
causing. In food spoilage, the changes in appearance or texture of the food, such as
rottenness, softness and change in colour, taste or odour are usually obvious,
whereas in contaminated food such characteristics may not be noticed. A large
majority of the microorganisms responsible for food spoilage are not pathogenic to
humans. However, you should advise people in your community that they should not
eat food that is spoiled because it is not nutritious and may make them sick (cause
vomiting).
8.6 Factors affecting food spoilage
Finally, we turn to the factors that can increase or delay the process of food spoilage.
They include its water content, environmental conditions, packaging and storage.
8.6.1 Water content
The amount of water available in a food can be described in terms of the water
activity (aw).
 Can you recall the aW of pure water?
Reveal answer
The water activity of most fresh foods is 0.99. This means that they have a very high
water content and can support a lot of microbial growth.
 Meat is traditionally dried by adding table salt to it. Can you suggest why salting
enables the meat to be stored for a long time?
Reveal answer
8.6.2 Environmental conditions
No matter whether food is fresh or processed, the rate of its deterioration or spoilage
is influenced by the environment to which it is exposed. The exposure of food to
oxygen, light, warmth or even small amounts of moisture can often trigger a series of
damaging chemical and/or microbial reactions. Changing the environment can help
to delay spoilage. For example, storing foods at low temperatures reduces spoilage
because both microbial and enzymic decay is faster at higher temperatures.
8.6.3 Packaging and storage
Packaging is a means of safeguarding food when it is raw, or after it has been
processed or prepared. It helps to protect food against harmful contaminants in the
environment or conditions that promote food spoilage including light, oxygen and
moisture. The type of packaging is a key factor in ensuring that the food is protected.
Packaging of foods in cans, jars, cartons, plastics or paper also serves to ensure
food safety if it is intact, because it provides protection against the entry of
microorganisms, dust, dirt, insects, chemicals and foreign material.

Summary of Study Session 8
In Study Session 8, you have learned that:
1. One of the main, and most effective, ways of protecting food consumers is to
prevent food from becoming contaminated by pathogenic microorganisms.
2. Cross-contamination is a process whereby pathogens are transferred from one
food source to another, e.g. when pathogens in raw food are transferred to
cooked foods which will not be cooked again, so any pathogens they contain
will survive to infect the consumer.
3. Food may become contaminated by food handlers, contaminated surfaces and
utensils, pests, and contaminated water used in food preparation.
4. Separate storage and preparation areas, and separate utensils, should always
be used for raw foods.
5. Foods can be contaminated through the mishandling of chemicals such as
pesticides, bleach and other cleaning materials.
6. Food can be contaminated by physical contaminants such as stones, glass,
bones and feathers at any stage of the food chain.
7. Food spoilage is the process of changing the physical and chemical properties
of the food, making it unfit for consumption.
8. Food spoilage is caused by living microorganisms and also by enzymic action
(autolysis). Spoilage can also be brought about by physical or chemical factors.
Micro-organisms in Foods
Micro-organisms, in relation to food, can have one of these 3 roles:
1. Pathogenic micro-organisms can cause infections or intoxications
2. Saprophytic micro-organism play a role in biodegradation and cause food spoilage
3. Cultured micro-organisms like probioticbacteria are used in food processing.
Pathogenic micro-organisms[✎ edit | edit source]
Pathogenic micro-organisms cause food-borne infections or intoxication, and include
bacteria, viruses, parasites and moulds. It is important to note that pathogenic bacteria and
viruses usually do not cause food spoilage, their contamination cannot be seen nor tasted.
 The main factors that contribute to occurrence of foodborne diseases are:
1. The use of raw food and ingredients from unsafe sources

2. Inadequate cooking or heat processing
3. Improper cooling and storing, for example leaving cooked foods at room
temperature for longer periods of time, or storing foods in large containers in the
fridge
4. Allowing several hours to pass between preparation and eating of food
5. Inadequate reheating
6. Improper hot holding, meaning below 65°C
7. Food handling by infected persons or carriers of infection
8. Cross contamination from raw to cooked food. For example by cutting vegetables for
salad on a cutting board where you have cut raw meat before
9. Inadequate cleaning of equipment and utensils
Bacteria[✎ edit | edit source]
 Campylobacter jejuni: Is a common cause of diarrhea humans as well as some animal
species. The transmission can be by direct contact between humans and infected animals
or their feces. More commonly, it is transmitted by the consumption of contaminated
food or water, t person-to-person spread. The symptoms range from mild diarrhea to
sever invasive disease which can include abdominal pain, fever, and blood and mucous in
stools.
 Non-typhi salmonellosis: There are more than 2000 serotypes of salmonella spp, of
which only a few cause Salmonella gasteroenteritis in humans. The symptoms include
acute watery diarrhea accompanied by nausea, cramps and fever. Blood in stool may
occur. Animals are the main reservoir, and transmission occurs by ingestion of
contaminated products. Foods especially at risk are poultry, meat, eggs and milk.
 Salmonella typhi and paratyphi: Cause typhoid fever and paratyphoid fever
respectively. Since the reservoir for both these bacteria are usually humans, transmission
occurs mainly through person-to-person contact or contamination of food by food
handlers.
 Staphylococcus aureus: The source of this infection are humans. The bacteria are often
found in smaller amounts in the nose and on the skin of clinically healthy people. Higher
amounts can be found in lesions of skin such as infected eczema, psoriasis or any other
pus draining lesion. These people should therefore not be handling food. Food
poisoning caused by this bacteria is caused by heat resistant staphylotoxin, resulting in
diarrhea, vomiting, cramps and fever. The symptoms start suddenly and usually
disappear within 24 hours.

 Escherichia coli: There are several serotypes, some of which are harmless to humans
whereas others can cause gastroenteritis. Enterotoxigenic E.coli is the most common
cause of traveller's diarrhea. The source is humans, and transmission usually occurs
through contaminated food and water.
 Listeria monocytogenes: This bacterium is highly associated with food stored for long
periods of time in the fridge because it is ubiquitous, and has the ability to grow slowly,
even at low temperatures. Can be fatal in immunocompromised, where it can cause
septicemia and meningitis.
 Shigella: The source is humans and primates. Because it has low infectious dose, the
main mode of transmission is person-to-person contact. It can also be transmitted
through infected food and water. The symptoms of shigellosis are fever and watery
diarrhea. The infection can also manifest as a dysenteric syndrome which includes fever,
abdominal cramps and tenesmus, and frewuent, small volume, bloody stools containing
mucous.
 Vibrio Cholerae 01: The source of this infection is humans. The main mode of
transmission is through contaminated water and food, or person-to-person spread in
overcrowded, unhygienic situations. It causes severe watery diarrhea, which can reach up
to 20 liters per day.
 Clostridium Botulinum: Its source is the intestinal tract of fish, birds, and mammals. It is
also widely distributed in nature. The bacterium is a spore producing anaerobe, with a
highly potent heat labile toxin that affects the nervous system.
Viruses[✎ edit | edit source]
Viruses, unlike bacteria, cannot multiply in foods. The main mode of transmission therefore
by food handlers and the use of dirty utensils, which transfer the virus to food whereupon it
is ingested by humans.
 Rotaviruses and Norwalk virus are the major causes of gastroenteritis

 Viral hepatitis A outbreaks are mainly caused by asymptomatic carriers which handle
food.
Parasites[✎ edit | edit source]
Many parasites, such as the helminths, have a complex lifecycle involving more than one
host. The major route of transmission for these parasites to humans is by the route of food.
The consumption of undercooked pork or beef, or the consumption of raw salads washed in
contaminated water seems to be the trend.
Taenia solium and T. saginata: also called pig and beef tapeworms. Their cysts,, present in
the muscle of the animal are ingested and the adult worm develops in the gut. The ova may
develop into larvae that may invade other tissues, such as the brain, forming cysticercosis
and severe neurological disorders as a consequence.
Trichinella spiralis: is found in undercooked pork. The larvae can invade tissues and cause a
febrile illness.
Giardia lambila: This infection can be foodborne, waterborne or spread by interpersonal
contact. It causes acute or subacute diarrhea, with malabsorption, fatty stools, and
abdominal pain and bloating.
Entamoeba histolytica: The transmission is mainly food- or waterborne. The cysts pose a
major problem since they are highly resistant to chemical disinfectants, including
chlorination. The infection is usually asymptomatic, but may appear as either a persistent
mild diarrhea or a fulminant dysentery.
Food Spoilage[✎ edit | edit source]
It is the change of look, consistency, flavor and odor of foods, and is caused by bacteria,
moulds and yeasts.
Bacteria: Examples of action of bacteria involvedin food spoilage:
1. Lactic acid formation: Lactobacillus, Leuconostoc
2. Lipolysis: Pseudomonas, Alcaligenes, Serratia, Micrococcus
3. Pigment formation: Flavobacterium, Serratia, Micrococcus
4. Gas formation: Leuconostoc, Lactobacillus, Proteus
5. Slime or rope formation: Enterobacter, Streptococcus

Moulds: Some strains produce mycotoxins under certain conditions
1. Aspergillus produces aflatoxin, ochrtoxin, citrinin and patulin
2. Fusarium
3. Cladosporium
4. Alternaria
Mycotoxins can penetrate into the parts of food that are not visibly mouldy as well. It is
therefore necessary to throw away all of the food if any part of it is mouldy. They are also
notoriously difficult to destroy as they are stable to both heat and chemicals.
 Hepatotoxins: aflatoxins, sporidesmins, luteoskyrin
 Nephrotoxins: ochratoxin, citrinin
 GIT toxins: trichocetens
 Neuro- and myotoxins: tremorgens, citreoviridin
 Dermatotoxins: verukarins, psoralen, sporidesmins, trichocetes
 Respiratory tract toxins: patulin
Foods most at risk for moulds:
1. Grains and grain products - many mycotoxin types
2. Peanuts, nuts and pulses - aflatoxin
3. Fruits and vegetables (raw and preserved) - patulin
4. Milk and milk products - aflatoxin
It is important to note that if any contaminated fodder is fed to animals, this is metabolized
and the toxic derivatives can be found in animal products consumed by humans, e.g. milk
and meat.
Microorganisms in food production[✎ edit | edit source]
Most commonly used microorganisms are yeast, bacteria, moulds, or a combination of these.
A good example of microorganism usage in food production is the process of fermentation,
which results in the production of organic acids, alcohols and esters. These help to either:
1. Preserve the food
2. generate distinctive new food products
Yeast in food production[✎ edit | edit source]

 Leavened bread and bakery products: Saccharomyces cervisiae ferments sugars to
produce CO2, the gas that gives the porous structure of bakery products. It also
contributes to the flavor by formation of alchols, aldehydes, esters etc.
 Beer
 Wine
 Vinegar
 Pickles
Bacteria in food production[✎ edit | edit source]
 Fermented milk products: Lactobacillus, Lactococcus, Bifidobacterium
 A variety of foods including Indian dosa, rabri: fermentation by Leuconostoc
mesenteroides, S. faecalis
 Probiotics: are live food supplements used in yoghurt and other fermented milk
products. It includes Lactobacillus acidophillus and Bifidobacterium bifidum. A minimum
of 108 bacteria per 1 ml must get to the colon alive to have any significant effect. These
bacteria improve the microbial spectrum in the gut and thus contribute to the following
effects:
1. Influence immunity and hence prevent or make diarrheal diseases milder
2. Decrease the risk of colon cancer
3. Decrease cholesterol absorption
4. Produce acids that decrease the pH in the gut and thus increase the absorption of
minerals such as calcium and phosphorous.
Mould in food production[✎ edit | edit source]
 Cheese: Penicillium roqueforti and Penicillium camemberti (note that this one produces
mycotoxin at 25°C, therefore the cheese production must happen at 15°C)
 Dry salami: makes the use of Penicillium and Scopulariopis moulds.
 Soy sauce: Aspergillus spp, especially A. oryzae, are involved in this production. There is
also a subsequent lactic fermentation where lactic bacteria produce lacticacid.
 Sake: is produced using a combination of the mould Aspergillus oryzae and yeast.

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