FOOD SPOILAGE

Food spoilage

Spoilage is the deterioration of food which makes it gosour, rotten or moldy.• Most fresh foods spoil within days when they are stored

without care in warm surroundings.When is food spoiled?• Offensive smell• Mouldy surface• Strongly sour or sharp flavor• Different color• Gas development (e.g. in bulging tins) or shiny surface. 1

Spoilage

When food is spoiled, the characteristics of the food are changed in such a way that it is no longer acceptable for consumption (not necessarily dangerous)

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Phytophtora on potato

Mouldy Bread

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Monilia on peach4

Gas production resulting in a blown can 5

Spoilage of food may be a result of one or more of the following:-

(1) Growth and activity of microorganisms in the food, often a succession of organisms is involved.

(2) Contamination of food by bacteria

(3) Action of enzymes of the plant or animal food product

(4) Worms, bugs, weevils fruit flies and moths may damage food and renders it unfit for human consumption

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The main microorganisms responsible for the contamination of food are:-

» Bacteria

» Moulds

» Yeast

Each group has many species which are responsible for different forms of contamination.

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• All three groups require a medium in which to grow andreproduce. food is an ideal medium as it provides nutrientand adequate moisture.

• Microorganism’s contaminate food by producing wasteproducts or toxins (poisons) or simply makes the foodinedible by their presence.

• In some cases, if contaminated food is eaten it may causeillness due to food poisoning. Microorganism which causesfood poisoning and /or infections are called pathogenic(harmful) bacteria.

• Note: Not all microorganisms are harmful; some are used inthe food industry to produce foods such as cheese yogurtand soy sauce.

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Examples of Micro-organisms in Food

Useful:Fermentation: Lactic acid bacteria, yeast, moulds

Spoilage (quality/shelf life):bacteria, yeast and moulds

Pathogenic (hazards):bacteria (Listeria monocytogenes, Salmonella, Campylobacter, E.coli, Clostridium botulinumStaphylococcus aureus, Bacillus cereus); parasites; viruses ;moulds

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Bacteria

• Are single celled organisms found in manyplaces including air, water (including man).

• There are thousands species some of which areharmful to man and some are beneficial.

• They can be classified according to their shape1. Spherical bacteria2. Rod shaped bacteria 3. Spiral shaped bacteria

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These are called cocci and they form chains called streptococci which are cause of disease such as tonsillitis

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Others forms pairs called diplococci which are the cause of pneumonia

Clusters: called staphylococci which are the cause of boils, septic wounds and food poisoning

» Many bacteria of this shape are called bacilli and are thecause of disease such as diphtheria, tuberculosis typhoidand food poisoning

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Some are called clostridia and cause food poisoning some have tiny hair projection called cilia to enable them to swim through fluids

» These can cause diseases such as cholera, syphilis and infection jaundice.

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Under suitable conditions of temperature, moisture andfood supply bacteria can multiply or reproduce veryrapidly. They reproduce by binary fission and in a spaceof twelve hours under right conditions a single bacteriacan give rise to 16,000,000.

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» When a large number of bacteria are present are inone place, they form a colony which is usually visibleto the naked eye.

» If conditions of division are unfavourable e.g.moisture is lacking, bacteria are able to form sporeswhich remain dormant until the right conditionsreturn, when the spore will germinate. Such sporesare often resistant to heat.

» Many bacteria do not require a source of oxygen togrow and multiply. Such bacteria are called anaerobicbacteria and this account for their ability to grow infood and intestines where oxygen supplies arelimited. Some bacteria do require oxygen and arecalled aerobic bacteria

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Effect of Temperature and time on growth of Bacteria

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Some bacteria can withstand extreme temperatures, butmost are destroyed at temperature of around 60oC.

Bacteria are able to multiply most rapidly at around 37oCand this has important implications for the preservationof food by heat.

At very cold temperatures most bacteria stop multiplyingand become dormant until the temperature conditionsbecome favourable again, this has important implicationsfor the freezing and cold storage of foods and their use.

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» Many bacteria are affected by high concentration ofsalt acid or sugar. These interfere with the normalmetabolic processes of the bacterial cells and eitherdestroy them or prevent reproduction suchsubstances are used for food preservation.

» There are some however some bacteria which thrivein such conditions and may therefore requiredifferent treatment to prevent their growth.

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» Bacteria can cause food poisoning symptoms in different ways:

» Physical presence of bacteria in the food if bacteria have hadthe opportunity to multiply in large numbers in a food, thenphysical present in the intestine may cause irritation and foodpoisoning symptoms. This is also referred to as infection

» Production of waster products (Toxins) bacteria like all otherliving things has to dispose off waste products which are theresult of metabolic processes. These can cause irritation to theintestine and food poisoning symptoms even when only asmall when only a small number of bacteria are present. Thetoxins are not destroyed by normal cooking temperatures

» Germination of spores: The germination of bacterial spores isusually accompanied by the productions of highly poisonssubstances (exotoxins) only a small amount of which can leadto severe illness or possibly death. In some cases, just onespore can produce sufficient toxin to cause food poisoning. 1

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˃ Using the same utensils to serve contaminated food and other foods

˃ Careless attention to personal hygiene while handling food e.g. not washing hands after visiting the toilet, touching nose while preparing food.

˃ Leaving skins infection and cuts covered while preparing food

˃ Coughing, sneezing or spitting while preparing food

˃ Incomplete cleansing of food utensils and serving dishes

˃ Pests e.g. houseflies, cockroaches, beetles and certain moths, rodent e.g. rats, mice etc

˃ Contaminated water supply˃ Household pets e.g. dogs, cats, hamsters ˃ Soil and dust.

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Bacteria types Name Incubation/Duration

Symptoms Cause notes

Cocci Stamphylococcus

1-6hrs1-6days

Severe vomitingdiarrheaexhaustion

Nose, skin cutscooked meat

Poisoning due totoxins heat doesnot destroytoxins

Bacilli Salmonellatyphimurium

12-48hr7days

Headache fevervomiting andabdominal pain

Faeces, slicedcooked meatpoultry,sausagesegg, pies

Cause foodpoisoning. Canbe fatal

Clostridia Clostridiumbotulinum

12-36hrs fatalwithin 7days

Double visiondifficulty withbreathingtakingand swallowing

Improperlycanned foodsespecially meatvegetables

Rare but in mostcases, exotoxinproduced

Clostridia Clostridiumwelchii

8-24hrs1-2 days

DiarrheaAbdominal painheadache

Meat, piesgravy, cannedmeat

Poisoning due totoxin andbacteria in gut

Bacilli Salmonella typhi 1-3 weeks 1-2months

HeadacheTiredness fever,rashhaemorrage

Sewage, waterflies cream, cakewater cress,canned meat

Can fatal slowrecovery

Bacilli Bacillus cereus 2-18 hrs1-3days

Vomitingdiarrhea

Faeces coldmeats gravy

Poisoningcaused by

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» Moulds are tiny microorganisms which are just visibleto the naked eye. They grow on many types of food,especially cheese, bread and fruit. They require warmmost conditions to grow, but are able to grow at aslower rate in cool places. Moulds reproduce by meansof sporulation. Spores are released into theatmosphere and carried in the air. If they land on asuitable food, the spores germinate and a new mouldappears. There are many types of mould, but amongthe more common types are

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Fusariumon maizeMouldy

cheese

Aspergillus

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» Food that is contaminated with mould often appears tobe safe to eat as only the outer part is affected by mouldgrowth. However, recent research has shown thatmetabolites (toxins) produced by mould which migrateinto the food could be harmful to many organs of thebody.

» These toxins are called mycotoxins it is thereforeadvisable to discard mould food completely rather justremove the mouldy part.

» Mould growth is prevented by cool dry storage, heatingto destroy moulds and acidic conditions. However, notall moulds are harmful. Specially produced moulds areadded to certain cheeses e.g. stilton, Danish blue, todevelop characteristic flavours.

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» Yeasts are microscopic single celled microorganismswhich are found in the air and soil and on the surface offruits. Some are able to tolerate fairly high acidic, saltand sugar concentrations and can grow without thepresence oxygen.

» Yeasts reproduce by budding in presence of water,warmth and food.

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Yeast cells

Budding

yeast

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» The cells remain dormant in very coldconditions and are killed at temperatureapproaching 100oC.

» Growth is inhibited in the presence of high saltconcentrations. Yeast can spoil foods such asjam and fruits by fermenting the sugar, toproduce alcohol and carbon dioxide gas.

» The time that this takes will depend on theconcentration of sugar in the food and lengthof time it is stored. Fruit flavoured yogurts mayalso be affected in this way. 27

» Enzymes are found in all fresh food and although theiractions is important to the ripening of certain foods(such as fruits and vegetables) the continuance of thisaction after the peak of maturity brings aboutundesirable changes in the food tissue these changesinclude darkness of cut tissue or surfaces the formationof soft sports and the development of off flavours.

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The bruises and cuts caused by these insects serve aspathways by which microorganisms reach the innertissue.

There are various sources of food spoilage microorganisms such as

i. Animals

ii. Sewage

iii. Soil

iv. Water

v. Air

vi. During handling and processing 29

Sources of microorganisms from animals include the surfaceflora, the flora of the respiratory tract and the flora of thegastrointestinal tract.

The natural surface flora of meat usually is not as importantas the contaminating microorganisms from their intestinalor respiratory tract. Howerer, hides, hoofs and haircontain not only large numbers of microorganisms fromsoil, manure, feed, and water but also important kind ofspoilage organisms.

Feathers and feet of poultry carry heavy contamination fromsimilar sources, the skin of animals may containmicrococci and staphylococci may find their way into thecarcass and then to the final raw products. The faeces andfecal contaminated products of animals can contain manyenteric organisms including salmonella

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» The natural surface flora of plants varies within plants but usually include, Pseudomonas Micrococcus and Coliforms and lactic acid bacteria.

» Exposed surfaces of plants become contaminated from soil, water sewage, air and animals some fruits have been found to contain viable microorganism in their interior.

» Normal healthy tomatoes have been found to contain Pseudomas and Coliforms. Yeasts have been found inside undamaged fruits.

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When untreated domestic sewage is used to fertilize crops,there is likelihood that the raw plant foods will becontaminated with human pathogens especially thosecausing gastrointestinal diseases.

The use of night soil as a fertilizer still persists in somecountries such as China.

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» The soil contains the greatest variety ofmicroorganisms than any source of contaminationnot only numerous kinds of microorganism but alsolarge total numbers are present in fertile soil ready tocontaminate surfaces of plants growing on or in themand the surfaces of animals coming over the land.

» Modern methods of foods handling usually involvewashing the surfaces, of foods and hence the removalof much of the soil from those surfaces.

SOIL

» Natural water contains not only their natural flora but alsomicroorganisms from soil and possibly from animals orsewage.

» Surface water from animals or pools and stored water inlakes and dams vary considerably in their microbialcontent. Ground water from springs and or wells havepassed through layers of rocks and soil to a definite leveland hence most of the bacteria as well as the greater partof suspended material, have been removed by subsequentfiltration.

» The kinds of bacteria in natural water are chiefly species ofPseudomonas, Proteus Micrococcus Bacillus andStreptococcus. 34

» Contamination of foods from the air may be importantfor sanitary as well as economic reasons.

» Disease organisms especially those causing respiratoryinfection may be spread among employees by air or tothe food.

» Microorganisms get into the air by means of dust, solidsuspended materials and moisture droplets fromcoughing sneezing or talking.

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Contamination of foods from the natural sources asdiscussed above take place before the food is harvestedor gathered or during handling and processing of thefood.

Additional contamination may come from equipmentcoming in contact with foods, from packaging materialsand from the personnel.

The processor attempts to clean and sanitize equipmentto reduce such contamination and to employ packagingmaterials that will minimize contamination.

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