MICROBIAL WORLD AND THEIR ROLES IN FOOD SPOILAGE - PART II

By Ahmad Mukhlis bin Abdul Rahman

FOOD SPOILAGE

Food spoilage is defined as damage or injury to food rendering in unsuitable for

human consumption.

Food must be considered spoiled if it is contaminated with pathogenic

microorganisms or various poisonous agents, such as pesticides, heavy

metals, parasites and other harmful agents

Development of “off-flavors,” odors

Development of slime/biofilmon foods

Bad taste Color change

YOU KNOW IT ….

….when you SEE it

…. or you SMELL it

…. or you TASTE it

INDICATIONS of spoilage

includes :

….or any other characteristic

that is undesirable to the

consumer

Yummy….they’re still good to eat

…right ??

Why Do Foods Spoil ?

Microorganisms Enzymes Chemicals

Includes bacteria, fungi,

viruses, protozoa etc

Molecules that speed up

or slow down chemicals

reactions usually released

by the microbes

Harmful chemicals may

result from the activity such

as oxidation of fat

Physical Injury

Could be caused

by insect damage

or moisture loss or

gain

Foods decompose from the moment they are harvested

due to attacks from enzymes, oxidation and

microorganisms.

As microbes enzymatically digest the food and use it

for themselves, they produce metabolic by-

products – some of these may be health hazards

Spoilage microbes do not have to be pathogenic –they usually just produce

toxic waste

Spoilage may be harmless or cause slight reduce of

quality; BUT some spoiled foods may be harmful to

consume

The toxic effects from consuming spoiled food are

referred to as "food poisoning", and more properly as "foodborne

illness or disease”

Why Do Foods Spoil ?

Microorganisms have to get into the food from a

source

Food environment should favour the growth of

microbes

Food need to be stored under the favourable

growth condition for a

sufficient length of time

To allow sufficient number

necessary to cause spoilage

or changes in food

To allow the produced enzyme

to spoil the food.

Sequence of Events in Food Spoilage

Microbial Spoilage in Fresh Meat, Poultry & Processed Meat

• The interior portions of meat are usually free of microbial contaminations if healthy animal is properly slaughtered.

• The fresh cut meat gets immediately contaminated with microorganisms derived from gloves, hands, tools used to cut the meat, skins, hairs, intestines of the animals and the air of the slaughter house.

• Each new surface of meat, resulting from a new cut, adds more microorganisms to the exposed tissue.

Spoilage in Fresh Meats

• The more common microorganisms occurring on fresh, meats include both bacteria and molds.

• Bacteria such as species of Bacillus, Clostridium, Escherichia, Pseudomonas, Lactobacillus, Micrococcus, Streptococcus. sp,Sarcina, Salmonella occur most commonly.

• •Molds that contaminate fresh meat include CladosporiumGeotrichum, Mucor, and Penicillium sporotrichum.

• Yeasts are less commonly occurring.

Spoilage in Fresh Meats

Spoilage in Fresh Meats under Aerobic Conditions

Indication What Happen? Microbes responsible

Surface slime Is an early indication of

spoilage, often

observed before expiry

date.

Pseudomonas,

Acinetobacter,

Moraxella, Alcaligenes,

Streptococcus,

Leuconostoc, Bacillus,

and Micrococcus

Changes in color of

meat pigment

The red color of meat,

called “bloom”, may be

changed to shades of

green, brown, grey as

result of the production

of oxidizing compound

. e.g. hydrogen

peroxides, hydrogen

sulfide.

Lactobacillus and

Leuconostoc

Under aerobic conditions bacteria may cause the following :

Indication What happen? Microbes responsible

Off odors and off taste The oxidation of unsaturated

fats may takes place

chemically in air and may be

catalyzed by light and

copper. e.g. oxidative

rancidity

Pseudomonas and

Achromobacter

Phosphorescence This rather uncommon

defect caused by

phosphorescent or luminous

bacteria which grows on the

surface of meat

Photobacterium spp.

Various surface colours due

to pigmented bacteria

• Red spot may be caused by Serratia marcescens or

other bacteria with red pigment.

• Pseudomonas syncyanea can impart blue color to the

surface

• Micrococcus or flavobacterium imparts yellow color with

yellow pigment

• Chromobacterium lividum and other bacteria gives

greenish blue or brownish black spot.Serratia marcescens

Photobacterium spp is a genus of

gram negative bacteria in the

family Vibrionacea

Indication What happen ?

Off odors and off taste • “Taints” or undesirable odors and tastes appear in a meat

• “Souring” is the term applied to almost any defect that

gives the sour odor that may be due to volatile acids. e.g.

formic, butyric,propionic acids

Under aerobic conditions MOLDS may cause the following :

Indication What happen ?

Stickiness Surface becomes sticky

Whiskers when meat is stored at temperatures near freezing, a limited

amount of mycelial growth may takes place without sporulation

Black spot This usually caused by Cladosporium herbarum

White spot Sporotricum carnis mostly causes white spots

Green patches This occurs due to species Penicillum such as P.expansum

and P.oxalicum

Decomposition of fats Many molds have lipase and hence cause hydrolysis of fats

Molds on meat

Spoilage in Fresh Meats under Anaerobic Conditions

Indication Causes

Souring It imparts sour taste to meat due to acids such as formic,

propionic, acetic acid.

Meat’s own enzymes are responsible for it

Putrefaction Putrefaction is the anaerobic decomposition of protein with

the production of foul smelling compound such as hydrogen

sulfide, indole, ammonia, amines due to species Clostridium

Taint • Undesirable odors and tastes, that appear in a meat

• Species which are responsible Psuedomonas sp. &

Psuedomonas fragi

• Sulphur compounds may also contribute off flavor

Facultative and anaerobic bacteria can able to grow within the meat under anaerobic

conditions and cause spoilage.

Following changes occurs in such conditions :

Putrefaction in progress

Poultry is a category of domesticated birds kept by humans for the purpose of collecting their

eggs, slaughtering them for their meat and feathers

Poultry is the second most widely eaten meat in the world,

accounting for about 30% of meat production worldwide

Even though poultry is concerned mostly with chicken meat, but the

principles also apply to meat of other fowl, such as turkey, goose, and

duck

Microbial Spoilage in Poultry

Microbial Spoilage in Poultry

• The skin of live birds may contain numbers of bacteria averaging 1,500 per centimeter and could also

be derived from the feet, feathers, and feces

• Contamination of the skin and the lining of the body cavity occurs during washing, plucking, and

evisceration. The process of sticking and bleeding can also introduce contamination

• Knives, cloths, air, and hands and clothing of the workers can serve as intermediate sources of

contamination

• After the handling of the meat, contamination can come from carts, boxes, or other containers

Sign of Spoilage in Poultry

Off-odour

Feels sticky,

slimy or tacky to

touch

Change in

colour

• Poultry held at 10𝐶 or below is spoiled mostly by Pseudomonas and to a lesser

degree by yeast (Torulopsis and Rhodoturula).

• Above 10𝐶 micrococci usually predominate and there is also growth of Alcaligens

and Flavobacterium.

• Iced, cut-up poultry often develops a slime that is accompanied by an odor

described as “tainted”, “acid”, “sour”, or “dishraggy”.

This is caused by the species of Pseudomonas and Alcaligens

Product Bacteria

Raw eviscerated carcasses Pseudomonas fluorescens, P. putida,

Acinetobacter, Moraxella

Dark meat, pH 6.4-6.7 Acinetobacter, Altermonas, Pseudomonas

White meat, pH 5.7-5.9 Pseudomonas sp

Chicken wrapped in oxygen- impermeable

films

Microaerophilic bacteria, lactic acid

bacteria

Vacuum-packed chicken Enterobacter

Pseudomonas on poultry’s meat

• Processed meat is defined as any meat preserved by smoking, curing or salting,

or with the addition of chemical preservatives; examples include bacon, salami,

sausages, hot dogs, hamburger, or processed deli or lunch- eon meats

• These products are composed of a variety of blended ingredients, any of which can

contribute microorganisms to the food.

• Yeasts and bacteria are the most common causes of spoilage, which is usually

manifest in 3 ways:

1. Slimy spoilage

• Like other meat products, this occurs on the surface and is caused by the

buildup of cells of yeasts, Lactobacilli, Enterococci or Brochothrix

thermosphacta.

• Washing the slime off with hot water can restore the product quality

Microbial Spoilage in Processed Meat

2. Sour spoilage

• Results from growth of lactic acid bacteria (which originate from contaminated ingredients like milk solids).

• These organisms ferment lactose and other carbohydrates in the product and produce organic acids.

3. Greening

• Due to hydrogen peroxide and hydrogen sulfide production.

• Because greening indicates more extensive product breakdown, it is not recommend eating green wieners.

Microbial Spoilage in Processed Meat

Microbial Spoilage in Fish and Seafood

Spoilage is depends on the microbial content of water in

which they live.

Microbes in different waters :

• Northern waters - Psychrophiles

• Tropical waters – Mesophiles

• Fresh waters – Aeromonas, Lactobacillus,

Brevibacterium, Alcaligens, Streptococcus

Intestine of fishes which contains most of main

microbes responsible for fish spoilage : Alcaligens,

Pseudomonas, Flavobacterium, Vibrio,

Bacillus,Clostridium, E.coli

Common genera are: Pseudomonas, Acinetobacter, Moraxella,

Alcaligens, Micrococcus, Flavobacterium, Corynebacterium,Sarcinae,

Serratia, Vibrio, Bacillus

Microbial Spoilage in Fish and Seafood

DIFFERENT MICROBES IN DIFFERENT SEAFOOD

seafood microorganism

Oysters & other shellfish Alcaligens, Flavobacterium,

Moraxella, Acinetobacter. Vibrio

including Vibrio

parahaemolyticus

Shrimps, crabs & Lobsters Bacillus, Micrococcus,

Pseudomonas, Acinetobacter,

Moraxella, Flavobacterium,

Alcaligens

Salt fish Salt tolerant or halophilic bacteria-

Micrococcus, Serratia, Bacillus,

Alcaligens, Pseudomonas

Smoked fish Molds

Seafood Microorganism

Fish Predominant organisms

vary with temperature

• At chilling temperature:

Pseudomonas,

Acinetobacter, Moraxella,

Flavobacteria

• At high temperatures:

Micrococcus, Bacillus

Autolyticenzymes

Oxidation

Bacterial activity

Spoilage due to :

Chemical spoilage processes are changes taking

place in the lipid fraction of the seafoods. Lipids

are oxidised to peroxides, aldehydes, ketones

and lower aliphatic acids. The hydro-peroxides

are tasteless but can cause brown and yellow

discolouration

Autolytic changes caused by the enzymes

increase the supply of nitrogenous compounds

(eg: amino acids, amines and glucose) From

these compounds bacteria make trimethylamine,

ammonia, amines lead to putrefaction

(decomposition of protein with the production of

foul smelling)

Fish have high nitrogen content but no carbohydrate

Unsanitized processing steps are principal

culprits in fish products with high microbial loads.

Bacteria on fresh fish are concentrated on the outer

slime, gills and intestine.

Fish undergoing spoilage has one or more of the

following signs: slime formation, discolouration,

changes in texture, off-odours, off-flavours and gas

production

Spoilage in Fish

Spoilage in other Seafood

• Crustaceans (shrimp, lobsters, crabs and crayfish)

have some carbohydrate (0.5%) and more free

amino acids so their spoilage can occur more

rapidly.

• Mollusks (oysters, clams, mussels, squid and

scallops) - have more carbohydrate (3-5%) and

less nitrogen than either fish or shellfish.

• Shellfish are filter feeders and can be expected to

contain almost any microorganism or virus that

occurs in the water where they were obtained. If

these products were taken from clean waters, then

the usual Pseudomonas and Acinetobacter-

Moraxella types of spoilage bacteria dominate.

Scallop with microbial spoilage

Microbial spoilage in fruits

& vegetables

• The organism responsible for taints (undesirable odors and tastes) are

acid tolerant bacteria: – Lactobacillus spp.

• Deterioration can be caused by action of animals, birds, bruising,

wounding, cutting, freezing, dessication or other mishandling and growth

of microorganisms, environmental conditions, and in contact with spoiled

foods.

• Microbial spoilage maybe due to:

– Plant pathogens acting on stems, leaves, flowers or roots

– Saprophytic organisms

Spoilage of Fruits and Vegetables

Fruits• 85% water,13% carbohydrate, 0.9% protein

(a bit low on nitrogen sources), 0.5% fat, 0.5% ash & trace amounts of vitamins, nucleotides, etc.

• Less water and more carbohydrate than veggies

• Low pH (1.8 - 5.6)

• Fruits are nutrient rich substrates but the pH of fruits does not favor bacterial growth.

• As a result, yeasts and molds are more important than bacteria in the spoilage of fruits.

Vegetables

• 88% water & 8.6 % carbohydrate.

• Includes readily available mono- and disaccharides like glucose and maltose, as well as more complex oligosaccharides, which are available to fewer types of microorganisms.

• 1.9% protein, 0.3 % fat & 0.84 % minerals

• Also contain fat and water soluble vitamins and nucleic acids (<1%).

• pH of most veggies is around 6.0; within the growth range of many bacteria.

• Vegetables are a good substrate for yeasts, molds or bacteria

• It is estimated that 20% of all harvested fruits and vegetables for humans are lost to spoilage by these microorganism

Spoilage of Fruits and Vegetables

Types of Spoilage in Fruits and Vegetables

1. Bacterial soft rot

• Caused by Erwinia carotovora, ferment pectins

• Pseudomonas marginalis, Bacillus and Clostridium cause water soaked appearance, a soft, mushy consistency and bad odour

2. Anthracnose

• Caused by Collectotrichum lindemuthianum

• Spotting of leaves and fruits

Bacterial soft rot in potato

Anthracnose on mangoes

Types of Spoilage in Fruits and Vegetables

3. Black mold rot

• Caused by Aspergillus niger

• Dark brown to black masses of spores of the mold termed as smut

4. Rhizopus soft rot

• Caused by species of Rhizopus

• Soft and mushy rot

• Cottony growth of mold forms black spots of

sporangia covering the foods.

Black mold rot on tomatoes

Rhizopus soft rot on sweetpotato

Types of Spoilage in Fruits and Vegetables

5. Alternaria rot

• Caused by Alternaria tenuis

• Greenish-brown to brown black spots

6. Fungal spoilage

• Results in water soaked mushy areas, brown or cream coloured areas.

• Rots of juicy fruits result in leakage

Alternaria rot on cabbage

7. Downy mildews on grapes – Phytophora, large masses of

mycellium on grapes

• caused by a fungus-like (Oomycete) organism.

• It is spread from plant to plant by airborne spores.

• Caused by Geotrichum candidum, a common soilborne

fungus that causes the disease not only in tomatoes,

but also in citrus fruits and vegetables. Also, it can be a

contaminant on tomato-handling equipment.

END OF PART II