Spoilage of Dairy,
Meat and Fish
Products
Of all foods, dairy, meat and fish products
are more vulnerable for microbial growth
High nutrient content
High level of simple nutrients
Favorable pH
High water activity
Absence of antimicrobial factors
FT 5105 Food Microbiology 2
The quality and safety of milk, dairy, meat
and fish products are of primary concern in
the industry
30 million cases of foodborne diseases are
reported each year in the U.S. at a cost of
$5-8 billion annually and 900 fatalities.
The incidence rate in Canada is estimated
at 2.2 million cases per year at a cost of $
1-3 billion annually.
FT 5105 Food Microbiology 3
Common foodborne pathogens
in dairy
Salomnella typhimarium
Salmonella typhi
Camphylobactor
E coli (verotoxigenic)
Listeria monocytogenes
FT 5105 Food Microbiology 4
Dairy Products
Milk is very nutritious
Fresh milk contains MOs of a large
variation
The type and number depend on the
hygienic conditions of the dairy farm,
cleanliness of utensils etc.
Milk contains lactoperoxidase and
agglutinins but not effective
5
Point of sampling Range (SPC/mL)
Aseptically drawn milk 500-1000
Milk pail/machine 1000-10,000
Bulk tank 5000-20,000
6
Diseases potentially arises from
contaminated milk
Tuberculosis
Diphtheria
Scarlet fever
Brucellosis
Mycobacterium paratuberculosis
post-pasteurization contamination
This may be as a result of cross-
contamination of finished product with raw
product, inadequate sanitation procedures
in the plant environment, or inadequately
sanitized equipment.
FT 5105 Food Microbiology 8
Commonly found spoilage bacteria in milk
Enterococcus Lactococcus
Streptococcus Leuconostoc
Lactobacillus Microbacterium
Propionibacterium Proteus
Pseudomonas
Upon pasteurization all Mos are destroyed except
thermodurics (Micrococci, Enterococci, Lactobacilli
and Sterptococci), spore formers of Bacillus group
and spores
72C for 15 sec. may go up to 79 for 25 sec.
Pasteurized milk is spoilt by heat resistant
Streptococci that utilize lactose
9
They produce lactic acid which brings
pH down to 4.5 thus, leading to
curdling
Molds can grow on the surface
bringing pH up to neutrality
Thus, proteolytic type bacteria can
start growing
Proteolytic Pseuodomonas can quickly
grow and liquefy curdle
10
Raw Milk
Milk spoilage
Sourness
Flavor changes
Curdling
Color changes
Gas formation
Fermentaiton
11
Sourness is developed and thus pH
decreases
Curdling happens and then whey is
released
Lactic acid formation is the major cause
Raw milk held at 10-37 is more likely to be
fermented by Streptococcus lactis
In addition Colifirms, Enterococci,
Lactobacilli and Micrococci also contribute 12
• 37-50C
• Sterptococcus thermophillus and S. faecalis
• Little acid is formed at elevated temperatures
• Gas production (hydrogen and carbon dioxide) is carried out by Clostridia
• Gas production is evidenced by frothing on top
• Proteolysis is favored at low temperatures
13
Proteolysis
1. Acid proteolysis
2. Proteolysis with little acidity
3. Sweet curdling
14
Ropiness (Sliminess) in Milk
Bacterial and non-bacterial
Bacterial sliminess is due to the slimy
capsular materials from cells (gums and
mucins)
Developed mostly at low temperature
Caused by Alcaligenes viscolactis
This is favored by low holding
temperatures
15
1. Surface ropiness Alcaligenes viscolactis
Grows best at 10C and Micrococcus spp.
2. Ropiness throughout and Klebsiella
oxytoca, Enterobacter cloacae
Alkaline producers
Pseudomonas fluorescens and A.
viscolactis 16
Hydrolysis
Color changes
Blue milk
Yellow milk
Red milk
Brown milk
17
Flavor changes
• Cheesiness
• Rancid
• Beany
• Musty
• Flat flavor
• Unclean
• Malty
• yeasty
18
Foods can be categorized into 3 groups
on the basis of spoilage
Stable – nonperishables – sugar, flour, dry
seeds, cereals
Semiperishable foods – potatoes, nuts
Perishable foods – meats, fish, poultry, eggs,
dairy etc.
FT 5105 Food Microbiology 19
Spoilage can happen due to
Growth and activity of MO
Damages due to insects
Physical damages
Enzymic action
Non-enzymatic chemical reactions
Physical changes due to freezing, burning
drying, high temperature etc.
FT 5105 Food Microbiology 20
FT 5105 Food Microbiology 21
Number and type of MO in a food depend
on
Source – where the food is originated
Microbial quality of raw materials
Sanitary conditions under which food is
handled/processed
Subsequent packaging/handling/storage
Inner parts of plant or animal tissues are
sterile
Contaminations are most likely to happen
FT 5105 Food Microbiology 22
Thus, the microbial number in a fresh
product reflects the quality of it
Therefore SPC is an important criterion in
determining the quality of a fresh product
FT 5105 Food Microbiology 23
Spoilage of Meat and Meat
Products
FT 5105 Food Microbiology 24
Composition of Meat
Constituent Percentage
water 75
Protein 19
Lipids 2.5
CHO 1.2
Soluble NPN 1.65
Minerals 0.65
FT 5105 Food Microbiology 25
Tissues of healthy animal are relatively
free of MOs
Microbial count of freshly slaughtered
animal tissues is less than 10 cfu/Kg
Most contaminated areas of animal body
are hide and GIT
Number and type of MOs depend on the
envt. The animal lived
FT 5105 Food Microbiology 26
Animal hide contains
Micrococci
Staphylococci
Pseudomonas
Yeasts and molds
Viscera contains large no. of MOs including pathogens
Surface microbial count goes up to 102-104/Cm2
Generally lamb and pork contains more MOs than beef
FT 5105 Food Microbiology 27
Skinning is not usually done with poultry
Thus, skin MOs are not removed
GIT of poultry too contain very high no. of
MOs and pathogens such as Salmonella
and Campylobacter
FT 5105 Food Microbiology 28
Common Genera of Bacteria Found in
Meats
Genus Fresh Vacu. Poultry Sea food
Acenetobacter
Aeromonas
Alcaligenes
Bacillus
Brocathrix
Carnobacterium
Corynebacterium
Enterobacter
Enterococcus
FT 5105 Food Microbiology 29
Genus Fresh Vacu. Poultry Sea food
Escherichia
Flavobacterium
Lactobacillus
Listeria
Micrococcus
Moraxella
Pseudomonas
Psychrobacter
Shewanella
Salmonella
FT 5105 Food Microbiology 30
Genus Fresh Vacu. Poultry Sea food
Staphylococcus
Vibrio
FT 5105 Food Microbiology 31
Common Molds in Meats Genus Fresh Poultry Proces
sed
Fish &
Seafood
Alternaria
Aspergillus
Botrytis
Cladosporium
Fusarium
Geotrichum
Mucor
Penicillium
Rhizopus
Thamnidium
FT 5105 Food Microbiology 32
Comminuted meats contain more MOs
Ground meat contains trimmings
Higher surface area – most spoilage MOS are
aerobic
Handled many times – contaminated blades,
saws, utensils
One heavily contaminated piece can inoculate
the whole lot
Organ meats such as kidney, liver, tongue,
heart contain less MO
FT 5105 Food Microbiology 33
MOs in Vacuum packaged meat – mainly
Pseudomonas
Oxygen permeability determines the
refrigerated storage life
The higher the permeability the lesser the
storage life
When permeability is very low CO2
concentration goes up and this favors
LABs an Brochothrix
FT 5105 Food Microbiology 34
Common bacteria in vacuum packaged
meats
Streptococci
Bacillus
Micrococci
Moraxella
Acinetobactor
Pseudomonas
FT 5105 Food Microbiology 35
Spoilage
Most common indications of spoilage are
Off odor and slimy surface due to the action of
aerobic bacteria on the cut surfaces
Fungal growth favored at water activity low for
bacterial growth
Bone taint = deep spoilage due to anaerobic
or facultative MOs
Discolorations due to change of myoglobin
color
FT 5105 Food Microbiology 36
A. Under aerobic conditions
Bacteria
Surface slime
Changes in meat color
Changes in fat
Off odors and off tastes
Yeasts
Sliminess
Lipolysis, off odors and tastes
White, cream-pink, brown colors due to yeast pigments
FT 5105 Food Microbiology 37
Molds
Stickiness
Whiskers – Thamnidium, Mucor and Rhizopus
Black spots - Cladosporium
White spots – Chrysoporium
Green patches – Penicillium
Decomposition of fats, off odors and tastes
FT 5105 Food Microbiology 38
Under anaerobic conditions
Souring
Putrefaction – production of foul smell under anaerobic conditions – hydrogen sulfide, mercaptans, indole, skatole, ammonia, amines.
When meat is stored in refrigerated conditions psychropilic and psychrotropic MOs attack
Sliminess
Discolorations & souring
FT 5105 Food Microbiology 39
Alcaligenes
Lactobacillus
Leuconostoc
Streptococcus
Flavobaterium
Mainly responsible MOs
FT 5105 Food Microbiology 40
Molds do not grow on meats at
temperatures less than -5C
Candida and Rhodotorula are partly
responsible for spoilage of refrigerated
meat
Ground meat is exclusively spoilt by
bacteria
Pseudomonas
Acinetobacter
Growth of MO on meat
1. Type and quantity of MO
E.g. If psychrotroph population is high very
high chance of spoilage under chilling
conditions
2. Physical properties of meat
The quantity of meat exposed to air has a
great influence
FT 5105 Food Microbiology 41
Mincing of meat greatly increases spoilage
Mincing increases aeration, distribute Mos
throughout the mixture and releases moisture
from tissues
3. Chemical properties of meat
pH
Moisture content – surface may go dry - this
will promote mold growth
FT 5105 Food Microbiology 42
Low in CHO thus non fermenting Mos grow
well
4. Availability of oxygen
Aerobic conditions favor mold and yeast
growth on the surface
True putrefaction is favored by anaerobic
conditions
FT 5105 Food Microbiology 43
5. Temperature
Putrefaction is very low at low temperatures
At room temperature mesophiles grow and
produce moderate amounts of acids using
limited quantities of CHO.
FT 5105 Food Microbiology 44
Types of Spoilage
1. Surface Sliming
Caused by Pseudomonas, Acinetobacter,
Moraxella, Alcaligenes, Streptococcus,
Leuconostoc, Bacillus and Micrococus
In addition, some Lactobacilli too can produce
Temperature and moisture mainly determine
the type of MO
FT 5105 Food Microbiology 45
At chilling temperatures with high moisture –
Pseudomonas and Alcaligenes
Less moisture favors Micrococus
2. Color changes
Red color may change to green/brown or gray
Color change is mainly due to production of
oxidizing compounds
FT 5105 Food Microbiology 46
Different colored spots are developed
Red spot – Serratia marcenscens growing on
surface
Blue spots – Pseudomonas synscyaneae
growing on surface
Yellow coloration – Micrococcus
FT 5105 Food Microbiology 47
Greenish-blue or brownish black spots –
Chromobacterium lividum
Purple (stamping ink color) – discoloration by
yellow pigmented cocci and rods due to
discoloration of surface fat
Off odors and taste
Called taints
Sour odor is formed by acids
FT 5105 Food Microbiology 48
Leuconostoc, Heterofermentative Lactobacilli
are mainly responsible
3. Changes in fat
Unsaturated fatty acids undergo oxidation
Hydrolysis
Adds off flavors to meat
FT 5105 Food Microbiology 49
B – Under Anaerobic conditions
1. Souring – due to
Acetic, succinic, butyric, propionic and higher
FAs
2. Putrefaction
True putrefaction is due to decomposition of
proteins under anaerobic conditions –
produce foul smell – hydrogen sulfide,
mercaptans, skatole. Ammonia and amines
FT 5105 Food Microbiology 50
Psuedomonas and Alcaligenes species
are mainly responsible
Species ending with putrefaciens, putida,
putrificum
Clostridium produces gases such as H
and CO2
FT 5105 Food Microbiology 51
3. Taint development –
Pseudomonas
Acinetobacter
Moraxella
Alcaligenes
Lactobacillus
Leuconostoc, Streptococcus, Flavobacterium
FT 5105 Food Microbiology 52
Number of Mos at the time of appearance of odor and
slime
Type When Odor is
identifiable (X106/cm)
Slime is identifiable
(X106/cm)
Poultry 2.5-100 10-60
Beef 1.2-100 3-300
Frankfurters 100-130 130
Bacon 1.5 -100
Fish 1-130
FT 5105 Food Microbiology 53
Spoilage of fresh beef
1. changes in hemoglobin and myoglobin
2. white, green, yellow and greenish blue
or brown spots and purple discoloration
3. Phosphorescence –
4. Spots due to bacteria, yeasts and molds
FT 5105 Food Microbiology 54
Cured meat
Curing selectively favor the growth of
Lactic acid bacteria
Pathogens are destroyed
FT 5105 Food Microbiology 55
Sausages
Bacterial growth in encased sausages is
possible
On the casing
Between the casing and meat
Interior meat
Greening is common in sausages
FT 5105 Food Microbiology 56
Greening is favored by slightly acidic pH
and little oxygen
This happens 12-36 after production even
under refrigerated conditions
Production of peroxides, mainly H2O2 is
attributable
FT 5105 Food Microbiology 57
Lactobacillus and Leuconostoc and other
catalase negative bacteria are responsible
for peroxide production
FT 5105 Food Microbiology 58
Bacon
Molds are common
Aspergillus, Fusarium, Mucor, Rhizopus,
Monilia, Oidium, Botrytis and Penicillium
Streptococcus faecalis – salt tolerant and
can grow at low temperatures
Micrococcus can be present on surface
FT 5105 Food Microbiology 59
FT 5105 Food Microbiology 60
Sausage, Frankfurters, Bologna etc.
Three major types
Souring – caused by Lactobacilli,
Enterococci.
Sliminess – also known as slimy spoilage
occurs on the outside of the casing
Greening – two types of greening can
occur by H2O2 and H2S
Greening due to H2O2 occurs mainly in
frankfurters and other vacuum packaged
meats
Generally appears after exposing
anaerobically stored meat into air
Upon exposure to air H2O2 is produced
and it reacts with nitrosohemochrome
This produces green color oxidized
porphyrin
FT 5105 Food Microbiology 61
Greening also occurs due to the
accumulation of H2O2 in the core where
Redox potential is low.
Lactobacillus viridescens is the major
causative agent
H2S type greening occurs in fresh red
meats held at 1-5C packed in vacuum
packages
H2S reacts with myoglobin to produce
sulphmyoglobin
FT 5105 Food Microbiology 62
Microorganisms in cured meat
Meat
MO type
Salami Lactobacilli
Bologna Leuconostoc mesenteroides , hetero
Lactobacilli
Pork (fresh) Leuconostoc, Lactobacillus,
Pseudomonas
Bacon Lactobacilli, Micrococcus
Ham Lactobacilli, Micrococcus,
Microbacterium
FT 5105 Food Microbiology 63
POULTRY
Poultry is mainly spoilt by
Pseudomonas
Acinetobacter
Flavobacterium
Corynebacterium
Fungi is less importance in poultry
spoilage
Main symptom of poultry spoilage is
sliminess on the surfaces and cut surfaces
FT 5105 Food Microbiology 64
Unlike meats in poultry spoilage is mainly
restricted to the surface
The inner tissues do not contain high no.
of Mos
Pseudomonas is the major spoilage
organism which forms colonies on the
surface which finally coalesce to form
sliminess
FT 5105 Food Microbiology 65
FT 5105 Food Microbiology 66
Methods to Determine Meat Spoilage
Measurement of
Mercaptans, H2S, TMA, tyrosine complexes
Catalase, creatinine, hypoxanthine
Lactic acid
Change in color
pH changes
RI of meat juices
Impedance
FT 5105 Food Microbiology 67
Bacteriological Methods
Total aerobes
Total anaerobes
Ratio of aerobes to anaerobes
Extract Release Volume (ERV)
This method is used to measure spoilage
and potential shelf life
FT 5105 Food Microbiology 68
ERV is the volume of aq. Extract released
by a homogenate of meat when allowed to
pass through a filter paper
Detection of foul odor due to H2S etc.
happens only when amino acids are
started to be utilized
FT 5105 Food Microbiology 69
Dark firm and dry meats (DFD) have high
pH values (>6) are spoilt quicker than
other meats
In vacuum packed meats – nitrites control
Bacillus thermoscapta
Lactobacillus is insensitive to nitrites and
thus they predominate
Spoilage of Fish and
Shellfish
FT 5105 Food Microbiology 70
Fat is interspersed between muscle fibers
Little connective tissues
In non-fatty fish fat content is 0.5%
Fatty fish may contain from 3-25%
Contains 1% CHO
71
Like meat, fish and other sea foods are spoilt by
Autolysis
Oxidation and
Microbial activity
Fish muscles are more quickly spoilt than meats due to
higher enzyme activity
Presence of highly unsaturated fats and
Higher pH
72
Factors affecting fish spoilage
Type of fish
Flat fish spoil more rapidly than the round fish
as flat fish undergo rigor mortis rapidly
Fish with high content of PUFA undergo
deterioration rapidly
Condition when caught
Struggled, exhausted fish spoil faster
Fish underwent lack of oxygen conditions
73
Fish with the full gut contents are more
perishable
The extent of contamination
Microbes come from water, mud, slime
on the surface and gut contents
Gills are rich in MOs
The greater the microbial load the quicker
the spoilage is 74
Spoilage might start in the net during
transporting etc.
75
Microflora associated with fish
Depends upon the environment they live in
They can be contaminated during
catching, handling and storage
The slime is rich in
Pseudomonas
Alcaligenes
Micrococcus
Flavobacterium
76
Corynebacterim
Serratia
Vibrio
Bacillus
Fish intestine is rich in
Alcaligenes
Pseudomonas
Vibrio
Bacillus
Clostridium
E coli
77
Skin contains 102-107 cfu/cm2
Gills and guts 103 – 109 cfu/g
Most crucial factor in fish spoilage is
temperature
Fish stored at 0C starts spoiling with a
lag of 1-2 days
In fish spoilage the following microbes
become dominant
Pseudomonas
Acinetobacter and
Flavobacterium 78
As spoilage progresses the
Pseudomonas population increases
rapidly
The type of species changes with
spoilage
When temperature is increased
Pseudomonas population goes down
and mesophilics start dominating
Trimethylamine oxide (TMAO) naturally
present in fish is reduced to TMA
This is a volatile compound and
responsible for the fishy odor
79
As spoilage progresses volatile bases,
amines and organic acids are formed
due to decarboxylaiton or deamination
of amino acids
Hydrogen sulfide, mercaptans and
disulfides are the main compounds
producing the odor other than TMA
Spoilage organisms use TMAO,
creatine, taurine, anserine and amino
acids
80
Total volatile compounds include
Total volatile bases (TVB)
Total volatile acids (TVA)
Total volatile nitrogen (TVN)
Total volatile substances (TVS)
Fish odor is explained as a complex of
Fishy
stale
81
◦ Musty
◦ Rancid
◦ Sour
◦ Ammonical
◦ Fruity and
◦ Acids
Discoloration of fish leads to development of green and yellow colors
Pseudomonas fluorescens is mainly responsible
82
Histidine present in fish is converted to
histamine by bacteria
Only bacteria that have decarboxylase
enzymes can do the converion
Histamine is associated with scombroid
poisoning
83
Indicators of Fish Spoilage
Histamine
Cadaverine – a diamine
Putrescine – a diamine
Total volatile substances
84