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