4. When Microbial Spoilage occurs?
• Initially, a food produced under proper sanitary conditions generally
contains microorganisms at a level (per g, ml, or cm2) much lower than that
at which spoilage is detected.
• Subsequently, growth of some of the microbial species among those initially
present enables the microorganisms to reach the spoilage detection level.
• Many factors dictate which species will multiply relatively rapidly to become
the predominant spoilage microorganisms.
• Along with microbial types, food types and food environments (both intrinsic
and extrinsic factors) have important roles in determining the predominant
spoilage microflora in a food.
6. Factors affecting growth of microbes
Intrinsic
Nutrients
aw - Water activity or aw is the partial vapor pressure of water in a
substance divided by the standard state partial vapor pressure of
water – distilled water – 1.0; Bacteria - 0.91 and fungi 0.7
pH
Redox potential - is a measure of the tendency of a chemical
species to acquire electrons and thereby be reduced. Reduction
potential is measured in volts (V), or millivolts (mV).
Inhibitors
Extrinsic
Temperature
Humidity
Atmosphere
Implicit
Interactions of microorganisms
7. MICROBIAL SPOILAGE – HOW DOES IT
MANIFEST ITSELF?
Visible growth
Gas production
Slime
Enzymes
Off-flavours
8. MICROBIAL SPOILAGE
Food Types of Spoilage Spoilage Microorganisms
MEAT
Fresh
Putrefaction
Clostridium, Pseudomonas, Proteus,
Alcaligenes, Chromobacterium
Souring
Chromobacterium, Lactobacillus,
Pseudomonas
Cured
Mouldy Penicillium, Aspergillus, Rhizopus
Souring Pseudomonas, Micrococcus, Bacillus
Slimy Leuconostoc
Vacuum
Packed
Souring
Greening
Lactobacillus, Carnobacterium,
Leuconostoc
Poultry Odor, Slime
Pseudomonas, Alcaligenes, Xanthomonas
Putrefaction- Decomposition of organic matter, especially protein (under anaerobic
condition), by microorganisms, resulting in production of foul-smelling.
Souring - Foods go sour when certain bacteria produce acids. A common example is
when milk sours from the production of lactic acid
9. MICROBIAL SPOILAGE
Food Types of Spoilage Spoilage Microorganisms
DAIRY
MILK
Bitterness Pseudomonas spp.
Souring Lactobacillus thermophilus
Sweet curdling Bacillus cereus
CHEESE
Green discoloration Penicillium
Green to black discoloration Cladosporium
Black discoloration Candida
Sliminess (high pH) Pseudomonas spp.
“Gassy” cheese Coliforms, LAB, Clostridia
11. MICROBIAL SPOILAGE
Canned food
Flat Sour
Bacillus coagulans, B.
sterothermophilus
Thermophillic acid Clostridium thermosacchrolyticum
Sulphide stinker Clostridium nigrificans
Butyric acid fermentation C. butyricum
Softening of fruits Byssochlamys fulva
Sliminess Yeast and molds
Wine Off Flavor, bitterness Acetobactor, Oenococcus
Food Types of Spoilage Spoilage Microorganisms
FRESH FRUITS AND
VEGETABLES
Bacterial soft rot
Erwinia carotovera, Pseudomonas
spp.
Gray mould rot Botryitis cinerea
Rhizopus soft rot Rhizopus nigrican
Blue mould rot Penicillium italicum
Black mould rot Aspergillus niger, Alternaria
Sliminess and Souring Saprophytic bacteria
12. Chemical changes caused by micro organisms
Degradation of carbohydrates
Degradation of N- compounds
Degradation of lipids
Pectin hydrolysis
18. Off flavor
Off flavor Chemical compounds Food
Fishy Trimethylamine Meat, egg, fish
Fruity Esters Milk, fish, wine
Alcoholic Ethanol Fruit juices,
mayonnaise
Musty odour Trichloroanisole Bread, wine
Cheesy odour Diacetyl, acetoin Meat
Medicinal odour 2-methoxy phenol Juice, wine
Souring Acetic acid, lactic acid,
citric acid
Wine, bear, dairy
19. Texture and Visual problems
Texture problem Chemical Food
Slime Polysaccharide Meat, juices, wine,
confectionery
Softening Pectin degradation Fruits and vegetable
Curdling Lactic acid Milk
Holes Carbon dioxide Hard cheese
Visual problems Chemical Food
Bloaters Gas production Fermented cucumber
Holes Gas production Hard cheese
Can swelling Gas production Canned foods
21. Microbial spoilage of Cereals
Cereals and cereal products are significant and important human
food resources.
Cereal grains and legumes are food staples in many countries.
The main cereal grains used for foods include corn, wheat,
barley, rice, oats, rye, millet, and sorghum.
Cereal products that are derived from cereal grains include
wheat, rye, and oat flours and doughs, breads, breakfast cereals,
pasta, snack foods, dry mixes and cakes.
22. Microbial spoilage of Cereals
Microorganisms that contaminate cereal grains may come from
air, dust, soil, water, insects, rodents, birds, animals, humans,
storage and shipping containers, and handling and processing
equipment.
The microflora of cereals and cereal products is varied and
includes molds, yeasts, bacteria (psychrotrophic, mesophilic, and
thermophilic/thermoduric), lactic acid bacteria, rope-forming
bacteria (Bacillus spp.), bacterial pathogens, coliforms, and
Enterococci.
Bacteria are frequent surface contaminants of cereal grains. For
bacteria to grow in cereal grains, they require high moisture or
water activity (aw) in equilibrium, with high relative humidity.
23. Microbial spoilage of Cereals
Generally, bacteria are not significantly involved in the spoilage of dry
grain and become a spoilage factor only after extensive deterioration
of the grain has occurred and high moisture conditions exist. spore
former (Lactic acid bacteria-Lactobacillus)
The filamentous fungi that occur on cereal grains are divided into two
groups.
These groups have been referred to as field fungi and storage fungi.
Field fungi invade grain in the field when the grain is high in moisture
(18 to 30%) (i.e., at high aw) and at high relative humidities (90 to
100%). Field fungi include species of Alternaria, Cladosporium,
Fusarium, and Helminthosporium. Storage fungi invade grain in
storage at lower moisture contents (14 to 16%), lower aw and lower
relative humidities (65 to 90%). These main storage fungi are species
of Eurotium, Aspergillus, and Penicillium.
24. Microbial spoilage of Fruits and Vegetables
The types and levels of microbes on fresh fruits and vegetables vary
with commodity and level of post-harvest processing.
In general, Pseudomonas fluorescens, Erwinia herbicola, and
Enterobacter agglomerans are major components of the epiphytic
microflora of many vegetables.
Leuconostoc spp., Lactobacillus spp., Enterobacter agglomerans,
molds, and yeasts can also be found on various fruits and vegetables.
Pectinolytic P. fluorescens, Xanthomonas spp., Cytophaga spp., and
Flavobacterium spp.
25. Microbial spoilage of Fruits and Vegetables
Seed sprouts in particular frequently have higher microbial levels,
including fecal coliforms, than other produce items.
Spoilage of produce has been characterized as a
brown discoloration, necrosis of tissue, loss of
texture, and exudation and production of off-flavors
and off-odors
• The bacterial pathogens Salmonella spp. and E. coli O157:H7 (and
other pathogenic E. coli) tend to be transmitted predominantly by
animal fecal wastes, either directly or indirectly through fecal-
contaminated water or soil.
26. Microbial spoilage of packed and canned foods
In various parts of the world, there is an abundance of food, and to
make it available to everyone throughout the year, we have developed
ways to preserve it.
In ancient times this involved drying, salting, and fermenting foods.
In the past 150 years, we have developed canning procedures, and
recently, freezing procedures to preserve foods.
It is vital that the methods used prevent the growth of spoilage and,
more important, pathogenic microorganisms.
27. Microbial spoilage of packed and canned foods
Typically, preservation accomplishes one or more of the following
objectives:
killing the microorganisms;
inhibiting microbial growth;
removing microorganisms;
destroying enzymes,
Retarding chemical changes.
Canning is a science that resulted from the French military offering a
reward for anyone who came up with a way that could be used to feed
hungry soldiers during the French Revolution and the Napoleonic
wars.
In 1809, Nicolas Appert, a French confectioner, developed a process
for canning foods.
28. Microbial spoilage of packed and canned foods
Canned foods fall into two categories. The first is low-acid canned
foods (LACFs), which have a pH above 4.6.
These foods must receive a severe thermal process designed to destroy
Clostridium botulinum spores - 116 to 121◦C
The second category of canned foods includes those that have a pH of
4.6 or lower. These are referred to as acid or acidified foods.
A common practice used in the canning to accomplish this in the food
industry is referred to as hot-fill-hold.
29. Microbial spoilage of packed and canned foods
While C. botulinum is by far the most dangerous pathogen of concern
in low-acid canned foods - botulinum toxin
Thermophilic spores are very heat resistant, and thermal processes are
not designed to destroy them.
30. Microbial spoilage of packed and canned foods
Frozen foods are another group of preserved foods.
This method of food preservation started early in the twentieth century
when Clarence Birdseye worked near the Arctic and observed fish
being frozen after being caught. When thawed and eaten, these fish
still had their fresh characteristics. Company in 1922.
When water is frozen (ice), it is no longer available for
microorganisms to use; thus, they cannot grow and spoil or
decompose the food.
contaminated with Salmonella
31. Microbial spoilage of Poultry
Poultry, including broilers, turkey, duck, and quail, rank in third place
among products incriminated in foodborne illness.
The data show the highest contamination of poultry carcasses,
including broilers and turkeys, with Campylobacter (∼90%),
Salmonella (∼20%), and Listeria monocytogenes.
Campylobacter and Salmonella inhabit the intestinal tract of clinically
healthy birds. In contrast, in humans, consumption of contaminated
undercooked poultry results either in no clinical illness or in nausea,
vomiting, diarrhea, fever, dehydration, and headaches.
32. Microbial spoilage of Poultry
Campylobacter jejuni
Campylobacter grow in low-oxygen environments
(5% O2) and are termed microaerophiles
• Salmonella enterica
• Flock-to-Fork Concept
Maintaining product quality and reducing the number of
microorganisms
monotrichous
Peritrichous
34. Microbial spoilage of Eggs
Salmonella spp. can survive for up to 26 days on the surface of shell
eggs stored at 28 to 35◦C.
SALMONELLOSIS
Pseudomonas and Yersinia enterocolitica
can penetrate and infect shell eggs.
35. Microbial spoilage of milk and milk products
RAW MILK
Milks are transferred to refrigerated bulk storage tanks, where it is
held prior to transportation to processing facilities.
The implementation of refrigerated storage has resulted in a dramatic
change in the microflora of raw milk, due to microbial selection and
adaptation.
Considerable evolution of bacterial populations was found during
storage of milk at 4◦C with the emergence of psychrotrophic bacteria
such as Listeria spp. or Aeromonas hydrophila
36. Microbial spoilage of milk and milk products
UDDER
Mastitis are Staphylococcus aureus, Streptococcus agalactiae, and
Escherichia coli.
Bedding materials, mud, dung, soil, and other matter are all a rich
source of microorganisms that can adhere readily to skin.
Listeria monocytogenes
• Outbreaks of illness are due to consumption of raw and pasteurized
milk contaminated with a variety of organisms, including
E. coli O157:H7, Salmonella spp., Campylobacter jejuni, Yersinia
enterocolitica, and Listeria monocytogenes.
37. Microbial spoilage of milk and milk products
CHEESE AND FERMENTED DAIRY PRODUCTS
• Salmonella and enterohemmorhagic E. coli, can survive in hard
cheeses for prolonged periods.
• E. coli O157:H7 has also been shown to be able to survive in yogurt
and ice cream
• BUTTER - Listeria monocytogenes
• MILK POWDER - Enterobacter sakazakii
38. Microbial spoilage of Fish
• Fish and fishery products are at the forefront of food safety and
quality improvement because they are among the most internationally
traded food commodities.
• Approximately 45% of the fish used for human consumption is sold
fresh, 30% frozen, 14% canned, and 12% cured
• The total number of bacteria found on fish varies enormously.
Between 102 and 107 CFU/cm2 can be found on the skin surface and
between 103 and 109 CFU/cm2 on the intestine or gills
39. Microbial spoilage of Fish
• Fish caught in cold, clean waters tend to carry fewer microorganisms
than fish caught in warm waters
• Clostridium botulinum and Listeria spp. are most common in colder
climates
• Temperate-water fish are psychrotrophic gram-negative rod-shaped
bacteria (Pseudomonas, Moraxella, Acinetobacter, Shewanella, and
Flavobacterium spp.), Vibrio and Photobacterium spp., and
Aeromonas spp. Gram-positive bacteria (Bacillus, Micrococcus,
Clostridium, Lactobacillus, and coryneforms) are also found on
temperate fish in lower numbers.
40. Microbial spoilage of Fish
• The dominant microorganisms on coastal and estuarine fish are
mesophilic Vibrio cholerae and Vibrio parahaemolyticus, gram-
positive bacteria, and enteric bacteria.
• In aquaculture are Vibrio anguillarum, Vibrio salmonicida, Vibrio
vulnificus (fish pathogens), and Vibrio harveyi (shrimp pathogen,
particularly in white shrimp, Litopenaeus vannamei, and tiger shrimp,
Penaeus monodon).
• Pseudomonas spp. appear to be the main bacteria involved with fresh
water and tropical fish spoilage during aerobic storage.
41. Microbial spoilage of Fish
• Many seafood species have a symbiotic relationship with the bacteria
in, or on, their bodies.
• Photobacterium leiognathi and P. phosphoreum have symbiotic
associations with fish
• P. leiognathi, V. logei, and V. fischeri have symbiotic associations with
squid.
• These bacteria colonize the light-producing organs of the host and
emit the light that the host uses for communication, prey attraction,
and predator avoidance.
• Enzyme that is responsible for the generation of the light is alkanal
monooxygenase (FMN-linked)
42. Microbial spoilage of Meat
• Upon the death of the animal, invasion of tissue by contaminating
micro organism takes place.
• Factors influence that invasion includes following:-
• The load in the gut of the animal
• The physical condition of the animal immediately before
slaughter
• The method of killing and bleeding
• The rate of cooling
• Meat is an ideal culture for many microbes because it is high in
moisture, rich in nitrogenous foods.
43. Microbial spoilage of Meat
• Under aerobic conditions bacteria may cause the following-
• Surface slime – which may be caused by species of 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, gray as result of
the production of oxidizing compound. e.g. hydrogen peroxides,
hydrogen sulfide. Lactobacillus and Leuconostoc are basically
responsible.
• Changes in fats:- 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 are responsible
for oxidative rancidity or by yeast.
44. Microbial spoilage of Meat
• 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.
• Actinomycetes may be responsible for Musty or earthy flavor
45. Microbial spoilage of Meat
Fungi
• 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 P. oxalicum
• Decomposition of fats- many molds have lipase and hence cause
hydrolysis of fats .
46. Microbial spoilage of Meat
Under anaerobic condition
• Souring – it imparts sour taste to meat due to acids such as formic,
propionic, acetic etc. meat’s own enzymes are responsible for it .
• Putrefaction- true 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 - Taints” or undesirable odors and tastes, that appear in a meat
47. Microbial spoilage of Meat
• Off odors such as sweet and fruity, putrid, sulphury and
cheesy, are characterized in aerobically stored meat.
• Species which are responsible Psuedomonas sp. &
Psuedomonas fragi.
• Sulphur compounds may also contribute off flavor
• Clostridium spp. have been associated with the production
of large amount of gas in vacuum packaged meat.
