FOOD MICROBIOLOGY SPOILAGE

1. Microbial food spoilage

2. Group # 1
Presentation team ;
 Ayesha Batool (109)
 Nisha Kafeel (104)
 Maryam Zulifiqar (105)
 Tahreem Fatima (106)
 Saleha Ashfaq (107)
Mahreen Gul (108)
Bareera Ashraf (110)
Alisha Faiz (111)
Farah Irshad (112)
Balqees Fatima (113)

3. Content
 Definition of microbial food spoilage
 Causes of microbial food spoilage
 Classification of food
 Microorganisms involved in food
spoilage
 The process of microbial food spoilage
 Refrences

4. Microbial food spoilage
 The microbial food spoilage is defined as the
contamination of food by the growth and
enzymatic activity of microorganisms.
 Food spoilage is the process, in which the
quality of the food deteriorates to some extent
that renders food unacceptable for human
consumption.
 Food spoilage occurs due to the microbial
attack, enzymatic digestion, chemical
degradation, physical injury etc.

5.  The microbial food spoilage can be
determined physically by the following
changes:
• Change in appearance:
it is
characterized by the cloudiness and
liquid formation in the food.
• Change in texture:
occurs due to an
accumulation of microbial cells and tissue
degradation resulting in slime formation
and rotting.

6.  Colour change:
it mainly occurs due to
the chlorophyll breakdown and mycelial
growth.
• change in test and odour:
the taste and
odour of the food changes due to the
oxidation of nitrogenous compounds,
sulphides, organic acids etc. by the
mocrobial enzymes.

7.  Microorganisms like bacteria, yeasts and
moulds primarily cause food spoilage.
 Food serves as a good growth medium and
contains proteins, carbohydrates and lipids
that are utilized by the microorganisms
residing in the food.
 The degradation of food material typically
involves hydrolysis of proteins (putrefaction)
via proteolytic microorganisms, undesired
fermentation through saccharolytic
microorganisms and rancidity by the lipolytic
microbes.

8.  In this post, you will get to know the
definition, causes and the mechanism of
microbial food spoilage along with the
microorganisms involved in the food.

9. Definition of Microbial Food
Spoilage:
 Microbial food spoilage is the biological
process that causes degradation or
decomposition of the food item due to
microbial growth and activity that brings
undesirable changes and makes the
food undesirable for consumption.
 It primarily depends upon the two
factors, namely food matrix (physical
and chemical properties of food), the
type of microorganisms and the storage
conditions.

10.  Food spoilage merely refers to the
physical state where it does not meet
the quality characteristics. Microbial food
spoilage can be controlled by subjecting
the food under refrigeration,
lyophilization and by adding
preservatives.

11. Causes of Microbial Food
Spoilage
 Two common factors favour the growth
and multiplication of microorganisms:

12. Storage Conditions of the Food
 The storage conditions basically involve
environmental factors like temperature,
pH and oxygen that favours the
microbial growth.
 Temperature:
The psychrophilic
temperature, i.e. -17, is considered to be
safe, and it can prevent the growth of
microorganisms.
 The temperature above this is called
mesophilic temperature that is the most
favourable for the microbial growth.

13.  Oxygen:
There are aerobic and anaerobic
microorganisms that attack the food in
storage conditions in the presence or
absence of oxygen, respectively.
Aerobic storage conditions favour the
aerobic bacteria and moulds. If there are
anaerobic storage conditions, it will
favour anaerobic bacteria like
Clostridium species.

14. Chemical Properties of the
Food
 The food spoilage is caused due to the
degradation of the food components by
the microorganisms’ enzymatic activity.
The chemical properties of the food that
influence microbial growth includes:

15. Classification of Food
 The food is classified into three types
based on the spoilage:

16.  Non-perishable: food has no water
content, and it can be stored for a long
time. These have a long shelf life.
 Semi-perishable: food has less water
content, and it can be stored for some
time. These have a medium shelf life.
 Perishable: food has high water
content, and it cannot store for a longer
period. These have a short shelf life.

17.  The high water or moisture content is a
factor that directly influences microbial
growth, as water promotes the growth of
all living beings. Therefore, the food
which is susceptible to the spoilage
process called perishable food.

18. Microorganisms Involved in
Food Spoilage
 There are commonly three kinds of
microorganisms, which causes food
spoilage:
Yeasts:
Yeast, a eukaryotic organism, is
a subgroup species of organism known
as fungus. Yeasts are well recognized
for their beneficial fermentations that
produce bread and alcoholic beverages
and can grow with or without oxygen.

19.  In addition, they are used to increase
the surface of cheese and meat as well.
They generally colonize foods with
maximum sugar or salt content, such as
sauerkraut, pickles, maple syrup, low pH
fruits, and liquids, and deteriorate them.

20. cause’s of yeast
 The four main yeast species that cause
yeast spoilage are Zygosaccharomyces,
Debaryomyces
hansenii,Brettanomyces, and Candida.
Zygosaccharomyces species spoil the
foods such as honey, dry fruits, jams,
and soya sauce by releasing the off
odors or flavors and carbon dioxide that
sometimes causes containers to swell
and burst.

21.  Debaryomyces hansenii can grow in
high salt concentration (approx. 24%)
so, are frequently isolated from salt
brines used for cured meats, cheeses,
and olives.
Saccharomyces spp., and Candida, spoi
ls fruits, some vegetables, and dairy
products.
 Dekkera/Brettanomyces only spoil
fermented foods such as alcoholic
beverages and dairy products by

22.  Mould:
that are characterized by
multicellular filaments known as hyphae.
It is an organism that helps in decaying
dead animals and plants. They also ruin
the wide range of food products.
 Some molds that cause food spoilage
are Zygomycetes, a primitive fungus that
proliferates on fruits and vegetables rich
in fruits like strawberries and potatoes.
Some of them also grow in bread.

23.  The Zygomycetes that are commonly
observed in spoiled products
are Mucor and Rhizopus.
Penicillium and related genera
(Furcatum) are found in soil and plant
debris. Many of these species produce
antibiotics used as medicine by
humans.

24.  Still, some species cause harm by
releasing mycotoxin (spatulin,
ochratoxin, citreoviridin, penitrem) in
different fruits and vegetables ( pear,
citrus fruits, and apples).
 Byssochlamys are the genera that
cause spoilage to pasteurized juices due
to heat-resistant
spores. Aspergillus typically develop
more quickly, are much more resistant to
high temperatures and low water

25.  This mold affects a wide range of food
products (grains, dried beans, peanuts,
tree nuts, and some spices) and non-
food products (paper, leather) by
releasing the mycotoxins such as
aflatoxins, ochratoxin, territrems, and
cyclopiazonic acid.
 Fusarium spp. does not spoil the food,
but the mycotoxins released in
harvested grains can cause a health
threat.

26. Bacteria
 The bacteria-producing spore is present in
heat-treated food due to their abilities to
sustain life even in high temperatures.
Spore-producing bacteria are Gram-
positive, thermophiles anaerobes. Some of
them can be facultative.
 These bacteria produce hydrogen sulfide
(e.g., Desulfotomaculum), and others
release hydrogen and carbon dioxide
(e.g., Thermoanaerobacterium) when kept
at high temperatures (like soups sold in
vending machines).

27.  Psychrotolerant spore-producer
organisms such as Clostridium
spp release gas and sickly odors in food
products (meats and brine-cured hams),
whereas Bacillus spp produces off-
fragrances and gas in chilled and milk
products.
 Lactic Acid Bacteria (LAB) such
as Lactobacillus, Pediococcus,
Leuconostoc, and Oenococcus help to
form fermented foods such as yogurt

28.  Still, they damage the foods (meat,
wine, or juices) in low oxygen, low
temperature, and acidic conditions
producing off flavors (mousy, cheesy,
malty, sour, buttery).

29.  These organisms secrete gas and vast
amounts of extra-polysaccharides
resulting in slime on meat and ropy
spoilage in some food products.
 Pseudomonas generally need maximum
water activity for growth and are
inhibited by a pH below 5.4. Some
species (psychrophilic) require
refrigeration to grow, whereas others
can thrive and grow at warmer ambient
temperatures.

30.  The Pseudomonas groups of four are
mainly responsible for causing food to
spoil, i.e., P. fluorescens, P. fragi, P.
lundensis, and P. viridiflava. P.
fluorescens, P. fragi, P. lundensis, and
S. putrefaciens ruin foods originating
from animals (meat, fish, and milk) by
secreting lipases and proteases that
result in the release of sulfides and
trimethylamine (off-odors), as well as by
producing biofilms (slime) on surfaces.

31.  Some strains ruin the meals in the
refrigerator since they can grow at low
temperatures, whereas X. campestris, P.
fluorescens, and P. viridiflava secrete
enzymes such as pectic lyase enzymes
that break down the pectin in the plant-
derived food and produce musky or
slime layer within it (3).

32.  Other than these microorganisms, other
factors can also cause food
deterioration. The insects such as flies,
mites, moths, beetles, and weevils are
the leading cause of spoilage of stored-
food products like flour, dried fruits,
grains, nuts, cheese, corn, and dried
vegetables. These insects carry
disease-causing microorganisms or
toxins produced in their body.

33.  The indigenous enzymes such as
catalase, proteinase, and lipase
amylase in plants and animals continue
to function. In addition, they deteriorate
the quality of food if not appropriately
destroyed during storage. For example,
the peroxidase enzyme causes off-
flavors during storage in green
vegetables.
 The temperature is an essential factor
that may cause food spoilage as well.

34.  For instance: the food kept at a low
temperature makes it partially frozen,
which leads to the breakage of cells and
damages food quality.
 The foods are exposed to irradiation to
kill the deteriorating microorganism,
increasing the shelf-life of food.
However, prolonged exposure of food to
rays cause a loss in micronutrients
(mostly vitamin A, B, C, and E), affecting
the nutritional value of food (5).

35. The Process of Microbial Food
Spoilage
 Microbial food spoilage can be
summarized into the following steps:

36.  Microbes first attack the food:
As the food
contain all the nutrients required by the
microorganisms, at a favourable
temperature, pH, moisture, oxygen etc.
 Food degradation:
Microorganisms
degrades the food material by utilizing
the nutrients available in the food and
decompose the food material.

37.  Decomposition:
The enzymatic reaction
occurs between the food components
like protein, lipid, fat, carbohydrates etc.,
and the microbial enzymes carry out
some chemical changes.
 Changes as a result of food
decomposition: The changes appear
in the form of appearance, texture,
colour, taste, odour etc. as a result of
spoilage.

38. Prevention of Food Spoilage by
organisms
 Food preservation is a technique to
keep food safe and unharmed from the
metabolic activities of microorganisms.
The best way of preserving the food
depends on the abilities of
microorganism metabolism. The most
common food preservative methods are:
 The use of weak organic acids such as
acetic acid, lactic acid, benzoic acid, and
sorbic acid reduces the chance of
deteriorating the food products (pickles,

39. by preventing the growth and
development of various species of
bacteria and fungi.
 The addition of sugar concentration in
about 68% -70% helps to prevent food
like jam and jelly by exerting osmosis
and limiting the water activity for the
multiplication of microbes.

40.  15%-20% of salt concentration in food
products hinders growth by exerting
osmotic pressure that creates plasmolysis
of cells and restricts abilities dissolving the
oxygen.
 The heating and freezing also increase the
shelf life of food (4)
 Pickling is a method of preserving food in
an edible anti-microbial liquid. Pickling can
be broadly categorized into two categories:
chemical pickling and fermentation pickling.

41.  Drying is one of the most ancient food
preservation techniques, which reduces
water activity sufficiently to prevent
bacterial growth.
 Vacuum-packing stores food in a
vacuum environment, usually in an air-
tight bag or bottle. The vacuum
environment strips bacteria of oxygen
needed for survival, thereby slowing
spoiling. Vacuum-packing is commonly
used for storing nuts to reduce the loss
of flavor from oxidation.

42.  smoking is used to lengthen the shelf life
of perishable food items. This effect is
achieved by exposing the food to smoke
from burning plant materials such as
wood. Most commonly subjected to this
method of food preservation are meats
and fish that have undergone curing.
Fruits and vegetables like paprika,
cheeses, spices, and ingredients for
making drinks such as malt and tea
leaves are also smoked, but mainly for
cooking or flavoring them. It is one of the
oldest food preservation methods, which

43.  Canning involves cooking food, sealing
it in sterile cans or jars, and boiling the
containers to kill or weaken any
remaining bacteria as a form of
sterilization. Foods have varying
degrees of natural protection against
spoilage and may require that the final
step occur in a pressure cooker. High-
acid fruits like strawberries require no
preservatives to can and only a short
boiling cycle, whereas marginal fruits
such as tomatoes require longer boiling
and addition of other acidic elements.

44.  Low acid foods, such as vegetables and
meats require pressure canning. Food
preserved by canning or bottling is at
immediate risk of spoilage once the can
or bottle has been opened.

45. References
 Hayes PR. Food Spoilage. Food Microbiol
Hyg. 1995;106–83.
 El-Hay MMA. Processing and preparation of
fish. Postharvest Postmortem Process Raw
Food Mater Unit Oper Process Equip Food
Ind. 2022 Jan 1;315–42.
 Rawat S. Food Spoilage: Microorganisms and
their prevention. Pelagia Res Libr Asian J
Plant Sci Res [Internet]. 2015;5(4):47–56.
Available
from: www.pelagiaresearchlibrary.com
 Blackburn CDW. Food spoilage