Presentation on milk and milk products spoilage .The topic of food microbiology.The proper display of bacteria and them causing spoilage in butter , frozen products and milk and its products.The fungi also effects milk and its products is displayed in the form of flow charts and tables .Gas production , rancidity in cream and milk ,milk fat .The colour change and flavour is described clearly .

1. Food microbiology
Millk spoilage
Submitted To:-Diksha Mam
Submitted By:-Sukhmanpreet kaur
A51339422007
M.Sc DAN
Semester 3

2. Milk
▪ Milk is one of the most complete single foods available in
nature for health and promotion of growth , the cow is
considered as a sacred animal and even worshipped in India
.
▪ The constituents of milk are 3-6% milk fat ,3% protein , 5%
milk sugar , and -0.7% ash .
▪ The water accounts for 85.5-88.5%.
▪ Buffalo milk contains more amount of fat {7.44%}, and
protein {4.78%}, human milk is low in protein {2.14%}.

3. Milk and its dairy
products
✓Dairy products or milk
products ,also known as
lacticinia , are food products
made from mil milk .
✓Dairy products include
market milk and cream ,
butter ,frozen dessert ,
chesse , fermented milk , and
condensed dried milk
products .

4. Spoilage of milk and milk products
● Spoilage of milk and milk products refers to the process by which these products
deteriorate in quality and safety , making them unsuitable for consumption .
● This deterioration can occur due to various factors , such as growth of spoilage
microorganisms [bacteria , yeast , and molds ], enzymatic reactions , exposure to
light , heat , or oxygen , which can lead to changes in taste , texture , odor , and
appearance , making product unpalatable or unsafe to consume .
● Spoilage in 3 types of dairy products Milk and cream , Frozen desserts ,
butter

5. Composition of milk
● Milk is an excellent culture medium for many kinds of microorganisms ,
being high in moisture , nearly neutral pH , and rich in microbial food .
● A plentiful supply of food for energy is present in the form of milk sugar
(lactose), butterfat, citrate ,and nitrogenous compounds in many forms
(proteins , amino acids , ammonia , urea and other compounds ), and
the accessory foods and minerals required by microorganisms are
available .
● Some inhibitory substances (lactoperoxidase and agglutinis ) present in
fresh milk , soon gets ineffective .
● The presence of fermentable sugar , an acid fermentation by
bacteria is most likely to occur under ordinary conditions in raw
milk .

6. Milk and cream
•When milk sours , it usually is considered spoiled , especially if it curdles.
•The evidences of acid formation are first a sour flavor and then coagulation
of milk to give a solid jelly like curd or weaker curd that releases clear whey .
The lactic acid fermentation is most likely to take place in raw milk held at
room temperatures.
•In raw milk bacteria causing souring
Temperature Bacteria
10-37 degree celsius Streptococcus lactis with some growth of
coliform bacteria , enterococci , lactobacilli ,
and micrococci .
37-50 degree celsius Streptococcus thermophilus , streptococcus
faecalis , produce 1% acid and followed by
lactobacilli such as Lactobacillus bulgaricus
which produce more acid .
Above 50 degree celsius Some lactobacilli ,but produce less acid
Thermophilic bacteria Lactobacillus thermophilus

7. •Pasteurization of milk kills the more active acid- forming bacteria
but may permit the survival of heat-resistant lactics (eg-
enterococci , streptococcus thermophilus , and lactobacilli ), that
causes lactic acid fermentation if storage temperature is high .
•If conditions are unfavorable for lactic acid bacteria than the
coliform bacteria produce some lactic acid and considerable
amounts of volatile products , such as hydrogen , carbon dioxide ,
acetic acid , formic acid , alcohol , etc .Micrococcus ,
Microbacterium , and Bacillus can produce acid in milk but not
strong as lactics .
•The heat treatment that destroys all vegetative cells of bacteria
but allows the survival of spores of clostridium , its action leads to
butyric acid fermentation with the production of hydrogen and
carbon dioxide gas .

8. Gas production
• Gas production by bacteria usually is accompanied by acid formation .
• The chief gas formers are the coliform bacteria , clostridium spp., gas forming Bacillus species that
yield both hydrogen and carbondioxide , and the yeasts , propionics , and hetro-fermentative lactics
that produce only carbon dioxide .
• The production of gas in milk is evidenced by foam at the top .
• If milk is liquid and is supersaturated with the gas , by gas bubbles caught in the curd or furrowing it ,
by floating curd containing gas bubbles , or by a ripping apart of the curd by rapid gas production ,
causing the so-called stormy fermentation of milk .
• The likelihood of gas formation and the type of microorganisms causing it depend on the
pretreatment of the milk and the treatment of holding .
• In raw milk the coliform bacteria are most appropriate to be the main gas former .
• Heterofermentative lactics also may produce gas , but actually not enough to be evident in the milk .
• Gas forming Clostridium and Bacillus do not compete well with acid formers at higher temperatures
but may function if acid formers are absent ..
• When milk is heated at high temperature during pasteurization the chief acid formers will be killed ,
the spores of clostridium and bacillus species will survive , and gas formation by sporeformers .
• Propionic acid –forming bacteria are not active in milk but form gas (carbon dioxide ) in cheese.

9. PROTEOLYSIS
● The hydrolysis of milk proteins by microorganisms often leads to the
production of a bitter taste due to peptides released during the process .
● Proteolysis is influenced by factors such as low storage temperature ,
destruction of lactic acid bacteria by heat , and neutralization of acid by
organisms .
● Types of proteolytic changes:-
❖ Acid proteolysis :-It causes production of a shrunken curd and whey .
Some micrococcus species causes it.
❖ Proteolysis with little acidity or alkalinity occurs with minimal acid
production .
❖ Sweet curdling caused by rennin like enzymes , resulting in curd formation
with little acidity .
❖ Slow proteolysis by intracellular enzymes occurs by bacterial autolysis .
❖ Residual proteolytic activity of heat stable proteinase , by bacteria like
Pseudomonas fluorescens , ca survive pasteurization .
● Different bacteria exhibit varying degrees of proteolysis , from complete
curd digestion to minimal acid production .
● Proteolysis is caused by bacteria such as Micrococcus , Alcaligenes
,Pseudomonas , Flavobacterium , Bacillus , and Clostridium .
● Bacillus species can grow at low temperatures and contribute to
proteolysis and milk bitterness .Bacillus cereus has been implicated in
sweet curdling of pasteurized milk .
● Slow proteolysis by intracellular bacterial enzymes is significant in cheese
curing and products with extented shelf life .

10. Ropiness
•Ropiness and sliminess can occur in milk , cream ,
•or whey but are important mostly in market milk and cream .
•Non bacterial ropiness or sliminess may be due to
•1) Stringiness caused by mastitis and in particular by fibrin and leukocytes from the cow’s
blood ( in contrast to ropiness produced by bacteria , it is present when the milk is drawn ,
not developed during holding of milk )
•2)Sliminess resulting from the thickness of cream , eg : at the top of a bottle .
•3) Stringiness due to thin films of casein or lactalbumin during cooling , as sometimes is
observed on surface coolers .
•Bacterial ropiness is caused by slimy capsular material from the cells , usually gums or
mucins , and ordinarily develops best at low storage temperatures .
•Ropiness usually decreases as the acidity of milk or cream increases .
•There are 2 main types of bacterial ropiness , one in which the milk is most ropy at the top
and the other in which the milk becomes ropy throughout .

11. ➢Surface ropiness is caused most often by Alcaligenes viscolactis , an organism chiefly from water
or soil that can grow fairly well in the vicinity of 10 degree celcius .Surface of the thermoduric
micrococci , eg : Micrococcus freudenreichii, can cause surface ropiness.
Since the sources of the bacteria causing ropiness are water , manure , utensils , and feed the
reduction or elimination of contamination from these sources helps prevent ropiness .
Ropiness throughout the milk may be caused by any of a number of kinds of bacteria :-
Bacteria Effect on milk
Enterobacter aerogenes , E. cloacae ,
Klebsiella oxytoca , and rarely
Escherichia coli .
Ropiness caused by Enterobacter
usually is worse near the top of the
milk .
Lactic acid bacteria common species
like Streptococcus lactis var.
hollandicus .
It is used in making a Scandinavian
fermented milk .
Lactobacillus casei , Lactobacillus
bulgaricus , and Lactobacillus
plantarum and strains of Streptococcus
cremoris
It occassionaly produces ropiness
.Most of these lactic bacteria can grow
in long chains , a characterstic that
supposedly contributes to the stringy
condition of the milk .
Alkali formers bacteria like micrococci
, streptococci , and bacilli
These would be suppressed by the acid
formers .

12. Changes in
Milkfat
● Milkfat may be decomposed by various bacteria , yeasts , and molds that do not constitute
distinct groups on the basis of other characteristics .nThese microorganisms are typically
aerobic , proteolytic , and non –acid-forming .
● The following changes in the milkfat takes place :-
● 1) Oxidation of unsaturated fatty acids , which , leads to production of aldehydes , acids , and
ketones , results in tallowy odors and taste .This process is accelerated by metals , sunlight
and oxidizing microorganisms .
● 2)Hydrolysis of butterfat into fatty acids and glycerol is carried out by an enzyme called lipase
.Lipase can originate from the original milk or microbial sources .Combined oxidation and
hydrolysis can result in rancidity .
● Lipase forming bacteria :Pseudomonas , Proteus , Alcaligenes , Bacillus , Micrococcus ,
Clostridium , produces lipase.
● Pseudomonas fragi , and Staphylococcus aureus are known to produce heat-resistant lipases ,
it can survive pasteurization .

13. Flavor changes
● The flavor of milk as drawn is low , delicate , and easily altered , the reason for abnormal flavor is
because of individual cow , mastitis , the stage of lactation of cow , or feed .
● Some of the off-flavors caused by microorganisms .
Flavor and bacterial action
Sour or Acid flavor :
Acidity may be described as :
Clean: Produced by Streptococcus lactis and other lactics
Aromatic: When lactic streptococci and aroma forming Leuconostoc species grow together
Sharp: When appreciable amounts of volatile fatty acids (formic , acetic , or butyric) are
produced by coliform bacteria , Clostridium spp.
Clean and aromatic flavors are desired in fermented milk products .
Bitter flavors:
Bitterness usually results from proteolysis but may follow lipolysis or fermentation of lactose .
Milk from late lactation cows is bitter . Certain strains of coliform bacteria and of asporogenous
yeasts .Some cocci cause very bitter milk , and actinomycetes sometimes give bitter –musty
flavors .
Burnt or caramel flavor :
Certain strains of Streptococcus lactis var. maltigenes produce this flavor , which resembles the
cooked flavor of overheated milk .

14. Miscellaneous
Other flavors
Bacteria
Barny flavor Enterobacter oxytocum
Soapiness Ammonia formers like Pseudomonas sapolactica
Turnip like flavor Escherichia coli and Pseudomonas fluorescens
Fruity flavor Pseudomonas fragi
Potato like flavor Pseudomonas mucidolens
Fishiness Aeromonas hydrophila or various cocci that produce
trimethylamine from lecithin
Earthy or musty flavors Actinomycetes
Fruity ,esterlike , and alcoholic flavors Yeasts
An amyl alcohol flavor White and orange micrococci
Putrefaction Clostridium , Pseudomonas putrefaciens
Inadequately cooled raw milk that has been held in a tightly
covered can so that volatile products of bacterial metabolism
have collected above the milk has an undesireable odor that
varies in nature . Milk in this condition is termed as
smothered .

15. Color changes
● The color of milk or cream is affected by its physical and chemical composition eg: by the amount and
yellowness of the butterfat , the thinness of the milk , the content of blood and pus , and the feed of
the animal .
● The color may be due to the surface growth of pigmented bacteria or molds in the form of a scum or
ring or may be present throughout the milk .
● The color changes caused by microorganisms:-
Color Bacteria
Blue milk Pseudomonas syncyanea produces a bluish –gray to brownish color in
milk in pure culture but when growing with an acid former like
Streptococcus lactis causes a deep- blue color .This defect and the blue
color produced by actinomycetes or species of the mold Geotrichum
are rare .
Yellow milk Pseudomonas synxantha , may cause a yellow color in the cream
layer of milk , coincident to lipolysis and proteolysis . Species of
Flavobacterium can also give yellowness .
Red Milk Red milk is caused by species of Serratia , eg : Serratia marcesscens , is
rare because other bacteria ordinarily outgrow the red pigmented
species . Brevibacterium erythrogenes produces a red layer at the top
of the milk , followed by proteolysis .Micrococcus roseus may grow
and produce a red sediment , and yeast may produce pink or red
colonies on the surface of sour milk or cream .
Brown milk A brown color may result from Pseudomonas putrefaciens or by the
enzymic oxidation of tyrosine by Psedomonas fluorescens .

16. Spoilage of Milk at different Temperatures
Temperature (raw milk) Bacteria and their action
At refrigeration temperature Proteolysis initiated by psychrotrophic
bacteria such as Pseudomonas , and
molds
At room temperature Acid fermentation by lactic streptococci
and coliform bacteria and acid tolerant
lactobacilli
Pasteurization kills yeasts , molds , most psychrotrophic bacteria , the coliforms ,
and rapid rapid acid producers like Streptococcus lactis .
The spoilage of pasteurized milk is done by sporeformers , psychrotrophic bacilli .
Alkali production in milk
The group of bacteria that causes an alkaline reaction in milk without an evidence of
proteolysis .The alkaline reaction may result from the formation of ammonia , as from urea or
of carbonates , as from organic acids like citric acid . The bacteria grow from moderate to low
temperatures . Examples of alkali formers are Pseudomonas fluorescens and Alcaligenes
viscolactics .

17. Condensed and dry
milk products
● It includes evaporated milk (unsweetened) , bulk condensed
milk, frozen milk , butter milk , and sour skim milk, dry milk .
● The defects in raw material carry over to condensed product .
● Condensed products contain high solutes that inhibit bacterial
growth .
● Spoilage of condensed butter milk and sour skim milk is by
molds when exposed to air .
● High acid and solutes prevent the growth of bacteria or yeasts .

18. Sweetened condensed milk
● It contains high sugar ,50-60 percent .
● Spoilage include :-
▪ Gas formation, often caused by sucrose fermenting yeasts or , less commonly
,coliform bacteria .
▪ Thickening of the milk , caused by micrococci that produce renin like enzyme .
▪ The development of buttons , which are mold colonies growing on milk
surface.The size of these buttons depends on amount of air in can .
▪ Species of Aspergillus and Penicillium are implicated in growth of these mold
colonies.
● Sweetened condensed milk undergoes high temperature treatment during
forewarming (71.1 to 100 degree celcius) and mild heat treatment during
condensing (48.9 to 54.4 degree celcius) , it destroys yeasts, molds and most
vegetative bacteria cells .

19. Bulk condensed milk Plain condensed milk is made using mild
temperatures similar to pasteurization , and its
evaporating process allows thermophiles to grow
.Despite refrigeration , it has a short shelf life and is
prone to spoilage by thermoduric bacteria that can
withstand high solute concentration .Superheated
condensed milk is produced at high temperature ,
spores did not get destroyed .
Evaporated milk ▪Unsweetened evaporated milk is heat processed under
steam pressure to eliminate microorganisms and prevent
spoilage .
▪Spoilage can occur if heat process is insufficient or
defects in can .
▪Swelling of can caused by gas forming anaerobic
sporeformers Clostridium ,also bulging occurs when acid
constituents of milk act on iron of can and produce
hydrogen .
▪Coagulation of milk in can varies from flakes to a solid
curd and is often caused by species of Bacillus , including
mesophiles and thermophiles .Proper cooling prevents
spoilage .
▪Bitterness in milk results from proteolysis by Bacillus or
Clostridium species .
▪Spoilage due to leakage can lead to gas and swelling from
coliform bacteria or yeast ,coagulation by streptococci , or
bitterness caused by cocci.

20. Frozen desserts
● The types of frozen desserts include ice cream , ice milk , frozen
custards , sherbets , and ices .
● The ingredients include milk, cream , evaporated milk ,condensed
milk , dried milk , coloring materials , flavors , fruits , nuts ,
sweetening agents , eggs , egg products , and stabilizers .
● Ingredients may contain bacterial contents or coliforms bacteria
that impact the dessert quality .
● Frozen dessert remain safe .
● Pasteurization of the mix before freezing helps prevent spoilage ,
but prolonged exposure to temperatures above freezing can lead to
souring by acid forming bacteria .

21. Butter
● The defects in butter originate from the cream its made , if
cream is several days old .
● Then lactic acid bacteria , gas formers , and other spoilage
organisms may grow and be followed by molds eg
:Geotrichum candidum .
● Salted butter is less likely to support microbial growth ,
due to high salt concentration and less moisture content .
● Butter is kept refrigerated and during commercial storage
it is kept at about -17.8 degree celcius ,hence no microbial
growth .

22. Flavor defects
● Undesirable flavours come from cream ,such
flavours received from cow feed ,absorbed
from atmosphere or during microbial growth .
● Feeds such as onion , garlic , French weed
,peppergrass , and poor spoilage causes off-
flavours to cream .
● Volatile produces that may be absorbed from
the air are odors from barn and from chemicals
like kerosene , gasoline , fly sprays ,
disinfectants .

23. Growth of microorganisms in cream and
milk results in bad flavours :-
● Cheesiness ,caused by lactobacilli.
● Rancidity by lipolytic bacteria and molds, lipase enzyme .
● Barny flavor, produced by species of Enterobacter.
● Malty flavor , by Streptococcus lactis var. maltigenes
● Yeasty flavours produced by yeast
● Musty flavours ,by molds and actinomycetes.
● Metallic flavours , caused by dissolved metals in highly acid cream .
● Flat flavor by Pseudomonas species
● Highly acid flavor when cream has excessive acidity
● Unclean flavor ,caused by coliform bacteria

24. ● Butter absorbs volatile material from air ,
microorganisms in butter can cause :-
● Surface taint , also called rabbito and
putridity ,which is blamed on
Pseudomonas putrefaciens ,it is worse in
unsalted or low -salt butter .
● Fishiness ,caused by Aeromonas
hydrophila.
● Esterlike flavours , resulting from the
action of Pseudomonas fragi .
● Skunklike flavors , caused by
Pseudomonas mephitica.
● Roquefort like flavors , by molds .

25. Colour defects
● The colour defect could also be caused by mottling .

26. Thank you