Dairy product processing and marketing

By: Solomon A.
*Dairy product
processing and
marketing

*
Objectives:
Dictation on:
Principles of dairy production, processing and marketing
Importance of dairy product processing and marketing

*1. Principles of dairy production,
processing and marketing
Dairy producers ensure the safety and quality of their products will
satisfy the highest expectations of the food industry and consumers.
On-farm practices should ensure that milk is produced by healthy
cattle under sustainable economic, social and environmental
conditions.
It is important to note that the focus of these Principles and Practices
is on the desired outcomes, rather than on specific, prescriptive
actions/processes.

It is important to note that good management of a farming system
constitutes the grassroots of the system’s economic, environmental
and social sustainability.
1.Sustainable Farming
Site selection and management
Sustainability management system
Animal breed
Animal health
Milking hygiene, milk storage and milk safety
Animal feeding and water
Animal welfare

2. Economic Sustainability
Safety, quality and transparency
Financial and market stability
3. Social Sustainability
4. Environmental Sustainability

Objectives:
Lecture on:
Physics and chemistry of dairy products
Composition of milk
Week-2

What is milk?
Milk is secreted by the mammary glands of mammals to feed
their young.
It is also described as a colloidal suspension, containing
emulsified globules of fat, a heterogeneous family of major and
minor proteins, the carbohydrate lactose, minerals, vitamins and
enzymes.
Cow milk is a white fluid of low viscosity and slightly sweet taste,
most commonly used as human food.
Species Total solids Fat Protein Lactose Ash
Human 12.4 3.8 1.0 7.0 0.2
Cow 12.7 3.7 3.4 4.8 0.7
Goat 12.3 4.5 2.9 4.1 0.8
Sheep 19.3 7.4 5.5 4.8 1.0
Domestic rabbit 32.8 18.3 13.9 2.1 1.8
Camel 12.9 4.2 3.7 4.1 0.9
Milk composition of some species of mammal.

1.Proteins
It is found partly in solution and partly in colloidal suspension
Cow’s milk protein is commonly divided into two classes on the
basis of the solubility at pH 4.6: the insoluble caseins and the soluble
whey (or serum) proteins.
Whey proteins
Represent 20% of total milk protein in cow’s milk.
In their native form are soluble at pH 4.6 or in saturated NaCl,
It remain soluble after rennet-induced coagulation of casein micelles
and cannot be sedimented by ultracentrifugation.
It consists a number of proteins, primarily
β-lactoglobulin (β-lg),
α-lactalbumin (α-la),
blood serum albumin,
immunoglobulins and
proteose peptones.

β-lactoglobulin
β-lg is the first most abundant whey protein.
It is synthesized in the epithelial cells of the mammary gland.
Monomeric cow’s β-lg consists of 162 residues per monomer.
In cow’s milk at natural milk pH, it is found in the form of dimers,
formed through hydrophobic interaction.
α-Lactalbumin
α-La is the second most abundant whey protein in cow’s milk.
It consists the polypeptide chain of 123 amino acid residues.
Synthesized in the rough endoplasmic reticulum; and then
transported to the Golgi apparatus, where it has an important function
in the synthesis of lactose.
It contains eight cysteine residues, which form four intra-molecular
disulphide bonds, and contain a tightly bound calcium ion.

Serum albumin (SA)
It is the most abundant protein in the circulatory system of the cow,
It consisting of ∼50% of the protein in bovine blood serum, but
present in small quantities in milk (0.1–0.4 g/L).
It consists of 582 amino acids; contains 17 disulphide bonds and one
free sulphydryl group.
It has little influence on the properties of cow’s milk.
Immnoglobulins (Ig)
It is present in the colostrum and, milk of all lactating species
It providing immunological protection to the offspring
It’s level is very high in the colostrum, but will decline rapidly.
The Ig classes of cow’s milk are IgG, IgM and IgA.
IgG occurs predominantly in two subclasses, IgG1 and IgG2.
IgM plays an important role in the creaming of cow’s milk.

Proteose peptones
They are often classified as the pH 4.6-soluble proteins
They are not denatured by heat treatment, but are insoluble in 12 g
/100 mL trichloroacetic acid.
It’s fractions of milk appears to consist of two groups of
proteins/peptides; osteopontin, and proteose peptone 3 (PP3)
They are derived from the action of proteolytic enzymes, primarily
plasmin, on caseins.

Caseins
The caseins represent 80% of total protein in cow’s milk.
The caseins are a class of phosphoproteins whose properties differ
considerably from most other proteins;
They are hydrophobic, have a relatively high charge and contain
many proline and only few cysteine residues.
Cow’s milk contains four types of caseins, denoted
αs1-casein,
αs2-casein, β-casein and
-casein,
which occur at a ratio of ∼4:1:4:1.6, respectively.


αs1-Casein
It has the highest charge; consists of 199 amino acids and contains
eight phosphoserine residues per molecule.
Exhibits progressive self-association to dimers, tetramers, hexamers,
etc.
αs1-Casein is easily precipitated by addition of calcium.
αs2-Casein
It is the least abundant of the caseins
It is the least hydrophobic and most highly and variably
phosphorylated of the caseins.
Consist 207 amino acid residues and behaves very similarly to αs1-
casein.

β-Casein
It is the most hydrophobic of the caseins and contains a large number
of proline residues, has a hydrophilic C-terminal end and a very
hydrophobic N-terminal end.
Consists of 209 amino acid residues contains five phosphoseryl
groups.
β-Casein is readily cleaved by the indigenous milk proteinase, and
plasmin enzyems
Which leading to the formation of β-caseins and proteose
peptones.
β-Casein is precipitated in the presence of calcium and, at a
temperature >50C,
β-casein molecules undergo self-association, leading to the
formation of micelles.

-Casein
It is differs from the other caseins,
because it is glycosylated.
Approximately 2/3 of the molecules are glycosylated; carbohydrate
groups include
galactosamine,
galactose and
N-acetylneuraminic acid residues.
It is amphiphatic, with a very hydrophobic N-terminal end and a
rather hydrophilic C-terminal end,
important in stabilizing the casein micelles.
It consists of 169 amino acid residues.
Unlike the other caseins, it is not sensitive to calcium, but it does,
like β-casein, tend to form micelles in solution.

Casein micelles
Casein micelles are the amphiphilic nature of caseins and their
phosphorylation facilitate interaction with each other and with
calcium phosphate to form highly hydrated spherical complexes.
It consists of an aggregate of spherical sub-micelles.
Calcium phosphate and α-s and β-casein are linked by the
involvement of the phosphoserine residues in the structure of the
calcium phosphate.
κ-Casein is localized on, or very close to, the surface of the casein
micelle.

2. Lactose
It is a disaccharide which is present in milk of most mammalian
species.
Cow’s milk contains small amounts of other carbohydrates also
occur;
∼10 mg/L monosaccharides (glucose and galactose) and
∼100 mg/L oligosaccharides.
It is responsible for ∼50% of the osmotic pressure of cow’s milk.
The concentration of lactose decreases progressively and
significantly with
lactation stage
increasing somatic cell count of the milk;
In both cases, this is due to the influx of NaCl from the blood and the
resultant need for a reduction in lactose concentration to maintain the
osmotic equilibrium.

Lactose is synthesized from glucose in the Golgi apparatus of the
mammary secretory cells.
The whey protein α-lactalbumin plays an important role in the
synthesis of lactose
Because α-lactalbumin has the ability to, if necessary, terminate the
synthesis of lactose and regulate and control osmotic pressure.

3. Lipids
Cow’s milk compose of
98% triglycerides and ∼1% phospholipids, plus small amounts of
diglycerides, monoglycerides, cholesterol, cholesteryl esters and
traces of fat soluble vitamins and other lipids.
Over 400 different fatty acids have been detected in cow’s milk fat,
although most occur only in trace amounts.
Milk fat globules
Almost all the lipids in milk are found in milk fat globules
Milk can be considered as an oil-in-water emulsion.
Cow’s milk typically contains >1010 milk fat globules per milliliter.

Globules are naturally emulsified by a surface layer, the milk fat
globule membrane (MFGM).
The MFGM resembles the mammary cell membrane, from which it
is largely derived, quite closely, and consists
protein including enzymes such as alkaline phosphatase and
xanthine oxidase,
phospholipids,
cerebrosides,
Cholesterol,
other substances (neutral glycerides, water, caretenoids, vitamin
A, iron and copper) are also present at lower levels.

4. Milk salts
The primary salts in milk are phosphates, citrates, chlorides,
sulphates, carbonates and bicarbonates of sodium, potassium,
calcium and magnesium.
Since milk contains organic and inorganic salts, the level of salts is
not equivalent to the level of mineral substances, and the level of
salts is by no means equivalent to the ash content.
Salts exist partially in soluble form and partially in a colloidal form,
i.e. associated with the casein micelles.
The colloidal salts are commonly referred to as micellar calcium
phosphate (MCP) or colloidal calcium phosphate (CCP), although
some magnesium and citrate are also present.
MCP plays an important role in the structure and stability of the
casein micelle.

5. Vitamins
The concentration of fat-soluble vitamins A, D, E, and K, and water-
soluble vitamins B and C and other minor constituents are found.
Bovine milk contains
Thiamine (B1),
Riboflavin (B2),
Niacin,
Pyridoxine (B6),
Pantothenic acid,
Biotin,
Folic acid,
Vitamin B12,
Vitamin C,
Vitamin A,
Vitamin D,
Vitamin E and
Vitamin K.

6. Milk enzymes
Milk contains a large number of enzymes approximately 60.
They occur in various states:
Unassociated forms in solution,
Associated or an integral part of membrane fractions,
Associated with casein micelles, and
Part of the microsomal particles.
They can affect by processing and storage conditions of milk.
They origin from udder (synthesized enzymes) or from bacterial
enzymes (bacterial source).
Several of the enzymes in milk are tested for quality assurance of
raw milk and processed milk products.
Enzymes associated with membrane fractions will occur in both
cream and skim milk.

Enzymes known or potential for technological significance are:
Plasmin,
Lipoprotein lipase,
Alkaline phosphatase,
Lactoperoxidaes,
Sulhydryl oxidase,
N-acetyl-β-D-glucosaminidase,
Catalase,
Xanthine oxidase,
Superoxide dismutase,
γ-glutaryltransferase, and
Lactose synthase.

Objectives:
Lecture and discussion on:
Biosynthesis of milk
Week-3

Biosynthesis of milk constituents
Mammary gland
Biosynthesis of milk proteins

The substrate, amino acids from blood, is transported through the
basolateral membrane to mammary secretory cell.
The transporting systems may be sodium dependent or independent.
Different groups of amino acids require different transporting
system.
The biosynthesis is initiated by gene expression
Following essential steps are involved in protein biosynthesis:
Transcription
Activation
Translation
Milk Enzymes
Many enzymes in milk are original enzymes coming from the cow’s
udder.

Biosynthesis of milk sugar, lactose

Secretion of milk constituents into lumen

Rate of milk secretion
It is related to time since the previous milking of the cow.
After 10 hours from previous milking, the average secreting rate
slows down and after 35 hours it stops completely.

Structural and Physical properties of milk
Milk is a fluid with characteristics of three physical phases:
 Emulsion,
 Colloidal dispersion, and
 Solution.
Milk lipids present as an “oil-in-water” type emulsion can be broken
by low-speed centrifugation and the milk separates into lipid and
aqueous phases, each with a characteristic composition.
Colloidal phase contains casein micelles, calcium phosphates, and
globular proteins.
Whey proteins are in colloidal solution and the casein is in colloidal
suspension.

Lactose, vitamins, acids, enzymes, and some inorganic salts are
present as true solutions.
The physical equilibrium of milk destabilize by factors such as
addition of polyvalent insoluble salts;
concentration of serum solids;
changes in pH;
heat treatment; and
addition of precipitant such as alcohol.
These factors can change the structure of milk and its physical
equilibrium.

The physical properties of milk are of great importance to the dairy
technologist,
They will affect most of the unit operations during processing.
These include
fluid flow, mixing and churning, emulsification and
homogenization, and also
heat transfer processes such as pasteurization,
sterilization, evaporation, dehydration, chilling, and
freezing.

Objectives:
Influences on milk quality
Week-4

Influences on milk quality
Interval between milking
The fat content of milk varies
SNF content does not vary
Stage of lactation
Fat, lactose and protein contents of milk vary
SNF content is highest the first 2-3 weeks, then decreases slightly.
Fat content is high immediately after calving but fall for 10 to 12
weeks, and then tends to rise again until the end.
High protein content of early lactation milk is due mainly to the
high globulin content.

Age and health
As cows grow older
fat content decreases by about 0.02%
SNF content fall about 0.04%.
But both fat and SNF contents can be reduced by disease.
Feeding regime
Underfeeding reduces both the fat and the SNF content of milk.
SNF content may fall if fed a low-energy diet, but is not greatly
influenced by protein deficiency, unless the deficiency is acute.
Fat content and fat composition are influenced more by roughage
intake.

Completeness of milking
The first milk drawn from the udder contains about 1.4% fat
while the last milk contains about 8.7% fat.

Objectives:
Dairy products analysis
Purpose of Analysis of dairy products
Sampling techniques
Types of analysis
 Tests for milk composition
 Tests for milk quality
Week-5

Purpose of Analysis of dairy products
What are the purpose of analyzing the dairy products?

Sampling techniques
Accurate and representative sample must be obtained.
Milk must be mixed thoroughly before sampling and analysis to
ensure a representative sample.
If the volume of milk is small, e.g. from an individual cow, the milk
may be poured from one bucket to another and a sample of milk
taken immediately.
If large volumes of milk are handled, the milk or cream must be
mixed by stirring thoroughly; and small samples taken from three or
more places of the container.
For best results, milk or cream must be sampled at temperatures
between 15 and 32°C.
Sour milk or cream, in which casein has coagulated, must be
sampled frequently.

If the milk or cream has been standing for a long time and a deposit
has formed on the surface and sides of the container, it should be
warmed while agitating before a sample is removed.
For certain analyses, milk samples can be preserved and stored.
Samples of milk or cream for butterfat analysis can be preserved
using formalin or potassium dichromate.
Plungers and dippers are used in sampling milk from milk cans/
bulk tanks.
Sampling for bacteriological testing
Dippers should be sterilized in an autoclave or pressure cooker for
15 minutes at 120°C before use.
On-the-spot sterilization with 70% alcohol swab and flaming, or
scalding in hot steam may also be used.

Preservation of milk samples
If a milk sample cannot be analyzed immediately after sampling:
 It must be cooled quickly to near freezing point until
transported to the laboratory.
 If samples are taken from field they can be preserved in ice
boxes with ice packs.
Milk samples cooled in a refrigerator or ice-box must first be
warmed in 40°C water bath then cooled to 20°C and mixed well
before analysis.
Milk samples for butterfat testing may be preserved with potassium
dichromate one tablet or 0.5 ml of a 4% solution in a 0.25 liter
sample bottle is adequate.
Other chemical preservatives include 0.08% sodium azide and
0.02% Bronopol.

Labeling and record keeping
Samples must be clearly labeled with:
the name or code number of farmer,
date of sampling and
the place where the sample was collected.
This information should also be included in standard data sheets.
Records must be kept neat and stored in a dry place.

Types of analysis
1) Tests for milk composition
 Fat determination
 Total solids (TS) in milk
 Determination of protein content of milk by formaldehyde
(formal) titration
2) Tests for milk quality
Physiochemical quality
 Milk pH
 Measuring pH using indicator
 Electrometric measurement of pH
 Titratable acidity test

 Alcohol test
 Clot-on-boiling test
 Specific gravity of milk
 Formaldehyde in milk
Microbiological quality
 Methylene blue reduction test
 Resazurin 10-minute test
Sensory evaluation of dairy products

Objectives:
Unit operations in dairy products
processing
Receiving and storage of milk
Straining, filtration and clarification
Standardization
Pasteurization
Sterilization
Homogenization
Cream separation
Membrane processing
Week-6

Receiving and storage of milk
Milk collection
When milk is brought from the farm to the dairy for processing the
following information on the milk is required:
 Quality: acidity, pH, alcohol and clot-on-boiling
 Quantity
 Composition: total solids (TS), specific gravity
 Presence of contaminants - neutralizers, preservatives etc
 Adulteration: fat, titratable acidity and specific gravity tests
Milk storage

Straining, filtration and clarification
The object is to improve aesthetic quality of milk by removing
visible foreign matter which is unsightly and may therefore, cause
consumer complaints.
Straining is separation milk according to breed, health states of
animal and so
Filtration is removes suspended foreign particles by the straining
process,
Clarification is removes the same by centrifugal sedimentation

Standardization
The adjustment of fat and SNF of milk to the desired level, to meet
the legal standards
Correct calculations by Pearson’s method regarding ingredients to
be used for standardization

Pasteurization
Pasteurization is the most common process used to destroy bacteria
in milk.
In pasteurization, the milk is heated to a temperature sufficient to
kill pathogenic bacteria, but well below its boiling point.
Also kills many non-pathogenic organisms and thereby extends the
storage stability of the milk.
Numerous time-temperature combinations are recommended

High Temperature Short Time (HTST) treatment
Is 72°C for 15 seconds followed by rapid (less than 2 minutes)
cooling to below 10°C.
Batch pasteurization
Fixed quantities of milk are heated to 63°C and held at this
temperature for 30 minutes.
The milk is then cooled to 5°C using iced or cold water before
packing.

Effects of pasteurization on milk
Fat
Reduces the cream layer.
Inhibits clustering of the fat globules and consequently reduces
the extent of creaming.
However, it does not reduce the fat content of milk.
Nutritive value
It has little effect and the major nutrients are not altered.
It has insignificant loss of vitamin C and vitamin B group.
The process kills many fermentative organisms as well as
pathogens but putrefactive micro-organisms survive.

Sterilization
Ensures almost complete destruction of the microbial population.
Time/temperature treatments of above 100°C for 15 to 40 minutes.
The product has a much longer shelf-life than pasteurized milk.
Ultra high temperature treatment (UHT).
Milk is heated under pressure to about 140°C for 4 seconds.
It retains more of the properties of fresh milk than conventionally
sterilized milk.

Homogenization
Cream separation
Membrane processing
Separation of dairy fluids using semi-permeable membranes has
been used to clarify, concentrate and fractionate a variety of dairy
products.

Objectives:
Dairy products manufacturing
Beverage milk
Concentrated and dried dairy products
Ice cream
Butter
Cheeses
Yoghurt and other cultured milk by
products
Week-7

1) Beverage milk
2) Concentrated and dried dairy products
The unit processes in the manufacture of dry milk products include
standardization, preheating, concentration, homogenization, and
drying.
The approximate compositions of the milk powder products are as
follows:
 Skim milk powder: 36% protein,<1% fat, 51% lactose, 8% ash
water, 3–4% moisture;
 Full-cream milk powder: 26% protein, 27% fat, 38% lactose,
6% ash, moisture 3%.

Flow chart for manufacture of selected dry milk products

3) Ice cream
In order to make an ice cream mix, three categories of ingredients
are necessary.
 Concentrated source of milk fat,
 Concentrated source of milk solids-not-fat (aka serum solids), and
 Balancing ingredient.
The prioritization of ingredient selection can be said to approximate
the hierarchy as follows:
 Select milk fat content
 Select nonfat milk solids level to complement the fat content
 Sweetener ingredient
 Stabilizer and emulsifier
 Label considerations

Representative Formulae for Ice Creams of Different Grades
Constituent
Grades of Ice Cream (%)
Minimum
Standard
Regular Premium Super
Premium1 2
Milk fat 10 12 14 16 18
Milk solids non fat 7.5 9 10 10.5 9.5
Whey solids 2.5 2 - - -
Sucrose 4.5 7.6 12 15 15
Corn syrup solids 9 6.8 5 - -
High fructose solids 4.5 2.6 - - -
Stabilizer 0.35 0.25 0.13 0.12 -
Emulsifier 0.25 0.25 0.15 0.1 -
Total solids 38.7 40.5 41.28 41.72 42.5

4) Butter
Preparation of cream by centrifugal separation of liquid milk to a
fat content typically ca. 40%.
Cream ageing to promote crystallization of milk fat using
selected temperature regime(s).
Emulsion destabilization and phase inversion from an oil/water
cream emulsion to water/oil butter emulsion achieved by
physical agitation (churning).
Physical working of butter grains to form larger granules, expel
buttermilk, distribute moisture, and create a homogeneous butter
mass.

Key processing steps involved in the commercial manufacture of butter

5) Cheeses
Cheese is the generic name for a group of fermented milk-based
food products.
Cheese making originated as a crude form of food preservation.
The preservation of cheese is as a result of the combined action of:
 Dehydration
 Acid
 Antibiotic
 Anaerobic condition.
 Addition of NaCl.

General description of steps involved in the cheese manufacture:

6) Yoghurt and other cultured milk by products
Yogurt
Yogurt manufacture includes several steps including
standardization of the yogurt base,
homogenization,
heat treatment,
cooling to incubation temperature,
inoculation with yogurt cultures,
incubation,
cooling, and
packaging.

Other cultured dairy products
 A number of different cultured dairy products exist on the market.
 In addition to classification based on the type of starter cultures involved
in the processing, another way to group these products is based on the
 state of water and includes gel/liquid, concentrated/strained, frozen, or
dried products.
 The quality of cultured products varies with the composition and
microbial quality of the raw materials, addition of ingredient, unit
operations involved, and handling of the coagulum after fermentation.
 The steps involved in the manufacturing are fairly similar and could be
summarized in the following: standardization of the milk base,
homogenization, heat treatment, starter culture addition, and cooling.

Cultured dairy products produced by mesophilic lactic starter
cultures
These products are produced by metabolic activity of lactic starters,
whose growth optimum is between 20 and 30◦C. The main
representatives of this group are cultured buttermilk, Scandinavian
sour milk products, and sour cream.
Cultured dairy products produced by thermophilic lactic starter
cultures
This group of products is likely commercially the most important
and involves the fermentative ability of the starter cultures, which
grow in thermophilic temperature range, frequently above 370C.

Cultured dairy products produced by mixed fermentation
This group of cultured dairy products comprises of products
fermented by mixed lactic starter and lactose and/or non-lactose
fermenting yeast and mold. These products are rather contained to
specific areas, consumed locally and, in some instances, there is
little commercial importance.

Objectives:
Fermented milk and starter culture
Types of fermented milk
Micro-flora of starter culture and related
enzymatic activities
Types and utility of starter culture
Flavor generation in dairy products
Week-8

Types of fermented milk
Fermented milks are wholesome foods and highly acid milk does
not putrefy.
Bacteria in milk are responsible for acid development by the
anaerobic breakdown of lactose to lactic acid and other organic
acids.
The conversion of carbohydrate to organic acids or alcohols is
called fermentation.
Pyruvic acid formation is an intermediate step common to most
carbohydrate fermentations
Fermentations are usually described by the end product such as
lactic acid or ethyl alcohol and carbon dioxide.

Milk fermentation can be either homofermentative, with one end
product, or heterofermentative, with more than one end product.
Lactic acid fermentation: is the most important one in milk and is
central to many processes.
 Propionic fermentation is mixed-acid fermentation and is used in the
manufacture of Swiss cheese varieties.
Spoilage fermentation: coliform gassy fermentation is an example.
 Large numbers of coliform bacteria in milk indicates poor hygiene.
 Coliform gassy fermentation disrupts lactic acid fermentation, and
also causes spoilage in cheese.

Outline of four important lactose fermentations

Microbial growth affect milk fermentation.
Fermentation rates generally parallel the microbial growth curve up
to the stationary phase.
Type of fermentation depends on
 Numbers and types of bacteria in the milk,
 Storage temperature and
 Presence or absence of inhibitory substances.
The desired fermentations can be obtained by temperature
manipulation or by adding a selected culture of micro-organisms
(starter) to pasteurized or sterilized milk.
Fermentation continues until either the substrate is depleted or the
end product accumulates.

Types of fermented milk are made by controlled fermentation.
 By inoculating the desired micro-organisms in the milk and
 By maintaining at a favorable temperature to fermentative organism.

Common steps to making different types of fermented milk products

Micro-flora of starter culture and related enzymatic
activities
The major functions of microbial starter cultures in food and dairy
products are:
To bio-preserve the product due to a fermentation that results in
an extended shelf life and enhanced safety.
To enhance the perceived sensory properties of the product.
To improve the rheological properties (i.e., viscosity and
firmness) of the product and in some instances encourage gas
production or color.
To contribute dietetic/functional properties to food, such as
occurs with the use of probiotic micro-floras.
Several microorganisms are employed in the manufacture of cheese
and other fermented milk products.

The following are examples of starter culture in the dairy industry:
Genus Lactococcus
Genus Leuconostoc
Genus Pediococcus
Genus Streptococcus
Genus Lactobacillus
Genus Bifidobacterium
Genus Enterococcus
Genus Propionibacterium
Genus Brevibacterium
Miscellaneous Microorganisms
Molds
Yeasts

Types and utility of starter culture
Dairy starter cultures are active microbial preparations added
intentionally to dairy bases in order to achieve desired
modifications.
These cultures may consist of single strains used alone or in
combinations or undefined mixtures of strains (mixed-strain
cultures).
On the basis of their optimal growth temperature, they can be
classified as either mesophilic (optimum temperature around 260C)
or thermophilic (optimum temperature around 420C).
Reading assignment

Flavor generation in dairy products
The three main constituents of milk (fat, proteins and lactose) can
be degraded to build flavor of milk, or derivatives from each can
react with each other to form new products that have a flavor.
Degradation of milk fat results large number of different volatile
flavors.

Off-flavors in milk and their chemical or biological origin
a) Off-flavors induced by light and/or metal ions
Independent of heating, each oxidation process in milk has to start
with a reaction of dioxygen with one of the milk ingredients.
A notorious oxidation off-flavor is formed by a combination of
light, riboflavin and dioxygen or metal ions and dioxygen.
 Both systems are able to generate activated dioxygen that is
reactive enough to break down serum proteins and produce
 Volatile thiols,
 Sulphides and disulphides or to
 Form organic peroxides from fatty acids

b) Off-flavors transferred from cow to milk
During lactation, the digestive tract, blood circulation and
respiratory system of the cow are important organs for determining
the sensory and nutritional quality of the raw milk.
Compounds which have been reported to be responsible for feed-
related off-flavors are:
 Dimethyl
 Sulphide
 Acetone
 Butanone
 Isopropanol
 Ethanol
 Propanol
 Indole,
 Skatole
 Mercaptans
 Sulphides
 Nitriles
 Thiocyanates

c) Off-flavors in milk caused by micro-organisms or enzymatic
reactions
Lipolytic rancidity caused by the liberation of C4-C12 fatty acids
from milk fat by milk lipase or bacterial lipases.
Psychotrophic bacteria can cause
 Unclean flavor occur due to an increment of dimethylsulphide above
the threshold of 14 μg/kg.
 Fruity off-flavor occur due to production of ethyl esters of butyric,
isovaleric and caproic acids.

Milk contaminated with Streptococcus lactis var. maltigenes may
develop a malty flavor as a result of
 3-methylbutanal,
 2-methylbutanal and
 2-methylpropanal formation.
Sterile milk produced by mild UHT heating may develop a bitter
off-flavor on ageing as a result of thermostable bacterial proteinases
activity, which break down milk proteins to bitter peptides.

Objectives:
Dairy microbiology and safety
General dairy microbiology
Growth of microorganisms in milk and dairy
products
Inhibition and control of microorganisms in milk and
dairy products
Week-9

*Dairy microbiology:-is the study of micro organism found in
milk and its product.
*Microorganism classified as
1.Beneficial –desirable for fermentation
2. Harmful- spoilage degradation of milk constituent
$pathogenic for human health
Common micro organism found in milk are :
Bacteria
Fungi (yeast and Molds)
Viruses
Classified based on :Morphology, Biochemical characteristics,
and Genome

The levels and types of micro-organisms in milk and dairy products
depend on:
 The microbial quality of the raw materials,
 The conditions under which the products are produced and
 The temperature and duration of storage.
The most common spoilage micro-organisms of milk and dairy
products are:
 Gram-negative rod-shaped bacteria (e.g. Pseudomonas spp.,
coliforms),
 Gram-positive spore-forming bacteria (e.g. Bacillus spp.,
Clostridium spp.),
 Lactic acid producing bacteria (e.g. Streptococcus spp.) and
 Yeasts and moulds.

Bacteria
Is single cell prokaryotes
The major types of bacteria which found in milk are:
 LAB and related genera
 Coliform bacteria
 Spore forming Bacteria
 Pseudomonas and related genera
Cells are either spherical or rod-shaped; spherical bacteria are
called cocci while those that are rod-shaped are called bacilli.

LAB(LACTIC ACID BACTERIA)
This are the normal flora of milk
Facultative anaerobes, Non spore forming gram positive
It consists cocci and rods
Convert lactose(Milk Sugar) to lactic acid
Used mostly as a starter culture
It include :
Lacto coccus  Lactobacillus
Streptococcus  propionibacteria
Leuconostoc  Bifidobacteria
pediococcus  Bravbacteria

Lactococci
Streptococci originally isolated from milk or cream
They occurs singly in pairs or in chains
Non-motile, mesophilic and homo fermentative
The most famous species is lactococus lactis used as starter
culture for dahi and some cheeses
Streptococcus thermophiles
Occurs in long chains(18-20 cells)
Grows at 45 c
This microorganism used as starter for yoghurt in association
with lactobacillus delbrueckii subsp. Bulgaricus
leuconostoc

Leuconostoc
Ellipsoidal in shape
Occurs in pair and chains
Hetrofermentative
Ability to produce aroma compound so used as starter
Eg. leuconostoc mesentroides subsp,dexitranicum
Pediococci
Characterstic features is division in to two planes and
formation of tetrad
Homo fermentative
The most famous example
P.acidilactici
P.

Lactobacilli
Large group of rod shaped bacteria
Shape varies from long to short rods
Three sub groups
1. Termobacterium: Lb. bulgaricus
2. Streptobacterium: Lb.casei
3. Betabacterium : Lb.bravis
Propionic bacteria
Non-spore forming, anaerobic to aero tolerant, mesophilc
gram +ve rods
Convert lactate to propionoc acid ,co2 and other compound
Responsible for eye formation and flavor in swiss cheese

Bifidobacteria
Obligate anaerobes
Non-spore forming, gram +ve catalase –ve, non-motile rods
Ferment lactose to lactate and acetate
Probiotic effect ( beneficial effect on the health of the host
when ingested)
 Bif.bifidum
 Bif. Longum
Brevi bacteria
Aerobic , gram +ve , catalase +ve obiligate aerobes
Exhibit pleomorphism
Optimum growth temprature (20-25 c)
Proteolytic in nature
Flavor in surface ripened cheese ,brevibacterium linens

2. COLIFORM BACTERIA
Thise are gram –ve, Non sporeforming coccabacillary rodes
which have capable of converting lactose to lactic acid and gas
Growth at 30-37 c
Post pasteurization contamination and poor hygienic
condition
Excessive gas production and even mastitis in milch animal
Indirect indicators of pathogens of faecal origin
Escherichia Coli
Entrobacter aerogenes

3.SPORE FORMING BACTERIA
1. Bacilli
Gram positive , aerobic , sporegenous
Majority thermophilic
Proteolytic, Pathogenic
B. subtils , B.antheracis , B. cereus
2. Clostridia
Also known as butyric acid bacteria
Found in soil, plant and manure
Anaerobes capable of forming spores
Major spoiler of cheese
Pathogenic
Cl.botulinum,Cl.perfringens

4. PSEUDOMONACE AND RELATED GENERA
Gram –ve, motile aerobic , non-spore forming rods
Use fat and protein as energy source
Majority are psychrotrophs
Produce heat stable enzyme such as lipase and protienase
Grow during refrigerated storage
Also associated with post pasteurization contamination
The most common species
Ps.fragi
Ps.putrifaciens

Moulds
They are used in the production of a certain cheese varieties.
Yeasts
They are used industrially to ferment carbohydrates to such
products as alcohol and citric acid.
They are also considered as spoilage organisms in dairy products.
Viruses
Viruses are extremely small organisms comprising a spherical head
containing the genetic material, and a cylindrical tail.
Viruses that attack bacterial cells are known as bacteriophages.
Bacteriophages attack acid-producing bacteria inhibit acid
production in milk thereby causing problems

Fungi (a group of micro organism consisting of yeasts and
moulds)
1. YEAST
Single cell eukaryotic organism
Spherical ,ellipsoidal or cylindrical in shape
Reproduce asexually by budding and sexually by forming
spores
Groth temprature 20-30 at Ph 3-6
Facultative anaerobes
Desirable yeast (alcohol fermentation)
Species include
Kluvyveromyces
saccharomyces

Undesirable yeast (spoilage and defects) Such as ; coloration
, gassiness, abnormal flavor
MOULDS
Thread like fungi
Consists of mycelium,made up of hyphae (septate/ asepate)
Reproduction by variety of spores
Grows temprature 20-30 c and Ph ranges from 3 to 8.5
1. Desirable ( used as starter and for production of microbial
rennet)
White mould :penicillium camemberti
Blue mould : penicillium roqueforti
2. Undesirable mould
 spoilage (discoloration, button formation) common genera
involved are alternaria, aspargillus, candida,mucor e.t.c

Food poisioning (produce heat stable mycotoxin-most lethal
aflatoxin
 Viruses
A cellular , obligate intracellular parasitis
Seen by EM
Classification based on their host type
Public health significance of pathogenic human and animal
viruses
Bacteriophages
Are viruses of bacteria
Hazard to dairy industry
Cause starter failure

Growth of microorganisms in milk and dairy products
Bacterial
It refers increase in cell numbers rather than an increase in cell size.
They are reproduce by binary transverse fission.
The time taken from cell formation to cell division is called the
generation time.
The following are the phases of bacterial growth:
1) Lag phase
2) Log phase
3) Stationary phase
4) Death phase

Inhibition and control of microorganisms in milk and
dairy products
a) Temperature
 Psychrotrophic bacteria grow at temperatures below 16°C
 Mesophilic bacteria grow best at temperatures between 16 and 40°C
 Thermophilic bacteria grow best at temperatures above 40°C.
Moulds can be killed by relatively mild heat treatments, but mould
spores are more resistant to heat.

Moulds
Moulds are a heterogeneous group of multicelled organisms which
reproduce asexually either by spore formation or by fragmentation.
They can grow on a wide variety of substrates.
Yeasts
Yeasts are unicellular organisms which reproduce asexually by
budding.
Viruses
They must invade other cells to reproduce.

b) Nutrients
Micro-organisms normally feed on organic matter
The organic matter must be soluble in water and of low molecular
weight to be able to pass through the cell membrane.
Bacteria therefore need water to transport nutrients into the cell.
If the nutrient material is not sufficiently broken down, the micro-
organism can produce exo-enzymes which split the nutrients into
smaller, simpler components so they can enter the cell.
Inside the cell the nutrients are broken down further by other
enzymes, releasing energy which is used by the cell.

c) Water
Distilled water has an water activity (Aw) of 1.
Salt reduces the availability of water to the cell and the Aw drops
At Aw less than 0.8 cell growths is reduced.
Cells that can grow at low Aw are called osmophiles.
d) Oxygen
Aerobic bacteria need O2 for growth
Anaerobic bacteria need CO2 for growth.
Facultative anaerobic bacteria live either with or without oxygen.
Moulds are aerobic organisms and their growth on foods can be
retarded by excluding air through careful packaging.

e) Acidity
Most bacteria prefer a growth environment with a pH of 7.
Bacteria that can tolerate low pH are referred to as aciduric.

Objectives:
Dairy plant sanitation and the principles of
HACCP
Dairy product safety and quality
Dairy plant management
Principles of HACCP and its implementation
Dairy products Handling, and Transportation
Week-10

Dairy product safety and quality
HACCP can be applied as a tool to assess hazards and establish
control systems that focus on preventive measures rather than
relying mainly on end-product testing.
Critical key aspects with respect to milk and dairy products are:
 Ensuring raw materials are of the best quality,
 Elimination of spoilage and pathogenic bacteria from raw milk
and other raw materials by heat treatment,
 Prevention of subsequent contamination, and
 Growth limitation of undesirable micro-organisms during
storage prior to consumption.

Dairy plant management
Micro-organisms and spores are widespread in the natural
environment.
Milking and milk storage equipment being the major sources of
contamination.
If milk is produced under sanitary conditions, bacteria of the udder
surface, mainly Micrococcaceae, and less than 10% of the total
flora is psychrotrophs.
Under unsanitary conditions of production, milk can contain more
than 75% psychrotrophs.

Gram-negative organisms predominated (96-100%), the majority
being Acinetobacter spp., followed by Pseudomonas spp. and
Flavobacterium spp.
Most important is to minimize contamination at the farm and keep
the levels as low as possible by good hygienic practices.
These include proper cleaning and sanitizing of milking equipment
and rapid cooling to temperatures of 4ºC or less.

Principles of HACCP and its implementation
The overall and specific benefits of an HACCP system include:
 Focus on prevention.
 Utilizes science-based food safety data and principles.
 Provides a high level of assurance of dairy product safety.
 Focuses appropriate technical resources and control on critical
points in the production process.
 Lessens emphasis on end product testing.
 Places the primary responsibility for food safety on processors,
where it belongs.
 Meets customer needs and expectations.
 Increased consumer confidence in dairy products.

 Assured brand integrity.
 Decreased numbers of consumer complaints.
 Reduced incidence of product holds and/or recalls.
 Increased sales opportunities.

Steps to HACCP implementation
The preliminary tasks in the development of an HACCP plan
include the following:
Assemble the HACCP team,
Describe the food and its distribution,
Describe the intended use and consumers of the food,
Develop a flow diagram, which describes the process and
Verify the flow diagram.

Hazard components
Biological hazards
Chemical hazards
Physical hazards

Principles of an HACCP plan
There are seven principles in establishing an effective HACCP plan,
 Conduct a hazard analysis
 Determine CCPs
 Establish critical limits
 Establish monitoring procedures
 Establish corrective actions
 Establish verification procedures
 Establish record-keeping and documentation procedures

Dairy products Handling, and Transportation

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