Dairy Science and
Technology
Dr. Willem Marsman
International Food Safety Consultancy
Copyright 1996-2001 © Dale Carnegie & Associates, Inc.
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introduction
• It focuses on the biological, physical and
microbiological aspects of milk itself and
on the technological (processing )aspects
of the transformation of milk into its
various consumer products including
beverages, fermented products,
concentrated and dried products, butter
and ice-cream
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• Milk is ancient as man kind itself as it is the substance
created to feed mammalian infant
• Many centuries ago ancient man learned to domesticate
species for the provision of milk to be consumed by them
• Fermented products such as cheese were discovered by
accident but their history has also been documented for
many centuries as has the production of concentrated milk,
butter and even ice cream
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• The role of milk in nature is to nourish
and provide immunological protection for
the mammalian young. Milk and honey
are the only articles of diet whose sole
function in nature is food
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Milk production and biosynthesis
• Milk is the source of nutrients and immunological protection
for the young cow
• Gestation for the female cow is 9 month
• At parturition fluid from the mammary gland known as
colostrum is secreted-is yellowish colored, salty liquid has a
very high serum protein content and provides antibodies to
help the newborn until its own immune system is
established
• Within 2 hours the composition of colostrums returns to
that of fresh milk allowing to be used in food supply
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• The period of lactation then continues for an
average of 305 days producing 7000 kg of milk.
This is quite a large amount considering the calf
only needs about 1000 kg for growth.
• The highest yields is 2-3 months post
parturition yielding 40-50 l/day
• a cow reaches a peak in production about her
third lactation but can be kept in production for
5-6 lactations if the yield is still good
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• About 1-2 months after calving the cow begins
to come into heat again. She is usually
inseminated about 3 months after calving so as
to come into a yearly calving cycle
• Heifers are normally first inseminated at 15
months so she is 2 years when the first calf is
born .
• About 60 days before the next calving the cow
is dried off
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Effects of milk handling on quality
and hygiene
• Cleanliness:
• The environment of production has a
great effect on the quality of milk
produced from the food science
perspective the production of the highest
milk should be the goal, however this is
not always the greatest concern of those
involved in milk production
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•
Hygienic quality assessment test include:
1. Sensory test
2. Dye reduction test for microbial activity
3. Total bacterial count (standard plate count)
4. Sediment
5. Titratable acidity
6. Somatic cell count,
7. antibiotic residues and
8. added water
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• The two common dye reduction tests are:
• Methylene blue and reazurin, as part of natural metabolism
active micro organisms transfer electrons and thus rate at
which dyes added to milk are reduced is an indication of
the level of microbial activity:
• Methylen blue turns from blue to colorless
• While resazurin turns from blue to violet to pink to colorless
• The reduction time is inversely correlated to bacterial
numbers
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Effects of milk handling on quality
and hygiene
•
Temperature:
•
Following chart
1. 5 degree Celsius-numbers of bacteria
per milliliter of milk after 24 hours-2.600
2. 10 Celsius:11.600
3. 20 Celsius: 450.000
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Effects of milk handling on quality
and hygiene
•
Mastitis and antibiotics;
•
Mastitis is a bacterial and yeast infection of udder:
1. Lactose content decreased
2. Na and Cl level increased
3. Increase in bacterial numbers-possible human pathogen
4. Increase in somatic cells (leukocytes and epithelial cells)
•
Clinical mastitis pus can be observed, sub clinical level
mastitis is not obvious
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•
Presence of antibiotic residues in milk is very
problematic:
1. Residues can slow or destroy the growth of
fermentation bacteria
2. Some human allergic for specific antibiotic
3. Low level antibiotics can cause micro
organism to become resistant through
mutation
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Effects of milk handling on quality
and hygiene
• Anti microbial systems in raw milk-natural:
• Lysozyme- enzym that’s hydrolyses glycosidic
bonds in gram positive cell walls
• Lacto ferrin –an iron binding protein that
sequesters iron from micro organisms thus
taking away one of growth factors
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• Lactoperoxidase - an enzyme naturally
present in raw milk that catalyzes the
conversion of hydrogen peroxide to water.
When hydrogen peroxide and thiocyanate are
added to raw milk, the thiocynate is oxidized by
the enzyme/hydrogen peroxide complex
producing bacteriostatic compounds that inhibit
gram negative bacteria, E.coli, Salmonella spp,
and streptococci (means of increasing the self
life of raw milk)
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Milk bio synthesis
• Milk is synthesized in the mammary
gland
• Within the mammary gland is the milk
producing unit, the alveolus. It contains a
single layer of epithelial secretory cells
surrounding a central storage area called
the lumen
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• The raw materials for milk production are
transported via the blood stream to the
secretory cells. It takes 400-800 liter of
blood to deliver components for 1 liter of
milk
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• Protein
• Lipids
• Lactose
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• Milking stimuli such as a suckling calf ,a
warm wash cloth, the regime of parlor
etc., causes the release of a hormone
called oxytocine
• Oxytocine is released from the pituitary
gland, below the brain to begin the
process of milk let down
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Milk grading and defects
• Milk grading;
• The sense of taste, there are four different types of nerve
ending on the tongue which detect sweet ,salt ,sour and
bitter
• The sense of smell
• Milk grading techniques , temperature should be 15.5-21
Celsius ,need of representative sample (mixing and
agitation), take a generous sip, notice after taste (breath of
fresh air)
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Flavor defects
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