Công nghệ Chế biến và Bảo quản sữa
Milk and Dairy Technology
Dr. Ing. Thien Trung Le
Department of Food Engineering
Faculty of Food Science and Technology
Nong Lam University – HCM City
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ĐỀ CƯƠNG TỔNG QUÁT (TOPICAL
OUTLINE)
Chapter 1: Sữa: Các đặc trưng chính (Milk: Main
characteristics)
Chapter 2: Các cấu phần của sữa (Milk components)/ tính
chất hóa học của sữa (Chemical properties)
Chapter 3: Tính chất vật lý của sữa (Physical properties)
Chapter 4: Vi sinh vật học sữa (Microbiology of milk)
Chapter 5: Các quá trình chế biến (Milk & dairy processes)
Chapter 6: Các sản phẩm sữa (Milk & dairy products)
Chapter 7: Tính chất dinh dưỡng (Nutritional properties)
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References
• Dewettinck K., Huyghebaert A., & Rombaut R. Milk and Dairy
Technology – UGent course 2004-2005
• Walstra P. Dairy Science and Technology, Second Edition,
CRC 2006
• Tetra Pak. Dairy processing handbook, Tetra Pak 1995
• Fox P.F. Dairy Chemistry and Biochemistry, Blackie 1998
• …
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Chapter 1: Milk: Main characteristics
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Introduction
Composition and structure
Milk formation and excretion
Different kinds of milk
Factors influencing milk composition
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Introduction
– Milk is defined as the secretion of the mammary
glands of mammals
– Primary natural function being nutrition of the young.
– Milk of some animals, especially cows, buffaloes,
goats and sheep, is also used for human
consumption, either as such or in the form of a range
of dairy products
– The word ‘milk’ indicates the ‘normal’ milk of healthy
cows
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Composition and structure
• Milk
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Composition and structure
• Milk at x 5000
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Composition and structure
• Milk at x 50,000
Plasma = milk – fat globules
Serum = plasma – casein micelles
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Composition and structure
Milk = polydispersed system of water with:
– Emulsified fat globules enveloped by a membrane (
0,1-15 m)
– Caseine micelles ( 20-400 nm)
– Lipoprotein particles (remnants of mammary
secretory cell membranes) ( 10 nm)
– Soluble components such as globulins, salts
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Milk formation and secretion
Digestion:
– Food – enzymes  simple, soluble, low-molar-mass
components: monosaccharides; small peptides and
amino acids; and fatty acids and monoglycerides
– These are taken up in the blood, together with other
nutrients, such as various salts, glycerol, organic
acids, etc.
– The substances are transported to all the organs in
the body, including the mammary gland, to provide
energy and building blocks (precursors) for
metabolism, including the synthesis of proteins, lipids,
etc.
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Milk formation and excretion
Milk synthesis:
– A greater part of the synthesis of milk components occurs in the
secretory cells of the mammary gland
– precursors of milk components are taken up from the blood at
the basal end, and milk components are secreted into the lumen
at the apical end .
– Proteins are formed in the endoplasmic reticulum  transported
to the Golgi vesicles (in which other soluble milk components are
collected)  The vesicles grow in size while being transported
 open up to release their contents in the lumen.
– Triglycerides are synthesized in the cytoplasm, forming small
globules, which grow while they are transported to the apical end
of the cell. They become enrobed by the outer cell membrane (or
plasmalemma) while being pinched off into the lumen. This type
of secretion is called merocrine, which means that the cell
remains intact.
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Milk formation and excretion
Milk synthesis:
– A greater part of the synthesis of milk components occurs in the
secretory cells of the mammary gland
– precursors of milk components are taken up from the blood at
the basal end, and milk components are secreted into the lumen
at the apical end .
– Proteins are formed in the endoplasmic reticulum  transported
to the Golgi vesicles (in which other soluble milk components are
collected)  The vesicles grow in size while being transported
 open up to release their contents in the lumen.
– Triglycerides are synthesized in the cytoplasm, forming small
globules, which grow while they are transported to the apical end
of the cell. They become enrobed by the outer cell membrane (or
plasmalemma) while being pinched off into the lumen. This type
of secretion is called merocrine, which means that the cell
remains intact.
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Milk formation and excretion
Milk synthesis:
– Most are synthesized in the cell.
– Others are taken up from the blood but, generally, not in
the same proportion as in the blood; see, especially, the
salts.
– Some substances, notably water and small lipophilic
molecules, can pass the cell more or less unhindered.
– Some other components, such as serum albumin and
chlorides, can ‘leak’ from the blood into the milk by passing
through the spaces between secretory cells.
– Also, some leukocytes somehow reach the lumen.
– Cell remnants, such as part of the microvilli and and tiny
fragments of cytoplasm that occasionally adhere to a fat
globule, are secreted and form the lipoprotein particles
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Milk formation and excretion
Excretion
– A cow has four teats  four separate mammary glands,
commonly called (udder) quarters.
– Excretion does not happen spontaneously. The alveoli have to
contract  contraction of muscle tissue around the alveoli 
hormone oxytocin  released into blood by stimulation of the
teats  by the suckling young or by the milker
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Milk formation and excretion
Lactation
– When a calf is born: lactation = the formation and
secretion of milk starts
– First several days: colustrum (greatly differs in
composition from milk)
– Milk yield increases for some months, after which it
declines. The yield greatly varies among cows and
with the amount and the quality of the feed taken by
the cow.
– Lactation period: from parturition to leaving the cow
dry
– Stage of lactation: the time elapsed after parturition
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Different kinds of milk
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Different kinds of milk
• human milk
– specific composition
– more natural defense components
(immunoglobulines, oligosaccharides, Bifidus factors)
– large amounts of lactose
– low in proteins (more whey proteins, fewer caseins)
• goat's milk
– relatively more proteins and fat
– used for cheese manufacturing
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Different kinds of milk
• sheep's milk
– rich in proteins and fats
– used for cheese manufacturing (Feta, Roquefort,…)
• buffalo milk
– composition comparable to cow's milk
– high fat content (6-7%)
• horse's milk
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low fat and protein content
used for yogurt
low nutritional value
used in Eastern countries, Russia
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Different kinds of milk
Distinction is made between:
• casein-rich milks:
– cow, sheep, goat, buffalo
– usable for cheese manufacturing; compact
coagulation
– difficult digestion
• albumin rich milks:
– humans, horse
– no cheese manufacturing possible; fine coagulation
– better digestion
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Different kinds of milk
 We focus on cow milk
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Factors influencing milk composition
• Breed
– a wide diversity of breeds of cows exists
– predominately the result of selection by people: e.g,
suitable for the production of milk, meat, or draught
power and fit for local conditions, such as climate,
feed, terrain, and customs.
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Factors influencing milk composition
• Season/ nutrition
– is influenced by seasons: different feeding; silaged
feed during winter months instead of fresh grass
during summer months
– Differences are found in fat and protein content 
has major implications for processing
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Factors influencing milk composition
• Season/ nutrition
– Homeostasis: i.e., the capability of an organism to
maintain a constant composition of body fluids and
cells, despite gross differences in food
– Nutrition: comparatively small effect on most milk
constituents (grass, ensilaged food, hay, ... )
• Fat content and fat composition are affected distinctly by the
feed.
• A high-protein diet causes nonprotein N content of milk to
increase.
• Several minor components, such as carotene and fatsoluble vitamins, are strongly affected by the content in the
feed. This is the same for some trace elements.
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Factors influencing milk composition
• Season/ nutrition
– Climate conditions: little effect on milk composition
• High ambient temperatures (>30 C) tend to give higher fat,
lower N and lower lactose contents.
• At temperatures below freezing, fat and N contents both tend
to be higher.
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Factors influencing milk composition
• Stage and number of lactation
– gestation period: 9 months
– The period of lactation or milk production: 305 days
• the cow produces about 6000 to 8000 kg of milk. (note: the
calf only needs about 1000 kg of milk for growth).
– peak in milk production: ~ the third lactation
– the total amount of lactations is around 5-7.
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Factors influencing milk composition
• Stage and number of lactation
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Factors influencing milk composition
• Stage and number of lactation
– The time elapsed after parturition or calving considerably
influences milk composition, presumably because the
needs of the calve change with age.
– Colostrum: differs from normal milk; more salts, proteins
(mainly serum proteins) and less lactose.
– Normal milk: after 4 days. further changes occur:
decrement in protein content, casein, serum proteins,
ashes, fat-free dry matter. At the end of the lactation an
increment occurs.
– Lactose content is almost constant during lactation; fat
content is correlated to fat-free dry matter during lactation.
– pH changes: 6,6  6,7  6,9 at the end
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Factors influencing milk composition
• Age
– The age of the cow has a very small but consistent
effect on milk composition. Fat and fat-free dry matter
decrease slightly with each successive lactation.
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Factors influencing milk composition
• Mastitis
– Several species of pathogenic bacteria may cause
inflammation of the udder  called mastitis
– It causes a decrease in milk yield and a change in
milk composition
• Decrease in fat content, fat-free dry matter, lactose and
casein and increase of serum proteins and chloride content
– The number of somatic cells in milk also increases ( >
400.000 cells/ml)
– Catalase activity increases
– Cl/lactose ratio increases
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Factors influencing milk composition
• Mastitis
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Factors influencing milk composition
• Mastitis
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Factors influencing milk composition
• Mastitis
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Factors influencing milk composition
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Methods of milking
Individuals
Quarters
Other factors
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