Bài giảng Công nghệ Chế biến và Bảo quản sữa - Chương 1: Sữa và các đặc trưng chính

Chapter 1: Milk: Main characteristics • Introduction • Composition and structure • Milk formation and excretion • Different kinds of milk • Factors influencing milk composition

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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 1 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) 2 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 • 3 Chapter 1: Milk: Main characteristics • Introduction • Composition and structure • Milk formation and excretion • Different kinds of milk • Factors influencing milk composition 4 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 5 Composition and structure • Milk 6 Composition and structure • Milk at x 5000 7 Composition and structure • Milk at x 50,000 8 Plasma = milk – fat globules Serum = plasma – casein micelles 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 9 10 11 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. 12 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. 13 14 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. 15 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 16 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 17 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 18 Different kinds of milk 19 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 20 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 – low fat and protein content – used for yogurt – low nutritional value – used in Eastern countries, Russia 21 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 22 Different kinds of milk We focus on cow milk 23 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. 24 25 26 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 27 28 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 fat- soluble vitamins, are strongly affected by the content in the feed. This is the same for some trace elements. 29 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. 30 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. 31 Factors influencing milk composition • Stage and number of lactation 32 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 33 34 35 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. 36 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 37 Factors influencing milk composition • Mastitis 38 Factors influencing milk composition • Mastitis 39 Factors influencing milk composition • Mastitis 40 Factors influencing milk composition • Methods of milking • Individuals • Quarters • Other factors 41

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