Milk basics
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MILK BASICS. Chemical components. Milk composition. LIPIDS. Organised into globules (1-10 μ m ) having membranes of phospholipid-protein complexes 200 kinds of fatty acids

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MILK BASICS

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Milk basics

MILK BASICS


Milk basics

  • Chemical components


Milk composition

Milk composition


Lipids

LIPIDS

  • Organised into globules (1-10 μm ) having membranes of phospholipid-protein complexes

  • 200 kinds of fatty acids

  • Fatty acids of saturated (palmitic, myristic, stearic, butyric, etc.), mono- and polyunsaturated (oleic, palmitoleic, linoleic, linolenic, etc.)

  • Holstein:3.3-3.4%, Jersey: 4.5-4.6 %


Milk proteins

MILK PROTEINS


Caseins

Caseins

  • Caseins (α1, α2, ß, κ)

    • Colloidal micelles (0.12 μm)

    • Submicelles are bound together by calcium phosphate and, organised into spherical particles of micelles (20-300 nm)(κ-casein at the surface of micelles)

    • Rennin or <pH 4.7→ coagulation


Whey proteins

Whey proteins

  • Remaining in milk after precipitating casein (include proteose-peptones

  • Albumin

    • ß and α –lactoglobulin

    • Serum albumin

  • Globulin

    • Immunoglobulins

    • Lactoferrin

  • α and ß lactoglobulins (synthesis in mammary gland),

  • Serum albumin and immunoglobulins are from blood


Enzymes

Enzymes

  • Lipase

    • In fresh milk: inactive

    • In cream: concentrated

    • Inactivation at 70 °C, pH optimum: 7,6-7,8

  • Amylase

    • In fresh milk: low

    • During storage activity ↓↓→ detection of freshness

    • 52-56 °C, 30 min

  • Protease

    • Only raw milk, longer storage at 37-42 °C temperature.

    • Pastuerised milk→ putrid taste

    • Clostridium, Achromobacter spp. →cheese production


Enzymes1

Enzymes

  • peroxidase

    • 75 °C 2,5 min, 85 °C 1-2 s →flash pasteurization

  • alkaline phosphatase

    • 62 °C 30 min, 72 °C 15 s → pasteurization

  • xanthine oxydase

    • Cow milk ↑, human ↓ ( Schärdinger reaction)

  • Catalase

    • Activity ↓

    • Mastitis: activity ↑


Composition and properties

Composition and properties

  • Carbohydrates

    • Lactose

      • 4.7-4.8 % (mastitis→↓)

      • 80 °C→lactocaramell (taste of boiled milk)

      • Lactobacilli → lactic acid

  • Minerals, micro-macroelements

    • 0.7-0.9 %

    • Mastistis: Na, Cl →↓, K, Ca, Mg, P→↑


Avarage minerals and microelement content of cow milk

Avarage minerals and microelement content of cow milk


Milk basics

  • Trace elements

    • 1 μg – 5 mg/litre

  • Vitamins

    • A, B12, E, K, D3, C

    • Thiamine, riboflavin, nicotinic acid, panthothenic acid, pyridoxine, biotin, folic acid

    • Concentration is depending on species, age, stage of lactation, nutrition, environment, etc.

    • Sensitivity to light, air, metals, acid, etc.


Structure of milk

Structure of milk

  • Polydisperse structure of milk

  • Milk as polydisperse system consits of:

    • Dispersing medium of water

    • Emulsified fat

    • Collodial proteins


Biological components

Biological components

  • Somatic cell

  • ≤ 400 00

    • 70-80 % tissue origin

    • Blood origin (granulocyte, lymphocyte, monocyte)

  • Microorganisms

    • ≤104


Physical properties of milk

Physical properties of milk

  • Freezing point: -0.5 °C

  • Colour

    • Normal: bluish-white (golden-yellow), depending on breed, feed, lactation period, etc. (white: fat globules, collodial components; bluish: after removing fat; yellow: carotene)

  • Taste

    • Normally, slightly sweet, pleasent (lactose and chlorine)

    • Fat and protein give the body to the flavour

  • Consistency (substance) of milk

    • Normal milk is a watery liquid


Microbiology of raw milk

Microbiology of raw milk

  • Milk

    • High aw,

    • neutral pH,

    • Rich in nutritional materials

  • Antimicrobial substances

    • Lactoferrin

      • Fe binding, bacteristatic effect

      • Against Gr- bacteria

    • Lactoperoxidase

      • Against Gr- bacteria

    • Lysosyme

      • Muramidase

      • Against Gr+ bacteria


Source of bacterial contamination of the raw milk

Source of bacterial contamination of the raw milk


Microflora of fresh milk

Microflora of fresh milk


Bacterial growth in fresh milk

Bacterial growth in fresh milk

  • Milk is sterile at time of secretion from glandular cells (healthy uddder)

  • Contamination is inevitable (quantity and composition; aseptically: micrococci, streptococci)

  • Aseptically drawn milk: 100-1000 bacteria/ml

  • Drawn under clean conditions: 1000-10000 bacteria/ml

  • Following milking, rate of growth: number&type of bacteria and temperature

  • Drawn clean (1000-10000 bacteria/ml): doubles in 24-48 hours and reaches next decimal in 72-96 hours at 4 °C. At 10 °C storage, it reaches 1 decimal in 24 hours and 2-3 decimals in 48 hours.

  • Psychrotropic microorgansisms (e.g. Pseudomonas fragi) are present in fresh milk (sources: unsterilized utensils, milking machines, water supply, dust.

  • Off-flavours: fruity, bitter, sour, oxydised.


Microbiological requirements of raw milk 853 2004 ec

Microbiological requirements of raw milk (853/2004 EC)


Mastitis

Mastitis


Mastitis milk hygiene

Mastitis – Milk hygiene

  • Milk drawn from healthy mammary gland contains

    3-400000 cells/cm3

  • Mastitis is caused by mechanical, chemical or bacterial influences

  • Cells in milk

    • From mammary gland: epithelial cells,

    • From blood: granulocytes, lymphocytes, mononuclear cells (macrophages, giant cells)

    • Cell content changes: systemic disease, mechanical influences including (machine) milking, physiological conditions, feeding, housing, stress

    • Somatic cell count in healthy udder is 30% and it may be increased up to 95% in mastitis


Changes of somatic cell during mastitis

Changes of somatic cell during mastitis


Mastitis1

Mastitis

  • Somatic cell ↑

  • Plasma proteins ↑

    • Bovine serum-albumin (BSA) alpha-antitrypsine

  • Ion concentration

    • Na, Cl ↑( together with the electrical conductivity ↑)

  • Intracellular enzymes

    • N acetyl-glucose-aminidase (NaGase)

  • Epithelial cell secretion

    • Lactose, fat, casein, ↓


Methods for cell detection

Methods for cell detection

  • Indirect test

    • Mastitest

    • Whiteside-test

  • Quantitative method


Microbes causing mastitis

Microbes causing mastitis

  • SOURCE OF INFECTION

    • From animal to animal

    • From enviroment to the udder

  • MAJOR MICROBES CAUSING MASTITIS

    • Streptococcus agalactiae, dysgalactiae, uberis, pyogenes animalis, faecium, faecalis, pyogenes humanus

    • Staphylococcus aureus

    • Escherichia coli

    • Klebsiella pneumoniae

    • Pseudomonas aeruginosa

    • Algae, fungi


Contagious pathogens

Contagious pathogens

  • From the infected udder

  • During milking, teat cup, rubber,

  • Cow, calf

  • Staphylococus aureus, streptococcus agalactiae, Corynebacerium bovis, Mycoplasma bovis and other Mycoplasma spp., Streptococcus dysgalactiae


Staphylococcus aureus

Staphylococcus aureus

  • Skin of the animal, teat cup, rubber,

  • End of milking

  • (Hand of the workers)

  • Alveolar epithel cells destroyed

  • Subclinical (common), clinical form

  • Watery, flakes,


Staphylococcus aureus1

Staphylococcus aureus

  • The incidence of staphylococcal mastitis is increasing (as incidence of streptococcal mastitis decreasing). About 1-1.5 million staphylococci per gram of food must be present for producing sufficient amount of enterotoxin required to induce symptoms in man.

  • Below 10 °C, no growth and no toxin production take place.

  • The toxin is heat-stable.

  • Symptomless humans carry the causative in the nose, and skin but the udder and skin of dairy animal is also infected (human origin). Milkworkers with cuts, boils and other lesions on hand should not be allowed to handle milk or milk products.

  • The main-line of protection, however, is to prevent the growth of staphylococci by cooling below 8 ° C as soon as possible.


Streptococcus agalactiae

Streptococcus agalactiae

  • Typically from animal to animal

  • Milking!

  • No serious clinical symptoms

  • R

    Rarely


Listeriosis

Listeriosis

  • Listeria monocytogenes was isolated from milk and one of the vehicles of the infection (to humans) is considered to be milk.

  • The organism is able to grow in milk at ambient temperatures.

  • The control of milk-borne infection with Listeria depends on adequate heat-treatment: 72 °C for 15 sec is sufficient.

  • Many cases of human listeriosis occurred in the last years following the consumption of different types of soft cheeses which are made from raw milk.

  • Sheep!


Enviromental pathogens

Enviromental pathogens

  • Streptococcus uberis and other fecal streptococci

  • Intestine

  • Lactoperoxidase


Coliforms

Coliforms

  • E. coli and Klebsiella

    • Endotoxin, mastitis

    • Acute, peracute alveolar mastitis

    • Milk amount↓

    • Watery, yellow-withish flakes


Algae fungi

Algae, fungi

  • Algae

    • Prototheca zopfii

    • Chronic or subclinical mastitis

  • Fungi

    • Due to widespread use of antibiotics in mastitis may lead to increase in incidence of mycotic mastitis. No direct evidence for milk-borne infection to man.

    • Nocardia asteroides and braziliensis, Candida tropicalis, albicans, krusei were isolated from mastitic udder and from milk. They may survive usual pasteurization processes


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