MILK BASICS

Chemical components

Milk composition

Water % Dry mat(%)

Fat(%)

Proteins(%)

Lactose(%)

Minelars(%)

cow 87,5 12,5 3,7 3,3 4,7 0,8

sheep 80,7 19,3 8 5,6 4,8 0,9

goat 87 13 4 3,6 4,5 0,9

buffalo 82 18 7,9 4,5 4,8 0,8

horse 89 11 1,9 2,5 6,3 0,3

human 87,6 12,4 4 1,2 7 0,2

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

Casein%

Whey protein%

cow 82 18

sheep 80 20

goat 80 20

buffalo 85 15

pig 40 60

horse 45 55

dog 50 50

human 40 60

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

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

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

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 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

minerals microelements

g/l μg/l

Phosphate 2,1 Zn 4000

Citrate 2 Fe 400

K 1,4 F 200

Ca 1,2 Cu 100

Cl 1 I 40

Na 0,5 Mn 30

Mg 0,1 Se 10

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

Polydisperse structure of milk Milk as polydisperse system consits of:

Dispersing medium of water Emulsified fat Collodial proteins

Biological components

Somatic cell ≤ 400 00

70-80 % tissue origin Blood origin (granulocyte, lymphocyte,

monocyte) Microorganisms

≤104

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

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 Cell/ml Microbes

Healthy udder 100-500Micrococcus, Staphylococcus, Streptococcus,

Lactobacilli

Subclinical mastitis 104-105 Staphylococcus, Streptococcus

Skin of the udder 102-104Micrococcus, Staphylococcus, Streptococcus,

Lactobacilli, coliforms, pathogens

Air of stable 102 Aerobe spores

Milking machine, tubes

103-106 G-, Pseudomonas, eneterobacteria

Microflora of fresh milk

Micro-organism Occurence (%)

Micrococcus, Staphylococcus 30-99

Streptococcus,, Lactococcus 0-50

Microbacterium, Lactobacillus <10

Bacillus, Clostridium <10

Pseudomonas, E. coli, Alcaligenes,

Acinetobacter<10

Yeast, mould <10

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)

Raw cow milk Other species’ raw milk

Total count 30 °C/ml ≤100 000 ≤ 1 500 000

Somatic cell/ml ≤ 400 00 ≤ 500 000

Antibiotic residues ≤ MRL ≤ MRL

Mastitis

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

Healthy milk Subclinical mastitisClinical mastitis

Cell number 2 x 104-105/ml >5 x 105 /ml >106

Neutrophyl gr. ≤22% >22 % 70-98 %

Lymphocyte ≤ 8 % ≥8 % 16% (>40 %)

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, ↓

Parameter Normal value Change (xN)

Somatic cell 2-10 x 104/ml >10

Neutrophyl gr. 12-22 4-8

NaGase 0,03 >2

Catalase 0,08 >20

Lysosyme 1 >100

Lactoferrin 0,1-0,2 100

Lactose 4,7 0,9

αcasein 13,3 0,5

α -lactalbumin 1-1,2 0,5

Bovine-serum-albumin 0,1-0,2 2-10

Na 24,9 2

Cl 23-29 1,2-2

Methods for cell detection

Indirect test Mastitest Whiteside-test

Quantitative method

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

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

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 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

Typically from animal to animal Milking! No serious clinical symptoms R

Rarely

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

Streptococcus uberis and other fecal streptococci

Intestine Lactoperoxidase

Coliforms

E. coli and Klebsiella Endotoxin, mastitis Acute, peracute alveolar mastitis Milk amount↓ Watery, yellow-withish flakes

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