milk basics. chemical components milk composition water % dry mat (%) fat (%) proteins (%) lactose...
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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