Transcript milk_properties

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
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Immunoglobulins
Lactoferrin
 α and ß lactoglobulins (synthesis in mammary gland),
 Serum albumin and immunoglobulins are from blood
Enzymes
 Lipase

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
In fresh milk: inactive
In cream: concentrated
Inactivation at 70 °C, pH optimum: 7,6-7,8
 Amylase
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In fresh milk: low
During storage activity ↓↓→ detection of freshness
52-56 °C, 30 min
 Protease
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
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
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62 °C 30 min, 72 °C 15 s → pasteurization
 xanthine oxydase

Cow milk ↑, human ↓ ( Schärdinger reaction)
 Catalase
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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
Phosphate
Citrate
K
Ca
Cl
Na
Mg
microelements
g/l
2,1
2
1,4
1,2
1
0,5
0,1
μg/l
Zn
Fe
F
Cu
I
Mn
Se
4000
400
200
100
40
30
10
 Trace elements
1 μg – 5 mg/litre
 Vitamins
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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

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Polydisperse structure of milk
Milk as polydisperse system consits of:
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Dispersing medium of water
Emulsified fat
Collodial proteins
Biological components

Somatic cell
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≤ 400 00
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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
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Microbiology of raw milk
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Milk
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High aw,
neutral pH,
Rich in nutritional materials
Antimicrobial substances
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Lactoferrin
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Lactoperoxidase
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Fe binding, bacteristatic effect
Against Gr- bacteria
Against Gr- bacteria
Lysosyme
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Muramidase
Against Gr+ bacteria
Source of bacterial contamination
of the raw milk
Source
Cell/ml
Microbes
Healthy udder
100-500
Micrococcus, Staphylococcus, Streptococcus,
Lactobacilli
Subclinical mastitis
104-105
Staphylococcus, Streptococcus
Skin of the udder
102-104
Micrococcus, 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
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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
Cell number
Healthy milk
Subclinical mastitis
Clinical
mastitis
2 x 104-105/ml
>5 x 105 /ml
>106
>22 %
70-98 %
≥8 %
16% (>40 %)
Neutrophyl gr. ≤22%
Lymphocyte
≤8%
Mastitis


Somatic cell ↑
Plasma proteins ↑

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Ion concentration


Na, Cl ↑( together with the electrical
conductivity ↑)
Intracellular enzymes

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Bovine serum-albumin (BSA) alphaantitrypsine
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
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Mastitest
Whiteside-test
Quantitative method
Microbes causing mastitis
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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


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
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
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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
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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
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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
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Endotoxin, mastitis
Acute, peracute alveolar mastitis
Milk amount↓
Watery, yellow-withish flakes
Algae, fungi
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Algae
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Prototheca zopfii
Chronic or subclinical mastitis
Fungi
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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