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Milk Composition and Properties
Art HillUniversity of Guelphwww.foodscience.ca
American Cheese Society
Contents
• Milk structure• Amounts and properties of principal
milk components• Transfer of milk components to cheese• Q & A
2
WHAT’S IN THE BAG?
3
4
Milk Structure
• Milk is a dispersion of fat globules (fat particles) and casein micelles (protein particles) in a continuous phase of water, sugar (lactose), whey proteins, and minerals.
• Milk Plasma = milk minus fat globules ≈skim milk
• Milk Serum = plasma minus micelles ≈ Cheese whey
• Milk permeate = serum less whey proteins
5
Milk
Plasma500X
Serum50,000X
Figure 8.1. Structural elements of milk. After Walstra and Jenness in Dairy Chemistry & Physics, Wiley & Sons., N.Y.
fatglobules0.1 - 10 microns
caseinmicelles10-300nM
6
Electron microscope image of skim milk showing a large micelle casein micelle in the foreground and smaller ones around it. Photo credit, Paul Spagnuolo, University of Guelph.
Gravity creaming
0
0.2
0.4
0.6
0.8
1
1.2
0 30 60 90 120 150 180 210Time (min)
Norm
alize
d Fa
t
Tank C Tank D
NF = % fat/control fat
8
Vertical gravity creaming device, Lodi, Italy
Contents
• Milk structure• Amounts and properties of principal
milk components• Transfer of milk components to cheese• Q & A
9
10
Proximate Analysis (kg/hl)
Fat 3.90 Most diverse Protein 3.30 Casein 2.54 (77%)
Whey 0.76 (23%)Lactose 4.8 Glucose + galactose
Ash 0.70 Includes all essential minerals
Solids 12.7 We truck a lot of water
Species
• Milk from any of the order ruminant can be used to make cheese, especially those of the suborder ruminata.
• Camels and Illamas are ruminants of the suborder Tylopoda, and their milk is not great for cheese.
• None ruminant milk is low in casein
11
Typical gross composition (kg/100 kg) of milk of cow, sheep, buffalo and goat milk).
12
Cow Sheep Buffalo Goat
Fat 3.9 7.2 7.4 4.0
Total protein
3.3 4.6 3.8 3.2
Casein 2.6 3.9 3.2 2.6
Whey protein
0.7 0.7 0.6 0.6
Lactose 4.6 4.8 4.8 4.3
Ash 0.7 0.9 0.8 0.8
Some properties of caseins that are important to cheese making.
13
Name Symbol Percent of casein
Properties
Alpha-S1 casein
α-S1 33 Binds Ca strongly.Broken down by rennet, but not by plasmin.
Alpha-S2 casein
α-S2 11 Binds Ca strongly
Beta-casein β 33 Partially soluble in cold milk.Broken down by plasmin, but not rennet.
Kappa-casein
κ 11 Stabilizes casein against coagulation.Bonds with whey proteins during heating.
Some properties of whey proteins that are important for cheese making.
14
Name % of Whey
Protein
Properties
Beta-lactoglobulin 40 Interacts with kappa-casein at T >65ºC. Principal component of ricotta cheese.
Alpha-lactalbumin 15 Coagulates slowly at temperature >60ºCOther heat sensitive proteins
10 Mainly immunoglobulin's and serum albumin.
Heat stable proteins
14 Cannot be removed by heat, not recovered in ricotta cheese.
Non-protein nitrogen
21 Amino acids, ammonia, urea and small protein fragments.
15
Raw milk
Vat, 85 C, 10 min
HTST, 98 C, 1.87 min
UHT, 140 C, 6 s
Effect of milk heat treatment on yogurt viscosity Effect of milk heat treatment on yogurt viscosity versus incubation time. versus incubation time.
16
50
40
30
20
10
70 75 80 85 90Pasteurization temperature °C
Whey protein denaturation versusHTST (16s) temperature (Fox et al 2000)
1 2Maximum curd firming rate versus whey protein denaturation (Fox al, 2000)30
25
20
15
10
5
00 10 20 30 40Whey protein denaturation (%)
90
70
50
300 10 20 30 40Whey protein denaturation (%)
Time from setting (rennet addition) to cutting versus whey protein denaturation (Fox et al, 2000)
4
30
25
20
15
10
5
00 10 20 30 40
Whey protein denaturation (%)
Curd firmness versus whey protein denaturation (Fox et al, 2000)
3
17
Factors affecting composition
• Species• Genetics (Breed)• Feed• Milking frequency• Stage of lactation• Number of lactations• Season
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• Species– Goat milk
• Fat globules: Mean 2.76 μM, Range 0.73 – 8.58 μM versus 3.5 and 0.92 – 15.8 μM for cow milk
• More lipolysis especially greater release of short chain fatty acids relative to cow milk
• Low heat stability at native pH relative to cow milk;
• Casein reduced in Alpha-S1 null milk• More fat relative to protein• Plasmin activity
– Sheep milk • Much higher solids• More fat relative to protein• Traditionally valued for hard cheese
19
Breed: typical fat and protein contents (kg/100 kg) for the milk of several breeds of dairy cows (various sources)
20
Breed Fat Protein Protein/Fat Ratio
Jersey 5.4 3.8 0.7
Holstein 3.8 3.2 0.84
Guernsey 4.9+ 3.6 0.73
Ayershire 4.0 3.3 0.83
21
Protein group or
phenotype DistributionMilk Com-
position
Curd Prop-erties
Cheese Yield
κ-CN vs other casiens
13% casein +protein -RCT, +CF,
+Y
-SYNκ-CN B vs A
% B 25 in Holstein; 88 in Jersey
+protein, +CN
-RCT, +CF, +SYN
+Y, +FR
β-LG B vs A
B in most breeds
+CN#, +Fat, +CN/fat, +Plasmin
-RCT, +CF, -SYN
+Y
22
• Feed– More roughage = higher fat and lower
P/F– Nutritionally functional fats
Fish MealFunctional Fats in Milk
DHA and CLA
• Direct addition
• Genetics
• Feed
• Stage of Lactation– Milk production peaks at about 60 days of
lactation and declines there after– Fat and protein are minimum at 60 days and
increase thereafter– Protein/fat ratio peaks at sixty days and
decreases thereafter.
24
Lactation number
25
# Fat Prot Lact Ash SNF Solids
1 3.55 3.21 4.89 0.68 8.76 12.33
2 3.65 3.49 4.72 0.74 8.94 12.60
3 4.09 3.80 4.51 0.80 9.05 13.20
4 4.54 4.10 4.19 0.86 9.19 13.67
Bhosale et a;. Veterinary World Vol.2, No.1, January 2009
26
Mean fat content by month kg/hl
3.703.753.803.853.903.954.004.054.10
Aug Sep OctNov Dec Ja
nFeb Mar Apr May Ju
n Jul
Fat k
g/hl
91/92 96/97 97/98 98/99 99/00 00/01
Figure 4.1 top left
27
Mean protein content by month kg/hl
3.103.153.203.253.303.353.403.453.50
Aug Sep OctNov Dec Ja
nFeb Mar Apr May Ju
n Jul
Prot
ein
kg/h
l
91/92 96/97 97/98 98/9999/00 00/01
Figure 4.1 top right
28
Mean Other Solids content by month kg/hl
5.64
5.68
5.72
5.76
5.80
5.84
Aug Sep OctNov Dec Ja
nFeb Mar Apr May Ju
n Jul
Oth
er S
olid
s kg
/hl
91/92 96/97 97/98 98/9999/00 00/01
Figure 4.1 bottom left
29
Mean protein/fat ratio by month
0.810.820.830.840.850.860.870.88
Aug Sep OctNov Dec Ja
nFeb Mar Apr May Ju
n Jul
Prot
ein/
fat r
atio
91/92 96/97 97/98 98/9999/00 00/01
Figure 4.1 bottom right
30
Summary of seasonal effects
§ Fat minimum in August, maximum in October§ Protein content changes roughly in parallel with
fat content, but the fat variations are smaller causing high protein fat ratios (P/F) during the summer and low P/F ratios in the winter.§ Casein content also varies with season.§ Casein can be estimated as:
casein = (0.833 x protein) - 0.208
Contents
• Milk structure• Amounts and properties of principal
milk components• Transfer of milk components to
cheese• Q & A
31
32
12.1. Distribution of Milk Components(kg/100 kg of standardized milk, assuming cheese of 40% moisture and 50% FDM; expected yield is
about 10% of milk weight)
Fat Prot CHO Ash SolidsMilk 3.3 3.2 5.0 0.73 12.4Cheese 31.0 25.0 1.7 2.2 60.0Whey 0.22 0.61 5.3 0.58 7.0%Transfer 93 78 3 30 49
33
Q and A