Milk Composition and Properties Art Hill University of Guelph www.foodscience.ca American Cheese Society

Contents • Milk structure • Amounts and properties of principal milk components • Transfer of milk components to cheese • Q&A

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WHAT’S IN THE BAG? 3

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 4

Milk

Plasma 500X Serum 50,000X

fat globules 0.1 - 10 microns

casein micelles 10-300nM

Figure 8.1. Structural elements of milk.

After Walstra and Jenness in Dairy Chemistry & Physics, Wiley & Sons., N.Y.

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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. 6

1.2

Normalized Fat

1

Gravity creaming

0.8 0.6 0.4

NF = % fat/control fat

0.2

Tank C

Tank D

0 0

30

60

90

120

Time (min)

150

180

210

Vertical gravity creaming device, Lodi, Italy

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Contents • Milk structure • Amounts and properties of principal milk components • Transfer of milk components to cheese • Q&A

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Proximate Analysis (kg/hl) Fat Protein

3.90 3.30

Lactose 4.8 Ash

0.70

Solids

12.7

Most diverse Casein 2.54 (77%) Whey 0.76 (23%) Glucose + galactose Includes all essential minerals We truck a lot of water 10

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

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Typical gross composition (kg/100 kg) of milk of cow, sheep, buffalo and goat milk). Cow

Sheep

Buffalo

Goat

Fat

3.9

7.2

7.4

4.0

Total protein Casein

3.3

4.6

3.8

3.2

2.6

3.9

3.2

2.6

Whey protein Lactose

0.7

0.7

0.6

0.6

4.6

4.8

4.8

4.3

Ash

0.7

0.9

0.8

0.8 12

Some properties of caseins that are important to cheese making. Name

Symbol

Percent Properties of casein

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.

Kappacasein

κ

11

Stabilizes casein against coagulation. Bonds with whey proteins during heating.

13

Some properties of whey proteins that are important for cheese making. 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 >60ºC

Other 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.

14

Vat, 85 C, 10 min

UHT, 140 C, 6 s HTST, 98 C, 1.87 min

Raw milk

Effect of milk heat treatment on yogurt viscosity versus incubation time. 15

1

Whey protein denaturation versus HTST (16s) temperature (Fox et al 2000) 50

Maximum curd firming rate versus whey protein denaturation (Fox al, 2000) 30

2

25

40

20

30

15 10

20

5

10

0 70

75

80

85

0

90

Pasteurization temperature °C

Curd firmness versus whey protein denaturation (Fox et al, 2000) 30 25

10

20

30

40

Whey protein denaturation (%) 3

Time from setting (rennet addition) to 4 cutting versus whey protein denaturation (Fox et al, 2000) 90

20 70

15 10

50

5 0 0

10

20

30

40

Whey protein denaturation (%)

30 0

10

20

30

40

Whey protein denaturation (%) 16

Factors affecting composition • • • • • • •

Species Genetics (Breed) Feed Milking frequency Stage of lactation Number of lactations Season 17

• 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

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– Sheep milk • Much higher solids • More fat relative to protein • Traditionally valued for hard cheese

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Breed: typical fat and protein contents (kg/100 kg) for the milk of several breeds of dairy cows (various sources) 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 20

Protein Curd group or Milk Com- Propphenotype Distribution position erties κ-CN vs 13% casein +protein -RCT, other +CF, casiens -SYN κ-CN B vs % B 25 in +protein, A Holstein; 88 +CN in Jersey β-LG B vs B in most A breeds

-RCT, +CF, +SYN

+CN#, -RCT, +Fat, +CF, +CN/fat, SYN +Plasmin

Cheese Yield +Y

+Y, +FR

+Y

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• Feed – More roughage = higher fat and lower P/F – Nutritionally functional fats

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Fish Meal

Functional 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.

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Lactation number #

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

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Ju l

Ju n

ay M

r Ap

ar M

b Fe

Ja n

ec D

N ov

O ct

p Se

g

4.10 4.05 4.00 3.95 3.90 3.85 3.80 3.75 3.70 Au

Fat kg/hl

Mean fat content by month kg/hl

Figure 4.1 top left

91/92

96/97

97/98

98/99

99/00

00/01

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3.50 3.45 3.40 3.35 3.30 3.25 3.20 3.15 3.10

91/92

96/97

99/00

00/01

97/98

l Ju

n Ju

ay M

Ap r

ar M

Fe b

n Ja

ec D

N ov

O

Se

p

ct

Figure 4.1 top right

Au g

Protein kg/hl

Mean protein content by month kg/hl

98/99

27

5.84 5.80 5.76 5.72 Figure 4.1 bottom left

5.68

91/92

96/97

99/00

00/01

97/98

Ju l

Ju n

ay M

r Ap

ar M

b Fe

Ja n

ec D

ov N

ct O

p Se

g

5.64 Au

Other Solids kg/hl

Mean Other Solids content by month kg/hl

98/99

28

0.88 0.87 0.86 0.85 0.84 0.83 0.82 0.81

91/92

96/97

99/00

00/01

97/98

Ju l

Ap r M ay Ju n

M ar

b Fe

Ja n

ec D

N

ov

ct O

Se p

g

Figure 4.1 bottom right

Au

Protein/fat ratio

Mean protein/fat ratio by month

98/99

29

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

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Contents • Milk structure • Amounts and properties of principal milk components • Transfer of milk components to cheese • Q&A 31

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

Solids

Milk

3.3

5.0

0.73

12.4

Cheese

31.0 25.0 1.7

2.2

60.0

Whey

0.22 0.61 5.3

0.58

7.0

30

49

%Transfer 93

3.2

78

3

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Q and A 33