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

2 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

fat Plasma globules 500X 0.1 - 10 microns

Serum casein 50,000X micelles 10-300nM

Figure 8.1. Structural elements of milk. After Walstra and Jenness in Dairy Chemistry & Physics, Wiley & Sons., N.Y. 5 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

1 Gravity creaming 0.8

0.6

0.4

Normalized Fat NF = % fat/control fat 0.2 Tank C Tank D 0 0 30 60 90 120 150 180 210 Time (min) Vertical gravity creaming device, Lodi, Italy

8 Contents

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

9 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

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

11 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 3.3 4.6 3.8 3.2 protein Casein 2.6 3.9 3.2 2.6 Whey 0.7 0.7 0.6 0.6 protein Lactose 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 α-S1 33 Binds Ca strongly. casein Broken down by rennet, but not by plasmin. Alpha-S2 α-S2 11 Binds Ca strongly casein Beta-casein β 33 Partially soluble in cold milk. Broken down by plasmin, but not rennet. Kappa- κ 11 Stabilizes casein against casein coagulation. Bonds with whey proteins during heating. 13 Some properties of whey proteins that are important for cheese making.

Name % of Properties Whey Protein 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 10 Mainly immunoglobulin's and serum sensitive proteins albumin. Heat stable 14 Cannot be removed by heat, not recovered proteins in ricotta cheese. Non-protein 21 Amino acids, ammonia, urea and small nitrogen 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 Whey protein denaturation versus 1 Maximum curd firming rate versus 2 HTST (16s) temperature (Fox et al whey protein denaturation (Fox al, 2000) 2000)30 50 25 40 20

30 15 10 20 5 10 0 70 75 80 85 90 0 10 20 30 40 Pasteurization temperature °C Whey protein denaturation (%)

Curd firmness versus whey protein 3 Time from setting (rennet addition) to 4 denaturation (Fox et al, 2000) cutting versus whey protein denaturation 30 (Fox et al, 2000) 25 90 20 70 15 10 50 5

0 30 0 10 20 30 40 0 10 20 30 40 Whey protein denaturation 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 18 – 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)

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- Prop- Cheese phenotype Distribution position erties Yield κ-CN vs 13% casein +protein -RCT, +Y other +CF, casiens -SYN κ-CN B vs % B 25 in +protein, -RCT, +Y, +FR A Holstein; 88 +CN +CF, in Jersey +SYN β-LG B vs B in most +CN#, -RCT, +Y A breeds +Fat, +CF, - +CN/fat, SYN +Plasmin 21 • Feed – More roughage = higher fat and lower P/F – Nutritionally functional fats

22 Functional Fats in Milk Fish Meal 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 # 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 25 Mean fat content by month kg/hl

4.10 4.05 4.00 3.95 3.90 3.85 Fat kg/hl 3.80 3.75 3.70

Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Figure 4.1 top left

91/92 96/97 97/98 98/99 99/00 00/01 26 Mean protein content by month kg/hl

3.50 3.45 3.40 3.35 3.30 3.25

Protein kg/hl 3.20 Figure 4.1 top right 3.15 3.10

Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul

91/92 96/97 97/98 98/99 99/00 00/01 27 Mean Other Solids content by month kg/hl

5.84 5.80 5.76 5.72 5.68 Figure 4.1 bottom left Other Solids kg/hl 5.64

Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul

91/92 96/97 97/98 98/99 99/00 00/01 28 Mean protein/fat ratio by month

0.88 0.87 0.86 0.85 0.84 0.83

Protein/fat ratio 0.82 Figure 4.1 bottom right 0.81

Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul

91/92 96/97 97/98 98/99 99/00 00/01 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

30 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 3.2 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 %Transfer 93 78 3 30 49

32 Q and A

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