Food state - del 1

1.Milk composition. Milk products and human health.

🥛 Milk composition

• Milk = ~87.3% water + 11.9–14.2% solids ⭐

• Solids:

  • 🧈 Fat (min 3.3%)

  • 🥛 MSNF (milk solids non-fat, min 8.6%)

💧 Water

• Almost 90% of milk

Species:

• 🐮 Cow: 87.3%

• 🐑 Sheep: 82.0%

• 🐐 Goat: 86.7%

• 🐴 Mare: 88.8%

⭐ Solids in cow milk = 12.7%

🧬 Proteins (2.8–3.7% in cow milk)

Protein content influenced by:

• Nutrition, Breed, Age, Milk yield, Mastitis

⭐ Impacts payment for milk

Protein determined with Kjeldahl’s method:

digestion à neutralisation & distillation à titration

Estimate total nitrogen content, assume all N is protein, use conversion factor based on % of N in the food protein: Protein (%) = %N x F

1⃣ Casein (≈80% of total protein) ⭐

• Thermostable, Water-insoluble

• Precipitates at: pH 4.6, 40°C

• Separated by: Acids, Rennet

⭐ Important for cheese-making

• Bound to calcium phosphate

Types:

• αs1-casein, αs2-casein, β-casein, κ-casein

Functions:

• Carries insoluble calcium and phosphorus, Forms clot in stomach

• Improves the nutrition of young mammals

2⃣ Whey proteins (≈20% of total protein) ⭐

• Water-soluble

• Denature at 60–70°C

Contain:

• 20 amino acids, Leucine, Valine

Types:

• α-lactalbumin, β-lactoglobulin, Proteose peptones, Bovine serum albumin

• Immunoglobulins: IgG, IgM, IgA, IgE, J-chain, Secretory component

Minor proteins

• Enzymes, Lactoferrin, Serum transferrin, Immunoglobulins, Blood serum albumin, Bioactive milk proteins

Non-protein nitrogen (NPN)

• Urea ⭐ (important for heat stability), Nitrates, Nitrites

⚙ Enzymes

⭐ Higher activity in colostrum

Exogenous enzymes (from bacteria)

• Heat-stable lipases, Proteinases, Produced by psychrotrophic bacteria

Indigenous enzymes (produced by cow)

• Lipoprotein lipase, Plasmin, Alkaline phosphatase

🧈 Fat (lipids) 3.3–3.8%

⭐ Mainly saturated fatty acids
⭐ Melting point ≈ 37°C

Origin:

• Microbial activity in rumen, Secretory cells

Types:

• Triglycerides (98–99%) ⭐, Diglycerides (2%), Other lipids (1–2%) including cholesterol

Fat determined with Gerber method:

Separation of fat in a butyrometer, determine its volume & calculate % of fat content. Mixing of milk, sulphuric acid & amyl alcohol. Heat + centrifuge.

Solid non-fat calculated by: SNF = S - F

S = dry matter content in g/100g milk

F = fat content in g/100g milk

🍬 Carbohydrates

Lactose (4.8%) ⭐

Influenced by:

• Breed, Individual animal, Mastitis ↓, Stage of lactation

Formula:

• C₁₂H₂₂O₁₁

Disaccharide:

• D-glucose, D-galactose

Functions:

• Nutritive value, Milk product production

Lactase (β-galactosidase)

Hydrolyses lactose into:

• Glucose and Galactose

Used for:

• Sour milk products, Cheese, Lactose-free milk

Other carbohydrates:

• Monosaccharides, Sugar phosphates, Nucleotide sugars

Lactose determined with e.g. titration against a standard reagent solution.

🧂 Minerals

Major elements:

• Calcium, Phosphorus, Sulphur, Chlorine, Potassium, Magnesium, Sodium

Trace elements:

• Cobalt, Copper, Fluoride, Iodine, Iron, Manganese, Selenium, Zinc

⭐ Milk contains all essential elements
⭐ Rich in calcium and phosphorus
⚠ Low in iron

💊 Vitamins

⭐ Important source of Vitamin A
⚠ Low in Vitamin D

Fat-soluble

• Vitamin A (retinol), Vitamin D (calciferol), Vitamin E (tocopherol), Vitamin K (phylloquinone)

Water-soluble

• B-complex:

  • B1 thiamine, B2 riboflavin, B3 niacin, B7 biotin

• Vitamin C (ascorbic acid)

👶 Milk products and human health

⭐ Almost complete and well-balanced food

Benefits:

• Growth, Energy, Bone development, Immunoglobulins for infants

Deficiencies:

• Vitamin D too low, Iron too low

⚠ Lactose intolerance

Reduced milk consumption:
→ reduced lactase production

Lactose not hydrolysed:
→ fermented by intestinal microorganisms

Signs:

• Abdominal cramps, Diarrhoea, Flatulence

Often associated with:

• β-lactoglobulin ⭐

📊 Species comparison

Species	Total solids %	Fat %	Protein %	Lactose %	Ash %
🐮 Cow	11.9–14.2	min 3.3	min 2.8	4.7	0.7
🐐 Goat	12.3	3.6–4.5	2.9–3.18	4.1–4.3	0.8
🐑 Sheep	19.3 ⭐	7.4 ⭐	4.5–5.5 ⭐	4.8	1.0

General lab tests:

Fat: Gerber method;

Protein, fat, lactose, SNF: Lactoscan/LactiCheck

⭐ Most important exam facts

• Milk = 87.3% water + 11.9–14.2% solids

• Casein = 80%, whey = 20%

• Casein precipitates at pH 4.6 and 40°C

• Whey proteins denature at 60–70°C

• Lactose = 4.8%

• Fat = 3.3–3.8%

• Rich in Ca and P

• Poor in iron and vitamin D

• Sheep milk = highest fat, protein and total solids.

❓ How much free fatty acids (FFA) are present in milk immediately after milking?
✅ 0.1–0.5% ⭐

❓ How does lactose change during lactation?
✅ Lactose concentration progressively and significantly decreases during lactation. ⭐

❓ Why is goat milk whiter than cow milk?
✅ Goats do not transfer β-carotene into milk.
✅ β-carotene is converted into vitamin A.
✅ Therefore goat milk appears whiter, while cow milk has a slightly yellow colour. ⭐

❓ What is absent in goat milk compared with cow milk and affects appearance?
✅ β-carotene ⭐

❓ How is lactose-free milk produced?
✅ By adding lactase (β-galactosidase).
✅ Lactose is hydrolysed into:

• Glucose, Galactose

❓ What is the maximum lactose content in lactose-free milk?
✅ Practically 0% lactose ⭐

❓ When is milk considered raw milk?
✅ Milk that has not undergone heat treatment above 40°C ⭐

❓ What is the minimum fat content of raw cow milk?
✅ 3.3% fat ⭐

❓ Which milk enzymes are important for verification of heat treatment?
✅ Alkaline phosphatase ⭐
✅ Peroxidase ⭐

Used to verify: PasteurisationUHT treatment

❓ What is lactose intolerance?
✅ Reduced lactase activity.
✅ Lactose is not hydrolysed.
✅ Fermented by intestinal microorganisms.

❓ Can people also be allergic to milk?
✅ Yes. ⭐

⚠ This is different from lactose intolerance.

❓ Which protein causes milk allergy?
Committee answers reported:

✅ β-lactoglobulin ⭐ (Commission 2, 2025)

Also know:
✅ Caseins can cause milk protein allergy and are often mentioned by examiners.

❓ What can be done in milk protein allergy?
✅ Avoid milk consumption.
✅ Check food ingredients.
✅ Some products are marketed as A2 milk (contains A2 β-casein only).

2. Physico-chemical properties of cow's milk

🥛 Milk is a complex colloidal dispersion
Properties depend on:

🔹 Intrinsic factors

• Composition, Structure

🔹 Extrinsic factors

• Temperature, Post-milking treatment

⭐ Raw milk samples are taken at the dairy reception to test:

• Acceptability, Composition, Hygienic quality, Adulteration (addition of foreign substances)

1⃣ Density ⭐

Definition:

• Weight of 1 ml milk at 20°C

🧪 Determined by:

• Lactometer test

Normal range:

• 1.029–1.033 g/ml ⭐

Used to detect adulteration:

💧 Water density = 1
🧈 Fat density = <1
🥛 Non-fat solids density = >1

⭐ Fat and added water decrease density!

2⃣ Freezing point ⭐

Depends on:

• Molarity of dissolved substances

Used to detect:

• Added water, Added lactose, Added salt

Normal:

• −0.522°C

• Range: −0.512 to −0.550°C

💧 Added water → Increases freezing point

🧂 Salt/lactose → Decrease freezing point

3⃣ Viscosity

Important for:

• Creaming rate, Heat transfer, Flow during dairy processing

Affected by:

• Temperature, pH

⭐ Increased by:

• Cooling, Heating above 65°C
  (due to whey protein denaturation)

4⃣ Acid-base equilibrium ⭐

• Milk has buffering capacity due to: Casein, Phosphates

• pH: 6.4–6.8 at 25°C ⭐

• High pH: Mastitis

• Low pH: Colostrum, Bacterial infection

• pH measures: Free hydrogen ions only

Titratable acidity: measures all titratable hydrogen ions

• Normal: 13–20 mmol/L OR 6.2–7.8 °SH ⭐

• Used when milk is suspected sour

5⃣ Heat stability ⭐

Milk normally withstands heating without coagulation

Possible changes:

🟤 Darkened milk:

• Protein-lactose complexes, Lactose caramelisation

🔥 Prolonged high temperatures:

• Casein destabilisation, Protein coagulation

⭐ Heat stability increases with increasing pH

6⃣ Electrical conductivity ⭐

• Used for detection of mastitis

• Normal: 4.7–5.5 mS/m

• Instrument: Conductometer

⭐ Milk checker: Screening device, uses microcomputer calculation

7⃣ Sediment

🧪 Filter test

Milk is sucked through filter using vacuum

Detects:

• Dirt, Soil, Feed, Dust, Manure, Hair

Used to evaluate cleanliness

8⃣ Refractive index (RI)

Normal:

• 1.3440–1.3485

• At 20°C

• D-line of sodium spectrum

👃 Organoleptic properties of raw milk

🎨 Colour

• White, Slightly yellowish

🥛 Consistency

• Homogeneous, Liquid, No sediment

👃 Flavour and odour

• Typical milky smell, No strong foreign odours

❌ Reject milk when

🩸 Blood present

🧹 Large quantities of dirt

🎨 Abnormal colour

🧪 High viscosity

⚠ Destabilised milk

🍋 Sour flavour or smell

⭐ Committee questions

❓ How do you detect mastitis milk on the farm?

✅ California Mastitis Test (CMT) ⭐

✅ Electrical conductivity measurement ⭐

Where is milk tested?"Milk is tested both at collection before entering the milk tanker and again at the dairy processing plant laboratory when it arrives for processing.

⭐ Most important numbers to memorize

• Density = 1.029–1.033 g/ml

• Freezing point = −0.522°C

• pH = 6.4–6.8

• Titratable acidity = 13–20 mmol/L or 6.2–7.8 °SH

• Electrical conductivity = 4.7–5.5 mS/m

• Refractive index = 1.3440–1.3485

• Heat stability affected above 65°C

• Mastitis → ↑ electrical conductivity and ↑ pH.

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