Cow milk is a complex colloidal emulsion of fat and protein in water containing dissolved carbohydrates (lactose), minerals, vitamins, and numerous bioactive compounds.
1. Average Composition of Cow Milk (per 100 g)
| Component | Amount | % of Total |
|---|---|---|
| Water | 87.0–88.0 g | 87–88 % |
| Total Solids | 12.0–13.0 g | 12–13 % |
| Fat | 3.5–4.5 g | ~30 % of solids |
| Protein | 3.2–3.8 g | ~26 % of solids |
| Lactose | 4.6–5.0 g | ~38 % of solids |
| Ash (minerals) | 0.7–0.8 g | ~6 % of solids |
| Energy | 60–70 kcal | — |
2. Major Chemical Components
A. Water (87–88 %)
The continuous phase; holds all dissolved and dispersed components.
B. Milk Fat (3.5–4.5 %)
- Exists as tiny globules (0.1–10 µm) surrounded by milk fat globule membrane (MFGM)
- 98 % triglycerides; 2 % phospholipids, cholesterol, etc.
- Rich in saturated fatty acids (~65 %), but also contains important unsaturated and short-chain fatty acids
- Contains fat-soluble vitamins A, D, E, K
| Major Fatty Acids | % of total fat |
|---|---|
| Palmitic acid (C16:0) | 25–30 % |
| Oleic acid (C18:1) | 20–30 % |
| Stearic acid (C18:0) | 10–15 % |
| Myristic acid (C14:0) | 10–12 % |
| Butyric acid (C4:0) | 3–5 % (unique to milk fat) |
C. Proteins (3.2–3.8 %)
| Type | Proportion | Main Proteins |
|---|---|---|
| Caseins (80 %) | ~2.6 g/100 ml | αs1-, αs2-, β-, κ-casein (form micelles) |
| Whey proteins (20 %) | ~0.6 g/100 ml | β-lactoglobulin, α-lactalbumin, immunoglobulins, BSA, lactoferrin |
Structure of a Casein Micelle
D. Lactose (4.6–5.0 %)
The milk sugar; disaccharide of glucose + galactose (β-1→4 linkage). Only naturally occurring carbohydrate in milk. Responsible for osmotic pressure and sweetness.
E. Minerals (Ash ≈ 0.7–0.8 %)
| Mineral | Concentration (mg/100 ml) |
|---|---|
| Calcium | 110–130 |
| Phosphorus | 90–100 |
| Potassium | 130–150 |
| Sodium | 40–60 |
| Magnesium | 10–12 |
| Chloride | 90–120 |
| Citrate | 150–200 (important for micelle stability) |
F. Vitamins
- Fat-soluble: A (retinol), D, E, K
- Water-soluble: B-complex (especially B2-riboflavin, B12), vitamin C (small amount)
G. Enzymes (≈ 60 different enzymes)
- Lipase, phosphatase, xanthine oxidase, lysozyme, catalase, lactoperoxidase (natural antimicrobial)
3. Physicochemical Properties
| Property | Value |
|---|---|
| pH | 6.5–6.7 (slightly acidic) |
| Titratable acidity | 0.14–0.16 % lactic acid |
| Density (at 20 °C) | 1.028–1.033 g/cm³ |
| Freezing point | −0.52 to −0.55 °C |
| Boiling point | ~100.2 °C |
| Oxidation-reduction potential | +0.25 to +0.30 V |
4. Colloidal System of Milk
- Emulsion: Fat globules dispersed in water
- Colloidal suspension: Casein micelles (50–500 nm)
- True solution: Lactose, minerals, whey proteins, vitamins
Summary
Cow milk is a highly complex natural fluid designed by evolution to nourish calves. Chemically it is an oil-in-water emulsion with casein micelles, lactose, and a rich mineral profile, making it one of the most complete single foods in nature and the foundation of the entire dairy industry.
Related Topics
Chemistry of Human Milk
Chemistry of Buffalo Milk
Chemistry of Goat Milk
Chemistry of Camel Milk
Chemistry of Sheep Milk
Chemistry of Donkey Milk