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Milk composition in general

Bovine milk contains the nutrients needed for growth and development of the calf, and is a resource of lipids, proteins, amino acids, vitamins and minerals. It contains immunoglobulins, hormones, growth factors, cytokines, nucleotides, peptides, polyamines, enzymes and other bioactive peptides. The lipids in milk are emulsified in globules coated with membranes. The proteins are in colloidal dispersions as micelles. The casein micelles occur as colloidal complexes of protein and salts, primarily calcium [6]. Lactose and most minerals are in solution. Milk composition has a dynamic nature, and the composition varies with stage of lactation, age, breed, nutrition, energy balance and health status of the udder. Colostrums differ considerably to milk; the most significant difference is the concentration of milk protein that may be about the double in colostrum compared to later in lactation [7]. The change in milk composition during the whole lactation period seems to match the changing need of the growing infant, giving different amounts of components important for nutrient supply, specific and non-specific host defence, growth and development. Specific milk proteins are involved in the early development of immune response, whereas others take part in the non-immunological defence (e.g. lactoferrin). Milk contains many different types of fatty acids [8]. All these components make milk a nutrient rich food item.

Components in milk and their health effects

Lipids

Fatty acids

In average, milk contains about 33 g total lipid (fat)/l [9] (Table 1). Triacylglycerols, which account for about 95 % of the lipid fraction, are composed of fatty acids of different length (4–24 C-atoms) and saturation [8]. Each triacylglycerol molecule is built with a fatty acid combination giving the molecule liquid form at body temperature. Other milk lipids are diacylglycerol (about 2% of the lipid fraction), cholesterol (less than 0.5 %), phospholipids (about 1%), and free fatty acids (FFA) accounting to less than 0.5% of total milk lipids [8]. Increased levels of FFA in milk might result in off-flavours in milk and dairy products, and the free volatile short-chain fatty acids contribute to the characteristic flavours of ripened cheese.

Table 1. Milk composition and percent contribution to the daily dietary reference intakes of some nutrients in 0.5 l whole milk, and their main health effects

Milk composition and percent contribution to the daily dietary reference intakes of some nutrients in 0.5 l whole milk, and their main health effects
Milk component Concentration in 1 l whole milka Percent contribution of 0.5 l whole milk to reference intakeb Health effects
Fat 33 g/l   Energy rich
Saturated fatty acids 19 g/l   Increase HDL, small dense LDL, and total cholesterol. Inhibition of bacteria, virus
Oleic acid 8 g/l   Prevent CHD, gives stable membranes
Lauric acid 0,8 g/l   Antiviral and antibacterial
Myrisitc acid 3,0 g/l   Increase LDL and HDL
Palmitic acid 8 g/l   Increase LDL and HDL
Linoleic acid 1,2 g/l   Omega-6 fatty acid
Alpha linolenic a 0,75 g/l   Omega-3 fatty acid
Protein 32 g/l 30–40% Essential amino acids, bioactive proteins, peptides. Enhanced bioavailability
Lactose 53 g/l   Lactosylation products
Calcium 1,1 g/l 40–50% Bones, teeth, blood pressure, weight control
Magnesium 100 mg/l 12–16% For elderly, asthma treatment
Zinc 4 mg/l 18–25% Immune function. Gene expression
Selenium 37 ug/l 30% Cancer, allergy, CHD
Vitamin E 0,6 mg/l 2 % Antoixidant
Vitamin A 280 ug/l 15–20% Vision, cell differentiation
Folate 50 ug/l 6 % DNA synthesis, cell division, amino acid metabolism
Riboflavin 1,83 mg/l 60–80% Prevent ariboflavinosis
Vitamin B12 4,4 ug/l 90% Key role in folate metabolism

a data from USDA Food Composition Data [9].

b Dietary reference intake (DRI) for men and women [4].