The Amazing Complexity of Milk

Milk is very complex and contains compounds that have not yet been identified.Milk is an amazing substance. It is a very complex food containing numerous compounds, many of which are not identified yet.

The females of more than 5,000  species of mammals –including humans — produce milk to nurse their young. Milk’s composition varies greatly among  species, but the main components are emulsified fat, protein and lactose. Humans (and their pet cats and dogs) are the only species that  drink milk from other species and continue drinking it into adulthood.

Unless you live on a farm and own a cow or a goat, you likely drink pasteurized milk. Unpasteurized raw milk  is more nutritious, but can be associated with a variety of bacterial diseases. Cow’s milk that you buy in the store is homogenized, i.e., the fat globules are decreased in size from 1-10 microns to 0.2-2 microns to prevent the fat rising to the top. Decreasing the size of fat globules results in better absorption of fat, fat-soluble hormones, and associated proteins and enzymes.

Three medical conditions are linked to milk metabolism: lactose intolerance (insufficient amount of the enzyme lactase, which breaks lactose disaccharide into glucose and galactose for absorption), milk allergy (immune response to one of the milk proteins, typically casein), and PKU (phenylketonuria, the inability to break down aminoacid phenylalanine). Overall, epidemiologic studies confirm the nutritional value of milk in the human diet. Drinking milk is related to preventing cardiovascular disease, diabetes, obesity, and some types of cancer.

Milk’s Complexity

In addition to fats, proteins and sugars, milk contains vitamins (A, D, E, K, B1, B2, B3, B6, B12 and panthothenic acid), essential minerals (including sodium, potassium, calcium, magnesium, phosphorous and others), immunoglobulins, oligosaccharides, growth factors, essential fatty acids, and other compounds. With advances in food analysis techniques and nutrition research, new components in milk are constantly discovered and identified.

The modern analytical method liquid chromatography, coupled with mass spectrometry (LC-MS), has been especially useful for the separation and identification of nonvolatile and thermally unstable biomolecules, including peptides, glucans, and glycolipids. An article in Advances in Dairy Research explains:

Many of milk’s functional molecules could not be discovered until the right concordance of novel separation and analytical technologies were developed. […] Bovine milk is a source of a wide array of known bioactive compounds from a variety of molecular classes, including free glycans, lipids, glycolipids, peptides, proteins, glycoproteins, stem cells and microRNA. Because milk is such a complex mixture, when analyzed without fractionation or purification, many components mask the analytical signal of others, so some components cannot be detected. […] Liquid chromatography paired with electrospray ionization allows the separation of peptides, glycans and glycolipids for improved mass spectrometric detection. Target proteins and glycoproteins can now be purified from intact milk or other dairy streams by chromatography in order to better characterize these proteins for new bioactivities.

Benefits of Analysis

Analyzing milk can lead to improvement of  infant formula. Thus, oligosaccharides, which are abundant in milk while not being digestible by humans, are responsible for growth of protective bifidobacteria and prevent pathogens from binding to intestinal cells. Although human milk oligosaccharides exceed bovine in variety, some of the most abundant ones share the similarity in structure and function. Such oligosaccharides, which may be used in future for supplementation of infant formula, have been identified in bovine milk and in whey (a byproduct of cheese production) using a combination of HPLC and mass spectrometry.

And while nothing replaces mother’s milk in its completeness, knowing the composition of the milk and the roles of individual compounds helps us mimic it for next-best results.

Image by volff/123RF.
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