What is the Chemical Composition of Milk?

The chemical composition of milk, like many common substances that are essential for life, is frequently taken for granted, with its complex nature often unappreciated. What exactly is milk made of? Let's take a closer look.

So important in the nutrition of all newborn mammals, milk at its base is an emulsion, or colloid, consisting of butterfat globules inside a fluid that is made up mostly of water. Within this medium, however, the chemical composition of this substance contains important carbohydrates and protein aggregates that have minerals, which are in themselves essential building blocks of life.

Fats are an essential part of milk

All the fat globules in milk are encased in a membrane made up of complex phospholipids and proteins. The globules themselves consist mainly of triacylglycerols. The membranes not only stop the fat globules from coalescing but keep the enzymes in the fluid portion of milk from harming the contents of the globules.

While between 97-98% of lipids are triacylglycerols, di- and monoacylglycerols are also present, along with free cholesterol, cholesterol esters, phospholipids and free fatty acids in the chemical composition of milk.

The fatty portion of milk contains the vitamins A, D, E, and K, as well as linoleic and linolenic acids. Some of the fatty acids present in the milk of mammals include butyryl, myrystyl, palmityl and oleyl.

Casein provides protein found in milk

Cow's milk usually contains between 30-35 grams of protein in every liter, 80% of which is inside casein micelles, an aggregate of phospholipid molecules in a colloidal suspension. These micelles constitute the largest portion of the fluid part of milk. Made up of thousands of protein molecules bonded together with calcium phosphate, each micelle is only one tenth of a micrometer in diameter; they are more or less spherical in shape.

Of course, casein can also be added to products which are meant to boost protein levels. Commonly taken by people who are interested in putting on muscle weight and dampening the appetite, they are extremely popular now. Such industrial grade casein is available for $3/G at ECHEMI, via this link: https://www.echemi.com/wholesale/food-ingredients.html.

Casein proteins come in four different types: α1, α2, β, and κ. Although there remains more to be discovered about the nature of the casein micelles as part of the composition of milk, the majority of the casein proteins are bound inside them. However, it is indisputable that the outermost layer of the micelle consists of strands of κ-casein only, which also go outward into the fluid surrounding the structure.

All of these κ-caseins have a negative electrical charge and therefore repel the others, which has the effect of keeping the micelles separate from one another and helping maintain a state of colloidal suspension in the milk.

Chemical composition of milk varies amongst mammals

However, milk also contains a wealth of other proteins as well, all geared to specific needs of the young. These are present in whey, the fluid portion of milk that remains after the caseins have coagulated into curds. Since they are water soluble, they cannot form the structures that caseins do. Known as whey proteins, lactoglobulin is by far the most common of them all in milk. There are 82 caseins for every whey protein in cow, buffalo and yak milk; however, the ratio is almost completely reversed in human milk, with 32 caseins for every 68 whey proteins.

Reindeer milk is very close to that of cows, buffalo and yaks, with between 80 - 83 caseins per 20 and 17 whey proteins respectively, while goat milk is next in this ratio, with 78 caseins for each 22 whey proteins; sheep have 76 caseins for every 24 whey proteins; horses follow, with 52 caseins to 48 whey proteins; and camels produce milk with 76 caseins for every 24 whey proteins.

Essential minerals also part of the chemical makeup of milk

A range of minerals also exist within milk; when they occur in this essential substance they are often referred to as milk salts. A range of cations and anions, in cow's milk they are calcium, phosphate, magnesium, sodium, potassium, citrate and chloride. They are seen at concentrations between 5-40 mM.

These minerals -- most notably calcium phosphate -- interact in major ways with the casein in milk; it not only is present in large amounts but it is also much more soluble than solid calcium phosphate. Naturally, in addition to all this calcium, the chemical makeup of milk provides a range of other vital minerals and other substances that are necessary for life, including A, B6, C, D, E, K, thiamine, niacin, biotin, riboflavin, folates and pantothenic acid.

Carbohydrate lactose gives milk sweet taste

Carbohydrates such as lactose, glucose, galactose and other oligosaccharides are also present in milk; Lactose, a disaccharide containing two simple sugars, glucose and galactose, gives milk its sweet taste and rep