There are two types of proteins in milk: caseins and whey. There are four casein proteins: alphas1, alphas2, beta and kappa- casein; and two main whey proteins: beta-lactoglobulin and alpha-lactalbumin. Different animals produce different amounts of each of these proteins. Goat milk has much less alphas1-casein and more beta-casein compared to cow milk. These features contribute to the formation of a softer curd and gentler digestion process.
Not all goat milk is the same however. The level of alphas1-casein in goat milk varies with different genetics of goats. Goat milk supplied to DGC typically has low levels of alphas1-casein compared to cow milk.
The fat in milk is made up of individual fatty acids, within a structure called triglyceride. There are three types of fatty acids - saturated, monounsaturated and polyunsaturated fatty acids. Milk contains more saturated than unsaturated fatty acids. After being absorbed by the intestine, the carbon molecules of saturated fatty acids are metabolised to provide energy. Saturated fatty acids are further classified as short chain (with 4 carbon chains), medium chain (6 to 10 carbon chains) and long-chain (12 to 22 carbon chains) fatty acids. Goat milk fat contains twice as much medium chain saturated fatty acids (caproic C6:0, caprylic C8:0 and capric C10:0) as cow milk.
Medium chain fatty acids are digested more readily than long chain saturated fatty acids.
Nucleotides are major components of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Rapid growth in young infants or stress can increase the requirement for nucleotides. Because cow milk is low in nucleotides, infant formula made from cow milk is now routinely supplemented with synthetic nucleotides. In contrast, goat milk is more like human milk, with a complex array of nucleotides and nucleosides. Infant formula made from goat milk requires no additional supplementation of synthetic nucleotides.
Taurine is another important ingredient of infant formula. Goat milk naturally has 20-fold more taurine than cow milk.
Milk secretion process
Goat milk is secreted differently to cow milk. Milk is produced by forming minute droplets containing proteins, lactose, minerals and vitamins within cells in the mammary gland. These milk droplets are released from the mammary cell by two processes:
- merocrine secretion, where the milk droplets combine with the cell membrane to release the contents without the loss of any other cell components.
- apocrine secretion, where the milk droplets are pinched off from the cell along with some of the cell components.
Most of the protein in milk is secreted by the merocrine process, but the apocrine process plays a much greater role in the goat and human than the cow. It is this feature that is thought to naturally endow goat and human milk with components such as nucleotides.