Protein:
Bovine milk contains about 3.0 – 3.9g/100g of protein with a mean value of ~3.4% w/w. Proteins are an extremely valuable class of naturally occurring compounds that are essential to all life processes [1]. Milk proteins represent one of the greatest contributions of milk to human nutrition. As I’ve just mentioned above, the protein content of whole cow’s milk is 3.3g/100g which is more than double that of human milk (1.3g). This is due to the amount of protein in milk being linked to the amount of time it takes a certain species to of animal to grow [2]. Growing calves need more protein to allow them to grow quickly, whereas human infants need less protein and more fat as their energies are expended mainly in the development of the brain, spinal cord and nerves [2].
Leucine is an amino acid that is unique due to the way it stimulates muscle protein synthesis. The higher the protein plus leucine content of milk, the faster the neonate doubles its birth-weight [2]. For example, cow’s milk contains 3.3g/L of protein and the calf doubles in size after 40 days, human milk on the other-hand contains 1.3g/L and the infant doubles its birth-weight after 180 days. During
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Bovine milk has a ratio of casein to whey proteins of 80:20, however, human milk has a ratio of 40:60. The protein content of human milk decreases rapidly during the first month of lactation (14-16g/L during early lactation, 8-10g/L at 3-4 months, and 7-8g/L at 6 months and later). The reason behind this decrease is due to the diminution in whey protein concentration [1]. These changes lead to a whey protein to casein ratio of 90:10 (early lactation), 60:40 in mature milk and 50:50 in late lactation. Within the casein fraction the relative proportion of various subclasses differ between bovine and human milk. α-S1 caseins constitutes the largest fraction in bovine milk, while β-caseins dominate in human milk by far