Magnificent Milk

Milk is unique to the mammal family and has been a source of survival for millions of years. The mammalian families ability to secrete nourishing liquid to their youth has been the reason the mammalian family has strived and succeeded (McGee, 8). Today, milk is still used for nourishment and is found in other products such as cheese, yogurt, and ice-cream. This class of products are called diary (McGee, 10). Milk is comprised of five main components: fat, protein, lactose, minerals, and water (McGee, 13). Since the mineral portion is a small amount, minerals are left out of the composition, leaving four main components of milk. 

The fat content in milk gives milk its creamy taste and will vary depending on the amount the animal secretes into its milk. The fat contains the fat soluble vitamins A, D, E, K and is the primary source of nourishment (McGee, 18). Depending on the amount of fat, milks can be classified as 1%, 2%, whole, or cream. Milk fat exist as fat globules or circular structures that are surrounded by a phospholipid membrane.  Milk proteins are also a circular shape, resembling sun bursts. The two main proteins in milk are curds and whey. The curd proteins are also known as the casein proteins. The proteins, mostly casein’s help stabilize the milk structure. Unlike other products, milk does not destabilize in heat, but acidic conditions do effect the proteins (McGee, 19). The kappa casein is the policeman in milk. Kappa prevents the other casein micelles from growing too large and keeps them separated. Kappa keeps the micelles apart with its negatively end tail. Who knew milk was charged! When milk proteins are exposed to acidic conditions, the negatively charged tail on kappa casein is neutralized and the alpha and beta caseins can bond to one another, curdling the milk (McGee, 20).

Casein Protein

 Lactose is the milk sugar.  Lactose is made of glucose and galactose and gives milk half its calories (and sweetness!). To breakdown lactose, the body needs the enzyme, lactate. The inability to breakdown lactose results in lactose intolerance. Lactose also plays a part in the souring of milk. The bacteria Lactobacilli grows on lactose and converts it to lactic acid. Again, the acidic environment causes milk to sour (McGee, 18). 

Along with the fat and protein content of milk, milk contains calcium which strengthens our bones.  Calcium builds our bone mass since calcium phosphate is the mineralized filler in bones. Osteoporosis is a disease of the bones and their lack of calcium, which effects the bone mass (McGee, 15). Milk on its own is not enough calcium and many women supplement their diet with calcium tablets and eating yogurt for example. 

With all of the ingredient in milk, how is milk one liquid layer? The answer is milk is an emulsion, meaning it is an unstable mixture that will not mix together. The milk emulsion needs an emulsifier to stabilize the liquid so the fat does not separate out from the water content. The fat globules have a phospholipid membrane which acts like the lecithin in eggs and holds the mixture together (McGee, 630).

McGee, A. (2005). On food and cooking, the science and lore of the kitchen. Scribner Book Company.