xperiment 3 Extraction and Characterization of Casein from Milk and Test of Its Other Nutrients

Milk

is the most nutritionally complete food found in nature.

(thiamine, riboflavin, pantothenic acid, and vitamins A, B12, and D)

All kinds of milk, human or animal, contain

vitamins (principally/_______/________/________/____/___ )

Calcium, potassium, sodium, phosphorus, and trace metals

minerals (______/_______/________/_________/________)

(principally lactose) (fats)

proteins, carbohydrates (_____________), and lipids (___).

(Cows' milk and goats' milk) (Human milk) (sugar) (iron and vitamin C)

The amounts of these nutrients present in different types of milk differ greatly, however. (________________) are almost identical in every respect. (_________) contains less than half of the proteins and minerals of (1) (____________), but almost 1.5 times as much (_____). The only important nutrients lacking in milk are (_____________).

(Casein, lactalbumin, and lactoglobulin.)

There are three kinds of proteins in milk: (________/__________/_________)

(globular proteins) (spheroidal) (water) (fibrous proteins)

casein, lactalbumin, and lactoglobulin. All three are (___________), which tend to fold back on themselves into compact, nearly (________) units and are more easily solubilized in (______) as colloidal suspensions than (__________) are.

("complete proteins”) (building blood and tissue)

They are (___________), so

called because they contain all the amino acids essential for (_____________), and they can sustain life and provide normal growth even if they are the only proteins in the diet.

(plant) (eggs and meats.)

These proteins not only contain more amino acids than (_____) proteins, but they contain greater amounts of amino acids than the proteins in (_____________)

(Casein) (phosphoprotein)

(______) is the main protein in milk. It is a (___________), meaning that phosphate groups are attached to the hydroxyl groups of some of the amino acid side-chains.

(molecular weight and the amount) (α-casein, β-casein, and κ-casein)

It is a mixture of at least three similar

proteins which differ primarily in (_______________) of phosphorus groups they contain. These are (____/______/______).

α-casein and β-casein

(_____________) are both insoluble in water.

(κ-casein) (micelles)

(_______) is responsible for solubilizing the other two caseins in water by promoting the formation of (_______).

(calcium salt, calcium caseinate)

Casein exists in milk as the (________/__________).

(isoelectric) (4.6) (4.6) (6.6) (negative) (salt)

Calcium caseinate has an (_______) point of pH (______). Therefore, it is insoluble in solutions of pH less than (____). The pH of milk is about (____); therefore, casein has a (_________) charge at this pH and is solubilized as a (____). If acid is added to milk, the negative charges on the outer surface of the casein micelles are neutralized (by protonation of the phosphate groups) and the neutral protein precipitates, with the calcium ions remaining in solution:

(sours) (microorganisms) (glucose and galactose) (lactobacilli) (lowers)

A natural example of this process occurs when milk (____). The souring of milk is an intricate process started by the action of (__________) on the principal carbohydrate in milk, lactose. The microorganisms hydrolyze the lactose into (_____/_____). Once galactose has been formed, (________), a strain of bacteria present in milk, convert it to the sour-tasting lactic acid. Since the production of the lactic acid also (______) the pH of the milk, the milk clots when it sours due to the precipitation of casein.

(globular) (heat) (isolated)

Lactalbumin, like any albumins, is a (______) protein that is soluble in water and in dilute salt solutions. They are, however, denatured and coagulated by (___). Once the caseins have been removed, and the solution has been made acidic, the lactalbumin can be (________) by heating the mixture to precipitate them.

lactalbumin

The second most abundant protein types in milk are the (__________)

lactoglobulins

A third type of protein in milk is the (___________). They are present in smaller amounts than the albumins and generally denature and precipitate under the same conditions as the albumins.

(immunological)

The lactoglobulins carry the (_____________)

properties of milk. They protect the young mammal until its own immune system has developed.