Whey Protein

Whole milk is approximately 87% water, with the remaining 13% as solids. The 13% solids are composed of 30% fat, 37% lactose, 27% protein, and 6% minerals. Of the 27% of milk that is protein, 20% is whey protein and 80% is casein protein. Thus, by consuming whole milk, an individual will ingest a larger portion of protein in the form of casein than whey. During the process of making cheese, whey protein is separated out into a liquid fraction and was originally thought to be a waste product.1 However, whey is now considered to be a good source of protein and is commonly processed into protein powders and many other products.

Whey protein contains all 20 amino acids and contains the highest naturally occurring portion of the branched-chain amino acids (BCAAs) leucine, valine, and isoleucine.2 Branched-chain amino acids are important for athletes and active individuals, as they are metabolized for energy in working muscle. Additionally, leucine has been found to play a crucial role in the regulation of protein synthesis.3-5

TABLE 8.1

Percentage w/w Amino Acid Values for Specific Subfractions of Whey Protein

Amino Acid ß-Lactoglobulin a-Lactalbumin Glycomacropeptide Ion-Exchange Whey

TABLE 8.1

Percentage w/w Amino Acid Values for Specific Subfractions of Whey Protein

Amino Acid ß-Lactoglobulin a-Lactalbumin Glycomacropeptide Ion-Exchange Whey

Essential

48.1

47.2

47.0

42.1

BCAA

25.1

21.0

22.5

21.2

Isoleucine

6.2

6.4

11.9

4.7

Leucine

13.6

10.4

1.7

11.8

Valine

5.4

4.2

8.9

4.7

Lysine

10.5

10.9

5.8

9.5

Methionine

2.9

0.9

2.0

3.1

Phenylalanine

3.2

4.2

0.0

3.0

Threonine

4.4

5.0

16.7

4.6

Tryptophan

2.0

5.3

0.0

1.3

Histidine

1.5

2.9

0.0

1.7

Arginine

2.6

1.1

0.0

2.4

Alanine

5.4

1.5

6.4

4.9

Asparagine

3.1

9.7

5.1

3.8

Aspartic Acid

6.9

7.3

1.7

10.7

Cystine

2.8

5.8

0.0

1.7

Glutamine

6.3

4.5

3.8

3.4

Glutamic Acid

11.3

7.3

15.5

15.4

Glycine

0.9

2.4

0.0

1.7

Proline

4.2

1.4

11.7

4.2

Serine

3.3

4.3

7.8

3.9

Tyrosine

3.6

4.6

0.0

3.4

The whey protein fraction is composed of numerous individual proteins, including P-lactoglobulin, a-lactalbumin, bovine serum albumin, lactoferrin, immunoglobulins, lactoperoxidase enzymes, and glycomacropeptides67 (see Table 8.1). P-Lac-toglobulin is the most abundant protein in whey, accounting for 50 to 55%, and is very high in the BCAAs. The biological function of P-lactoglobulin is not fully understood, but it has been recognized for its ability to bind hydrophobic molecules. a-Lactalbumin is the second most abundant protein found in whey and accounts for 20 to 25%. It is also the primary protein found in breast milk and is high in tryptophan and BCAAs. It has been shown to bind calcium and potentially can increase calcium absorption. Immunoglobulins make up about 10 to 15% of the protein in whey. They may provide immunity-enhancing benefits and are the predominant protein found in colostrum. Lactoferrin makes up approximately 1 to 2% of whey protein and may help to reduce inflammation. The amount of these native proteins remaining intact in the final whey product depends on the processes used to separate out the fat and lactose and purify the proteins. Additionally, the health benefits of these protein fractions are derived mainly from the bioactive peptides that enter the blood.1

Treatment with strong acids and high heat tends to indiscriminately denature all of the protein fractions and essentially hydrolyze the proteins into smaller peptides and free amino acids. This procedure also has a tendency to oxidize cystine and methionine, destroy serine and threonine, and convert glutamine and asparagine to glutamate and aspartate, respectively.8 A better method to hydrolyze proteins is by adding specific proteolytic enzymes to break down the proteins into small peptides. However, it has been shown1 that many of the health benefits associated with whey protein intake are associated with their individual proteins and not necessarily the amino acid content. These health benefits will be discussed later in this chapter. On the other hand, individuals with milk allergies may be able to safely digest highly hydrolyzed whey protein as a protein source without adverse effects because the allergenic native proteins are no longer present.

There are a few main types of whey protein supplements available for use. The first is undenatured whey, which is basically purified whey protein with most of its individual proteins in their native or undenatured form. Originally, undenatured whey concentrates ranged from 25 to 40% protein, with the remaining percentage coming from fat, lactose, mineral, and ash. This type of whey is still used in some baking and other food product applications. Newer techniques such as ultrafiltration have been developed to make the current whey concentrates, which range from 50 to 89% protein. The other main type of whey protein is whey protein isolate, which is approximately 90 to 95% whey protein. It contains minimal fat, lactose, or minerals and may be the best choice for lactose-intolerant individuals. However, some companies are now adding lactase to their whey protein powders to help with lactose digestion.

As stated previously, the native protein fractions of whey protein are implicated as offering the most health benefits associated with whey protein intake. Separating the fat, lactose, and minerals from these protein fractions without denaturing them was rather difficult and expensive until recently. One of the easiest ways to purify whey protein is to treat it with high heat and acid conditions to precipitate the proteins in a denatured form. Whey protein processed in this manner is typically referred to as hydrolyzed whey. The resulting small peptides are absorbed even faster than the larger native proteins present in the whey fraction.8

Researchers have recently developed four main types of processes to separate and purify whey proteins in an attempt to leave them in their more biologically active native forms. The types are selective precipitation, membrane filtration (ultrafiltration), selective adsorption, and selective elution (ion exchange).7

Selective precipitation is a more advanced method of precipitating proteins out of solution than simply adding acid and heat or proteolytic enzymes. There are numerous fraction-specific methods currently in use to precipitate and purify the proteins without applying as much heat or acid, thus limiting the denaturing of the protein fractions.

Membrane filtration procedures are separated into two subcategories, ultrafiltration and cross-flow filtration, as seen on some nutrition labels. These procedures separate the whey proteins by molecular mass (typically 5000 to 1000 g/mol) and are used to produce most whey concentrates.7 However, this process does not fully separate out the lactose and fat; thus, whey concentrates derived from this method typically have higher levels of these two macronutrients. This method typically allows a majority of the proteins to remain in their native forms and in their original frequency of unprocessed whey.

Selective absorption is a process used to separate one type of protein out of the whey protein mixture while leaving the other proteins in solution, but it has not yet been widely applied to commercially available products. With the recent findings of health benefits associated with some of the subfractions of whey and the recently developed large throughput of manufacturing, some companies will soon start marketing whey protein subfractions.

Selective elution, also known as ion exchange chromatography, is the process most often used to make whey protein isolates. Using selective elution, whey protein solution is applied to an ion exchange column so that all of the proteins bind to the column. The column is then rinsed and the individual proteins are eluded one by one to produce highly purified whey proteins. This process can be used to both concentrate and fractionate the proteins. If done carefully, the native protein structures can be retained. However, some of the smaller peptides such as lactoferrin may have a decreased concentration, while the P-lactoglobulin protein fraction tends to increase in whey protein isolates.

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