AMINO ACIDS

III. AMINO ACIDS

Amino acids are the structural parts of proteins. Each amino acid unit contains a base NH 2 group and an acid COOH or carboxyl group. Because they contain both a base and an acid, they are capable of both acid and base reactions in the body. There are 22 amino acids divided into two categories, essential and nonessential. Essential amino acids are those that cannot be adequately synthesized in the body from other amino acids or protein sources and must be provided by diet. The body can synthesize nonessential amino acids. Under certain disease states or special needs states, there are other amino acids that become essential, known as conditionally essential. In addition, these are frequently needed only during early development (126).

Conditionally

Essential Nonessential

essential

Histidine Alanine

Arginine

Isoleucine Arginine

Cysteine

Leucine Asparagine

Glutamine

Lysine Aspartate

Isoleucine

Methionine Cysteine

Leucine

Phenylalanine Glutamate

Taurine

Threonine Glutamine

Tyrosine

Tryptophan Glycine

Valine

Valine Proline Serine Tyrosine Valine Proline Serine Tyrosine

According to the American Dietetic Association, high protein diets do not build muscle or burn fat. In fact, diets high in protein may result in missing nutrients from the other food groups: fruits, vegetables, and grains. Very high protein diets can put a strain on one’s liver and kidneys and are not a healthy eating plan for life-long health (129). Various types of amino acid solutions are available depending on individual needs. There are conventional solutions available for individuals with normal organ function and special purpose formulas are available, for example, situations such as trauma and liver failure (130).

Amino acids are nonvolatile, crystalline white solids in their pure form. They can decompose at temperatures ranging from 185 °C to 342°C. They are all soluble in water to various extents. Glycine is the only amino acid that is not optically active. All are capable of forming salts and these are more cheaply obtained and more stable. The follow- ing are FDA approved amino acids for functional use in foods as nutrients (131,132):

DL-Alanine

CAS: 302-72-7

L-Alanine

CAS: 56-41-7

L-Arginine

CAS:74-79-3

L-Arginine monohydrochloride

CAS: 1119-34-2

L-Asparagine anhydrous

CAS: 70-47-3

L-Asparagine monohydrate

CAS: 5794-13-8

DL-Aspartic acid

CAS: 617-45-8

L-Aspartic acid

CAS: 56-84-8

L-Cysteine monohydrochloride Monohydrate

CAS:7048-04-6

Anhydrous

CAS: 52-89-1

L-Cystine

CAS: 56-89-3

L-Glutamic acid

CAS: 56-86-0

L-Glutamic acid hydrochloride

CAS: 138-15-8

L-Glutamine

CAS: 56-85-9

Glycine

CAS: 56-40-6

L-Histidine

CAS: 71-00-1

L-Histidine monohydrochloride Monohydrate

CAS:5934-29-2

DL-Isoleucine

CAS: 443-79-8

L-Isoleucine

CAS: 73-32-5

DL-Leucine

CAS: 328-39-2

L-Leucine

CAS: 61-90-5

L-Lysine monohydrochloride

CAS: 657-27-2

DL-Methionine

CAS: 59-51-8

L-Methionine

CAS: 63-68-3

L-Proline

CAS: 147-85-3

DL-Serine

CAS: 302-84-1

L-Serine

CAS: 56-45-1

L-Threonine

CAS: 72-19-5

DL-Tryptophan

CAS: 54-12-6

L-Tryptophan

CAS: 73-22-3

L-Tyrosine

CAS: 60-18-4

L-Valine

CAS: 72-18-4

Food processing offers several dangers to amino acids. Lysine, for example, when in the presence of reducing sugars, may be lost in a treatment of mild heat. In the presence of severe heating conditions, food proteins become resistant to digestion. Lysine and cys- teine when exposed to alkali will react together and form lysinoalanine, which is toxic. Methionine is lost when sulfur dioxide is used for oxidation (133).

Analysis of amino acid profiles in foods is a challenge as most amino acids are present as components of proteins. To analyze the individual amino acid, it is necessary to hydrolyze the amide bonds linking the amino acids without destroying the amino acids themselves. Two major categories of analysis exist, free amino acid analysis and amino acid analysis of peptides and proteins. With the creation of HPLC analysis of amino acids in food matrixes, routine procedures can be conducted within a 24-h turnaround period. Recent advances have included the use of microwave heating. According to Baxter (126), with microwave heating, hydrolysis that once took 22 to 24 h can now be completed in minutes, saving considerable analysis time.