Fundamentals of Food Technology

Classification of proteins

Proteins are biochemically classified into three groups based on their chemical composition. They are simple proteins, conjugated proteins and derived proteins.

1.Simple proteins
On hydrolysis simple proteins yield only amino acids.

eg. Albumins, globulins, glutelins, prolamins, fibrous protein and histamines

2. Conjugated Proteins
On hydrolysis conjugated proteins give a protein fraction and a non-protein fraction

eg. haemoglobin, nucleoprotein, glycoprotein and lecithoprotein

3. Derived Proteins
Derived proteins are derived from a mother protein either through hydrolysis or digestion

eg. metaprotein, coagulated proteins, peptides and peptones

Nutritional classification of Proteins
Proteins are classified into complete proteins, partially incomplete proteins and incomplete proteins based on the presence of essential amino acids in them.
Complete Protein
A complete protein food contains all essential amino acids in proper proportion. It helps the protein to promote growth, maintenance and repair,

eg. Milk, egg and fish




Partially Incomplete Proteins
Partially incomplete proteins lack one or more essential amino acids and hence will help to maintain the body but cannot promote growth.

eg: red gram, peas and green gram





Incomplete proteins
Incomplete proteins neither help maintenance nor growth.

eg. Zein in maize

Nutritional classification of amino acids
Essential amino acids
Essential amino acids are ones that cannot be synthesized by the body at a rate sufficient to meet the needs for growth and maintenance.

eg. Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine

Non essential amino acids
Non essential amino acids are ones that the body can make in adequate amounts if nitrogen is available in the diet.

eg. Alanine, aspartamine, aspartic acid, glutamic acid, glutamine and serine

Conditionally essential amino acids

Conditionally essential amino acids are needed in the diet unless precursors are available for the synthesis. The new born may not have enzymes in adequate amounts to synthesize nonessential amino acids or in intestinal metabolic dysfunction arginine may not be synthesized.

eg. Histidine, arginine, cysteine, glycine, proline and tyrosine