Essential amino acids

Proteins are biopolymers of acids, so named because the amino group is bonded to the carbon atom, next to the carbonyl group. The physical and chemical properties of a protein are determined by its constituent amino acids.

Amino acids are the fundamental constituents of body proteins and serve as substrates for protein synthesis. There are about 300 amino acids occur in nature. Only 20 of them occur in proteins.

Proteins are synthesized from the set of 20 L-α-amino acids encoded by nucleotide triplets called codons. Common amino acids are those for which at least one specific codon exists in the DNA genetic code.

Humans can synthesize about half of the amino acids needed to make proteins. Other amino acids, called the essential amino acids, must be provided in the diet.

The essential amino acids are arginine (required for the young, but not for adults), histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. These amino acids are required in the diet.

Proteins that provide all the essential amino acids in about the right proportions for human nutrition are called complete proteins. Examples of complete proteins are those in meat, fish, milk, and eggs. About 50 g of complete protein per day is adequate for adult humans.
Essential amino acids

Protein in milk

The proteins of milk are of great importance in human nutrition and influence the behavior and properties of the dairy products containing them.

Milk contains a wide range of protein that provide protection against enteropathogens or are essential for the manufacture and characteristic nature do certain dairy products.

Milk proteins, because of high surface activity, rapidly adsorb at the oil-water interface, producing the surface layer that stabilize oil/fat droplets against flocculation or coalescence.

Milk contains a number of different proteins and can be classified to:
1. Casein
2. Whey proteins
3. Milk fat globule membrane
4. Minor proteins
5. Enzymes

Casein and whey are the two predominant types of protein found in milk.

Casein is a phosphoprotein, meaning that phosphate groups are attached to some of the amino acid side chains. Casein exists in milk as the calcium caseinate. This salt has a complex structure.

Whey is the liquid portion of milk, consisting primarily of 93% water, lactose, whey proteins (primarily lactalbumin and lactoglobulin).

Both casein and whey protein have been found to be increasingly important for physiological and biochemical functions that have crucial impacts on human metabolism and health.

Biological active peptides released from caseins and whey proteins contain 3 to 20 amino acids per molecule.

Researchers have demonstrated that these peptides posses very important biological functionalities, including antimicrobial, antihypertensive, anti oxidative, anticytotoxic, immunemodularity, opioid and mineral carrying activities.
Protein in milk

Protein consumption

Protein consumption
Protein seems to have more positive image than the other macronutrients. Unlike carbohydrates and fats, protein is usually associated with promoting good health and increasing one’s strength and vitality.

Athletes often choose high protein foods or take protein supplements with the promise of increasing muscle mass, strength and endurance.

But does dietary protein deserve such a positive reputation? Does it really increase a person’s strength and vitality? Should we be concerned about eating to much protein?

First, as an essential nutrient, protein is required in the diet to replace body proteins that degraded as part of normal metabolism.

Most people in developed countries consume about twice as much protein as the body needs.

Second, the body uses only what it needs, so excess dietary protein in mostly “burned” for energy. Consuming excess protein doest not automatically make muscles larger or become stronger – only exercise will do that.

Finally, consuming high protein diets does have some risks. The processing of protein in the body requires lots of water.

Consequently, dehydration is a common problem, particularly for people who exercise and lose even more water through sweat and evaporation.

Also, the kidneys arte the only organs that can process the waste products metabolism for elimination in the urine.

An excess of dietary protein over time can overwhelm the kidneys and cause permanent damage.

Like all nutrients, protein should be consumed as part of an overall balanced diet that contains adequate - but not excessive - amounts of protein.

Overconsumption of protein can easily occur in economically developed countries where both animal and plant foods containing protein are readily available.
Protein consumption

Proteins in Human Diet

Protein constitutes 10-15 per cent of the energy in almost all human diets. It is also important in the structure of all cells in the body, as well as forming enzymes, molecules that transport substances in the blood and some hormones.

The problem of providing adequate protein for an expanding world population is a second only to the overall food problem.

Apart from their nutritional significance, proteins play a large part in the organoleptic properties of foods.

Proteins exert the controlling effect on a texture of foods from animal sources.

Foods in meat, poultry, dry peas and beans, eggs, ad nuts group and in the milk, yoghurt and cheese group contribute an abundance of high quality protein.

Two others, the vegetable group and the grains group, contribute smaller amounts of protein, but they can add up to significant quantities.

Protein content of wheat and flour is considered one of the best single indices of bread making quality.

Protein often occurs in foods in physical or chemical combinations with carbohydrates and lipids.

The glycol proteins and lipoproteins affect the rheological properties of food solution or have technical applications as edible emulsifiers.

During the heating (boiling, baking or roasting) the amino acid side chains are degraded or interact with other food component (e.g. lysine with reducing sugar) to give typical flavor.

Excessive heating may, on the other hand, reduce nutritive value.

The protein quality of the diet determines, in large part, how well children grow and how well adults maintain their health.

High quality protein provide enough of all the essential amino acids needed to support the body’s work, and low quality proteins do not.

Two factors influence protein quality – the protein’s digestibility and its amino acid composition.
Proteins in Human Diet

The functions of protein in human body

Protein molecules serve as some of the major structural elements of living systems.

There are thousands of different proteins with a specific functions.

Proteins have many different biological functions Proteins are classified according to their biological roles.

Enzymatic Proteins
Protein found in many enzymes. Enzymes are catalysts, meaning that they increases the rate of reactions e.g. food digestion , sometimes by more than a million times without being destroyed.

Enzymes necessary for the digestion of carbohydrates, fats, proteins.

Transport Proteins
It transport iron, fats, minerals and oxygen.

Structural Proteins
It serves as structural components of cells and organisms. It is the fundamental structural material of every cell in the body.

This functions depends on specific association of protein subunits with themselves as well as with other proteins, carbohydrates or others.

Hormonal Proteins
Hormones are chemical messengers secreted into the bloodstream by various organs, such as the liver. It regulates certain activities so that a constant internal environment is maintain.

For example insulin that plays a key role in regulating the amount of glucose in the blood. It is released from the pancreas in response to a rise in blood glucose levels.

Defensive Proteins
Protein used to build special white blood cells and antibodies as a part of the body’s immune systems for fighting invasion and infection by foreign substances.

Provide energy as last resort
Actually carbohydrates are the primary fuel source but in times of need, protein can be burned to supply energy.

Build and maintain the body
Proteins are used for building and maintaining body tissues. All this tissue must be repaired and replaced.
The functions of protein in human body

Summary of Protein and Carbohydrate

Summary of Protein and Carbohydrate
Protein
Proteins are composed of intercoiling strands, in turn composed of amino acids.

• The proteins function to regulate specific steps in metabolism – one step, one protein. Hence, many proteins are needed.

• The variety of protein structures is made possible by the order and arrangement of the amino acid building blocks.

• At any time, body protein is being both synthesized and degraded, an inefficient process which leads to urinary loss of the breakdown products of the amino acid building blocks.

• This loss is obligatory and necessities regular replenishment – hence the nutritional necessity for protein in the diet.

Carbohydrate
Carbohydrate are composed of sugar molecules, single, paired or in long strands. Dietary carbohydrates are predominantly starch, with some sucrose and lactose.

• Starch is digested to glucose units, which are observed to be used for energy or for the synthesis of fats.

• Rising blood glucose levels after a meal stimulates insulin release which disposes of this load. Falling blood glucose levels stimulates glucagon, which maintains a basic minimum level of glucose in the blood.

• Although sucrose is well tolerated, lactose is poorly tolerated by many people who lack the enzyme to digest it. Both these substances yield glucose or glucose-like compounds on digestion.

Summary of Protein and Carbohydrate