Classification ,Nutritional quality and

Evaluation of Protein

AbishaMFT16085

OutlineFunctions of proteinsProtein classificationAmino acid classificationProtein sources-predominantly usedProtein estimationNutritional value of proteinsPathologies resulting from deficiencies

Functions of proteins

As a source of energyRequired for the formation of hormones and enzymesTo repair worn or wasted tissue and to rebuild new tissuesServe as lubricants and protective agentsServe as substrates for CHO and FA synthesis

PROTEIN CLASSIFICATION

Protein classification based on chemical composition

On the basis of their chemical composition, proteins may be divided into two classes:

simple and complex

Simple proteins

Also known as homoproteins, they are made up of only amino acids. Examples are plasma albumin, collagen, and keratin

Conjugated proteins

Sometimes also called heteroproteins, they contain in their structure a non-protein portion. Three examples are glycoproteins, chromoproteins, and phosphoproteins.

GlycoproteinsThey are proteins that covalently bind one or more carbohydrate units to the polypeptide backbone.

Examples of glycoproteins are:

glycophorin, the best known among erythrocyte membrane glycoproteins;

fibronectin, that anchors cells to the extracellular matrix through interactions on one side with collagen or other fibrous proteins, while on the other side with cell membranes;

all blood plasma proteins, except albumin;

immunoglobulins or antibodies.

ChromoproteinsThey are proteins that contain colored prosthetic groups.

Typical examples are:

hemoglobin and myoglobin, which bind, respectively, one and four heme groups;

chlorophylls, which bind a porphyrin ring with a magnesium atom at its centre;

rhodopsins, which bind retinal.

PhosphoproteinsThey are proteins that bind phosphoric acid to serine and threonine residues.Generally, they have a structural function and reserve function

structural function- tooth dentinereserve function,- milk caseins, egg yolk phosvitin.

Protein classification based on shape

On the basis of their shape, proteins may be divided into two classes:

fibrous and globular

Fibrous proteins

They have primarily mechanical and structural functions, providing support to the cells as well as the whole organism.These proteins are insoluble in water as they contain, both internally and on their surface, many hydrophobic amino acids.

The presence on their surface of hydrophobic amino acids facilitates their packaging into very complex supramolecular structures

ExamplesFibroinCollagenα-KeratinsElastin

Globular proteins

Most of the proteins belong to this class.They have a compact and more or less spherical structure, more complex than fibrous proteins. In this regard, motifs, domains, tertiary and quaternary structures are found, in addition to the secondary structures.

They are generally soluble in water but can also be found inserted into biological membranes (transmembrane proteins).

Unlike fibrous proteins, that have structural and mechanical functions, they act as:

enzymes;hormones;membrane transporters and receptors;transporters of triglycerides, fatty acids and oxygen in the blood;immunoglobulins or antibodies;grain and legume storage proteins.

Examples of globular proteins are myoglobin, hemoglobin, and cytochrome c

Protein classification based on biological functions

From the functional point of view, they may be divided into several groups.

Enzymes (biochemical catalysts). In living organisms, almost all reactions are catalyzed by specific proteins called enzymes. They have a high catalytic power, increasing the rate of the reaction in which they are involved.Therefore, life as we know could not exist without their “facilitating action”.

Transport proteins

Many small molecules, organic and inorganic, are transported in the bloodstream and extracellular fluids, across the cell membranes, and inside the cells from one compartment to another, by specific proteins.

Examples are:hemoglobin, that carries oxygen from the alveolar blood vessels to tissue capillaries.

Storage proteins

Examples are:

ferritin, that stores iron intracellularly in a non-toxic form;

milk caseins, that act as a reserve of amino acids for the milk;

egg yolk phosvitin, that contains high amounts of phosphorus;

prolamins and glutelins, the storage proteins of cereals.

Protein classification based on solubility

The different globular proteins can be classified based on their solubility in different solvents, such as water, salt and alcohol

Amino acid classification

Based on Chemical structure

Mono amino mono carboxylic acidsEx-Glycine,valine,theronine,leucine, isoluceine

Mono amino dicarboxylic acidsEx- Aspartic acid, glutamic acid

Diamino mono carboxylic amino acidEx- arginine,lysine

Sulphur containing acidEx- cystine, methionine

Aromatic and heterocyclic Amino acidEx- phenylalanine,tyrosisne,tryptophan,histidine,

proline

Types of amino acidsEssential amino acidsNon essential amino acidsSemi essential amino acids

Protein requirement in teleost

Protein level in aquaculture feeds generally average 18-20% for marine shrimp28-32% for catfish38-42% for striped bass32-38% for tilapia

Protein requirements usually lower for herbivorous fish and omnivorous fish than carnivorous fish.

Protein requirements are higher for fish reared in high density than low density systems

Protein requirements are higher for smaller fish.

As fish grows larger, their protein requirements usually decrease.

Protein requirements also varies with rearing environmentWater temperatureWater qualityFeeding rates of fishGenetic composistion

Carnivorous fish needs 40-50% Omnivorous fish needs 25-35%

Warm period and tropical climate require lesser protein and carbon and vice- versa

Linear relationship between dietary protein requirement and Specific Growth Rate exists

Warm water fish have faster SGR than temperate fish

Protein requirement in Crustaceans

Principal of providing protein for crustaceans is similar to fishes

In addition to Sp,food habits, water temperature, the source of protein energy level of diet as well as SD affects the Protein requirement in Crustaceans.

In intensive shrimp culture-commercial feed should contain not more than 35% protein In semi intensive- 20-35%

Usually protein from animal sources give better growth and survival than plant proteinsMarine crustaceans required high level of animal proteinFw prawns – better utilizers of plant proteins than marine shrimp

Protein requirementP.indicus- 36-63%P.japonicus- 35-60%L.vannamei- 30-35%M.rosenbergii- 25-45%

Very little known on protein requirement of mollusc.

Mollusc diet composition involvesIsochrysis galbanaEgg albuminYeastSalmon spermCrystalline AA

Protein requirement in Mollusc

Most of the diets used in larval rearing Micro algae were usedAbalone should not contain more than 30% protein

Factors affecting protein requirement

Size and ageFertility of the culture systemsLevels of anagement and intensificationSeasonsGeographic location

Protein sources – Predominantly used

Animal proteinsFish mealSquid mealClam mealMussel mealCrab head mealPrawn head mealSquilla mealSilkworm pupaePoultry waste mealSlaughter house waste

Plant sources

Soybean mealWheat productsYeastCotton seed mealPeanut mealCorn glutens mealRice branWheat branGround nut oil cakeTapioca flour

Protein estimation

Kjeldhal method-higher proteinBiuret methodFolin- lowry’s method

Nutritional value of proteins

Used as guide to the effectiveness of a particular protein sources in supplying animals required

3 main methods PERNPUEssential amino acid index.

PER-Protein Efficiency Ratio

Relates weight gained to g of crude protein fed

PER = g wet wt gain

g crude protein fed

This method makes no allowance for protein used for maintenanceBut widely used as method of determining appropriate protein sources for fish diets

NPU-Net Protein Utilization

most satisfactory method.

NPU= biological value × digestibility

Several technical difficulties occur when determining biological value and digestibility.

This was rewritten as

NPU = final body wt – initial body wt × 100

Total protein fed

Essential Amino Acid Index

EEA index = geometrical average of 10 essential amino acid

This is used only if the AA requirement for the given sp is known

Pathologies resulting from defeciencies

Decrease in amino acid- cause reduction in weight gainMethionine and tryptophan – not only incorporated into proteins but also used for the synthesis of other essential compounds.

Cataracts- methionine deficiency in salmonids lens become opaque after 2-3months

Sulfo -amino acids deficiencyIncreases lens opacity and gradually progress causing large reduction in light transmission.

Cataracts – due to tryptophan deficiency in rainbow trout(same pattern as in methionine deficiency)

Tryptophan deficiency – changes mineral metabolism in Rainbow trout

Increase in calcium ,sodium, potassium in kidney over 4 fold than control trout was observed.This leads to scoliosis In chum salmon scoliosis can be reversed by restoring tryptophan to normal condition in diet.

References

Handbook on Ingredients for Aquaculture feeds by Joachiom.W.hertramptFish nutrition and feed technology – S.Aathithan, N.Felix, N.VenkatasamyFish nutritionHandbook of aquaculturewww.ebi.ac.ukwww.tuscany.diet.netwww.cuchd.in

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