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PROTEIN
INTRODUCTION
Protein is an essential part of the diet. It helps to build, repair and maintain the body structures. Protein exist throughout the body, in everything from muscles and organs to the bone, skin and hair. Proteins are made up of Amino acid and they are used for almost every metabolic process in the body. However, different proteins can vary greatly in the types of amino acids they contain.
Proteins occur in animal as well as vegetable Products in important quantities. In the developed Countries, people obtain much of their protein From animal products. In other parts of the world, The major portion of dietary protein is derived From plant products. Many plant proteins are often deficient in one or more of the essential amino Acids. Essential amino acids are defined as those That cannot be synthesized by an organism and are only obtained from the diet. The amounts of these essential amino acids Present in a protein and their availability determine the nutritional quality of the protein. In general, animal proteins are of higher quality than Plant proteins.
When you eat a food with protein in it (and almost all foods contain some amount of protein – even salad!), your body breaks down the protein into its amino acids.These amino acids are then sent through the body.The amino acids are recombined to create new proteins (remember, there are 10,000+ different types of protein in your body!). So, some of the veggie burger you ate turns into muscle proteins, some into hair proteins, some into hormone proteins Usage.
Recommended Dietary Allowances (RDA)
The estimated amount of a nutrient or calories per day comgnsidered adequate to fulfill the known nutrient need of all healthy people. If small amount taken above the daily requirement it don't cause any harm, whereas amount below the daily requirement may cause health problems. When people'snutrient intake is less then the daily requirement, their nutrient store decline and by the time passes this cause poor health and deficiency symptoms. Therefore, to ensure that the nutrient RDA fulfill the needs of as many people as possible, the RDA are set according to the population estimated requirement.
PROTEIN RDA:
The protein RDA for adults is 0.8grams per kilogram of body weight per day. For infants and children the RDA is little bit higher. Protein RDA increases for infants, children, adolescents, and pregnant and lactating women as it fulfill the needs for building new tissue during growth. The protein RDA is the same for athletes as for others, although athletes may need more protein and their trainer recommend a higher range of protein intakes for athletes performing different activities.
Infants ➡ 2.4g/kg body wt/day
children upto 10 yrs ➡ 1.75g/kg body wt /day
Aldoscent(boys nd girls) ➡ 1.6 and 1.4g/kg body wt/day
Adults (men and women) ➡ 1.0g/kg body wt/day
pregnancy ➡ 2.0g/kg body wt/day
lactation ➡ 2.5g/kg body wt/day.
ANIMAL PROTEIN
Animal proteins contain a good balance of all the amino acids that we need, some plant proteins are low in certain amino acids. Animal proteins are considered to be complete sources of protein because they contain all of the essential amino acids thatyour body needs to function effectively.
Whey protein is a popular dietary protein supplement and one of the main proteins found in dairy products. It is a byproduct of cheese manufacturing. It have a immune-enhancing properties. Whey can also work as an antioxidant, antihypertensive, antiviral, and antibacterial agent.
ANIMAL PROTEINS SOURCES
Some animal products are complete source of protein. Some are listed below:
•Poultry from sources such as chicken •Fish •Eggs
•Dairy products for example milk, cheese, whey •Red meat from cow, bison.
ANIMAL PROTEINS USAGE
Animal proteins, such as meat, eggs, and milk, are complete proteins, meaning they provide all of the essential amino acids our body needs. Animal products provide the highest-quality protein sources.
The human body needs 20 different amino acids. Our bodies create 11 of them (these are called "non-essential amino acids"), but we must get the other 9 from food (essential amino acids).
The National Academy of Medicine recommends that adults get a minimum of 0.8 grams of protein for every kilogram of body weight per day, or just over 7 grams for every 20 pounds of body weight. For a 140-pound person, that means about 50 grams of protein each day. For a 200-pound person, that means about 70 grams of protein each day.
ANIMAL PROTEINS STRUCTURE
A. MILK PROTEINS
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The milk proteins obtained from multiple sources (cow, buffalo, goat etc.) can be divided into two main groups:
1. Caseins- these are phosphoproteins which comprise 78% of the total weight.
2. Milk serum proteins- these form 17% of the total weight. This group includes β-lactoglobulin (8.5%), a lactalbumin (5.1%), immune globulins (1.7%), and serum albumins.
1.Casein
Casein is a heterogeneous group of phosphoproteins precipitated from skimmilk at pH 4.6 and 20 °C. In milk it is found as relatively large and almost spherical particles of 30–300 nm diameter. Casein consists of four components:
•Î±s1 casein
•Î±s2 casein
•Î² casein
•Îº casein.
There is also γ-casein which was later identified as proteolytic fragments of β-casein.
The two αs-caseins show strong association. The association of β-casein istemperature dependent. At 4 °C only monomers exist; at temperatures greater than 8 °C association will occur. αs l- Casein has more acidic than basic amino acids and has a net negative charge of 22 at pH 6.5. The polypeptide chain contains 8.5% proline that is distributed uniformly, resulting in no apparent secondary structure. αs 2- Casein has the highest number of phosphorylations and a low proline content, β-casein is a single polypeptide chain with a total of 209 amino acids, and has seven genetic variants.
The amino acids arrangement in the polypeptide chain is quite distinct. The N-terminal segment has relatively high negative charge, giving it hydrophilicproperties while the C-terminal portion is highly hydrophobic. This arrangement lends surfactant properties to this protein.
Casein contains 0.86% phosphorus, and it is concocted that this is present exclusively in the form of monophosphate esters with the hydroxyl groups of serine and threonine. Limited and specific hydrolysis of casein with proteolytic enzymes has produced a number of large polypeptides that resist further hydrolysis. An electrophoretically homogeneous phosphopeptone has been isolated from a trypsin digest of β-casein by Peterson et al. (1958). This phosphopeptone has a molecular weight of about 3000 and consists of 24 amino acid residues of ten different amino acids.
The peptone contains five phosphate residues linked to fourserine and one threonine groups. This constitutes essentially all of the phosphorus of β-casein and it appears that the phosphate residues are localized in a relatively small region of the casein molecule.
In addition to ester phosphate, casein contains calcium phosphate in the colloidal form. It appears that the presenceof this colloidal calcium phosphate helps maintain the structural integrity of the casein micelle. The arrangement ofthe caseins and calcium phosphate into a micelle is not wellknown. Many models of micelle structure have been proposed which can be divided into three groups:
a. Coat-Core Models
b. Internal Structure Models
c. Subunit Models
In coat-core model, it is assumed that the core contains the calcium-sensitive αs-caseins and that this core is covered by a layer of κ-casein. The function of the κ-casein coat is to protect the micelle from insolubilization by calcium ions. The κ-casein is readily attacked by the enzyme rennin, thus removing the coat and resulting in coagulation of the micelles. This model most readily accounts for the action of rennin but does not explain the position of the colloidal calcium phosphate.
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2.Milk Serum Proteins
a)Lactalbumin :
b.Lactoglobulin:
β- lactoglobulin, is the most abundant of the whey proteins. It has a molecular weight of 36,000. β- lactoglobulin is rich in lysine, leucine, glutamic acid, and aspartic acid. It is a globular protein with five known genetic variants. Variants A and B have 162 amino acids and molecular weights of 18,362 and 18,276, respectively. β- lactoglobulin has a tightly packed structure and consists of eight strands of antiparallel β sheets. The interior of the molecule is hydrophobic. The molecular structure also contains a certain amount of α helix, which plays a role in the formation of the usually occurring dimer. The association is pH dependent, β-lactoglobulin A will form octamers at low temperature and high concentration and at pH values between 3.5 and 5.2. Below pH 3.5 the protein dissociates into monomers.
This protein is the only milk protein containing cysteine and therefore, contains free sulfhydryl groups, which play a role in the development of cooked flavor in heated milk. The cysteine group is also involved in thermal denaturation. At pH 6.7 and above 67 °C, β-lactoglobulin denatures, followed by aggregation. The minor differences between genetic variants causes changes in some of their properties. The two chains of β-lactoglobulin C differ from the chains of the B variant in that a histidine residue has taken the place of a glutamic acid or glutamine residue. The A chains differ in two places from the B chains: aspartic acid replaces glycine and valine replaces alanine. Because of these minute differences, A is less soluble and more stable when heated than B. Variant A has a tendency to form tetramers at pH 4.5, whereas this tendency is absent in B. These differences are thought to be the result of differences in the three-dimensional folding or tertiary structure of the amino acid chains.
c. Immunoglobulins and serum albumins:
The immune globulins were previously divided into euglobulin and pseudoglobulin. The level of these proteins in colostrum is very high and they have been shown to be transferred to the blood of the young calf, indicating that they are absorbed unchanged. The three classes of immunoglobulins in milk are designated IgM (γM), IgA (γA), and IgG (γG). IgG is subdivided into IgG1 and IgG2.
B. MEAT PROTEINS
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Muscle is made up of fibers that are several centimeters long and measure0.01–0.1 mm in diameter. The fibers are enclosed in membranes called sarcolemma and are arranged in bundles that enclose fat and connective tissue. The fibers are cross-striated due to the presence of cross-striated myofibrils. The myofibrils are embedded in the cell cytoplasm called sarcoplasm. The fibers contain peripherally distributed nuclei
In addition to the constituents mentioned, the muscle fibers contain other components including mitochondria, ribosomes, lysosomes, and glycogen granules. The fibers make up the largest part of the muscle volume, but there is from 12 to 18% of extracellular space. The fibrils are optically non-uniform, which accounts for the striated appearance. Compounds with different refractive indexes are arranged along the fiber.
Meat contains three main types of proteins:
- Myofibrillar proteins
- Stromal proteins
- Sarcoplasmic proteins
1.Myofibrillar Proteins
The muscle cell/fiber grouped into bundles are composed of myofibrils. Myofibril consist of two main constituents:
•Myosin
•Actin
a) Myosin
Myosin is the most abundant of the muscle proteins and makes up about 38% of the total. It is a highly asymmetric molecule with a molecular weightof about 500,000 comprising about 60–70% α-helix structure. The molecule has a relatively high charge and contains large amounts of glutamic and aspartic acids and dibasic amino acids.
Each head has the N-terminal part of that heavy chain as well as two light chains, named the essential light chain (ELC) and the regulatory light chain (RLC).
b) Actin
Actin makes up about 13% of the muscle protein, so the actin-myosin ratio is about 1:3. Actin occurs in two forms: G-actin and F-actin (G and F denote globular and fibrous). G-actin is a monomer that has a molecular weight of about 47,000 and is a molecule of almost spherical shape. Because of its relatively high proline content, it has only about 30% of α-helix configuration. F-actin is a large polymer and is formed when ATP is split from G-actin. The units of actin combine to form a double helix of indefinite length, and molecular weights of actin have been reported to be in the order of several millions.
Bodwell and McClain (1971) indicate that actin. polymers may have an apparent molecular weight of over 14,000,000, with a length of 1160 nm and a diameter of 6 nm.
Relaxation of muscle depends on regeneration of ATP from ADP by phosphorylation from creatine phosphate. The precise mechanism of contraction is still unknown, although a working hypothesis is available.
2. Stromal Proteins
Stromal proteins are the proteins found in the watery matrix of connective tissues. These are:
•Collagens
•Elastins
•Reticulins
a.Collagens
The myofibrillar proteins are separated and surrounded by layers of connective tissues. The amount and nature of this connective tissue is an important factor in the tenderness or toughness and the resulting eating quality of meat. Collagens form the most widely occurring group of proteins in the animal body.
The molecule consists of three domains:
•The N-terminal non-triple helical domain (N-telopeptide)
•The central triple helical domain
•The C-terminal non-triple helical domain (C-telopeptide).
The single (uninterrupted) triple helical domain represents more than 95% of the molecule. The triple helix is the tropocollagen molecule; these are lined up in a staggered array, overlapping by one-quarter of their length to form a fibril. The fibrils are stacked in layers to form connective tissue. Important in the formation of these structures is the high content of hydroxyproline and hydroxylysine. The content of dibasic and diacidic amino acids is also high, but tryptophan and cystine are absent. As a result of this particular amino acid composition, there are few inter-chain cross-bonds, and collagen swells readily in acid or alkali.
The structural unit of the collagen fibrils is tropocollagen with a length of 280 nm, a diameter of 1.5 nm, and a molecular weight of 360,000. Gelatin is a soluble protein derived from insoluble collagen. The process of transforming collagen into gelatin involves the following three changes:
•Rupture of a limited number of peptide bonds to reduce the length of thechains
•Rupture or disorganization of a number of the lateral bonds between chains
•Change in chain configuration
The last of these is the only change essential for the conversion of collagen to gelatin.
b.Elastins
c. Reticulins
Reticulin protein is present in much smaller amounts in comparision to collagen or elastin. It is hypothesized that reticulin may be a precursor to either collagen and/or elastin since it is found more prevalent in younger animals. Older animals can, but do not necessarily, have more connective tissue per unit of muscle in comparison to younger animals. Cross linkages between the collagen molecules increase (which results in decreased susceptibility of collagen to heat induced solubilization) in older animals resulting in formation of tougher muscles than those found in muscle from more youthful animals. In a nut shell, the less connective tissue in a cut of meat, the more tender it will be.
3. Sarcoplasmic Proteins
C. FISH PROTEIN
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The proteins of fish flesh can be divided into three groups on the basis of solubility:
Myogens – easily soluble, located mainly in sarcoplasm, muscle cell juice.
Structural – less soluble, located mainly in myofibrils.
Stromal – insoluble, located in connective tissues.
The skeletal muscle of fish consists of short fibers arranged between sheets ofconnective tissue, although the amount of connective tissue in fish muscle is less than that in mammalian tissue and the fibers are shorter. The myofibrils offish muscle have a striated appearance similar to that of mammalian muscle and contain the same major proteins, myosin, actin, actomyosin, and tropomyosin. The soluble proteins include most of the muscle enzymes and account for about 22% of the total protein. The connective tissue of fish muscle has different physical properties, which result in a more tender texture of fish compared with meat. The structural proteins consist mainly of actin andmyosin, and actomyosin represents about three-quarters of the total muscle protein.
D. EGG PROTEINS
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The proteins of eggs are characterized by their high biological value and can be divided into:
•The egg white proteins
•The egg yolk proteins.
•The membranes of eggs consist of keratins and mucins
1.Egg white proteins
The egg white contains at least six different proteins. Liquid egg white contains 10–11% of protein, and the dried form contains about 83%.
a.Ovalbumin
b. Conalbumin
It has a molecular weight of 70,000 and has iron-binding and antimicrobialproperties. It can render iron unavailable to microorganisms; this property is lost after heat denaturation. Iron is bound in the ferric form by coordination. The groups involved in the binding of iron are amino, carboxyl, guanidine, and amides. When these groups are blocked, the iron binding property is lost.
c. Ovomucoid
It is a trypsin inhibitor and a glycoprotein with a molecular weight of 27,000– 29,000, containing mannose and glucosamine. This protein is highly resistant to denaturation.
d. Lysozyme
It is classified as a globulin and has the ability to cause lysis of bacterial cells. It is divided into three parts, designated G1, G2, and G3. The activity resides in the G1 fraction. The protein has a molecular weight of 14,000–17,000 and is a basic protein with unusually high content of histidine, arginine protein with unusually high content of histidine, arginine, and lysine. It is stable to many agents that denature other proteins, such as heat, cold, and denaturing reagents. It is also quite resistant to proteolysis by enzymes such as papain and trypsin.
e. Ovomucin
It is an insoluble protein, which precipitates from egg white on dilution with water. It is not well known, has a high molecular weight (7,600,000), and is a mucoprotein. The ability of certain viruses to agglutinate red blood cells, calledhemagglutination, is inhibited by ovomucin.
f. Avidin
It is a protein characterized by its ability to bind biotin and render it unavailable. Heat denaturation destroys this property.
2. Egg yolk proteins
They precipitate when the yolk is diluted with water. The yolk contains a considerable amount of lipid, part of which occurs in bound form as lipoproteins. Lipoproteins are excellent emulsifiers, and egg yolk is widely used in foods for that reason. The two lipoproteins are lipovitellin, which has 17–18% lipid, and lipovitellenin, which has 36–41% lipid. The protein portions of these compounds after removal of the lipid are named vitellin and vitellenin. The former contains 1%phosphorus, the latter 0.29%.
ANIMAL PROTEINS ADVANTAGES
- Animal proteins, such as meat, eggs, and milk, are complete proteins, they provide all of the essential amino acids needed in ourbody.
- Animal product provide high quality protein sources.
- Foods that contain animal protein tend to be high in several nutrient.
ANIMAL PROTEIN HAS HEALTH BENEFITS
- Animal protein also associated with positive health effects.
- Fish , poultry and low fat diet were associated with lower heart diseases.
- People having fish in their diet are also likely to have a lower risk ofheart attack, heart strokes and deaths from many heart diseases.
- Eating eggs were also associated with improved cholesterol level and weight loss.
- Eating animal protein is associated with increased lean musclemass also associated with reduction in the muscle loss.
- Certain animal protein sources are linked to a reduced risk of heart disease, improved cholesterol levels, weight loss and increased muscle mass.
ANIMAL PROTEINS DISADVANTAGES
- Animal venoms are composed of varieties of protiens and peptides fine-tuned by millions of year of evolution.
- Toxin synthesized by venomenous animals from both terresterial animals nd marine animals such as scorpians,snakes,spiders,bees,cone snails nd sea anemones are injected in the body for hunt or defence by animal wounding apparatus, such as fangs barbs , spines and stingers.
- Some venomenous animals have been used to treat disease for milennea in many parts of the world.
- The high selectively and potency make animal toxins as brilliant pharmacological tools drug candidates.
- The number of disulfide bonds vary in different venomenous species,such as 10-40 cysteine residues have been found in cone snail.
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