Download PROTEINS

PROTEINS
M.SC IST SEMESTER
ADVANCE NUTRITION-I
INTRODUCTION
Protein is a complex, high molecular
mass organic compound that consist of
amino acids.
• Proteins were discovered by Jons
Jakob Berzelius in 1838.
• They are essential for structural and
functional use of all living cells.
• Proteins also act as an important macro
nutrient in the human diet, supplying the
body’s needs for amino acids, the
building blocks of protein.
•
CONT…..
Amino
end
COO- Carboxylic end
H3 N C H
R
a carbons
Side
Chain
All amino acids have the same general formula.
CHEMICAL COMPOSITION OF
PROTEIN
All proteins are synthesized from amino acid
molecules and 20 different amino acids are
used in protein synthesis although a protein
can contain many hundreds of amino acid
units overall
CLASSIFICATION OF AMINO ACIDS
Amino acids are the units of proteins. There
are 20 amino acids. They are classified into
four groups: 9 amino acids are termed as
dispensible or essential amino acids and 11
amino acids are non essential amino acids.
The amino acids are divided into four groups:
1. Essential
2. Non essential
3. Conditionally essential
4. Limiting amino acids
ESSENTIAL AMINO ACIDS:
These are not synthesized in the body un adequate
quantity. Therefore they have to be supplied through food
daily. Inadequate consumption of any one of these
essential amino acids may result in negative nitrogen
balance. The 9 essential amino acids are:
1. ISOLEUCINE
2. LEUCINE
3. LYSINE
4. METHIONINE
5. PHENYLALANINE
6. THREONINE
7. TRYPTOPHAN
8. VALINE
9. SERINE
NON ESSENTIAL AMINO ACIDS:
These non essential amino acids are those that can be produced
within the human body using carbon skeletons and amino groups
from other amino acids. These 11 non essential amino acids are:
1. ALANINE
2. ARGININE
3. ASPARAGINE
4. ASPARTIC ACID
5. CYSTINE
6. GLUTAMIC ACID
7. GLUTAMINE
8. GLYCINE
9. PROLINE
10.TYROSINE
11. HISTIDINE
ARGININE AND HISTIDINE are essential for infants as their body
is not capable of synthesizing these amino acids.
CONDITIONALLY ESSENTIAL AMINO
ACIDS:
Sometimes a non essential amino acid
becomes essential under certain
circumstances e.g. The body normally uses
the essential amino acid phenylalanine to
make tyrosine (a non essential amino
acid)but if the diet fails to supply enough
phyenylalanine or if the body cannot make
the conversion for some reasons, as
happens in the inherited disease
phenylketouria, then tyrosine becomes
conditionally essential. Similar is the case
with Cysteine and Methionine.
LIMITING AMINO ACIDS:
A limiting amino acid is an amino acid that is
present in relatively small amounts but below
the recommended essential amino acid
requirements e.g. wheat has less amount of
amino acid lysine.
Lysine would therefore be called as limiting
amino acids.
A vegetarian would therefore have to cope
up with lysine requirement by taking a
supplement or by eating foods high in lysine,
like soybeans and other legumes.
NUTRITIONAL CLASSIFICATION
OF PROTEINS DEPENDING ON
QUALITY
S.No.
Group
01.
Complete proteins: eg egg
proteins promote good
growth in rats and other
animals.
Limiting essential amino acids
02.
Partially complete proteins:
eg. Wheat protein promote
moderate growth.
Partially lacking in one or more
essential amino acids.
03.
Incomplete proteins: eg.
Gelatin or zein do not
promote growth.
Completely lacking in one or more
essential amino acids.
Nil
FUNCTIONS OF PROTEINS







Growth and maintenance of tissue.
Formation of essential body compounds (Insulin,
gastrin, growth hormone etc.)
Transport of nutrients
Regulation of water balance
Maintain of appropriate pH.
Defense and detoxification (the toxins present in
foods are detoxified by enzymes mainly in liver
which convert them into harmless substances).
Source of energy (though proteins can provide
4Kcal energy per gram like carbohydrates, they are
used for energy purpose only when the diet has
inadequate carbohydrate and fat.
DISEASES DUE TO PROTEIN DEFFICIENCY

PROTEIN ENERGY MALNUTRITION
Two severe forms of PEM are Kwashiorkor and Marasmus.
Kwashiorkor results from an acute deficiency of protein,
whereas, marasmus results from a more chronic deficiency.

Kwashiorkor:- It is an African word meaning a “Disease of
the displaced child” who is deprived of adequate nutrition.
Occurring mostly in children between the age of 1 and 3
years, when they are completely weaned (taken off the
breast).
CONT…..
Manifestation and signs of kwashiorkor:1. Odema
2. Moon face
3. Growth failure
4. mental changes
5. hair and skin changes
6. infection
7. Nutrient deficiency
8. Short supply of digestive enzymes, digestive tract lining deteriorates.
9. Blood protein is no longer synthesized, so the child become anemic.
10. Develop fatty liver, caused by lack of the protein carriers that
transport fat out of liver.
11. Antibodies to fight off invading bacteria are degraded due to which
child becomes more prone to infections.
12. Dysentry
13. Measles - which might make a healthy child sick for a week or two,
kills the kwashiorkar child within two or three days.
CONT…..

MARASMUS:- Marasmus is more common in children below the age of
1 years.
Manifestation and signs of Marasmus
1. Severe growth retardation
2. Old man’s or monkey’s face
3. Extreme emaciation
4. loose and hanging skin folds over arms and buttocks
5. Absolute weakness
7. Slow metabolism
8. Muscle wasting including weakened heart muscles
9. Slow brain development, permanent impairing learning ability.
10. There is little or no fat under the skin to insulate against cold
Protein deficiency can also cause fatigue, insulin resistance, hair loss,
loss of hair pigment, loss of muscle mass, low body temperature,
hormonal irregulation, as well as skin elasticity. Severe protein
deficiency, encountered only in times of famine, is fatal, due to the lack
of material for the body to construct its own proteins.
DIGESTION OF PROTEIN



Mouth: saliva does not contain any protein digesting enzyme. So
digestion of proteins does not occur in the oral cavity. However,
saliva can denature the uncooked natural proteins such as that
present in raw egg , unboiled milk or uncooked germinating
seeds.
Digestion of protein in stomach:
Action of gastric juice: The gastric glands of the stomach
secrete gastric juice. It contains hydrochloric acid,
Proenzymes*-Pepsinogen and prorennin. Hydrochloric acid
maintains a strongly acidic PH of about 2-3.7 in the stomach.HCL
Kills bacteria and other harmful organisms that may be present
alongwith food. HCI converts pepsinogen and prorennin into
pepsin and rennin respectively. Once pepsin is formed it changes
pepsinogen into pepsin. Such an activation is called
autocatalytic reaction. Pepsin and rennin are absent in
invertebrates. Gastric juice is thoroughly mixed with food until it
becomes a semifluid mass called chyme. Various reactions are
summarized below:
CONT…..
HCL
1. Pepsinogen
(Proenzyme)
pepsin
HCL
2. Prorennin
(Proenzyme)
Rennin
Rennin
3. Casein
(Milk Protein)
Paracasein
4. Paracasein+ Ca
Calcium Paracaseinate (Curd)
Pepsin
5. Calcium Paracaseinate
Pepsin
6. Proteins
Peptones
Peptones
CONT…..
Pepsin can digest even collagens of connective tissue
fibres, but not keratins of horn, hair, skin or nail.
Rennet tablets which contain rennin are extracted from calf
gastric mucosa. These tablets are often used commercially
for coagulating the casein of milk to curd. It is important to note that
adult cows and humans do not secrete rennin. The function of rennin
is then taken over by pepsin and other milk- coagulating enzymes.
Sometimes chime is squeezed into oesophagus. This causes
burning of some cells. It is called heart burn (hyper acidy).
FUNCTIONS OF HYDROCHLORIC ACID :
It kills harmful bacteria.
 It provides acidic medium in the stomach for
gastric digestion.
 It changes pepsinogen into pepsin and
prorennin into rennin.
 It softens the food and dissolve the cement
materials between the cells of the food in order
to make them readily available for enzyme
action.
 It stops the action of salivary enzyme.
 It is believed to control the opening and closing
of pyloric opening of the stomach.

DIGESTION OF PROTEINS IN THE SMALL
INTESTINE:
Action of Pancreatic juice: Pancreatic juice
contains proenzymes – trypsinogen,
chymotrypsinogen and
procarboxypeptidase. All these are
concerned with proteins digestion. The bile
provides alkaline medium for various
reactions. All these reactions are
summarized below:
CONT…..
Enterokinase of Intestinal juice
1. Trypsinogen
Trypsin
(Proenzyme)
Trypsin
2.Chymotrypsinogen
chymotrypsin
(proenzyme)
Trypsin
3. Procarboxypeptidase
Carboxypeptidase
(Proenzyme)
Trypsin
4. Peptones
Peptides
Chymotrypsin
5.Peptones
Peptides
Carboxypeptidase
6.Peptides
Smaller peptides + Amino acids
B. DIGESTION OF NUCLEO PROTEINS :
The cellular foodstuffs which are rich in nuclei (liver, kidney,
pancrease etc) are likewise rich in nucleic acid and
nucleoproteins.
HCL in stomach
Nucleo protein
Removes protein portion which is digested
together with other food proteins
ribonuclease &deoxyribonuclease
Free nucleic acid
nucleotides and nucleosides
from pancreatic juice in duodenum ph 8.0
Nuclease, nucleotidases, nucleosidases in small
peptones, purines and pyrimidines
Intestines, ph 7.6
ABSORPTION OF AMINO ACID



Absorption in amino acids takes place in small
intestine. The process requires energy.
The basic amino acids lysine, arginine and histidine
share a carrier system with cystine. The dependence
of amino acid transport on Na ion suggests a direct
interaction between the carrier and Na ion. This is
similar to that observed in the absorption of glucose.
According to the available information, the amino
acid associates with the carrier and Na ion in the
microville and the complex travels to the inner side of
the membrane where it dissociates, releasing the
amino acid and Na ion into the cytoplasm. The carrier
returns back and functions repeatedly. The Na ion is
then actively transported out of the cell.
PROTEIN UTILIZATION
1.
2.
Product of protein digestion and tripeptides and amino acid, as
well as protein secreted into the gut lumen (enzyme, slouged
cells etc.) are available for absorption and are transported in the
portal vein to the liver. The liver can deaminate amino acids to
carbohydrates or the amino acid can enter the amino acid pool.
Homeostasis regulations control the concentration of specific
amino acid in the amino acid pool.
Body protein synthesis and breakdown is regulated such that in
the health, the amount of protein taken in is exactly balanced by
protein excreted in feaces, urine and skin. Protein balance
studies have demonstrated the zero protein balance in health,
the negative nitrogen balance in infection or trauma, and the
positive balance in growth and pregnancy. Muscle mass is
maintained in steady state with a fraction of muscle protein
being destroyed and rebuilt daily using amino acids from the
pool.
CONT……
3.Amino acids are also required for synthesis
of visceral protein by liver and other tissues.
Albumin, transferrin, retinol binding protein,
and other serum protein are measured to
asses the capacity of the body to synthesize
visceral proteins. Albumin and globulin are
examples of simple proteins that yield only
amino acids on hydrolysis.
FACTORS AFFECTING PROTEIN
UTILIZATION
1.
2.
Amino acid balance: An excess of one amino acid
may in certain circumstances, reduce the total
nutritive value. It is now recognized that relative
amino acid requirements vary with age. Therefore
the value of the pattern of amino acids in a specific
food or diet towards promoting growth will vary
considerably depending on a person’s age.
Calorie intake: Protein content of diet cannot be
evaluated without consideration of the adequacy of
the calorie intake. When the calorie intake drops
below a certain critical point, protein will be
deaminated and used as a source of energy and
cannot be used for the synthesis of tissues.
3.Immobility :The ability to synthesize protein is greatly
reduced among people who are immobile. Elderly
who are bedridden loose protein mass even when
dietary protein and energy seem adequate. These
have been a similar problem among astronauts, who
lose protein as a result of both weightlessness and
immobility in space fight.
4. Injury: An increase in nitrogen loss after injury is well
documented. High protein intakes either before or
after injury do not prevent this loss. However loses
are recovered more rapidly once healing begins.
5. Emotional stability: Emotional stresses such as
fear, anxiety or anger increase the secretion of
epinephrine from the adrenal gland, which in turn
causes a series of changes that result in the loss of
nitrogen.
SOURCES OF PROTEIN
Animal foods are rich source of vital
dietary element, while protein is also
found in plant foods, such as grain and
legumes and in eggs and dairy products
such as milk and yogurt.
In order to obtain the full range of essential
amino acids, one should eat a variety of protein foods. Many
people choose meat (beef, pork and lamb) as their
main
source of protein, and eat it regularly through the
week. This is not necessarily the best approach. .
CONT…..
Animal meats commonly contain excess fat and
lack other important vitamins and minerals, such
as complex carbohydrates and dietary fiber.
Plant foods such as legumes, nuts, seeds and
grains also provide protein. Soya products are
particularly popular (e.g. tofu) but contain
phytoestrogens, which can be harmful in
excessive quantities. A combination of plant and
animal proteins is recommended for a balanced
diet.
PROTEIN AS A SOURCE OF
ENERGY
1 GM OF PROTEIN ON OXIDATION PRODUCES 4 KCAL OF ENERGY
PROTEIN TYPE
Enzymes
EXAMPLE
Amylase
Structural protein
Keratin, collagen
Hormones
Insulin, glucagon
Contractile proteins
Actin, myosin
Storage proteins
Transport proteins
Immunological proteins
Ferritin
Haemoglobin serum
albumin
Antibodies
Toxins
Neurotoxin
FUNCTION
Promote the breakdown of
starch to the simple sugar
glucose.
Hair, wool, nails, horns,
hoofs, tendons, cartilage
Regulate use of blood
sugar
Contracting
fibres
in
muscles
Stores iron in spleen
Carries oxygen in blood
Carries fatty acids in blood
Rid the body of foreign
protein
Cobra venom blocker of
nerve functions
PROTEIN REQUIREMENTS

Protein yields approximately 4 calories per gram,
which is the same energy concentration as
carbohydrate.

The recommended level of protein intake for the
general population is 12 to 15 percent of total
calories. Therefore, someone consuming 2,000
calories per day has an energy equivalent of 240 to
300 calories (60 to 75 grams) of protein per day.
Table: ICMR Recommended dietary Allowances of Proteins
GROWTH
PROTEIN GRAMS PER DAY
Man
60
Woman
50
Pregnant Woman
50+15
Lactation
• 0-6 Months
• 6-12 months
50+25
50+18
Infancy
• 0-6 Months
• 6-12 months
2.05/kg
1.65/kg
Children
• 1-3 yrs
• 4-6 yrs
• 7-9 yrs
22
30
41
Boys
• 10-12 yrs
• 13-15 yrs
• 16-18 yrs
54
70
78
• 10-12 yrs
• 13-15 yrs
• 16-18 yrs
57
65
63
Girls
FACTORS AFFECTING PROTEIN
REQUIREMENTS
1.Exercise
Both anaerobic and aerobic exercise affect protein requirements in different ways.
Exercise increases the oxidation of amino acids as well as the rate of protein
turnover in lean body mass during recovery.
2.Caloric Intake
Because protein can be used for tissue repair and synthesis as well as for
energy, protein requirements will increase as total energy intake decreases. As
total caloric intake is reduced, energy needs may no longer be satisfied by
carbohydrate and fat intake alone, necessitating that protein be used to provide
energy.
3. Negative Energy Balance
For clients pursuing body-fat reduction, body-fat loss goals require that a caloric
deficit be maintained until the goal is reached. These individuals seek to modify
their body composition. During a negative energy balance, amino acids are used
to assist in energy production. This is called gluconeogenesis. The increase in
gluconeogenesis is supported by the release of branched-chain and other amino
acids from structural proteins to maintain glucose homeostasis during exercise.
NITROGEN BALANCE
The term nitrogen balance refer to the amount of nitrogen intake
in food protein and the amount of nitrogen excretes in the urine.
Foreg.1 gm of urinary nitrogen result from 6.25gm of protein.
Thus if 1gm of nitrogen is excreted in the urine for 6.25gm of
protein is consumed, the body is said to be in the nitrogen
balance. The body’s nitrogen balance are indicates how will its
tissues are being maintained.
There are three state of Nitrogen Balance:
1.
Positive Nitrogen Balance
2.
3.
Negative Nitrogen Balance
Equilibrium
CONT……
Positive Nitrogen Balance: If an individual have
positive nitrogen balance. It means that person
consuming more protein than his body needs.
 Negative Nitrogen Balance: If an individual have
negative nitrogen balance. It means that
person’s nitrogen output is greater than his
nitrogen input.
 Equilibrium: If an individual nitrogen has
reached a state of equilibrium. It means that
person is excreting about the same amount of
nitrogen as he is taking in.

QUALITY OF PROTEIN
Protein quality is a measure of the usefulness of a
protein food for various purposes, including the
growth, maintenance, repair of tissues, formation of
new tissue and production of egg, wool and milk.
Protein quality of food:
There are two factors which determine the protein
quality of food:
i) How well the essential amino acid content matches
the requirement of the human body.
ii) How easily the protein is digested and absorbed into
the body for utilization.
METHODS FOR DETERMINING THE PROTEIN
QUALITY
1.) Biological value : The biological value of protein is defined as
the percentage of absorbed nitrogen retained by the body.
BV = Nitrogen retained
Nitrogen absorbed
× 100
For the measurement of BV, the experimental animals, namely
weaning albino rats are chosen. They are first fed with a protein –
free diet for 10 days. Then they are kept on a 10% protein diet to
be tested for BV. Urine and feces are collected for both the
periods i.e. protein – free diet and protein diet. Nitrogen is
estimated in the diet, feces and urine samples. Biological value
can be calculated by the following formula:
CONT….
BV = ( N absorbed – N lost in metabolism) × 100
N absorbed
BV = [ In – (Fn – Fc)] – ( Un – Uc) × 100
In – ( Fn – Fc)
Where In = Nitrogen ingested
Fn = Nitrogen in feces ( on protein diet)
Fc = Nitrogen in feces ( on protein – free diet)
Un = Nitrogen in urine ( on protein diet)
Uc = Nitrogen in urine ( on protein – free diet)
CONT…


This indicator is based on the assumption that more nitrogen is
retained when the essential amino acids are present in sufficient
amounts to meet the needs for growth. A food with a biological
value of 70 or more is considered capable of supporting growth.
The higher the biological value the better is the quality of the
dietary protein.
The biological value provides a reasonably good index for the
nutritive value of proteins. But unfortunately this method has an
inherent drawback. It cannot take into account the nitrogen that
might be lost during the digestion process. For instance, if the
ingested nitrogen is 100 mg, absorbed is 10 mg and retained is 8
mg, the BV 8/10 X 100 = 80.This figure is erroneous, since the
major part of the protein (90 mg ) did not enter the body at all for
utilization.
2.) NET PROTEIN UTILIZATION
The biological value makes no allowance for losses of
nitrogen in digestion. This is included in the net
protein utilization.
NPU = Retained Nitrogen
× 100
Intake of Nitrogen
Miller and Bender (1995) developed a direct method of
estimating NPU. Groups of 28 day old albino rats are
used. One group is fed on non – proteins diet while
other groups are fed on the test diets containing 10%
protein for 10 days. The animals are killed at the end
of 10 days. Body nitrogen is estimated by Kjeldahl
method.
CONT…
NPU = Body nitrogen of the test group – Body nitrogen of
the non – protein group + Nitrogen consumed by
by non – Protein group
Nitrogen consumed by test group
This is equal to BV × availability. NPU can be calculated
from nitrogen balance data in man.
To measure both quantity and quality of the protein in a diet
the net dietary protein value NDpV is used.
NDpV = Intake of Nitrogen × 6.25 × NPU op.
3.) NET DIETARY PROTEIN ENERGY RATIO
It is often convenient to express the protein
content of a food in terms of the percentage of
the energy content provided by protein. The
protein content of a diet can be similarly
expressed and an additional factor given for the
quality of the mixed protein.
Net dietary Protein energy ratio
Protein energy
Net dietary intake
× NPU op.
CONT…
The NPU of different protein sources ranges from
approximately 40 to 94 with the animal protein sources
near the top and that from vegetable protein sources near
the lower end. The average Indian diet has NPU of 65.
NPU measurements like BV which consider only one intake
level and zero, tend to overestimate the nutritional quality
of some proteins. The best biological estimated of protein
quality are provided by the slope of the intake response
line from several points in the range of intakes where the
line is linear, it should not include zero protein intake, If
carcass N retentions in animals are used in this way, the
index is the relative nutritive value and the line of the test
protein is related to a standard.
4.) PROTEIN EFFICIENCY RATIO
This test consists of feeding weaning ( 21 day old
) albino rats with a 10% test protein diet and
recording the gain in body weight for a period of
4 weeks. Protein efficiency ratio is represented
by gain in the weight of rats per gram protein
ingested.
PER = Gain in body weight (g)
Protein ingested (g)
The PER for egg protein is 4.5; for milk protein
3.0; for rice protein 2.2.
PER OF DIFFERENT PROTEINS
Diet
PER
Egg hen
Protein intake Gain in body
in 4 weeks (g) weight in 4
weeks (g)
28
132
Wheat flour
26
40
1.5
gelatin
20
-4
-0.2
4.7
CONT…
This method had been very useful in comparing a new
protein source against reference protein such as egg
protein and does evaluate other factors such as
relative digestibility.
The test has some serious limitations.
 The PER is not a true efficiency ratio because not all
the protein is used for growth only that consumed
above maintenance.
 It varies with the food intake.
 The calorie intake must be adequate.
In terms of speed of operation and expenses, however,
the PER method is advantageous.
5.) CHEMICAL SCORE
This is based on the chemical analysis of the protein
for the composition of essential amino acids which is
then compared with a reference protein (usually egg
protein). The chemical score is defined as the ratio
between the quantity of the most limiting essential
amino acid in the test protein to the quantity of the
same amino acid in the egg protein, expressed as
percentage.
Chemical score:

mg of the limiting amino acid / g test protein
mg of the same amino acid / g egg protein
× 100
CONT…
The chemical score of egg protein, for any one of
the essential amino acids, is taken as 100 and
the rest of the proteins are compared.
Chemical scores of foods are as follows : eggs
– 100; meat – 70; milk cow – 65; liver – 66; fish
– 60; rice – 60; soybean – 57; Bengal gram –
44; groundnuts – 44; wheat – 42; sesame – 40;
and gelatin – 0.
NUTRITIVE VALUE OF PROTEINS OF SOME
FOOD STUFFS
food
B.V
NPU
PER
Limiting
amino acids
Egg
96
96
3.8
Nil
Milk
90
85
2.8
SAA
Meat
74
76
3.2
SAA
Fish
80
74
3.5
Tryp
Rice
80
77
1.7
Lys,Thr
Wheat
66
61
1.3
Lys, Thr,
Maize
50
48
1.0
Lys, Thr, Tryp
Bengal gram
74
61
1.1
SAA
Groundnut
55
-
-
Lys, SAA, Thr
THANK YOU