estimation of protein contents in food
Transcript of estimation of protein contents in food
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Food’s nitrogen contents estimation
Presentation on
Dr. Kashif Aslam
Food Biotechnology
Presented to:
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Presented byHiba Ashfaq ………………. BSBT-01Hina Mushtaq …………… BSBT-02Zahra Naz …………………. BSBT-04
Ayesha Sadiqque ….…….. BSBT-05Asma Noor ………………. BSBT-06
BS-BIOTECHNOLOGY- 6TH Semester
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FoodFood is
“Any substance consumed to provide
nutritional support for the body.”
Usually of plant and animal origin.
Food contains essential nutrients such
as
Carbohydrates Protein Fats
Vitamins Minerals
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Composition Of Food
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Food contains essential nutrients as:
Carbohydrates e.g.
breads,rice,milk,sugar
Protein e.g. meat,grains,fish
Fats e.g.
oils,butter,nuts,seeds,
Vitamins e.g. citrus fruits,
strawberries
Minerals e.g. vegetables, fruits
Water
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Food Composition
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Nitrogen
Nitrogen, a chemical elementForms compounds -essential to life.
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Function of Nitrogen in body
Normal growth Cell replacement and tissue repair Used for protein synthesis in muscles,
skin, blood, hair, nails and DNA Used to make non-protein
Such as the heme in hemoglobin- which carries oxygen in red blood cells.
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ProteinsPolymer of amino acids.Amino acids are
“Biologically important organic compounds composed of amine and carboxylic functional groups , along
with a side chain specific to each amino acid.”
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Sources of
protein and
nitrogenMeat
Eggs
Fishes
Grains
Cereals
Products from milk
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Different forms of nitrogen in food
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Different forms of nitrogen in food
Nitrogen exists in two basic forms which are obtained from living organisms and environment:
Protein nitrogen Non-protein nitrogen (NPN)
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Protein nitrogen
Proteins are building blocks of body tissues and are made up of amino acids linked together by peptide bonds.
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Continued..
Nitrogen is a part of all amino acids Nitrogen is present in substances
like purines which are part of nucleic acids
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Purine rich foods
Nitrogenous bases (adenine, guanine) that are present almost in all food types.
Serve as carriers of genetic information, energy production and chemical signaling in body.
Purines consumption increases the level of uric acid in the body.
Intake of purines should not exceed 150 mg daily.
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Foods high in purines
Organ meats specially liver (high content)
Yeast Poppy seeds (high content of 170 mg
per 100g)
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Sea foods like shrimp, codfish, scallops, oysters, lobsters, etc
Nuts, dairy products, eggs, seeds, etc are low in nucleic acid contents
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Vegetables High - bean sprouts, mushrooms,
peapods, pea, broccoli, legumes, soy products etc
Moderate – spinach, cauliflower, cabbage, corn, bamboo shoots, asparagus, etc
Low- carrots, onion, radish, tomatoes, lettuce, eggplant, etc
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Non protein nitrogen (NPN)
NPN is formed as a result of the catabolism of proteins and nucleic acids. These include following compounds:
Urea Ammonia Nitrates and nitrites Uric acid Creatinine or creatine Amino acids
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Urea
It is the major product of protein metabolism
It is synthesized in liver from ammonia.
It is used in animal and plant foods as a basic nutrient.
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Creatinine It is synthesized in liver from amino
acids including glycine, arginine and
methionine. It is also present in blood plasma It is filtered in kidneys and excreted
in urine.
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Uric acid
Final product of purine metabolism It is present in blood plasma Its increased level causes a disease
called gout.
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Free amino acids
Animal fish and poultry products contain NPN in different concentrations
Fruits and vegetables contain relatively higher amounts
Glu, Asp and Lysine are the most important regarding NPN. These are present in most animal and plant foods.
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Ammonia , nitrates and nitrites
Organic nitrogen ( obtained from living organisms) undergoes ammonification to produce ammonium.
Nitrifying bacteria further convert it into nitrates and nitrites.
Then this nitrogen is taken up by plants which are a source of food for humans.
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Estimation of protein nitrogen in food
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Methods Two methods are used for estimating protein nitrogen
Kjeldahl method Dumas method
Kjeldahl method is prefer for protein nitrogen estimation
Dumas method is mostly used for non protein nitrogen estimation
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Nitrogen in food mostly comes from
protein
Nitrogen contents in food may vary
between 150-180 g/kg depends on the
amino acid
Purine , pyrimidine , free amino
acids ,vitamins, creatine , creatinine all
contributes to total nitrogen present.
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Kjeldahl method
About 1000 years old methodDeveloped by Kjeldahl in 1883Applied on variety of substances
e.g. meat ,grains ,waste water soil etc.
With the passage of time technique and apparatus modified The basic principle is same still now.
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Basic principleEstimation of nitrogen by digesting food in strong acid
Steps:The process is divided into 3 main steps. Digestion Distillation Titration
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Kjeldahl appratus
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1) Digestion
Proteins are first digested Digestion is carried out with concentrated H2SO4 In presence of an inorganic catalystDigestion converts any nitrogen in food to ammonia and other organic matter to Co2
and H2O
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2) Distillation Digestion flask is
connected with receiving flask
Ammonium is formed using distillation
capture of ammonium occurs with a weak acid (boric acid)
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3)Titration
The third step is quantification of the ammonium Done by titrationTitration with a strong acid (sulfuric acid) & suitable indicator to determine end point of the reaction
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Advantages
Kjeldahl method is used internationallyIt is a standarad method for comparison against all other methods due to it’s universality High precision and good reproducibility
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Disadvantages Time consumingDoes not measure true protein because all nitrogen in food is not in the form of proteinThis method uses sulfuric acid at high temperature it is also a health hazard.
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Dumas methodThis is an automated instrumental
technique
use to measure protein concentration
of food
described by a scientist Dumas in
1831
Is older than the Kjeldahl
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Basic principle
Sample of known mass is
combusted at high temperature
(900oc) chamber in the presence
of oxygen
This lead to the release of
Co2 ,H2o
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The method has three steps: Combustion Reduction and Separation Detection
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1.Combustion: Sample is weighed and purified It is heated in a high temperature
furnace Rapidly combusted in the presence of
pure O2 at about 1,000 ºcSample +O2 → CO2 + H2O + Nx Oy +
O2 + other oxides
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2.Reduction and Separation: The combustion products are collected
and allowed to equilibrate Gas mixture is passed over hot copper
to remove any oxygen and convert nitrogen oxides into molecular nitrogen.
The sample is passed through traps that remove water and carbon dioxide
CO2 + H20 + NxOy + O2 + Cu → CO2 + H20 + N2 → N2
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3.Detection: The measured signal from the
thermal conductivity detector for the sample can then be converted into total nitrogen content.
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AdvantagesMore convenient in many aspects such as
speed, safetycleanlinessproductivity cost per analysis
Disadvantages Require high cost Require large sample for testing
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Nitrogen conversion factor
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Nitrogen conversion factor“Factor by which nitrogen content of a foodstuff is multiplied to determine the
total protein content”.∆ It can not be calculated exactly as no one
can tell the accurate %age of protein in the food
Dependence:∆Nitrogen contents in food∆Amino acid composition of the protein
in food
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Examples:
Value of conversion factor: For wheat and most cereals - 5.8 most legumes and nuts - 5.3 milk - 6.38 Rice - 5.95 Soya - 5.7 Other foods - 6.25
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Used for:It is used to find out the value of crude protein in the food sample
Crude protein“The approximate amount of protein in
foods that is calculated from the determined nitrogen content by
multiplying by a factor”Crude protein =N × 6.25
N= mineral protein which is calculated by using different methods like dumas method etc
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How to obtain the conversion factor?
It is obtained by processing the reported %age protein in the food
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Examples:
For rice ,reported protein contents = 16.8%
Then Factor = 100/16.8=5.95
most legumes and nuts with 18.86% proteinFactor obtained will be
equal to 5.3
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Milk with 15.67% protein contents
Factor will be 6.38
wheat and most cereals protein contents are 17.24%
Its factor will be is 5.8;
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Find crude protein….
• If nitrogen measured in milk is 10% and we know that the N-factor for milk is 6.38 %.
• Then the total crude protein will be:C.P. =6.38 x 10
C.P.=63.8 %And the sample will rich in protein by
having protein more than half of its contents.
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