Food’s nitrogen contents estimation

Presentation on

Dr. Kashif Aslam

Food Biotechnology

Presented to:

Presented byHiba Ashfaq ………………. BSBT-01Hina Mushtaq …………… BSBT-02Zahra Naz …………………. BSBT-04

Ayesha Sadiqque ….…….. BSBT-05Asma Noor ………………. BSBT-06

BS-BIOTECHNOLOGY- 6TH Semester

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

Composition Of Food

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

Food Composition

Nitrogen

Nitrogen, a chemical elementForms compounds -essential to life. 

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.

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.”

Sources of

protein and

nitrogenMeat

Eggs

Fishes

Grains

Cereals

Products from milk

Different forms of nitrogen in food

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)

Protein nitrogen

Proteins are building blocks of body tissues and are made up of amino acids linked together by peptide bonds.

Continued..

Nitrogen is a part of all amino acids Nitrogen is present in substances

like purines which are part of nucleic acids

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.

Foods high in purines

Organ meats specially liver (high content)

Yeast Poppy seeds (high content of 170 mg

per 100g)

Sea foods like shrimp, codfish, scallops, oysters, lobsters, etc

Nuts, dairy products, eggs, seeds, etc are low in nucleic acid contents

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

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

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.

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.

Uric acid

Final product of purine metabolism It is present in blood plasma Its increased level causes a disease

called gout.

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.

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.

Estimation of protein nitrogen in food

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

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.

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.

Basic principleEstimation of nitrogen by digesting food in strong acid

Steps:The process is divided into 3 main steps. Digestion Distillation Titration

Kjeldahl appratus

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

2) Distillation Digestion flask is

connected with receiving flask

Ammonium is formed using distillation

capture of ammonium occurs with a weak acid (boric acid)

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

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

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.

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

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

The method has three steps: Combustion Reduction and Separation Detection

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

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

3.Detection: The measured signal from the

thermal conductivity detector for the sample can then be converted into total nitrogen content.

AdvantagesMore convenient in many aspects such as

speed, safetycleanlinessproductivity cost per analysis

Disadvantages Require high cost Require large sample for testing

Nitrogen conversion factor

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

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

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

How to obtain the conversion factor?

It is obtained by processing the reported %age protein in the food

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

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;

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.