Food biotechnology

2. Food’s nitrogen contents
estimation
Dr. Kashif Aslam
Food Biotechnology

3. Presented by
Hiba Ashfaq ………………. BSBT-01
Hina Mushtaq …………… BSBT-02
Zahra Naz …………………. BSBT-04
Ayesha Sadiqque ….…….. BSBT-05
Asma Noor ………………. BSBT-06
BS-BIOTECHNOLOGY-
6TH Semester

4. Food
Food 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

6. Composition Of Food

7. 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

8. Food Composition

9. Nitrogen
Nitrogen, a chemical element
Forms compounds -essential to life.

10. 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.

11. Proteins
Polymer 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.”

12. Sources of protein
and nitrogen
Meat
Eggs
Fishes
Grains
Cereals
Products from milk

13. Different forms of nitrogen
in food

14. 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)

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

16. Continued..
 Nitrogen is a part of all amino acids
 Nitrogen is present in substances like
purines which are part of nucleic acids

17. 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.

18. Foods high in purines
 Organ meats specially liver (high content)
 Yeast
 Poppy seeds (high content of 170 mg per
100g)

19.  Sea foods like shrimp, codfish, scallops,
oysters, lobsters, etc
 Nuts, dairy products, eggs, seeds, etc are
low in nucleic acid contents

20. 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

21. 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

22. 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.

23. 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.

24. Uric acid
 Final product of purine metabolism
 It is present in blood plasma
 Its increased level causes a disease called
gout.

25. 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.

26. 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.

27. Estimation of protein nitrogen
in food

28. 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

29. 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.

30. Kjeldahl method
About 1000 years old method
Developed by Kjeldahl in 1883
Applied 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.

31. Basic principle
Estimation of nitrogen by digesting food in
strong acid
Steps:
The process is divided into 3 main steps.
 Digestion
 Distillation
 Titration

32. Kjeldahl appratus

33. 1) Digestion
Proteins are first digested
Digestion is carried out with
concentrated H2SO4
In presence of an inorganic
catalyst
Digestion converts any
nitrogen in food to ammonia
and other organic matter to
Co2 and H2O

34. 2) Distillation
 Digestion flask is
connected with
receiving flask
 Ammonium is formed
using distillation
 capture of ammonium
occurs with a weak acid
(boric acid)

35. 3)Titration
The third step is
quantification of the
ammonium
Done by titration
Titration with a strong
acid (sulfuric acid) &
suitable indicator to
determine end point of
the reaction

36. Advantages
Kjeldahl method is
used internationally
It is a standarad
method for comparison
against all other
methods due to it’s
universality
High precision and
good reproducibility

37. Disadvantages
 Time consuming
Does not measure true protein because all
nitrogen in food is not in the form of protein
This method uses sulfuric acid at high
temperature it is also a health hazard.

38. Dumas method
This is an automated instrumental
technique
use to measure protein concentration of food
described by a scientist Dumas in 1831
Is older than the Kjeldahl

39. 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

41. The method has three steps:
 Combustion
 Reduction and Separation
 Detection

42. 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 ºc
Sample +O2 → CO2 + H2O + Nx Oy + O2 +
other oxides

43. 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

44. 3.Detection:
 The measured signal from the thermal
conductivity detector for the sample can
then be converted into total nitrogen
content.

45. Advantages
More convenient in many aspects such as
speed,
safety
cleanliness
productivity
cost per analysis
Disadvantages
 Require high cost
 Require large sample for testing

46. Nitrogen conversion factor

47. 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

48. 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

50. 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

51. How to obtain the conversion factor?
 It is obtained by processing the reported
%age protein in the food

52. Examples:
 For rice ,reported protein
contents = 16.8%
Then Factor = 100/16.8
=5.95
 most legumes and nuts
with 18.86% protein
Factor obtained will be
equal to 5.3

53.  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;

54. 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.