NUTRITION FOOD
TEST
In this practical, you should test a solution of unknown food substances for starch, protein, reducing sugars, non-reducing sugars, and fats/oils.
Record your procedure, observation, and conclusions,
Then answer questions about nutrition and the digestive system.
How to carry out food tests
When performing an experiment with the aim of
identifying certain food content
contained in the sample solution different reagents are used specifically in certain food sample as follows
Table for the food type, reagent used and reagent
colour
|
FOOD TESTED/FOOD TYPE |
REAGENT USED |
REAGENT COLOUR |
|
Starch |
Iodine solution |
Brown |
|
Reducing sugar |
Benedict’s solution |
Blue |
|
Non reducing sugar |
Benedict’s solution |
Blue |
|
Dilute Hydrochloric acid (HCl) |
Colourless |
|
|
Dilute sodium hydroxide (NaOH) |
Colourless. |
|
|
Protein |
Dilute sodium hydroxide (NaOH) |
Colourless. |
|
1% Copper
sulphate (CuS |
Blue. |
|
|
Lipids |
Sudan (III)
solution |
Red. |
Starch
Starch is a carbohydrate which made up by condensation of many glucose molecules.
Ø Food sources which starch is obtained include
potatoes, maize, wheat, rice e.t.c
Ø The chemical reagent
used to test starch is Iodine solution
Properties of starch
-
They are insoluble in water.
-
They are non-crystalline.
-
They are macromolecules.
-
They are not sweet
Uses of starch
Ø Provides the body with energy
Ø It is the food reserve in plant. It is the stored form of carbohydrate in plant
Procedures for testing starch
a. Measure 2ml of the prepared starch
solution in a test tube
b. Add 2 drops of iodine solution in a test tube containing the
solution of starch
c. Shake it thoroughly
d. Observe the color of the mixture
e. If starch is present,
the mixture will turn into blue black (dark blue)
f.
If starch is absent, the
mixture will retain the brown color of iodine
solution
Lipids
Lipids are compounds of carbon, hydrogen and oxygen. They are insoluble in water
Ø There are two forms of lipids which are fats and oil. Fats are in
solid form while oils are in liquid form
at room temperature (250).
Ø Natural sources of lipids include sunflower, coconuts, avocado, groundnuts and fat from animal meat.
Ø The chemical regent used in testing Lipids
is Sudan III solution
Ø White paper can also
be used
Properties of lipids
Ø They are insoluble in water
Ø They are soluble in organic solvents such as alcohol, chloroform and ether.
Ø When oil is shaken in water, the oil breaks down into droplets which disperse in water. After few minutes
water and oil separates into two layers.
Ø When water is added to a lipid that has dissolved in an organic solvent
a white milky suspension is formed. This is an emulsion.
Ø When fats rubbed against
paper, the paper became translucent. When the paper is
dipped in ether, translucent disappears because the oil dissolves in ether.
Ø In mixtures of lipid
and water, the lipid separates and moves to the top. When shaken
with Sudan III solution, this lipid absorbs the dye of Sudan III
solution, turns red, and produces a "red ring" at the top
of the test tube. Stained
lipids globules will float on the top
of water because they are less dense then water. This is the basis for testing lipids
by using Sudan
(III) solution.
Uses of lipids
Ø They are source of energy. They can be broken down during respiration process to release energy.
Ø Fat adipose tissues below the skin insulate the body against heat loss.
Ø Lipids act as a source of metabolic water when fats and oils are oxidized. This is an alternative source of
water for the animal living in desert
area like camel.
Ø Fats deposited around the major organs such as kidney, liver and heart
protect those organs
and they act as shock absorbers.
Ø They form major structural component of the cell membrane. For example phospholipid is a special type of
lipid which is a major component of cell membrane.
Ø They are medium for storing
fat soluble vitamins
like vitamins A, D, E and K
Procedures for testing
lipids
a.
Measure 2ml of a given solution
in a test tube
b. Add 3 drops of Sudan (III) solution then shake the content vigorously and let it settle for five minutes
c.
Observe the color changes
d. If lipid is present a red ring will be formed on the top of the solution
e. If lipid is absent the solution will form a homogenous red mixture with Sudan (III) solution
Protein (Biuret test)
Proteins are long chains of amino acid. They are made up of carbon, hydrogen, oxygen, and nitrogen.
Some proteins also contain Sulphur
and phosphorus
Natural sources of protein are categorized into plants, animal products
and fungi.
Ø Meat, fish eggs and
milk are animal products
Ø Mushroom and yeast are fungi proteins
Ø Beans, coconut and ground nuts are proteins from plants Chemicals used to test protein are
Ø Sodium hydroxide solution
(dil NaOH)
Ø Copper (II) Sulphate
solution (1% CuSO4)
Properties of protein
Ø They are insoluble in water.
Ø They coagulate on heating. This means that small particles of protein
clump together to form bigger particles when a mixture
of protein and water is heated.
Ø Protein reacts with sodium hydroxide and copper sulphate to produce
violet colour/ purple clour. This is called biuret test.
Note the following during testing of protein
Ø Sodium hydroxide is used to provide alkaline medium for the copper
sulphate to react with nitrogen
atoms of amino acids.
Ø The purple colour
formed during the test of protein is the result of a complex
between four nitrogen atoms in the peptide bonds and the copper (II) ion (Cu2+) of Copper sulphate solution.
Uses of protein
Ø They used for growth and repair of worn out body tissues. The protein we eat are used to make new cells
which will make tissues to replace those which are worn out.
Ø They provide body protection and defence against disease. For example protein make antibodies which
provide the body with immunity.
Ø They can be used to provide energy when the body lacks carbohydrate and fats. This happen during
starvation and when the person falls sick.
Ø They form the structural components to various materials such as nails, hair and muscle fibres.
Ø They are required
for the formation
of enzymes, hormones, and haemoglobin.
Ø They play role in clotting of blood. This is because the fibrinogen which control blood clotting is protein in nature.
Ø They transport oxygen in the blood. This is because the hemoglobin which transport oxygen
is protein in nature.
Procedures for testing protein
a. Measure 2ml of the given solution in a test tube
b. Add 2ml of sodium hydroxide followed by 2 drops of cooper
(II) sulphate drop by drop. Shake after each drop
c. Observe the color changes
d. The appearance of purple color indicates the presence of protein
e. Retention of the blue color of cooper (II) sulphate indicate
the absence of protein
Reducing sugar
Reducing sugars are based units of all carbohydrates which are easily
utilized by the body tissues.
Ø The natural sources of reducing sugar include germinating cereals like maize, millet, onion, tomato,
all sweet ripening fruits, honey and milk
Ø Glucose and Maltose
are example of reducing sugar
Properties of reducing sugar
Ø
They are soluble in water
Ø
They have sweet taste. They form sweet tasting
solutions.
Ø They are crystalline. They can form crystals. - They are small molecule.
Ø They are reducing sugar. This
is because the Benedict’s solution which contain copper (II)
sulphate when is mixed with
reducing sugar, the copper (II) ions of copper (II) sulphate will be reduced to copper (I) ions which form a brick red precipitate of copper (I)
oxide. This for form basis for testing reducing sugar.
Uses of reducing sugar
Ø It provides the body with energy. For example glucose is the most common respiratory which is oxidized
during respiration to release energy.
Ø Play role in synthesis of disaccharides. For example when two molecule of glucose are combined through
condensation reaction, maltose
is formed.
Ø They are used is synthesis of polysaccharides such as glycogen. Glucose
is particularly important
in this role.
Procedures for testing
Reducing sugar
a) Measure 2ml a solution put it in the test tube
b) Add 2ml of Benedict’s solution
to the solution
c) Heat the mixture
to boil
d) Observe the color change
e)
If reducing sugar is present in
the food sample, the mixture will experience
a series of color change from blue to green to yellow then orange and finally to brick red, this depends with the quantity of reducing sugar present in the
solution, brick red color indicates
the presence of large
quantity of reducing sugar
f)
If reducing sugar is absent the
solution will be of either blue or green color
Non-reducing sugar
Ø Non-reducing sugar is component of carbohydrate formed
when two molecules of
reducing sugar are condensed and release a molecule of water. Natural
sources of non-reducing sugar include sugarcane, beetroot, malt and unripen fruits
Ø Chemical reagents used when testing non-reducing sugar are
·
Dilute hydrochloric acid (dil HCl)
·
Sodium hydroxide solution (NaOH)
and
·
Benedict’s solution.
Properties of non-reducing sugar
Ø They have sweet taste. They form sweet tasting solutions.
Ø They are crystalline. They can form crystals. - They are small molecule.
Ø They are called non-reducing sugar because they cannot reduce copper
sulphate of Benedict’s solution.
Ø Note the following during testing of non-reducing sugar :-
§ Dilute hydrochloric acid is used to break down (hydrolyze) non-reducing
sugars to reducing sugars/converting complex sugar to simple sugar
§ Sodium hydroxide is used
to neutralize the dilute hydrochloric acid.
Uses of non-reducing sugar
They provide
the body with energy
Procedures for testing
non-reducing sugar
a) Measure 2ml of a given solution and put
in test tube
b)
Add 1ml of dil hydrochloric acid,
shake it then boil the mixture and cool it.
c) Add 1ml of sodium hydroxide
solution to neutralize the acid
d) Add 2ml Benedict’s solution then boil the mixture
e) Observe the color change
f)
If non-reducing sugar is
present, the color of the mixture will pass through
the series of color from blue to green to yellow and finally to brick red
g)
If non-reducing sugar is absent
in the solution it will retain the blue color of benedict’s solution
or turn to green
The way on how to write a report
Principles of writing the food test report
Ø
The report should be presented in a tabular
form
Ø
It must be written
in a reported form (passive speech)
Ø Solutions and reagents must be quantified, e.g 2ml or 2 drops and not few drops or little amount
of solution
Ø Commanding language like add, put should be avoided
Sample of
the report for the provided
solution V
|
Test for |
Procedures |
Observation |
Inference |
|
Starch |
To 2ml of |
The mixture |
Starch was |
|
|
solution V in a |
turned into
blue |
present |
|
|
test tube,
2 drops |
black |
|
|
|
of iodine solution |
The solution |
Starch was |
|
|
were added
then |
retained the |
absent |
|
|
shaken |
color of iodine |
|
|
|
|
solution |
|
|
Lipids |
To 2ml of |
A red ring was |
Lipids was |
|
|
solution V in a |
formed on the |
present |
|
|
test tube 3 drops |
top of solution |
|
|
|
of Sudan
(III) |
V |
|
|
|
solution were |
Solution V |
Lipids was |
|
|
added then |
retained the |
absent |
|
|
shaken |
color of Sudan |
|
|
|
|
(III) solution |
|
|
Protein |
In a test tube |
The mixture |
Protein was |
|
|
containing 2ml of |
turned in purple |
present |
|
|
solution V 2ml
of |
|
|
|
|
sodium hydroxide were
added followed by 2 drops of 1% Cooper (II) |
|
|
|
The mixture retained the
blue color of cooper (II) sulphate |
Protein was absent |
|
|
sulphate solution dropwise
while shaking after
each drop |
|
|
|
Reducing sugar |
To 2ml of solution
V in a test tube, 2ml of Benedict’s solution were added then
boiled |
A series of color change
was observed in the mixture from blue to green to yellow
and finally to brick red |
Reducing
sugar was present |
|
The solution retained the blue
color of Benedict’s solution |
Reducing sugar was absent |
||
|
Non- |
To 2ml of |
The series of |
Non |
|
reducing |
solution V in a |
color change |
reducing |
|
sugar |
test tube 1ml of |
was observed in |
sugar was |
|
|
dil hydrochloric |
the mixture
form |
present |
|
|
acid was added |
blue to green to |
|
|
|
shaken then |
yellow and |
|
|
|
boiled and |
finally to brick |
|
|
|
cooled. 1ml of |
red |
|
|
|
Sodium |
The solution |
Non |
|
|
hydroxide was |
retained the
blue |
reducing |
|
|
added followed |
color of |
sugar was |
|
|
by 2ml of |
Benedict’s |
absent |
|
|
Benedict’s |
solution |
|
|
|
solution and the |
|
|
|
|
mixture was re- |
|
|
|
|
boiled |
|
|
Preparation of solution
You can be provided with a specimen and then asked to prepare a solution by yourself then conduct the food test
Ø The procedure of preparing the solution should be included in the reported and they should be written in the
reported speech (passive voice)
Ø Indicate each procedure
that is taken while preparing a solution
Areas of concentration on food
test
The human digestive system
The table summarizing the digestion process
|
Part of th e alimentar y canal (Site of action) |
pH medium
(optimu m pH of the substrat e) |
Source of enzyme |
Digesti ve juice (secreti on) |
Enzyme |
Food digested |
Products of digestion |
|
Mouth |
Alkalin e |
Salivary gland |
Saliva |
Salivary amylase (ptyalin ) |
Starch |
Maltose |
|
Stomach |
Acidic |
Gastric gland |
Gastric juice |
Pepsin |
Protein |
Peptides |
|
Rennin |
Soluble milk protein (caseino gens) |
Insoluble milk protein
(casein) |
||||
|
Duodenu m |
Alkalin e |
Pancreati c gland |
Pancrea tic juice |
Pancrea tic amylase |
Starch |
Maltose |
|
Pancrea tic lipase |
Lipids |
Fatty acids and glycerol |
||||
|
Trypsin |
Protein |
Peptides |
|
Small intestine( ileum
) |
Alkalin e |
Intestinal wall |
Intestin al juice (Succus
entericu s) |
Erepsin (peptida se) |
Peptides |
Amino acids |
|
Maltase |
Maltose |
Glucose |
||||
|
Sucrase |
Sucrose |
Glucose and Fructose |
||||
|
Lactase |
Lactose |
Glucose and Galactose |
||||
|
Lipase |
Lipids |
Fatty acids
and glycerol |
Adaptations of the ileum for
digestion
Ø It has secretory
glands which produce digestive
enzymes.
Ø
It is connected to the liver by
the bile duct. The bile duct enables bile to reach the ileum.
Ø The ileum has mucus-secreting gland to
ensure a constant
supply
of mucus.
Adaptations of the ileum for absorption
i.
The lining of the ileum has
finger-like projections called villi. On the
villi are even smaller projections called microvilli. These structures increase
the surface area for the absorption of food.
ii.
The ileum is very long (about
six metres). It therefore has a large surface area for the absorption of soluble products of digestion.
iii.
The villi have a large network
of blood capillaries. These capillaries transport absorbed
food to all parts of the body.
iv.
The inner lining of the ileum
is folded. This increases the surface
area that is in contact
with food.
v.
The lining of the ileum is only
one cell thick. Thus, the digested food diffuses through
a short distance into the capillaries.
