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Food test are the method used to determine the types of
nutrients presents in a food specimen. At this level we will discuss how to test carbohydrate,
protein, and lipids.
CARBOHYDRATE
This is the organic compound made up of carbon, hydrogen
and oxygen, there are three types of carbohydrates that are;
1. Monosaccharide
2. Disaccharide
3. Polysaccharide
Monosaccharide
Monosaccharide’s are also known as simple sugar. They
include glucose, fructose (fruit sugar) and glucose (milk sugar).
These sugar dissolve in water to form sweet solution,
they are said to be reducing sugar
The general formula of monosaccharide is (CH2O)n (where n
represent the number of carbon atoms and has a value of between 3 and 6) Example the formula of glucose is C6H12O6
Disaccharides are formed when two monosaccharide
molecules combine together.
Examples
Two glucose combine to form maltose. Maltose is found in
germinating seed
Glucose + Glucose → Maltose
A glucose molecule and
fructose molecules combine to form sucrose, the sugar found in sugarcane
Glucose + Fractose → Sucrose
A glucose molecule and a
galactose molecules combine to form lactose, a sugar found in milk
Glucose + Galactose → Lactose
The process by which two
monosaccharides combine to form a disaccharide is called condensation.Disaccharides are soluble in
water and form sweet solution, this is
called hydrolysis
Example
Glucose
+ water → Glucose and glucose
Hydrolysis
Some disaccharide are
reducing sugar ( for example lactose and maltose) while other are non reducing
sugar (for example sucrose)
Polysaccharides are formed
by condensation involving several monosaccharides.Examples of polysaccharide
are starch, glycogens, cellulose and chitin
Properties
of polysaccharide
- They are insoluble in water
- They are not sweet
- They are non reducing sugar
- They form suspension when put in water
Test
for carbohydrate
Test for
|
Procedure
|
Observation
|
Conclusion
|
Starch
|
i. Add an small
amount in a clean and dry test tube
ii. Add a 2 or 3 drops of iodine solution
|
a. The blue black colour formed
b. the solution retained the yellowish
colour of iodine solution
|
a. Starch are present
b Starch are absent
|
Reducing
sugar
|
i. Add small amount of specimen in a dry and clean test
tube
ii. add an equal amount of benedicts
solution to the solution
|
a. colour change from blue to green to
yellow to orange
b. The solution retained the blue colour of
benedicts solution
|
a. reducing sugar are present
b. reducing sugar are absent
|
Non reducing
sugar
|
i. add small amount of specimen in a dry
and clean test tube
ii. add 1 cm3 of hydrochloric acid so as to
hydrolyze disaccharide to monosaccharide then heat gently
iii. add small amount of sodium hydrogen
carbonate and shake the test tube
iv add 2 cm3 of benedicts solution and then
boil the mixture
|
a. the colour change form blue to green to
yellow to orange
b. the solution retained the blue colour of
benedicts solutions
|
a. non reducing sugar are present
b. non reducing sugar are absent
|