Structure Of Large Molecules

& Food Test By Mansi Iyer & Priyal

Mehta

Structure of large molecules

• Large molecules are made from smaller basic

units.

• Like simple sugars to starch and glycogen,

amino acids to proteins and fatty acids and

glycerol to fats and oils.

Carbohydrates consist of carbon (C), hydrogen (H) and

oxygen (O). They include sugars, starches, cellulose and

others. In their basic form, carbohydrates are

monosaccharides. These simple sugars can combine with

each other to form more complex carbohydrates like

disaccharide or Polysaccharide.

The building blocks of proteins are amino acids, that

consist of a central carbon atom linked to an amino group,

a carboxyl group, a hydrogen atom. Within a protein,

multiple amino acids are linked together by peptide bonds,

thereby forming a long chain.

3 Fatty Acids 1 Glycerol Molecule

Fats

Triglycerides are the main components of vegetable

oils and animal fats. Triglycerides have lower densities

than water (they float on water), and at normal room

temperatures may be solid or liquid. When solid, they

are called "fats" or "butters" and when liquid they are

called "oils”

What is a food test

A food test is a simple test

which can easily be

performed in the

laboratory to identify the

main classes of food.

Types of Food Test

Sugar with Benedict solution

Protein with Biuret solution.

Starch with Iodine solution

Fats with Ethanol

Sugars

•To find if a liquid contains a

simple sugar, you will need to do a

Benedict’s sugar test

•Use a test tube.

•Fill the test tube one-third full of

the solution to be tested

•Add 3-5 drops of Benedict's

solution.

•Properly shake the test tube

The result is easy to identify

looking at the test tubes…

Proteins The Biuret Test is often used to determine the presence of peptide bonds in

protein. At this level you will be testing for the presence of protein in foods.

What to do-

•Add 2 cm3 of the liquid food sample to a clean, dry test tube

•Add 1 cm3 of sodium hydroxide solution and 1% copper (II) sulphate

solution.

• Shake well and allow the mixture to stand for 5 minutes.

•Observe any color change.

The Result

Blue = No proteins present

Violet = proteins are present

Pink = Peptides are present

( Peptides or peptones are short

chains of amino acid residues)

Starch

Procedure:

• Add a spatula of starch powder

• Add few drops of Iodine

• Notice color change

The Result

If it turns dark blue or black it contains

starch…

Fats Process:

• Add the food sample to 2 cm3 of ethanol, shake well.

• Allow to settle in a test tube rack for 2 minutes for food to dissolve in ethanol.

• Empty any clear liquid into a test tube containing 2 cm3 of distilled H2O.

• A milky white emulsion is a positive result: lipid is present.

• If the mixture remains clear, there are no fats present in the sample

The result

• If lipids are present in the mixture, it will precipitates and forms an emulsion.

A Resourceful Link

http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/food_detective/activity

BIBLIOGRAPHY

• Available on- http://brilliantbiologystudent.weebly.com/ethanol-emulsion-test-for-lipids.html [on-line] accessed on- 31st October

• Available on- http://www.biosci.ohiou.edu/introbioslab/Bios170/170_2/biuret.htm [on-line] accessed on- 4th November

• Available on- http://dev.nsta.org/ssc/pdf/v4-TS_33.pdf [on-line] accessed on- 8th November

• Available on- http://www.bayerpharma.com/en/research-and-development/technologies/small-and-large-molecules/index.php [on-line] accessed on- 8th November

• Google images accessed on 12th November.