food groups present in chemcial testina

In comparison to the structure of lipids and carbohydrates, protein molecules vary in size and structure.  They are large complex molecules, for example, if a water molecule were the size of a brick, proteins would be the building.  The building blocks that make up these proteins are called amino acids.  Amino acids contain an amino group (NH2) and a carboxylic acid group (COOH); both of these are attached to a central carbon atom, with a side chain (or R group) (see diagram below).

The side chain varies – with a total of 20 amino acids that make up all of the different proteins.  They contain the elements carbon, hydrogen oxygen and sometimes sulphur.  Proteins play a vital role within the human body in that they have intricate structural components, for example Keratin in hair, nails and skin.  They have a transportable role in haemoglobin in which they carry O2 around the body.  All antibodies are proteins, and without them we would be unable to fight against diseases.  Amino acids join together, with the help of peptide bonds to form long chains.  The two amino acid molecules react together causing the removal of a water molecule, this is known as a condensation reaction, and the amino acid is now a dipeptide.  The complexity of the protein molecule is shown in the following four different structures.

• Primary structure – This is a linear sequence of amino acids (PICTURE)

• Secondary structure – The polypeptide chains become twisted/coiled.  By doing so they form a stable arrangement of hydrogen bonds.  The two common secondary structures are α helix β pleated sheets.

• Tertiary structure – Polypeptides are folded into precise three-dimensional shapes.  The tertiary structure has a range of bonds; disulphide, hydrogen and ionic bonds, which give the protein its precise shape.

        

• Quaternary structure – Each protein consists of several polypeptide chains, which are bonded together to form intricate shapes.  For example, a haemoglobin molecule is form from four separate polypeptide chains.

Hypothesis

It is to be expected that it will be possible to use chemical testing to discover what food group is present in different food products.

Safety Assessment

Method

Each food product being tested needs to be pureed using a pestle and mortar, adding water to form a runny puree.

When testing for sugars (carbohydrates)

1. The hot plates were turned on, with a beaker of boiling water placed on top, which was left to boil.
2. Using a syringe, 2mls of the puree food was added to a test tube.
3. Using a separate syringe, 2mls of Benedict’s reagent was then added to the test tube.
4. Once the water had reached boiling point, the test tube was added to the beaker, and was left for 2 minutes.
5. Over this period of time, if a reaction were to have taken place a positive colour change from blue to orange/red would be identified.

When testing for starch (carbohydrates)

1. Using a syringe, 2mls of the puree food was added to a test tube.
2. A few drops of the iodine solution were then added to the test tube.
3. A positive test result shows a change in colour from yellow/orange to blue/purple.

When testing for Lipids

1. Using a syringe, 2mls of the puree food was added to a test tube.
2. 4mls of ethanol was then added to the test tube.
3. Placing a bung on top of the test tube, the mixture was shaken vigorously.
4. The mixture was then allowed to stand for approximately 2 minutes.
5. Then using a syringe, 2mls of water was added to the mixture.
6. A positive result would show a layer of un-dissolved fat/oil lying on top of the food mixture.

When testing for proteins

1. Using a syringe, 2mls of the puree food was added to a test tube.
2. 2mls of sodium hydroxide was then added to the test tube.
3. Using a pipette 4 drops of copper sulphate solution was added.
4. Placing a bung in top of the test tube, the mixture was shaken vigorously.
5. A positive test result shows a colour change from blue to purple

Results

Interpretation

From the results gained from this experiment, the hypothesis stated at the beginning of the experiment is correct, it is possible, using chemical testing to discover the food group present in different food products.  For a cereal bar, to contain all of the tested food groups is not unusual.  Most man made food products tend to contain lots of things that give it some form of ‘nutritional value’, despite the fact it’s not natural. Starch is commonly found in most plants, and for it not to show up when testing almonds, may be due to error when testing. The rest of the results were expected due to previous knowledge on both food product and food group.

Evaluation

When testing for lipids (the emulsion test), it was difficult to see if there were any un-dissolved fat/oil lying on top of the food and water mixture.  If the experiment were to be carried out again, instead I would use filter paper, as a positive result would turn part of the filter paper clear/translucent.  Another test is using , which will stain fat cells red if present. (www.sciencecompany.com)

  When testing for proteins with almonds, it originally didn’t turn purple.  It wasn’t until when clearing away that a slight colour change was observed.  For future testing, all test tubes should be left for the same length of time, to see if any take longer to produce a positive or negative result.  With this each test should be repeated twice to prevent any error.  I would also carry out further testing on other food groups, for example using  (dichlorophenolindophenol).  This is a blue indicator solution and will turn colourless when an end point is reached with a solution containing vitamin C. (www.sciencecompany.com)

        

Reference

Science Company:  (viewed: 24/02/2009)

Boyle, M., Senior, K., (Ed) (2002) Human biology. London: Harper Collins Publishers

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