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The aim of the experiments was to test food samples to see which food group the sample belongs to. I also did tests to determine what type of carbohydrate an unknown carbohydrate was.

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Introduction

Food Tests Write-Up The aim of the experiments was to test food samples to see which food group the sample belongs to. I also did tests to determine what type of carbohydrate an unknown carbohydrate was. I did the biuret test to determine if a sample was a protein, the benedict's test to determine if a sample was a reducing sugar, the emulsion test to determine if the sample was a fat and used hydrochloric acid to split a non-reducing sugar into its monomers and then used the benedict's test to check that the monomers are reducing sugars. I predict that the sample containing protein will turn purple, benedict's reagent will turn reducing sugars to a brick red colour, the emulsion test will produce a white precipitate and starch will turn iodine black/brown. Apparatus Lists Biuret test * Biuret Reagent * Test Tube * Pipette * Protein Sample (Egg Albumin) Benedict's test for reducing sugars * Benedict's reagent * Reducing Sugar Sample * Test tubes * Water Bath or heating apparatus (Bunsen burner, tripod, gauze, valve and heat-proof mat) ...read more.

Middle

Put about 2cm3 of the sample into a test tube with an equal amount of benedict's reagent 2. Put the test tube in a test tube rack in a bath of warm water 3. Wait until the changes have taken place 4. Remove test tube from the water bath Test for non-reducing sugars 1. Add a small amount of hydrochloric acid to a small amount of a sample of a non-reducing sugar solution 2. Wait for a few minutes for hydrolysis to take place 3. Neutralise the hydrochloric acid by adding a small amount of sodium hydrogen carbonate to the solution. 4. When the fizzing has ceased, add some benedict's reagent and heat in the water bath 5. Also put a test tube of the sample of the non-reducing sugar which has not been hydrolysed by the hydrochloric acid and sodium hydrogen carbonate. 6. Observe and record any changes Iodine Test for Starch 1. ...read more.

Conclusion

Once the lipids have been hydrolysed, the mixture of ethanol and the lipids are decanted into a test tube of water. A white precipitate is formed on top of the water if lipids are present. This is because lipids are hydrophobic and are trying to get as far away from the water as possible. When testing for non-reducing sugars, the glycosidic bonds must be hydrolysed by hydrochloric acid before performing the benedict's test for reducing sugars. In the biuret test for proteins, the sodium hydroxide in the biuret reagent breaks the peptide bonds linking the amino acids, this allows the copper to form a coloured substance with parts of the amino acids which shows the presence of proteins. Evaluation of the tests All the tests produced result as expected, despite having trouble with testing for non-reducing sugars in the unknown carbohydrate category. This was due to an excess of hydrochloric acid in the sample and the fact that the benedict's reagent had been added before the acid had been neutralised by the sodium hydrogen carbonate. Biochemical Tests - 1 - 27/04/07 ...read more.

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4 star(s)

A four star piece of work. Excellent introduction and description of each food test given. Great accurate set of results with an excellent scientific evaluation used. Overall this is a well planned experiment which shows a good understanding of each food test and how the results are achieved.

Marked by teacher Patricia McHugh 08/04/2013

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