CAPE BIOLOGY
LAB #1
UNIT 1
FOOD TESTS
DATE:
TITLE: Identification of biochemicals in pure form and in food samples.
AIM:
1.To carry out tests on the pure form of reducing sugars, starch, proteins and lipids to master techniques
and become familiar with the colour changes.
2. To identify the biochemicals present in pizza, apple, milk and fruit juice.
INTRODUCTION:
Carbohydrates are classed into three groups, monosaccharides, disaccharides and polysaccharides.
Monosaccharides are reducing sugars and include glucose and fructose. They can be identified by the Benedict’s
test. Disaccharides are non-reducing sugars and include sucrose and maltose. To identify a disaccharide, a nonreducing sugar test is done which first involves the acid hydrolysis of the disaccharide and then the Benedict’s test
is carried out. Polysaccharides are insoluble molecules such as starch and can be identified by the Iodine test. In
the presence of starch, iodine molecules become entrapped within the starch molecules forming a starch-iodine
complex that has a blue-black colour.
Fats are compounds made up of fatty acids and glycerol. Lipids or fats can be identified in a variety of ways, but
the most popular is the Emulsion test and the Grease Spot test. When shaken with water, fats will form an
emulsion that is cloudy white or opaque.
Proteins are polypeptides made from amino acids held together with peptide bonds. They are the most abundant
organic molecules to be found in cells, and have a wide range of structural and metabolic activities within the
organism. Proteins can be identified using the Biuret test. In the Biuret test, Biuret reagent made up of sodium
hydroxide and copper sulphate which is blue will react with the peptide bonds and turn purple. Hence a purple
colour indicates a positive reaction for proteins.
APPARATUS AND MATERIALS:
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Waterbath
Tripod stand
Bunsen burner
15 test tubes
Test tube holder
5 5ml syringes
Teat pipette
Labels
Glass rod
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Benedict’s solution
Dilute HCl
Ethanol
KOH or NaOH
CuSO4
I2/KI solution
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Sucrose solution
Glucose solution
METHOD:
See: Biological Sciences by Taylor, Green and Stout – Page 111- 113
Remember: Write in past tense.
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Starch solution
Oil
Egg solution
Milk
Fruit juice
Pizza
Apple
CAPE BIOLOGY
UNIT 1
FOOD TESTS
RESULTS:
Table showing the colour changes to identify pure form of biochemicals and those present in foods.
TEST
BENEDICT’S TEST
REDUCING SUGAR
TEST
STARCH TEST
EMULSION TEST LIPIDS
BIURET TEST PROTEIN TEST
SOLUTION TESTED
Glucose
Bread/ pizza
Apple
Milk
Juice
Starch
Bread/ pizza
Apple
Milk
Juice
Oil
Bread/ pizza
Apple
Milk
Juice
Egg albumen
Bread/ pizza
Apple
Milk
Juice
OBSERVATIONS
INFERENCE
DISCUSSION: This has to be an explanation of the steps in your method, and an explanation of what you observed.
POINTS TO DISCUSS:
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6.
Discuss the basis for each test with respect to the pure sample tested. – bonds involved in forming the
colour changes observed. Include also:
a. Why is Benedict’s solution blue?
b. Why are reducing sugars so called?
c. How does starch interact with iodine molecules?
If you test a food and find that it contains a simple sugar (reducing sugar), there is no point in doing the
non-reducing sugar test. Why not? but answer the following:
a. What is the purpose of the HCl and the NaOH in the non-reducing sugar test?
Why did you cut food into small pieces and try to dissolve it in water before you did the food tests?
Discuss what the results showed with respect to each biochemical that was found in the food tested; and
possibly state the amount of reducing sugar present in each food stuff.
Give an overall statement on the nutritional content of the bread/pizza, apple, milk and juice.
Which of those four food stuffs would be best to give a baby, a young boy, an adult, etc?
CONCLUSION:
This must be a statement (paragraph) related to your aim, and of course, summarise your findings based on your
results.
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