Name:________________________
IB Biology -
Date: ________________
Analysis of the sugars in a range of "Pepsi" drinks
Aim
To investigate a new range of Pepsi Cola drinks: Pepsi Mix, Pepsi Max,
Pepsi Mox. Your task is to find out which sugar is used in each drink.
The sugar could be glucose (monosaccharide in all cells), maltose
(disaccharide from seeds), starch (polysaccharide), sucrose (disaccharide,
cane sugar).
We can use two simple food tests to find out. Benedict's Reagent to test for
glucose (reducing sugars) and Iodine to test for starch.
Apparatus
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Dropping pipettes
Measuring cylinder
Benedict's Reagent (dropping bottle)
Iodine Solution (dropping bottle)
Amylase solution 1% x 100ml
Waterbath set to 80°C
Stopwatch
Dilute solutions of sucrose, glucose, starch, maltose (for testing)
Bottle of Pepsi MIX, 100ml
Bottle of Pepsi MAX 100ml
Bottle of Pepsi MOX 100ml
Information
Benedict's reagent tests for reducing sugars. Glucose and Maltose are
reducing sugars.
The pink glow in the diagram below is the reactive part of a glucose molecule
which reduces the Benedict's Solution.
Sucrose
Maltose
Glucose is the best reducing sugar because every ring has a "reducing
group". Maltose is not as much a reducing sugar than glucose. It is a
disaccharide made from two glucose molecules but it has used up one
reducing group to join the two glucose molecules. It does change the
Benedict's solution but more slowly than Glucose.
You will have to time the colour change to see this difference and ensure that
the other variables: volume of Benedict's solution, Volume of Sugar Solution,
Temperature of water bath, are the same each time.
Sucrose usually causes no change to any of the indicators. (Occasionally
Benedict's reagent turns green, perhaps because of impurities.) It has no
reducing group available.
Starch changes the colour of iodine. Non of the others cause the iodine to
change colour from brown to "blue-black". It has no effect on Benedict's
reagent because all the reducing groups are used to hold the chain of glucose
molecules together. (see arrows below).
Method -A
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Test all the Sugars with Benedict's Solution
Label 4 test tubes with the names of each sugar.
Put 5ml of each sugar into the correct test tube
Add 10 drops of Benedict's solution to each sugar
Put the test tubes into a water bath and start a stop watch.
Record the colour of the Benedict's solution at regular intervals (you choose)
for 5 minutes.
Method B
Test the Pepsi Drinks with Benedict's Solution & then Iodine to
test for starch
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Test all of the "Pepsi" drinks with the Benedict's reagent and Iodine.
Remember with Benedict's Reagent you have to put the test solution in a hot
water bath for a few minutes. You will need to time this change. The iodine
does not need heating.
Record your results in a table of your own design.
Extension-
Method C
Test the way the Pepsi drinks will react in the
Mouth.
Will the drinks change their taste while they are in your mouth? We can test
this using the enzyme amylase which is normally found in saliva. If it breaks
down the sugar then the drink will become sweeter as the sugar is breaking
down.
Does amylase break the bonds between the glucose molecules in the
maltose, or the bonds in the disaccharide sucrose molecules?
Does it break down the polysaccharide starch into glucose or maltose?
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Add 2ml of amylase enzyme to the "Pepsi" drinks and put in a water bath at
40oC for 5-10 minutes.
Retest the enzyme digested drinks with the Benedict's and Iodine.
Record your results in your results table.
Write a conclusion of your findings, point out any errors in the results
Evaluate the experiment for accuracy etc
Results
Design a table or results for Method A & B
This can be used for IB assessment of your Data Collection.