Name:______Date: ______

IB Biology -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

  • 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.

/ Maltose
/ Sucrose


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 -ATest all the Sugars with Benedict's Solution

  1. Label 4 test tubes with the names of each sugar.
  2. Put 5ml of each sugar into the correct test tube
  3. Add 10 drops of Benedict's solution to each sugar
  4. Put the test tubes into a water bath and start a stop watch.
  5. Record the colour of the Benedict's solution at regular intervals (you choose) for 5 minutes.

Method BTest the Pepsi Drinks with Benedict's Solution & then Iodine to test for starch

  • 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 CTest 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?

  • 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.