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Why does the colour leak out of cooked beetroot?

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Introduction

Why does the colour leak out of cooked beetroot? The aim of this experiment is to investigate the effect of temperature on the membrane structure of beetroot cells. I predict that as the temperature increases, the amount of pigment leaked out of the cells will increase. The cell membrane and the membrane of the vacuole (tonoplast) are made up of a phospholipid bi-layer, with protein channels and ion pumps to allow the diffusion and active transport of ions. Excessive heat causes the hydrogen bonds that hold the protein in its specific shape to break, causing it to malfunction. This will mean that the diffusion of molecules is no longer restricted, so in this case, the betalains can diffuse out of the vacuole and cell, and into the surrounding water, colouring it red and causing it to absorb more green/blue light. After a certain temperature, the % absorbance will level off, as there is only so much dye in the sample of beetroot to diffuse out. I expect a graph of the results to look like this: % Absorbance Temperature The variable I will be changing is the temperature of the water that the beetroot is submerged in. I will control this using water baths and check it using a 100�C thermometer. The variable that will change as a result of this will be the blue/green light absorbance of the beetroot's water. ...read more.

Middle

measures 1 cm pieces of beetroot o Constant temperature water baths with thermostats set to 20, 30, 40, 50, 60 and 70�C provide constant temperature for water surrounding beetroot o Boiling tube rack holds boiling tubes while pipette is filled o 6 boiling tubes hold beetroot and surrounding water o Thermometers (100�C) check temperature of water baths o Colorimeter (and cuvettes) measures colour of water objectively o Stopwatches monitors time beetroot has been heated o Distilled water allows betalains to diffuse out of beetroot o 5cm3 pipette (and filler) measures solution for cuvettes o 10cm3 measuring cylinder measures distilled water to surround beetroot Method o Using a size 4 cork borer, cut sections from a raw beetroot. Cut each section into 1cm lengths, discarding the skin. o Allow the beetroot pieces to soak in distilled water for 5 minutes, then drain them, refill with fresh distilled water, and allow to soak for another 5 minutes to wash off surface betalains from damaged cut cells. o Using the measuring cylinder, place 5cm3 distilled water in each boiling tube, and place each boiling tube in a different water bath. Leave until the distilled water has heated to the correct temperature. o Add one piece of beetroot to each boiling tube and start the stopwatch. Leave for 30 minutes. o Remove the beetroot piece and shake the solution to disperse the dye. ...read more.

Conclusion

The half-life of betalain pigment is 413 minutes at 25�C but only 83.5 minutes at 60�C. Beetroot Pigments and Membranes - Ian White, Godalming College, 2003. This could mean that even though more betalains were leaked, some broke down before we tested the absorbance. Evaluation As the beetroot at 70�C was not in a water bath - the test tube was placed in a beaker of water which had to be topped up with boiling water if it cooled down - the temperature was not kept constant. This will have affected the results, as the hydrogen bonds in the carrier bonds may have re-broken and re-formed many times. This probably meant the results for the absorbance were too low, since the hydrogen bonds reforming would restrict the diffusion of the betalains. The beetroot pieces were left in the water for different times, since only one cuvette of solution could be tested at any one time. This will also have affected the results. The higher temperatures were left in for longer, so the percentage absorbance is probably too high because of this factor. The use of the ruler incurred a 5% error when measuring 1cm pieces of beetroot. This was unlikely to have heavily influenced the results. Measuring out the 5cm3 distilled water carries an error of �0.05cm3. This is a 10% error, which may have affected the results by making the solution either too dilute or too concentrated, which in turn would have made the percentage absorbance either too high or too low. ...read more.

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