Why does the colour leak out of cooked beetroot?

In the cells of a beetroot plant, a substance called anthocyanin is contained within the plasma membrane. It is anthocyanin, which gives the beetroot its characteristic blue/purple colour. If a cell is damaged in a beetroot plant and the membrane is broken, the anthocyanin 'bleeds' from the cells like a dye. It is this characteristic that can be exploited to test which conditions affect the integrity of the cell membrane.

Because we are experimenting with the effects of temperature on the membrane, we will place the samples of beetroot into a water baths of varying temperatures and measure the colour change in the water. Temperature is just one of the possible variables. Others include effects of poisonous substances such as alcohol and/or various solvents. The dependant variable (DV) in this experiment is colour change in water caused by anthocyanin leakage.

Apparatus:

• Core borer
• White tile
• Knife
• Ruler
• Water baths at 1, 20, 30, 40, 50, 60, 70 oC
• Beaker about 250cm3
• 2 boiling tube racks
• Crushed Ice
• 7 Boiling Tubes
• Thermometer (one per water bath)
• Colorimeter
• Cuvettes
• Stopclock
• Distilled Water
• Pipette for measuring 2cm3

Method:

• Cut sections for a single beetroot using the core bore (from the same beetroot each time). Cut 7, 1cm length slices from these sections.
• Place the slices in a beaker of distilled water and leave for 10 minutes to wash away excess dye.
• After these 10 minutes, place 7 labelled boiling tubes containing 5cm3 of distilled water into to baths at 1oC, 20oC, 30oC, 40oC, 50oC, 60oC and 70oC. Leave them for 5 minutes until the water reaches the required temperature. Place 1 beetroot slice into each of the boiling tubes and leave for 30 minutes in the water baths.
• Remove the beetroot slices and shake the water/solution to disperse the dye
• Switch on the colorimeter and set it to read % absorbance.
• Set the filter dial to the blue/green filter.
• Using a pipette accurately measure 2cm3 distilled water into a cuvette. Place the cuvette into the colorimeter, making sure that the light is shining through the smooth sides.
• Adjust the colorimeter to read 0 absorbance through clear water. Do not alter the setting again during the experiment.
• Place 2cm3 of the dye solution into a colorimeter cuvette and take a reading for absorbency. Repeat the readings for all the temperature and record the results.

Results: Table:

Graph:

Conclusion: After collecting and correlating the results, I have come to the conclusion that the hypothesis is correct in that an increase in temperature will damage and denature the membrane and cause the substances contained within the membrane to leak out. This has been shown by a steady increase in anthocyanin leaked out of plant cells measured by the colorimeter light absorbance, as the temperature increases.

There is almost certainly an amount of experimental error. It is the breakdown of the lipids which make up the membrane that causes 'holes' to appear in the membrane, allowing fluids to pass out freely, but when the temperatures begin to get higher still, the proteins in the cells begin to decompose as well which blocks some of the holes and therefore slowing down the release of anthocyanin.

Evaluation: It is safe to say that the results have been repeated reliably however it still would have been beneficial to have repeated the experiment more times to make certain that the results were not gained through chance or by an external factor. The control experiment used was highly accurate, using distilled water, which is the clearest possible liquid, meant that even the slightest deviation in colour could be detected by the colorimeter.