Why does the colour leak out of cooked beetroot?

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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. I will measure this using a colorimeter, calibrated using a cuvette filled with distilled water as 0% absorbance. I will use the blue/green filter as the betalains will turn the water pink/red, meaning the water will absorb more blue/green light if it contains more pigment.

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This table shows the variables that I will control in order to keep the experiment a fair test:

Equipment

  • Raw beetroot provides betalains
  • Size 4 cork borer cuts beetroot into precise cylinders of the same diameter
  • White tile protects desk when beetroot is cut
  • Knife cuts beetroot into 1cm pieces
  • Ruler (with 1mm intervals) measures 1 cm pieces of beetroot
  • Constant temperature water baths with thermostats set to 20, 30, 40, ...

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