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I am doing an experiment on preservation of peas.

The first notable change to the peas over a period of one week is that they have changed colour from bright green to a dull colour... Why is this so?

The only test tube which did not have peas which changed colour was the one which was kept at 4 degrees Celcius in a fridge, so it probably has some relation to temperature...

Many thanks

N.B.: I know that the bacteria reproduce and could use the pea as their source of food, but how do they have any relation to the colour of the pea? I also put the tag "bacteria" and "thermodynamics" as I couldn't find any other related tags.

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Have you preserved them in a refrigerator ? –  biogirl Jan 26 at 19:08
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Might be interested in reading this –  biogirl Jan 26 at 19:10
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@biogirllajja Interesting, but I'll still have a look at the answers to this question... –  Tim Timmy Jan 26 at 19:13
    
I am tempted to post an answer, but I am not sure if it is ethical to do your homework for you completely. Do you have access to the full text of article biogirl lajja linked ? The introduction section, page 2, contains your answer. –  Barbara Jan 26 at 21:19
    
One more keyword - chlorophyll. –  Barbara Jan 26 at 21:22
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1 Answer

up vote 1 down vote accepted

Chlorophyll is a dye that makes leaves green, it plays a key role in photosynthesis. It is present also in unripe fruits, young peas etc. Maybe I should say chlorophylls, because it is a group of similar chemicals. They get degraded by heat.

(No assistence of microbes needed).

Bonus: Chlorophyll contains magnesium at the molecule core, which facilitates the green color. There were some creative people, who were upset, that the canned cucumbers are not green enough, so they added some copper-containing molecule during canning. It replaced magnesium and was more stable, so beautiful bright green cucumbers were on the market for a while. However, they turned out to be slightly poisonous and are not sold anymore.

Bonus 2: Most varieties of peas change color also naturally as they rippen. The seeds become yellow. The chlorophyll gets degraded in plant metabolism. The chloroplasts, i.e. the cell organelles responsible for photosynthesis change function to become storage organelles called leucoplasts.

(Edit: Ooops, I first wrote that chlorophyll supposedly contains iron. That was wrong, it is magnesium. Iron is present in a similar die called heme, which makes blood red. Probably I am getting too old :-) )

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