Chemistry behind the Color of cooked Beans

Cooked green beans can be a vivid green color, or they can turn gradually less colorful, sometimes becoming greyish or brownish.  Generally salt is added to the water before boiling vegetables. The reasons given for this include:

  • It makes them greener
  • It makes them firmer
  • It raises the boiling point of water to make them cook faster
  • It improves the flavor.

Chemists studied the truth behind these claims and found that first 3 of them are totally false. Adding salt slightly improves the flavor. The increase in the boiling point is insignificant to make any difference in the cooking time.

English: Cut Green Beans Español: Habichuelas ...

The color of the beans is dependent on the pH of the cooking water. The green color is due to chlorophyll present in the beans. If the water is acidic, the Magnesium ion bound to the chlorophyll is replaced by hydrogen ions and color is discharged. So depending upon the pH, their will be different degree of color changes.

If you cook the beans in hard water which contain bivalent ions calcium and magnesium, the pectin sugars present in the beans become firmly attached to each other and form a nice three dimensional network and give it a nice firm texture. Soft water on the other hand, dissolves the pectin quickly giving the cooked beans a mushy texture.


Color Changes in Chameleons

We have been told that chameleons change their color to conceal themselves by blending in with their surroundings. In fact, a person who is changeable or inconstant in behavior is called chameleon. It has been proved that the facts are something else. And it is a myth. .  Most of the reason chameleons change colour is as a signal, a visual signal of mood and aggression, territory and mating behaviour.

The chameleons are master molecular scientists. Their skin has transparent layers in which different color compounds are tucked away. These specialized cells store the different color compounds and these cells are called chromatophores. They contain various pigments.  These are xanthophores, containing particular specialised pigments that have a yellow colour.  Beneath that are pigment cells which are called erythrophores which have a red colour in them.  Beneath that, another layer of cells called iridiphores have a blue coloured pigment called guanine, which is actually also used in making DNA.  And underneath that is another layer of cells called melanophores which have a brown pigment – melanin – in them.

As such these pigments are confined to sacs. Depending on the signals from the brain, pigments are leaked and depending on the amounts released, mixed colors are formed. This is like artist mixing the different amounts of colors in the color palette. So if you mix red and yellow, you get orange for example, and this is how chameleons do this.  They mix different contributions of these chromatophores.

So a calm chameleon is a pale greeny colour.  When it gets angry, it might go bright yellow, and when it wants to mate, it basically turns on every possible colour it can which shows that it’s in the mood.  This is not unique to chameleons.  Other animals also have these chromatophores. Cuttlefish are another very elegant example of how this works.  So it’s not so much to do with camouflage.  It’s more to do with communication.