Have you ever wondered as to what each shade of colour in your most favourite vegetable indicate? You might not give it a thought while cooking and gorging them up, but colour or pigments in vegetables do have importance which signifies its health importance. Let’s see what these beautiful colours have got to tell us about them.
To begin with, there are three principle pigment categories and every pigment category has subgroups within it.
•Chlorophyll is the main pigment in green vegetables like broccoli, spinach, fenugreek, green capsicum, mustard greens, lettuce, etc.
•Carotenoids are the pigments which provide colour to the orange, red and yellow vegetables like tomatoes, yellow bell peppers, carrots, zucchini, pumpkin, etc.
•Flavonoids is the third group of pigments that give colour to the white, blue, purple and purplish-red vegetables like brinjals, radish, purple cabbage, etc. Within this only, there are two sub-groups: one that provides especially the white pigment as seen in cauliflower and this one is known as anthoxanthins and the other, anthocyanins which provides the rather deep reds, purples and blues like in beetroot, red bell peppers, etc.
These pigments not just provide colour to the vegetables, but also behave differently when cooked, and thus, this is the reason the results can be anything between pleasing to distinctly unpalatable. Because of this potential for negative changes, pigments require special consideration when planning cooking methods.
Keeping in mind these facts, boiling is one cooking process that comes first to the mind when the colour change in vegetables is thought about. The initial change in the original colour of vegetables, when plunged into boiling water is the result of the drastic change in temperature of water that apparently causes expulsion of the small amount of air between the cells, making pigments (particularly chlorophyll) appears even brighter than before heating. This abrupt start to heating vegetables has the added advantage of keeping cooking times as short as possible, which helps to avoid converting chlorophyll to pheophytin (a chemical electron carrier that helps in photosynthesis) and also aids in retaining nutrients. Further, the acidity or alkalinity of the water in which vegetables are being boiled modifies the colours of all pigments except the carotenoids.
If the water is acidic, the vegetables containing chlorophyll take on an olive-drab colour gradually while they are cooking or if the cooking period exceeds about 5-7 minutes. However, a slightly alkaline medium of the water promotes retention of chlorophyll. The flavonoids, both the anthoxanthins and the anthocyanins, retain a desirable colour in a slightly acidic medium, while alkali will cause poor colour.
Also, vegetable cells naturally contain some mild organic acids, but these acids may be released into the cooking medium, causing pigment changes to begin to develop. In the case of chlorophyll, the change will be towards an olive-green hue, a transition that should be avoided if possible. If green vegetables are boiled in an uncovered pan, the unstable organic acids will escape from the cooking medium, thus maintaining the water close to neutral. The desired chlorophyll pigment will be maintained by keeping the lid on pan, only until the water returns to boiling after the vegetable have been added and keeping the cooking time short.
The technique for boiling the flavonoids containing vegetables is the reverse of that for chlorophyll. Both the anthocyanins and anthoxanthins pigments are considered to be more desirable in an acidic than in an alkaline medium. Thus, using a lid on the pan retains the unstable organic acids and protects the pigments. Carotenoids can be viewed as pigments that are comparable in boiling water regardless of the fact acidity and alkalinity. There is no compelling reason either for using or not using a lid on carotenoids containing vegetables from the perspective of colour.
So, next time you want to cook a particular coloured vegetable and want to retain the colour as it is, remember these points for sure and you will surely end up with desired results!
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