What is Pigments and colour changes in vegetables??

 PIGMENT AND COLOUR CHANGES 

It is important for chefs to know the various kinds of pigments present in food and how they react to heat and various acidic and alkaline medium, as this would largely impact the style of cooking them. 

The colour of a vegetable is determined by the pigment it contains. Pigment is the colouring matter within the cells and tissues of the plant. 

The various types of pigments are affected differently by heat, acid, alkali, and other elements involved in cooking.

To maintain as much colour as possible in cooked vegetables, one needs to know about these pigments, Guests may reject vegetable dishes if they do not like vegetable has trace amount of acid present in it and we shall see how this acid could be used favourably. 

Flavones 

It is the pigment present in white vegetables. It is present in potato, onion, cauliflower, white cabbage, cucumber, zucchini, and the white of celery.

 This pigment stays white in an acid medium and turns yellow in an alkaline medium. Overcooking will also turn white vegetables yellow or grey This reaction is not reversible. 

Adding acid to yellowed white vegetables will not help in retaining their original white colour. 

Anthocyanin 

This pigment is present in red vegetables and it gives the their colour.

 It is present in very few vegetables, primarily red cabbage, purple peppers, purple potatoes, etc. It is strongly affected by acid and alkali mediums. 

An alkali medium wil turn them to a blue or bluish green colour. 

An acid medium will give them a brighter red colour. This red pigment is easily dissolved in water. 

The use of excessive amount of water while cooking will leach the colour out of the vegetable. 

Chlorophyll 

Green colour in green vegetables is due to the presence of a pigment known as chlorophyll, which is affected by pH.

 In an acid medium the colour of a green vegetable changes to olive green and in alkaline medium it changes to bright green. 

This is the reason why some cooks add cooking soda or any other alkaline medium while cooking greens. 

When a green vegetable is cooked covered, the plant's natural acid is leached into the cooking liquid and is trapped there creating an acidic cooking medium. 

This, combined with the heat present, destroys the pigment. Green vegetables should also be cooked uncovered so that the natural acids present, are expelled into the air. 

Carotene 

This pigment gives colour to yellow and orange vegetables such as carrot, corn, winter squash, sweet potato, tomato, and red pepper. 

This is the most stable of the colour pigments. It is only slightly affected by acids or alkalis.

 However, long cooking periods can make the colour of the vegetables dull. Short cooking times help retain the flavour and vitamins of most vegetables. 

Carotene pigment is fat soluble and leaches out into the fat used to cook the item. This is why red grease floats to the surface of stews and meat soups which contain tomatoes or carrots. 

Betalains 

The pigments in the root tissue of red beets are not chemically similar to anthocyanins; 

they contain nitrogen and are called betalains. Some of these pigments are purplish red, whereas others are yellow.

 Beets lose much pigment and become pale when they are pared and sliced before cooking, because the pigments are soluble in water and leach from the tissues.

  

Anthoxanthin 

The anthoxanthin pigment changes from white or colourless to yellow, as the pH increases from acidic to alkaline ranges. 

This pigment is widely distributed in plants and often occurs with anthocyanins. 

It may combine with some metals, such as iron, to form a dark, complex compound. When it combines with aluminium, a bright yellow colour is produced. The anthoxanthin pigment generally remains quite stable when heated.

If the cooking water is alkaline, the pigment may appear yellow. 

In case of excessive or prolonged heating, the pigment darkens.