Vegetable pigments

Vegetables are important part of our daily diet, It has essential nutrients that helps in normal functioning of the body. Pigments present in them are responsible for the colour before and prior to cooking. They too have nutritional aspects

1. VEGETABLE PIGMENTS Jyoti Pachisia 1

2. Vegetables are plants or parts of plants that are used as food. The term vegetable has through usage come to apply in a more narrow sense to those plants or parts of plants that are served raw or cooked as a part of the main course of a meal . The bright colours of many vegetables contribute much to their appeal. The colour result from the various pigments contained in their tissues. 2

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4. Vegetable Pigments Water insoluble Water soluble Carotenoids Anthocyanins Chlorophyll Betalins Anthoxanthins 4

5. WATER INSOLUBLE PIGMENTS 5

6. CHLOROPHYLL The green pigments of leaves and stems are usually held close to the cell wall in small bodies called chloroplasts along with some carotenes and xanthophylls. Chlorophyll-a is intense blue green in colour present in the florets of blue-green broccoli Chlorophyll-b is dull yellow green in colour present in stalks. Chlorophylls are mostly insoluble in water and dominant in unripe fruits. 6

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8. EFFECT OF COOKING ON CHLOROPHYLL All green leaves and green- colour vegetables like beans and peas contain chlorophyll. The structure and conjugation of proteins makes chlorophyll to chemical changes in cooking and the pleasant green colour is difficult to retain 8

9. Effect of cooking French Beans Effect of cooking leafy vegetables 9

10. Effect of putting in hot water: When a green vegetable is put in boiling water, the green colour becomes brighter. Solubility in water : Removal of the phytyl group from the molecule of chlorophyll is found in some vegetables. Hydrolysis of the ester linkage yields a compound chlorophyllide which is water soluble. A limited amount of chlorophyllide produced during storage of certain green vegetables prior to cooking possibly accounts for the light green tint of the cooking water from them. Effect of prolonged cooking : As the cooking process continues the colour of the green vegetables varies from the bright green colour of chlorophyll to the olive green. 10

11. A B C D Figure shows the effect of cooking on chlorophyll A - Raw vegetable B - Effect of acid C - Effect of alkali D - Effect of prolonged cooking 11

12. Effect of cooking time on chlorophyll reaction Cooking time (minutes) Percentage chlorophyll retention Appearance 100 Green 5 74 Green 10 62 Green 20 36 Brownish green 60 Yellowish As cooking continues, constituents including organic acids diffuse from the vacuoles throughout the cell and into the cooking water. 12

13. Effect of acid : A pale greenish gray compound known as pheophytin -a or an olive-green pheophytin -b results. No longer masked by the intense chlorophyll, the yellow and orange pigments in green tissue now show alongwith the green. This combination together with pheophytins give the vegetable a muddy olive colour . Green vegetables which are lower in acid retain the higher percentage of chlorophyll when they are cooked than do more acid vegetables Effect of canning : Vegetables like peas, beans, greens are sometimes canned. During canning, cholorphyll gets converted to pheophytin due to high temperatures used Effect of sodium bicarbonate : With this, the phytyl and methyl groups of chlorophyll are displaced and a bright green water-soluble chlorophyllin is formed which gives the cooked green vegetables an intense artificial greenness. 13

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15. Effect of freezing : The better retention of colour of frozen green vegetables is due to elimination of major part of the plant acids by blanching prior to freezing Effect of copper : The colour of chlorophyll is enhanced in the presence of copper and weak acid Effect of calcium salt : Addition of a small amount of calcium acetate or other calcium salt prevents the mushiness by blocking the breakdown of the hemicellulose. Mushy brussel sprouts 15

16. Chlorophyll can be retained best: By starting with boiling water which in turn reduces the actual time required to tenderize. Vegetables should be cooked less than 5 minutes as pheophytin forms between 5 and 7 minutes By using slight excess of water to dilute the acids By initially cooking in an open pan 16

17. CAROTENOIDS These are groups of yellow, orange, rat and fat soluble pigments widely distributed in nature Depth of carotene does not always indicate Vitamin A value as many carotenoid pigments cannot be converted to vitamin A. 17

18. Carotenoid Pigments in Food FOOD PIGMENTS Yellow Corn Cryptoxanthin Tomatoes Lycopene , β -Carotene Red Capsicum Cryptoxanthin , Capsorubin , β -Carotene, Violaxanthin , Capsxanthin Green Capsicum Lutein , β -Carotene, Violaxanthin and Neoxanthin Carrots β -Carotene, α -Carotene, ϓ -Carotene, lycopene , Xanthophyll Of all carotenoids, β -carotene is valuable in the synthesis of Vitamin A 18

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20. The colour is little affected by acid, alkali and the volume of the water. The nutritive value is protected during cooking by the insolubility in water. The high degree of unsaturation of carotenoids makes them susceptible to oxidation with the resulting loss of colour after the foos containing them has been dried. The finer the vegetable divided or cut and higher the temperatures that are used and longer cooking process can hasten the process of oxidation Appreciable amounts and enough to affect the colour will dissolve in ghee when carrot halwa or kheer is made. Blanching prior to dehydration is helpful in reducing the likelihood of oxidation. Blanching makes lipids free from proteins with which they are complexed as lipoproteins EFFECT OF COOKING ON CAROTENOIDS 20

21. A B C D Figure shows the effect of cooking on Carotenoids A - Raw vegetable B - Effect of acid C - Effect of alkali D - Effect of prolonged cooking 21

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23. WATER SOLUBLE PIGMENTS 23

24. ANTHOCYANINS It has cyanidin with attached sugars Cherries, red apples, various berries, blue and red grapes, Pomegranates and currants, Radishes and sweet potatoes achieve their colour appeal because of predominance of anthocyanins. Anthocyanins present in brinjal is water-insoluble in nature Anthocyanidins are anthocyanins without sugar in their structure e.g., delphinidin. 24

25. 25 FOOD SOURCES OF ANTHOCYANINS

26. Effect of pickling : Pickles are usually low in pH and anthocyanins change to deep crimson red in colour Effect of method of cooking: Anthocyanins are water-soluble cell sap pigments which can be leached from a vegetable by the cooking water. Cooking in a steamer or in a pressure pan which limit the contact of the vegtable with water are better methods than boiling in water.. To retain the red colour in red cabbage, the cooking water should be acidified otherwise the pigment will change to a dull and unappetising blue. Effect of alkali: Addition of alkali gives the pigment a bluish green shade which is probably caused by the anthocyanins + anthoxanthins. On the addition of alkali, the anthoxanthins turns yellow whereas anthocyanins turns blue and a mixture of two colours appear green. Such a colour can be seen in red cabbage 26 EFFECT OF COOKING ON ANTHOCYANINS

27. 27 Figure shows the effect of cooking on Anthocyanins: A - Raw vegetable B - Effect of acid C - Effect of alkali D - Effect of prolonged cooking A B C D

28. Effect of acid: Red cabbage exhibits unusually wild swings in colour with a change in pH because of the presence of more than four hydroxyl groups on the anthocyanin molecule. Red cabbage is frequently cooked with the addition of some slices of a tart apple to ensure that the pH is sufficiently acidic to avoid the development of a blue, highly unpalatable pigment colour. Effect of metal: Special enamel linings in the cans are used when canning anthocyanin containing fruits and vegetables. Unusual colours ranging from green to slate blue, develop when anthocyanins contact iron, aluminum and undesirable colour changes of anthocyanin compounds. Iron and aluminum produce considerable discoloration. The presence of ascorbic acid with copper or iron accelerates the oxidation and undesirable colour changes of the anthocyanin compounds 28

29. BETALAINS Betacyanins and betaxanthins are together known as betalins. High ratio of betacyanin to betaxanthin lead to violet, medium to red and low to orange tuber colours. The water-soluble pigments present within the betacyanin group are betanidin and betanin. A somewhat yellow pigment is contributed by the betaxanthins 29

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31. EFFECT OF COOKING ON BETALAINS Betalains diffuse rapidly into the cooking water resulted in highly pigmented water. Effect of pH : Betacyanins undergo colour changes parallel to anthocyanins. An acidic medium promotes reddish colour whereas a neutral or somewhat alkaline pH brings out brownish blue of the pigment. 31

32. A B C D Figure shows the effect of cooking on Betalains A - Raw vegetable B - Effect of acid C - Effect of alkali D - Effect of prolonged cooking 32

33. ANTHOXANTHINS They are colourless or pale yellow pigments (depending on the pH) closely related to anthocyanins They are water-soluble occurring in the vacuoles of the plant cells. Anthoxanthins give colour to cauliflower, onions and spinach or other leafy vegetables (In green leafy vegetables, the colour is masked by chlorophyll) 33

34. 34 Food sources of Anthoxanthins

35. Effect of pH: The colour of the vegetable will be whiter if little acid such as lime juice or vinegar is added during cooking. If the water in which cauliflower is cooked is slightly alkaline, it will have a distinctly yellow colour to it. They turn yellow or orange in the presence of alkali. Effect of metal: They cause the cooking water to turn a bit yellow when they are cooked in aluminum pans because the flavones scavenge aluminum and form a flavone aluminum chelate. Such reactions also takes place in cast iron pans. Pears and white potatoes sometimes develop a pinkish colour in their cut surface. Apparently this colour change is due to conversion of the proanthocyanin to the pigmented and closely-related compound cyanidin. 35 EFFECT OF COOKING ON ANTHOXANTHINS

36. 36 Figure shows the effect of cooking on Anthoxanthins: A - Raw vegetable B - Effect of acid C - Effect of alkali D - Effect of prolonged cooking