VEGETABLE AND FRUIT DEHYDRATION 



163 



alkaline solution the colors become unpleasantly weak or dull and 

 sometimes a complete change in hue, as from red to green or gray, 

 may occur. In the presence of salts of tin and iron, these anthocya- 

 nins develop metallic lusters, such as occur in canned sour cherries 

 or berries when the lacquer on the can is imperfect. These are un- 

 pleasant, although usually harmless. 



White vegetables are colorless because the pigments are largely 

 flavonols, and these are present in the colorless forms. When heated 

 in mildly alkaline solution, the brilliant-yellow forms are produced. 

 Thus yellowish-white or pale-yellow colors are typical of cooked cauli- 

 flower, potatoes, cabbage, and onions. These flavonol pigments are 

 also soluble in water. 



The orange or orange-yellow vegetables, such as corn, carrots, and 

 rutabagas, contain large quantities of carotinoid pigments. These 







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 AT 78° 



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Figure 71. — Effects of slice thickness on coefficient of rehydration of carrots : 

 a, one-eighth-inch slice ; 6, three-sixteenths-inch slice. 



are not soluble in water and they are little affected by either acid 

 or alkali solutions. However, the vegetables containing carotinoid 

 pigments also contain flavonols and a minor change in color in 

 alkaline solution, due to these latter pigments, will occur. 



The dominant colors in green vegetables are the chlorophyll pig- 

 ments. Chlorophylls are generally insoluble in water. The rich 

 green color is destroyed in acid solution and the vegetable becomes 

 a drab dull yellow or olive green, while in very mildly alkaline solu- 

 tion a lighter, more brilliant green is produced. Again, these vege- 

 tables contain flavonol and carotinoid pigments, which are invisible 

 because of the green but which may contribute to the color when 

 the green is destroyed. 



Since both drainage and well waters may be mildly alkaline, the 

 use of these in reconstitution tests may produce a light cream or 

 yellow color in white vegetables, a brilliant green in green vegeta- 

 bles, a purple, green, or gray in red vegetables, but will cause little 

 change in the orange or red of carrots and tomatoes. These mildly 



