VITAMmS — MUNSELL 243 



alpha-, beta-, and gamma-carotene, and cryptoxanthin. Beta-caro- 

 tene is by far the most important and most widely distributed in 

 natural food products. Cryptoxanthin occurs in only a few foods. 



The carotenoids, like vitamin A, are soluble in fats and fat-solvents 

 and are not readily inactivated by heat except as oxygen is present. 



Food sources. — The vitamin-A precursors may occur in any part 

 of a plant root, stem, leaf, flower, fruit, and seed. There is con- 

 siderable variation, however, in the amounts present in foods of 

 plant origin. Many contain them in abundance, and some carry only 

 small amounts or none at all. 



An orange-yellow color in foods of plant origin indicates the 

 presence of one or all of the plant carotenoids from which vitamin 

 A may be derived and furnishes a rough index of vitamin-A potency 

 in many vegetables as well as in fruits. Carrots and sweet potatoes 

 are outstanding examples of this relationship. This index holds 

 good where there are yellow and white varieties of a given product. 

 Yellow turnips, yellow peaches, yellow corn, and yellow tomatoes 

 are sources of vitamin A whereas the corresponding white varieties 

 are not. To avoid confusion as to the application of these findings 

 a word of caution seems advisable here. The fact of the presence of 

 vitamin A in yellow varieties of foods is no reason for ignoring the 

 white varieties. They may have values the yellow ones do not have. 

 There is a place in the diet for all types of foods and there is little 

 or no reason for consistently using certain ones and excluding others. 

 Care should be taken to avoid applying factual information on food 

 values in a fanatical way. 



A yellow color is not invariably associated with vitamin-A po- 

 tency, for there are yellow plant-pigments that do not yield vitamin 

 A. A red color has no relation to vitamin-A value and is not indica- 

 tive of it except that in some foods a red color may mask the orange- 

 yellow of carotene. An example is the red-fleshed tomato containing 

 carotene either in the flesh or the skin. 



Experience has led to the recognition that a green color ^ in plants 

 indicates vitamin-A value. Green leaves, and more especially thin 

 green leaves like those of spinach, kale, dandelion, and leaf lettuce, 

 are among the richest sources of vitamin A. Other green foods that 

 are notable in this respect are green string beans and green peppers. 

 The stems of asparagus, celery, and broccoli, and many other plants, 

 may be appraised for vitamin-A value on the basis of greenness. 

 Bleached parts of plants that would normally be green but do not 

 have the green color, either because the chlorophyll never developed 



* Chlorophyll, the green coloring matter of plants, does not Itself form any part of 

 vitamin A, but the high concentration of this vitamin in parts of the plant where chlorophyll 

 functions has led to the suggestion that it may play a role In the formation of the vitamin. 

 Vitamin-A potency in other parts of the plant would in that case be due to substances 

 transported to them for storage. 



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