BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE. 



ters is in the outer layers, this waste appears more important than is 

 generally realized. The mechanical potato parers now available 

 usually remove the skin with much less loss of edible material, and 

 they have the further advantage of saving time for all but very skill- 

 ful workers. There are a number of kinds on the market, which 

 either pare the potatoes in much the same way as is done by hand or 

 else rub off the skin. 



The carbohydrates stored in the potato form 18.4 per cent of the 

 edible portion. Most of this is starch, though there are also small 

 quantities of soluble carbohydrates or sugars. Young tubers have a 

 larger proportion of sugars and less starch than mature potatoes. If 

 the tuber lies in the ground the starch content increases for a time, 

 but when it begins to sprout part of the starch is converted by a 

 ferment in the tuber into soluble glucose. Thus, both young or early 



potatoes and old ones have a 

 smaller proportion of starch 

 and more soluble sugars 

 than well -grown but still 

 fresh tubers. 



Less than 0.5 per cent of 

 the carbohydrates is cellu- 

 lose, yet one sometimes 

 hears the statement that 

 potatoes are indigestible on 

 account of the large quanti- 

 ties of cellulose which they 

 contain. In reality there is 

 no more cellulose in the po- 

 tato than occurs in most of the cereals and in other vegetable foods, 

 and so such a criticism of the potato has no warrant in fact. 



Besides the carbohydrates mentioned, potatoes also contain a little 

 pectose, the French investigators quoted above reporting the pres- 

 ence of 0.2 to 0.4 per cent. Pectose, which is so important in jelly 

 making when it occurs in quantity, as in fruits, is believed to have 

 practically the same food value as other carbohydrates. 



Fat appears in such small quantities in potatoes that it may be 

 practically neglected in discussing their food value, especially as the 

 greater part occurs in a waxlike form in the inedible skin. 



The protein bodies are rather small in quantity, as compared with 

 those of cereals and such vegetables as peas and beans, and only about 

 80 per cent of the total amount present is available protein; that is, 

 protein in a form which can be used for the building and repair of 

 body tissues. This means that a pound of potatoes furnishes only 

 about 0.2 of an ounce of available protein and emphasizes the state- 



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of whole por^ro 



LOSS //V 



C/}J?£l rSS P£El /KG : 

 A0OVT Ort£ F/PTrt 



or H/z/O/Lf p>c?7?gro 



Pig. 4. — Loss of weight in peeling potatoes. 



