POTATOES AND OTHER STARCHY ROOTS AS FOOD. 7 
ment that potatoes alone make a very incomplete diet; only a very 
small amount of nitrogenous material would be obtained from 
a quantity of potatoes sufficient to supply the body with all the 
energy-yielding material required. 
The protein has been found to consist in part of a form of globulin, 
for which the name tuberin has been suggested. Other nitrogenous 
compounds present are a proteose, asparagin, and amino acids. 
The most important mineral matters found in potatoes are potas- 
sium and phosphorus compounds. There are several organic acids 
(such as citric, tartaric, and succinic acid 1 ), which vary in tubers of 
different ages and account in some measure for the flavor of potatoes. 
The potato, like many other foods, also contains minute amounts 
of physiologically active substance or substances valuable in nutrition 
and commonly called vitamins. 2 
The question is often asked, why the outer surface of freshly pared 
potatoes turns brown. According to experimental evidence this 
change is due to the action of enzyms, or ferments, naturally present 
in the plants. In the presence of the oxygen of the air they work 
upon tannin-like bodies in the tuber in such a way that the latter 
change color. This browning may be prevented by putting the pared . 
tubers into plain cold water or, better, into salted water. 
COOKING. 
When boiled, the temperature of the interior of the potato does 
not exceed 212° F. (the temperature of boiling water). When baked, 
the temperature of the interior of the potato reaches 212° F., but 
does not exceed it, if cooked only until it is done. If overcooked, 
the temperature may be considerably higher, which may account for 
changes which cause the peculiar taste of overbaked potatoes. The 
heat affects the various constituents of the potato in different ways. 
The water expands into steam, part of which evaporates from the 
surface. Within the minute cells making up the tuber it presses so 
hard against the walls "that the tough cellulose is ruptured, just as 
any air-tight vessel may be broken by the pressure of expanding 
steam. The starch grains inside the cells are thus released, some of 
them being also disintegrated, while part are changed into the soluble 
1 In proximate analyses such as those given on page 5 these acids would be included 
in the " carbohydrates," a matter of analytical convenience, not of chemical accuracy. 
Proximate analyses, it should be remembered, are designed to show group characteristics, 
and not the individual compounds which more detailed analyses would deal with. 
2 The vitamins are apparently in part dissolved in the juice and in part stored with 
the starch of the cortical layer of cells. Exactly what is their nature and the part they 
play in human nutrition is not yet fully understood, but recent investigations suggest 
that they do important work in regulating cell metabolism and are possibly concerned in 
the process of growth. It is not unlikely due to some of these compounds that potatoes 
prevent scurvy on shipboard or in other circumstances where fresh fruits and vegetables 
are not to be had. 
