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yy, BULLETIN No. 468 ¥g

Contribution from States Relations Service yy
A. C. TRUE, Director.

Washington, D. C. PROFESSIONAL PAPER : January 17, 1917

POTATOES, SWEET POTATOES, AND OTHER
STARCHY ROOTS AS FOOD.

By C. KF. LANaGwortHy, Chief, Ojfice of Home Heonomics, States Relations

Service.
CONTENTS.
Page Page
IOC UCTION: feanes oe VE Ee Sad oe ee 1 | The Jerusalem artichoke..................-.. 21
TPCOLEN SOLIS a a SS I ak AO OL CO DO 2 | Some tropical starch-bearing roots..-.......- 22
BWEObIPOLALOCS se ee ge ee es 17°) Conclusion: sac ea) s NO oe ek A Ta 23
INTRODUCTION.

Among vegetable food products those plants are very important
which lay up a supply of edible material during the favorable days
of summer in the form of thickened roots or underground stems and
bulbs. These root vegetables have different habits and characteris-
tics and accordingly belong to separate botanical groups; some axe
well known the world over, while others are rarely seen outside of
their native country. For convenience in discussing food problems
they may be divided into two groups: (1) Those which, like potatoes
and sweet potatoes, contain a fairly high proportion of food material,
chiefly starch and other carbohydrates; and (2) those like beets,
turnips, parsnips, and so on, which, although they resemble the first
group in many ways, nevertheless are different from them in other
respects, being more succulent, quite commonly of higher flavor, and
used in the diet in a Somewhat different way. This group is dis-
cussed in another ies Weenant bulletin. |

1U. S. Dept. Agr., Bul. 503.

Note.—This bulletin, which is a ROrision in part of Farmers’ Bulletin 295, summarizes
the results of experimental and other data regarding the nature and uses of potatoes and
other starchy roots as food, and is primarily of interest to housekeepers and to teachers
and students of home economics, 1

61353°—Bull. 468—17 1

2 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE.

in the pages which follow attention is paid particularly to the
potato, sweet potato, and Jerusalem artichoke; and more briefly to
the yam, cassava, dasheen, taro, and yautia—roots commonly known
in our island possessions and to at least a limited extent in the
United States proper. It is almost needless to say that the white,
or common, potato, judged both by the extent to which it is grown
and by its food value, is by far the most important representative
of the starchy-root group. Next in importance comes the sweet
potato, which is well known all over the country and is a staple root
crop in a large area of the more southern portion of the Southern
States. What a prominent place these two together hold in the diet
may be seen from the fact that in 376 American dietary studies they
were found to furnish an average of 12.5 per cent, or about one-eighth
of the total food material, and 8.3 per cent, or about one-twelfth of
all the carbohydrates eaten.

POTATOES.
HISTORY AND EXTENT OF CULTIVATION.

The potato, called in different regions white potato, Irish potato,
English potato, or round potato, was first introduced into Europe
from America toward the close of the sixteenth century by both
the Spaniards and the English, in the latter case as a result of the ex-
peditions sent by Raleigh to the Virginia colony. It is believed to be
a native of western South America, where wild forms are still found.

In 1915 the potato crop in the United States totaled, in round
numbers, 359,000,000 bushels, valued at $221,000,000. Part of the
annual crop is used for feeding farm animals, and the poorer grades
of tubers for manufacturing purposes, but the greater part is served
on our tables.

STRUCTURE AND COMPOSITION.

The food value and cooking quality of a potato depend upon its
structure and composition. The tuber is in reality a modified stem,
shortened and thickened to form a storehouse for material held in
reserve for the early growth of new plants. As in all other plant
forms, the framework of the tuber is made up of cellulose, or crude
fiber. This carbohydrate forms the walls of the multitude of tiny
cells, which make up the structure of the i and which vary in
shape and size in different sections of the tuber according to the part
they play in its life. The tuber has several distinct parts not
all equally nutritious. If a crosswise section of a raw potato be held

———-—_ << - -~- -

POTATOES AND OTHER STARCHY ROOTS AS FOOD. 3

up to the light four distinct parts may be seen (fig. 1). The outer
skin consists of a thin, grayish-brown, corky substance correspond-
ing roughly to the bark of an above-ground stem, which is ot

Fig. 1.—Transverse and longitudinal sections of the potato: a, Skin; b, cor-
tical layer ; c, outer medullary layer; d, inner medullary area.

in natural condition; b, cells of a partially cooked potato; c, cells of a thoroughly
boiled potato.

little value as food (see p. 5). The cortical layer (bark) is next
to the skin and may be from 0.12 to 0.5 inch in thickness. This

layer is slightly colored and turns green if exposed to the light for

some time, thus showing its relation to the tender green layer beneath

4 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE.

the bark of above-ground stems. Besides starch the cortical layer
contains a higher percentage of the mineral matter, soluble carbo-
hydrates, soluble nitrogenous matter, and acid substances than the
tuber as a whole. In the interior or flesh of the tuber lie the stored
starch grains (see fig. 2). This portion is made up of two layers
known as the outer and inner medullary or pithy areas. The outer
one forms the main bulk of a well-developed potato and contains
the greater part of the food (starch and other ingredients), the
proportion of the different carbohydrates! varying with the stage
of growth, degree of ripeness, and similar factors.. The inner medul-
lary area, sometimes called the core, appears in a cross section of
the tuber to spread irregular arms up into the outer area so that
its outline roughly suggests a star. It contains slightly more cellu- —
lose and water and food material than the outer medullary por-
tion. If it is overdeveloped, the potato is likely to be soggy when
cooked.

The relative proportions of the different parts of the tuber vary
with variety and doubtless other factors. According to determina-
tions made in connection with the department’s studies of the food
value of local-grown potatoes, it was found that the actual skin, as
distinguished from the portion usually pared off and sometimes
called the peel, made up about 2.5 per cent of the whole, and the
cortical layer 8.5 per cent, leaving 89 per cent for the medullary
areas. According to average values reported by French observers,?
the skin made up 8.8 per cent of the tuber and the cortical layer 36.2
per cent, while the outer medullary area made up 34.2 per cent and
the inner medullary area 15 per cent, or the two together 49.2 per
cent.

The composition of the potato varies with the variety, the char-
acter of the soil, the climate, and other conditions under which it
grows—a fact taken advantage of when the grower plants potatoes
in sandy soil with the expectation of getting a mealy tuber. The
needs of the potato plant, and consequently the composition of the
tuber, also vary at different stages of its growth, a young potato be-
ing more watery and less starchy than one fully ripe. As a result
of many analyses the average percentages of the different food ingre-
dients in potatoes are now well established. The figures in Table I
show the composition of raw and cooked potatoes and, for com-
parison, the composition of white bread. )

wat tT.

1In this connection it is well to recall that the carbohydrates (starch, the different
kinds of sugar, pentoses, cellulose, etc.) are all closely related and that under the
influence of ferments. certain acids, heat, or other agency, an insoluble form, such as
starch, may be changed into a soluble form, such as sugar, or vice versa—a kind of
change which takes place in nature, as for instance in the developing and ripening tuber
or seed and is also important in food manufacture and in digestion and assimilation.

2Coudon and Bussard. Ann. Sci. Agron, 2. ser., 3 (1897), I, No. 2, p. 250.

——-

POTATOES AND OTHER STARCHY ROOTS AS FOOD. ie

TABLE I.—Composition of raw and cooked potatoes.

As the table shows, the refuse, that is, the part removed in prepar-
ing potatoes for eating either before they are cooked or at the table,
makes up on an average about one-fifth of the whole tuber, and the
part commonly eaten, that is, the edible portion, four-fifths. Water
is the most abundant constituent of the potato and forms about three-
fourths of the edible substance. The remainder is mostly starch,
though there is a little nitrogenous matter (protein) and fat. The
amount of mineral matter (ash)
is actually small, but as compared
with that in other foods it is rela-
tively high, and is of much value
in nutrition. Figure 3 represents
in graphic form the composition
of the edible portion of the po-
tato and shows even more plainly
than the table that the bulk of the “70747 7~
potato tuber is water.

Theoretically, the skin is the
only refuse or inedible material in
the potato, but in practice a con-

WATER TBS

Fic. 3.—Percentages and loss in digestion

siderable part of the edible por- of nutrients of the potato. Shaded
: : : : portion shows a loss in digestion of 15
tion 1s removed with rt (fig. 4). per cent of the protein and 1 per cent

When the surface is irregular, or of the carbohydrates.

the tubers have shriveled in storage, a much greater proportion of the
flesh is likely to be cut off with the skin in paring than is the case when
the tubers are smooth and in good condition. It is estimated that in
paring raw potatoes by household methods the loss is about 20
per cent. This includes not only all of the skin and the corti-
cal layer, but also 9 per cent of the flesh. When we recall how large
is the proportion of water and how low that of nutrients in the tuber,
and also that the larger proportion of the protein and mineral mat-

6 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 lessstarch 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 havea
smaller proportion of starch
LOSS / and more soluble sugars
GL eenniy | ©vhan well-grown but still
OF WHOLE POTATO fresh tubers.

Less than 0.5 per cent of
the carbohydrates is cellu-

LOSS. //V

ADGOUT ONE FIF7/7 hears the statement that
OF WHOLE FOIATO eas :

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-

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

RELESS PEELING: ose, yet one sometimes ©

POTATOES AND OTHER STARCHY ROOTS AS FOOD. th

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-ylelding 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*), which vary in tubers of
different ages and account in some measure for the flavor of potatoes.

The potato, like many other toods, also contains minute amounts
of physiologically active substance or substances valuable in nutrition
and commonly called vitamins.”

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

1In 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.

2The vitamins are apparently in part dissolved in the juice and in part stored with
the starch of the cortical layer of cells. Hxactly 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.

8 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE.

form of dextrin by the heat, and part absorb water and swell. Pro-
tein coagulates or hardens, much as the white of egg does when
cooked, and at least a part of it is broken down into simpler bodies.
The mineral salts are probably less affected, but some are broken
down and form new compounds, at least a little sulphur being driven
off in volatile form when the potatoes are boiled. As is the case with
other vegetables, this sulphur no doubt contributes to the odor of
the potatoes while cooking. It is the sum of these and minor changes
which accounts for the difference of flavor and texture in a raw and
a cooked potato. As may be seen from the figures in Table I (p. 5),
the cooked potatoes, which contain no added fat or other materials,
do not differ much from the raw as regards composition. The effects
of cooking on the mechanical condition of the potato cells is shown
in figure 2, page 3.

The figures show the great changes in the mechanical condition of
the potato flesh under the influence of heat, the broken cell walls
and the increased bulk of the starch grains being particularly notice-
able. The mealy, soft, porous mass of the cooked potato is in.a fa-
vorable condition for the action of the digestive juices, as moisture
readily penetrates to all parts of it, while this is not the case with
the rather tough flesh of the uncooked tuber. It is commonly said
that raw starch, like that found in the potato, is not digestible, but
investigations indicate that this is not the case and that the digestive
juices will dissolve the starch, provided the cell walls are ruptured
by chewing or in any other way so that the ferments may come in
contact with it.

One of the great advantages in cooking potatoes and similar vege-
table foods is the improvement in flavor. This is due in part to the
development of the cooked-starch taste, which is much more pleasant
than that of raw starch. It is also due to changes in the flavor-yield-
ing bodies. Raw potatoes, especially old ones, often have a decidedly
bitter and disagreeable flavor (see p. 13), which is less marked after
cooking, because some of the flavor-yielding bodies are removed. The
reason why so many housekeepers consider boiling better for old po-
tatoes than baking is that the boiling extracts more of the disagee-
able elements. This also explains the common custom of soaking old
potatoes before cooking and that of throwing away the water in which
potatoes have been bciled.

There are also disadvantages in the results of cooking, and, though
they are less important than the advantages, they influence the food
value somewhat. There is some reason for believing that the protein
of the potato is stiffened by heat and becomes less readily digested
than when raw. A much more sericus matter is that considerable
quantities of the nutrients may be lost during cooking (fig. 5). Sev-
eral series of experiments have been made by investigators of the De-

POTATOES AND OTHER STARCHY ROOTS AS FOOD. | 9

,partment of Agriculture and by cthers to determine just how much
of the different nutrients is lost when the potatoes are cooked in vari-
ous ways. It was found that the loss is much the same whether the
water is hard or soft. Scaking the potatces in water before boiling
greatly increases the amount of nutrients extracted. When they
are put in cold water and brought to a boil they lose twice as much
of their protein (15.8 per cent) as when they are plunged at once into
boiling water; the loss of mineral matter is about 18 per cent of the
total present by both methods. On account of these losses in boiling
potatoes many persons consider steaming preferable.

The tests Just noted were all made with pared potatoes, but another
series was made with unpared ones, in which it was found that when
boiled in their jackets potatoes lose only 1 per cent of their protein

and a little over 3 per cent of

their ash, no matter what the
temperature of the water is at
the start. Almost no starch is
removed when potatoes are boiled
in their skins, but when pared
the mechanical action of the boul-
ing water wears off the outer
surface, and in this way as much
as 8 per cent of the carbohy- sromm4
drates may be lost. : vas
Evidently, then, by far the ‘
most economical way to boil po- SSS ISH OY
tatoes is in their jackets. When “Fic. 5.—Composition of the potato and

5 loss of nutrients when it is boiled with-
they are cooked. this way they out paring. Shaded portion shows loss

WATER 78.3%

ae 7: FAT O.1 Yo
CHPEOH VORFITE |
ee

should, of course, be thoroughly in boiling of 2.8 per cent of the water

Q % and 1 per cent of the protein. Unless
scrubbed before cooking and are pertions break off no starch (car-
sometimes, particularly in the bohydrate) is lost. <A little over 3 per

cent of the ash is lost in boiling.
case of new potatoes, scraped to

remove the greater part of the skin. In some families it is a common
practice to remove a section of the skin at each end of the potato or to
pare a ring around the middle of the tuber so that the moisture may
escape and the cooked potato may not become soggy on standing.
If they are pared before cooking, they should be placed directly in
hot water.

When baked in their skins, potatoes probably undergo much the
same changes as in boiling, but they lose practically none of their
ingredients except a little water which evaporates through the skin.
Some of their moisture changes to steam inside, and unless the pota-
toes are to be eaten immediately it must be allowed a way of escape
or it will change back to water and make the potatoes soggy. This
explains the practice of breaking, cutting, or pricking the skin of the
baked potatoes when they are taken from the oven.

61353°—Bull. 468—17——2

10 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE.

When raw potatoes are fried they lose some water by evaporation’
and may gain a considerable amount of fat. The thinner the pieces
the greater will be both these changes and the crisper the cooked
potato. Fried potato chips, as the table on page 5 shows, contain
only 2 per cent of water and 39.8 per cent of fat, whereas the raw
tubers contain about 78 per cent of water and 0.1 per cent of fat.

Potatoes may be prepared for the table in a great many ways, and
this is an advantage, as it helps to give variety to the diet. Direc-
tions for some of these, along with methods of cooking other vege-
tables as well, have been published elsewhere.t When other mate-
rials are added to the potatoes—for example, when boiled potatoes
are mashed with milk and butter—the composition of the finished
dish will be that of plain boiled potatoes plus the nutrients in the ma-
terials added. Mashed potatoes differ in color and consistency accord-
ing to the way in which they are handled. If the cooked potato is
simply run through a ricer, it yields a light, white mass in which one
can almost distinguish the shiny starch grains. If it is pounded with
a masher the starch particles are crowded together so that they catch
the hight less and look darker in color. Adding milk or butter tends
to make the mixture more yellow than the plain potato, but the more
it is beaten—that is, the more air is forced in between the parti-
cles—the whiter and more creamy it becomes.

In this country the chief test of excellence is mealiness, which
means that when cooked potato shall form a crystallinelike mass
with almost distinct starch particles. This quality depends largely
on the proportion of starch present. If it is abundant and evenly
distributed throughout the tuber the cells burst open in cooking and
a light, flaky, uniform mass results. If the proportion of starch is
small in any part of the potato, water or juice is likely to replace it,
which will make the potato soggy when cooked. As has been stated,
fresh, mature tubers hold more starch than either young or long-
stored ones, and the inner medullary layer or core is more likely to
be poor in starch than the outer layer. Therefore, well-developed
and well-ripened tubers are more likely to be mealy when cooked than
are the new or watery tubers or those which have a large core with
many long arms branching into the outer parts of the tuber (see

_ 4).
‘ This, however, does not tell the whole story. Anyone who cares
for early potatoes knows that there is a quality between sogginess and
mealiness that is commonly described as“ waxiness,” and in many parts
of Europe this is preferred to mealiness. While mealiness depends —
on abundant starch and sogginess on a large water content, waxiness,
which to some extent at least is a varietal characteristic, is attribut-

1U. S. Dept. Agr., Farmers’ Bul. 256 (1906).

POTATOES AND OTHER STARCHY ROOTS AS FOOD. iat

able to a large proportion of protein to starch. If the protein is suf-
ficiently abundant it will harden in cooking to form a sort of waxy
framework in which the starch will be lightly held together instead
of separating into distinct flakes as in mealy potatoes, in which there
is not enough protein present to resist the pressure of the starch.
Such waxy potatoes retain their shape better than the mealy ones
and are more suitable for garnishing meats, for salad making, and
for the preparation of many fancy dishes. As has been shown, the
proportion of protein to starch is greater in young than in mature
tubers, and therefore, in American potatoes at least, the early varie-
ties are most likely to have this waxitess. In point of flavor there is
almost as much difference as in consistency; the nitrogenous tubers

usually contain a larger proportion of acids, and perhaps also of

sugars and solanin (see p. 13), than. do the starchy ones.

POTATO PRODUCTS.

STARCH.

The chief article manufactured from potatoes is starch, which is
used for laundry purposes, for sizing paper and textiles, and for
other technical purposes; it also finds many uses in cookery, though
not so generally now as before cornstarch became common. One of
the good qualities of potato starch is that.a relatively short time is
required to cook it thoroughly, and so gravies, etc., can 1 be quickly
made with it and yet not have a raw taste.

Potato starch is sometimes marketed under the trade name of
potato flour, particularly that of foreign make. The term is also
apphed to a different kind of product fairly well known in some
European countries, which is made by grinding dried potatoes. Such
a product is also called potato meal, which is perhaps a more distinc-
tive name for it. A somewhat similar preparation is known as potato
flakes. Both of these are much used in certain parts of Europe in
bread making, particularly when wheat flour is scarce. Plain boiled
and mashed potato may be used for the same purpose. The best re-
sults are obtained when not more than one-third of the flour is re-
placed by potato meal or flakes. The recipes commonly call for not
more than one part of the latter to three parts of flour. Such potato
bread is more moist than ordinary wheat or rye bread, the potato
starch holding more water than that from the cereals. Similar mix-
tures of potato and flour are often used for pancakes, batter cakes,
etc., and sometimes a kind of batter cake or similar dish is made from
potato without flour. Many cooks think that ordinary wheat bread
and rolls are lighter if the yeast is started with potato before the
flour is mixed in, which would indicate that the potato supplies the
yeast with better food for its growth than does the flour.

12 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE.

DRIED OR EVAPORATED POTATOES AND CANNED POTATOES.

Potatoes are so valuable in the diet that many attempts have been
made to put them into a compact form in which they can be kept for
a long time. This is usually accomplished by drying, which pre-
serves them from decay and reduces their bulk. One of the oldest of
such preparations is that long used in Peru and known as “ chunno,”
made by freezing, thawing, and drying, which reduces the potatoes
to about one-fourth of their original weight. There are a number of
evaporated or dried-potato preparations in American and European
markets, and although the method of preparation differs considerably
in the various brands, the main principle is the same, namely, driv-
ing off water and so preventing decay. The changes which we call
decay are caused mainly by the development of bacteria, molds, and
yeast. These can grow and reproduce only where there are favorable
conditions, of which the necessary ones are suitable food, moisture,
and warmth. Therefore, if the moisture is removed, their’ growth is
prevented or retarded. The fact that the bulk and weight of the
potatoes is reduced at the same time is an advantage, because dried
or evaporated foods are often useful for camping expeditions and
under other conditions where fresh potatoes can not be easily pro-
cured, storage space is at a premium, or transportation is difficult.
The chemical composition of such desiccated or evaporated potatoes
is practically that of the original tubers minus almost all the water.
(See Table I, p. 5.) Of course, if extreme heat is used in the prepa-
ration, part of the starch may be changed to dextrin, and there may
be other minor changes in the chemical composition. ‘There ig no
reason to suppose that drying involves a loss of nutritive material.
Its influence on such substances as vitamins (see p. 7) is not defi-
nitely known.

The water content of various kinds of desiccated potatoes has been
found to range from 4.8 to 7.9 per cent and their total carbohydrates
from 77.9 to 80.6 per cent, showing their general composition to be
not very different from that of good white flour. Desiccated potatoes
are usually soaked in water before using, and the water which they
take up then and during cooking brings back their water content to
about that of ordinary potatoes. Their flavor and general character-
istics, however, are not quite those of good fresh potatoes.

The canned potatoes found on the market are prepared for use in
camps or wherever it is not convenient to cook food. In composition
such goods do not differ much from similar potatoes freshly cooked.

. STORAGE—ITS EFFECT ON QUALITY.

Tt is a fact of commen experience that potatoes suffer more or less
change during storage, and this is a matter of importance from the
standpoint of household costs as well as of the table quantity of

POTATOES AND OTHER STARCHY ROOTS AS FOOD. 13

this important vegetable. If the tubers were originally affected with
rots these will go on developing until the potatoes are quite unfit for
_ food. If the skin, which is the natural protection of the tuber against
the minute forms of life which cause decay, has been broken or
bruised, the injured portion offers an entrance to bacteria, etc., which
will develop in them, especially if the potatoes are stored in a warm,
moist place. Aside from these abnormal changes there are others
which occur under the best of conditions. The potato, it must be
remembered, is not a dead thing, but one from which active plant life
will be renewed as soon as conditions are favorable. Even during
the latent winter period the protoplasm of the cells is constantly pro-
ducing minute changes known as “ after ripening,” in which part of
the sugar is broken down and carbonic acid and water are given off.
Part of the insoluble starch is also changed into dextrin and other
soluble forms. This is believed to be due to the action of ferments
normally present, which aid the plant by thus changing its stored
food into a form which can be used for new growth. The extent of
these changes seems to depend ordinarily on the age of the tuber and
the temperature at which it is kept. Everyone knows that potatoes
stored where it is warm sprout more readily than those kept in a cold
cellar. The older the tuber is, the more ready it will be to begin its
new growth and the more abundantly will the starch be converted into
sugars. This explains why old potatoes are less starchy and mealy
and sometimes sweeter than fresh ones.. The temperature especially
affects the rapidity of new growth. This is one reason why potatoes
stored in a warm place are more likely to shrink than those in a
cool place. These facts also suggest why frozen potatoes have a
sweet taste; the change of starch into sugar by the enzyms goes on
regardless of the cold, but the activity of the cell protoplasm is

checked by the cold and the sugar accumulates instead of being broken |

down. The sweet taste is more noticeable in tubers which have been
slowly frozen than in those subjected to a sudden cold, because the
sugar has had a longer opportunity to form. If frozen potatoes are
left for a few days in a moderate temperature part of the sugar will
revert to starch, and the sweet taste will in a measure disappear. Of
course, the amount of material which is changed during storage will
vary with the conditions, but sound potatoes properly stored should
not shrink more than 10 or 12 per cent. The most favorable tem-
perature for keeping potatoes is from 32° to 50° F., and if the store-
room is dry, well aired, and partly hghted, they ae less kel to be
attacked by disease or harmful bacteria.

Solanin, an acrid poisonous substance, which is characteristic of the

nightshade family, develops in unusual quantities in sprouting po- —

tatoes and in those which have turned green from exposure to the
hght. A trace of it (0.01 per cent) is-present in ordinary potatoes

——

14 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE,

and is said to be what gives them their characteristic flavor. Such
very small quantities are not harmful, and for that matter the
amount which develops in sprouting or green tubers is not usually
dangerous; but since the flavor is very often bad, it is a good rule ©
to avoid green tubers or to cut out any green sections before cooking
them.

The illness (often serious and sometimes fatal) attributed to green
tubers, which occasionally results after eating cooked potato salad,
for instance, is due, not to solanin or any other such substance, but
to the rapid growth in the digestive tract of harmful bacteria
(usually of the group called fecal bacteria) accidentally present on
the potato or some food served with it and conveyed to the food
most often by the unclean hands of some one who has handled, cooked,
or served it.

SELECTION OF POTATOES FOR TABLE USE.

Appearance, taste, and consistency are the points by which we
judge a cooked potato. Unfortunately, it is not always easy to tell
from the appearance of raw potatoes which will prove the best, but
there are certain marks which aid in making a choice.

Young or new potatoes are preferable to old or stored ones. Such
tubers usually have a smoother skin, though they are not as mealy
and do not keep as well as the older ones. Very large potatoes are
not especially desirable, partly because it is hard to cook them
evenly and partly because they are often very variable in texture.
Smooth, regularly shaped tubers with comparatively few eyes are
more economical than irregular cnes which can not be pared without
considerable waste. .

Different varieties may have distinct flavors, but the soil and
climate in which they are grown and the fertilizers used cause such
great differences in flavor that variety alone is no sure guide. The
freshly gathered mature tubers usually contain a large proportion of
mineral matters and acids, and therefore have the better flavor.
Tubers old enough to sprout begin to develop an acrid taste, probably
due in part to an increased solanin content.

Very watery potatoes are always undesirable, because they become
soggy in cooking. Young tubers are more juicy than mature ones,
but their juice often holds so much more protein in solution that they
cook to the well-known waxy consistency. A good potato to be
mealy when cooked should feel firm when pressed in the hand. If
cut, it should separate crisply under the knife and be of even density
throughout. If the core is large and soft, it will make a soggy mass
full of holes in the center.

POTATOES AND OTHER STARCHY ROOTS AS FOOD. 15

In choosing potatoes, weight and size should be taken into account.
As a rule, the smaller the individual potatoes the greater the weight
of a bushel. The legal weight of potatoes in most States is 60
pounds! to the bushel, ér 15 pounds to the peck, and three or four
potatoes of average size weigh a pound. Hence, one may reckon 45
to 60 medium-sized potatoes to the peck. The time required for
cooking, of course, depends upon the size of the potatoes, smaller
ones needing less heat than larger ones. For this reason those of
uniform size are usually to be preferred to large and small ones
mixed. If a lot is not uniform, it is often worth while to sort them
and use the large ones with roast meats, or at other times when the
oven need not be especially heated, and save the small ones for occa-
sions when quick cooking is more convenient. When the potatoes are
very large, or time is pressing, it is often desirable to increase the
surface exposed to the heat by cutting them in pieces before cooking,
in spite of the fact that this slightly increases the amount of nutrients
lost. If they are pared and cut into small cubes or thin slices, they

will cook very quickly and may then be creamed, mashed, or served

in other ways.
FOOD VALUE OF POTATOES.

Potatoes are an important food in so many countries that much
experimenting has been done to test their nutritive value by scientific

methods, and the work fully bears out practical experience in prov-.
ing that they are wholesome and well digested. Many experiments ©

show that almost all of the carbohydrates and about four-fifths of
the protein which potatoes supply are actually utilized by the normal
body. 2

There is practically no reliable evidence as to the favorable effect
of cooking on the digestibility of potatoes, but what little there is
suggests that the different methods have less influence than is some-
times supposed. It seems probable that well-cooked, mealy potatoes
in which the starch grains are thoroughly broken open offer less re-
sistance to the action cf the digestive juices than ill-cooked, soggy
ones in which the flesh is only partially broken down and which
enter the alimentary tract in lumps. It is doubtful, however, if the
differences are great enough to be of importance in the ordinary diet.

When potatoes are selling at a dollar a bushel 10 cents spent for
them will buy about 6 pounds of tubers. The same sum spent for
wheat bread at 5 cents a pound loaf will purchase only 2 pounds of
material. At first glance it might seem that potatoes are much
cheaper than bread, but they contain so much more refuse and water

1In two States, namely, North Carolina and Virginia, the legal weight of a bushel of
potatoes is 56 pounds. z

16 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE,

than the bread that the 6 pounds of potatoes furnish decidedly less
protein and fat and slightly less carbohydrates than the 2 pounds of
bread. It is easy, therefore, to see why, in spite of their cheap-
ness and similar composition, they should not occupy the same place
in the diet as bread. A diet of bread alone would be rather too one-
sided for the best development of bodily powers, but would come
nearer to supplying the required protein without excess of carbo-
hydates than potatoes alone.

With respect to the total nutritive material they supply, raw pota-
toes resemble fresh fruits, such as bananas and apples, with their
seven or eight parts of water to one of food substance, more than they
do such foods as uncooked flour or rice, with their one part of water
to nine of nutritive material. Since raw potatoes consist of only
one-fifth and raw rice, for instance, of seven-eighths nutritive mate-
rial, one would naturally say that rice is more than four times as
nutritious as potatoes, and this is true of them as they are bought in
the market. This, however, is not the case when they are compared
in the state in which they appear on the table. When rice is cooked
water is added to it, with the result that when it is eaten it is not
very different in composition from cooked potatoes; thus a pound of
boiled rice and a pound of mashed potatoes would have very much
the same total fuel value, a fact which has been intuitively recognized
by housekeepers, who often use them interchangeably to serve with
meats, etc. They do not, however, have the same effect on the
alkalinity of body tissues and fluids.

According to generally accepted standards, a man at moderately
active work requires about one-fourth pound of protein a day, along
with sufficient fats and carbohydrates to give the total food an energy
value of about 3,500 calories. It would take about 9 pounds of
potatoes to furnish this energy, but that quantity would yield much
jess protein than the amount called for by the standard. About 19
pounds of potatoes would be needed to yield the required 0.25 pound
of available protein, an obviously impossible bulk for a day’s ration.
Except under stress of necessity, however, few persons try to live
entirely or even principally on potatoes. Ordinarily they are eaten
with other foods rich in protein, such as meat, milk, eggs, etc., and
thus they supplement these nitrogenous foods by furnishing the’
needed carbohydrates in an easily digested form.

The abundant mineral matters which they contain also supply the
body with important building materials and help to regulate its proc-
esses. As is the case with most vegetables and fruits, potatoes, when
they have been digested and assimilated by the body, tend to make
the tissues and fluids of the body more alkaline. Meats and eggs,
on the other hand, tend to make them more acid, while the cereals
(including rice) do not affect them greatly either way. Physiolo-

oe ee ee ee ee. ee ee oe

Fg a as

POTATOES AND OTHER STARCHY ROOTS AS FOOD. 17

- gists therefore speak of different food materials as being potentially

alkaline, acid, or neutral. The body performs its work best when its
condition is either neutral or slightly alkaline, and consequently, in
the ordinary mixed diet, it is important to counteract the effect of
the potentially acid foods like meats, eggs, and fish with potentially
alkaline ones like vegetables and fruits. It has been estimated that
a portion of potatoes large enough to supply the body with 200
calories of energy (over half a pound) would counteract the acidity
from a portion of meat yielding 100 calories (about 12 ounces).
These conclusions are in accord with the old custom in families
where living is simple of serving a goodly helping of potatoes and
other vegetables in proportion to the helping of meat.

Aside from these considerations, potatoes deserve their impor
place in the diet for other reasons. They are easy to cook and can
be prepared in so many ways that they add variety to the list of vege-
table dishes, especially in winter, when green vegetables are not com-
mon. They have a mild, agreeable flavor acceptable to almost every-
one and combining well with other foods, but not sufficiently pro-
nounced to become tiresome. Owing to the ease with which they are
grown and their abundant yield, they are usually a relatively cheap
food. Considering all these advantages, it is not surprising that in
the temperate regions of America and Europe they rank next to
the breadstuffs as a source of carbohydrates in the diet.

SWEET POTATOES.

The plants known in the United States as sweet potatoes are called
by botanists Impomea batatas or Batatas edulis, and are probably
natives of tropical America. They were introduced into Europe
earlier than the white potato and were formerly so commonly grown
in the warmer countries of Europe that when the white potato
supplanted them the latter took its English name from a corruption
of the usual European name of sweet potato—batatas. Since then,
however, they have fallen out of use in Europe, it is said because
they are considered too sweet for vegetables and not sweet enough
to take the place of cakes, sweet fruits, etc.

At present the sweet potato is grown throughout the Tropics and
warmer temperate zones, being a well-known food crop in the south-
ern part of North America, in Central America, and in the West
Indies, Hawaii, and the Philippines. In the southern United States
they play almost as important a role as white potatoes do in other
parts of the country and have almost usurped the name potato. Al- .
though the name yam (see p. 23) belongs rightly to an entirely
different tuber hardly known outside the Tropics, sweet potatoes
are sometimes so called in the United States, particularly certain

18 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE.

of the sweeter and more juicy kinds quite generally preferred in the
South, as distinguished from the dry, starchy varieties which are
preferred in northern markets.

The edible portion of the sweet potato is not a tuber like the white
potato, but a true root. Its internal structure is more uniform than
that of the white-potato tuber, but its réle in the life history of the
plant is much the same, that is, to act as a storehouse of plant food
for the growth and early development of a new crop of plants.
Above ground the plant is a vine which occasionally produces flowers
(and in warm countries seeds) resembling somewhat those of its
relatives, the morning-glories. The first touch of frost is fatal to the
vines of most varieties, so the cultivation is limited to warm countries
where the plants are perennials and the growth is practically con-
tinuous, or to regions where the summer is long enough to insure the
ripening of a crop. Some of the earlier maturing sorts are exten-
sively grown as far north as New Jersey.

The color of the sweet-potato skin ranges from light tan to dark
brown, or red and purplish tones, and the fiesh from almost white
or pale lemon yellow to a deep reddish orange. The medium and
lighter shades are most frequently seen in the northern markets. The
weight of the rdots also varies considerably, but those which are of
medium size and of regular shape are to be preferred for the table.

Although the bulk of the sweet-potato crop is used for human food,
some of the coarser kinds are fed to stock, and a small part is used
for the manufacture of starch.

COMPOSITION AND NUTRITIVE VALUE.

In general chemical composition the sweet-potato root resembles
the tuber of the white potato, although there are important differ-
ences between them. The average composition of sweet potatoes
raw and cooked is given in Table II, together with similar figures
for the white potato.

TABLE II.—Average composition of sweet and white potatoes.

Carbohydrates.
: Ref- Pro- ‘ el
Kind of potato. aa! Water. aia: Fat. Sugar, coe bs Ash. | value i
SERED, fiber. are

Per ct.| Per ct.| Perct.| Per ct.| Calories.
0.

ti
Sweet potato (edible portion).-..-.-..|-...--.-- 69.0 125 7 26.1 52) 49 560
Sweet potato (as purchased)....--- 20.0 55. 2 1.4 6 21.9 peo 450
Sweet potato (cooked)-....-.....---- baa 51.9 3.0 214 42.1 .9 905
Sweet potato (canned)-.-.......-- Se ee 55. 2 1.9 4 40.6 8 gig 800
White potato for comparison (edi- |

Bis portion) 524-5 222 eee. ene oe 78.3 2.2 1 18.0 4 1.0 375

Whit: potato for comparison (as |

8 1 14.7 8 305

PEIUCBASEG i a sine Sone a ae ee | 20.0 62. 6 : B

POTATOES AND OTHER STARCHY ROOTS AS FOOD. 19

The proportion of total sweet potato discarded with the skin as
refuse is probably about the same as in white potatoes, 20 per cent.
The most noticeable differences between white and sweet potatoes are
in the carbohydrates and water. Sweet potatoes contain on an av-
erage about 9 per cent less water and 9 per cent more carbohydrates
than white potatoes. They also contain as little, or even less, protein ;
but the proportion of available protein is higher than in white po-
tatoes, being about 1.3 per cent. This advantage, however, is hardly
large enough to be of consequence, nor is the fact that they contain
a trifle more fat.

More important than any of these differences is that in the nature
of the carbohydrates. Sweet potatoes contain a slightly larger pro-
portion of crude fiber than white, though the amount is no higher
than in most vegetables. As would be guessed from their flavor, they
contain considerable quantities of sugar, part of which is cane sugar
and part invert sugar or glucose. The proportion of sugar and
starch varies with the climate. The warmer the place in which the
plant is grown, the greater the proportion of food laid by in the form
of sugar. Tropical sweet potatoes sometimes contain almost equal
quantities of sugars and starch. Those grown in New Jersey, on the
other hand, probably do not average more than 5 or 6 per cent of
sugar, or about one-fifth of their total carbohydrates.

After harvesting, sweet potatoes are put through a curing process
during which they lose moisture. Sweet-potato marketing and stor-
age are of special interest to the grower and shipper. The house-
keeper who wishes detailed information on the subject will find it
in earlier publications of the department,’ as such questions have —
received careful study by the department specialists.

‘With respect to the storage of sweet potatoes in the home for
family use, it seems to be generally conceded that the best results are
obtained when the roots are kept in a dry, well-ventilated place, at a
moderately warm rather than a cold temperature. This would mean
that they should be stored in the pantry or some similar place rather
than in the cellar. In handling potatoes in the home care should be
taken not to bruise them, as when thus injured they are likely to
spoil. :

Little is accurately known about the chemical changes which take
place during storage. The chief one, however, is that of starch into
sugar. The most recent investigations indicate that after sweet
potatoes are first harvested there occurs a rapid transformation of
starch into cane sugar and reducing sugars, which is initially due to
internal rather than external causes. The somewhat slower and more
regular change which takes place during ordinary storage from |

1U. S. Dept. Agr., Farmers’ Buls. 324; 548..

20 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE,

starch to sugar seems to be associated in a general way with seasonal
changes in temperature. In sweet potatoes kept in cold storage (4°
C.) there is a rapid disappearance of the starch and an accompanying
increase in cane sugar. It is a matter of common experience that
late in the season sweet potatoes are apt to deteriorate in quality and
sometimes develop a disagreeable taste, especially if they have been
left in a cold place. The peculiar and characteristic flavor often
noted is due to a fungus disease resembling dry rot. These unde-
sirable changes may take place at any temperature below 50° F. To
lessen the danger of shipping in cold weather, the southern sweet-
potago crop is usually sent north early in the autumn and stored near
the retail market.

In choosing sweet potatoes at the market, firm, fresh-looking ones
should, of course, be preferred to the old and shriveled roots, and
medium-sized, regular-shaped roots are more satisfactory than very
large, very small, or irregular ones, for they cook‘more evenly,
give less waste in paring, and are of better size to serve. Early in
the season unripe sweet potatoes are sometimes marketed and may
be recognized by cutting them; the flesh will soon turn dark green,
whereas in the properly ripened roots it will not change color.

COOKING.

The changes which cooking makes in sweet potatoes are, in general,
similar to those in white potatoes. One special point is generally
noticeable—the longer the cooking is continued, the more moist does
the rootbecome. This is probably because part of the starch is made

‘soluble by the heat and then dissolved in the juice, while the cane

sugar is split up into simpler sugar. The very sweet southern
varieties become so moist during baking that a sirup frequently oozes
through the skin.

There are many different ways of preparing sweet potatoes for the
table, the most common being simply boiling or baking. They are
also fried, cooked with sugar and butter (when they are commonly
called “ candied”), used in making pies, ike pumpkin or squash, or
in other made dishes.

DRIED AND CANNED SWEET POTATOES.

Dried sweet potatoes were formerly prepared at home, and strings
of them were hung from the rafters along with apples and other
drying fruits and vegetables, but in these days of storage warehouses
the custom has very largely passed away. Special devices for evapo-
vating sweet potatoes are on the market, and desiccated sweet pota-
toes prepared in much the same way as desiccated white potatoes are

a er a ee ae

POTATOES AND OTHER STARCHY ROOTS AS FOOD. mea

sold to some extent.t Sweet potatoes cut into small cubes and roasted
or parched until brown are used like parched corn as a homemade
substitute for coffee.

Within recent years the practice of canning sweet potatoes has been
developed with so much success that it is now an important indus-
try. Medium-sized roots are preferred for canning and are usually.

‘put up in 3-pound tins. They are used like other canned vegetables

when it is not convenient to depend upon a fresh supply. Canned
sweet potatoes have been used in the Army ration in the Philippines
and are said to be in demand for lumber and mining camps.

Very rarely a flour is made from sweet potatoes. Like that from
white potatoes, it 1s prepared by ‘shcing, drying, and grinding the —
root..

DIGESTIBILITY AND PLACE iN THE DIET.

Not many special experiments have been made to test the degesti-
bility of sweet potatoes, but what little work has been done indi-
cates a degree of digestibility equal to that of white potatoes. The
protein may be sligthly less digestible, but the difference is too slight
to be of practical importance.

It is a matter of common experience that sweet potatoes are whole-
some, and they are ordinarily digested without distress. Many per-

sons find the starchy varieties so dry that they do not relish them

without large quantities of butter. This makes a rather rich mix-
ture and is perhaps accountable for the digestive disturbances oc-
casionally experienced.

Considering both composition and digestibility, it may be said that
the nutritive value of sweet potatoes is much the same as that of
white potatoes and that they are well fitted to occupy the same
place in the diet and furnish a palatable substitute for white pota-
toes. Their characteristic and pleasing flavor has the advantage
of giving variety to the diet. In the North they frequently cost
somewhat more than white potatoes, but are still among the cheaper
vegetables. In the South they are usually cheaper than white pota-
toes and merit their extensive use.

THE JERUSALEM ARTICHOKE.

The Jerusalem artichoke (Jerusalem being a corruption of girasole,
the Italian name for sunflower) is a tuber-bearing member of the
sunflower family and is entirely distinct from the French or true
artichoke, sometimes called globe artichoke. Like the sunflower, the
Jerusalem artichoke is of American origin and was an important

1 South Carolina Sta. Bul. 71 (1903), p. 6; U. S. Dept. Agr. Farmers’ Bul. 169 (1903),
0). PAIN

22 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE.

food of the Indian before America was discovered. Many farmers
in this country are prejudiced against the Jerusalem artichoke
because it spreads so rapidly and. becomes a weed; but in Europe,
and to a certain extent in the United States, it is considered a
valuable plant, since the forage may be fed to stock, and the
abundant tubers are useful as a vegetable and also for feeding

farm animals. The bright-yellow fiowers at the top of the tall

stalks no doubt help to make the plant welcome. It is often allowed
to grow on the edge of a garden or some similar place, and the tubers
are dug for home use. They are also fairly common in market in
certain localities. In flavor the tubers slightly resemble the true
artichoke, which doubtless accounts for their name. They contain
on an average 78.7 per cent water, 2.5 per cent protein, 0.2 per cent
fat, 17.5 per cent total carbohydrates, of which 0.8 per cent is crude
fiber, and 1.1 per cent ash. Judged by these figures the artichoke
tubers are quite similar in general composition to potatoes (see p.
5). They differ very markedly, however, in respect to the nature
of the carbohydrates present, inulin and Jevulin (which are chemi-
cally closely related to starch), and a considerable amount of pectose
bodies replacing the starch which is characteristic of potatoes. Little
is known regarding the digestibility of the typical carbohydrates
which these tubers contain, but recent investigation indicates that they
do not differ materially from starch in this respect. Jerusalem arti-
chokes used in various ways as a vegetable give a pleasant and whole-
some variety to the diet, particularly as they are not injured by frost
and may be dug in the early spring when fresh vegetables are not
very common. As the plant is very prolific and easily grown, the
Jerusalem artichoke is not an expensive vegetable. The tubers may
be boiled or steamed like turnips, creamed or fried like parsnips, or
used for making soups and in other similar ways. An old-fashioned

way of serving them is to slice the raw root, cover with vinegar, and ©

serve as a relish.

SOME TROPICAL STARCH-BEARING ROOTS.

In the Tropics a very large proportion of the carbohydrates of the
diet of both native and European residents is furnished by starch-
bearing roots, such as the cassava, yam, dasheen, yautia, and taro.
Mention may be made also of stachys (a curiously ribbed Japanese
tuber long known in the United States, but chiefly as a dietary curi-
osity). Most of these roots are not common vegetables in the United
States, though some or all are sold in the oriental quarters of our
cities and sometimes in a limited way in other markets, and the cas-
sava and dasheen are grown in the Southern States. In Porto Rico
and our other island dependencies, such starch-bearing roots are very

POTATOES AND OTHER STARCHY ROOTS AS FOOD. 23

important articles of diet, and as they may be readily shipped in
good condition and are eager to be palatable and wholesome, it
seems not unlikely that they may become important additions to fave
list of starchy vegetables commorly used in the United States. Most
of them have two distinct uses in the diet; that is, they are used much
like bread, as a common source of carbohydrate food, and, like succu-
lent vegetables, as accompaniments of meat or other dishes.

CASSAVA.

The cassava is an American plant widely used for food purposes.
throughout Central America, the West Indies, and the hot regions
of South America, and now cultivated to a considerable extent in
Florida, but as a cheap source of commercial starch, glucose, etc.,
and as a cattle food, rather than as a vegetable. There appear to be
two principal varieties, the sweet cassava and the bitter cassava
(which is poisonous unless specially prepared, owing to the prussic-
acid compound present), but only the sweet is cultivated in the
United States. Both varieties (but the bitter only after proper treat-
ment) are eaten as a vegetable, boiled, baked, fried, or cooked in
other ways, and by drying and grinding are made into a flour which
forms the basis of various sorts of bread and biscuits. Thin, crisp
cassava cakes are not uncommonly sold in the United States aude
a variety of trade names.

Judged by the figures given in Table IIT, page.27, the cassava is as
rich in starch as the potato, and like it can be classed as a succulent
carbohydrate food. The amount of protein and fat present is very
small, while the mineral matters are not remarkable in any way.
The culture and uses of cassava and related matters have been dis-
cussed in a previous publication! of this department.

Cassava starch in the form of tapioca is produced in large quan-
tities in the Tropics from the bitter cassava and is prized as a palat-
able and valuable food starch. It is a common article of commerce
much used for making puddings and other dishes.

YAMS.

True yams, sometimes confused in name with sweet potatoes, belong
to a group of tropical and semitropical climbing plants cultivated in a
number of varieties and producing edible starch-yielding roots. All
of the edible species are of Old World origin. These vary greatly
in size, some being no larger than potatoes and others several feet in
length and weighing 30 or more pounds. Yams are known in only
a limited way in the United States, but are common and important

1U. S. Dept. Agr., Farmers’ Bul. 167 (1903), pp. 32.

24 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE.

foods in Porto Rico, Hawaii, and the Philippines, ranking in Porto
Rico, for instance, next to the sweet potato in importance.

In appearance tubers of comparable size look much like sweet pota-
toes, while in flavor and in composition yams very closely resemble
potatoes. (See p. 27.) They have not, however, the keeping
qualities of sweet potatoes, and in countries where they grow
are usually left in the ground until required for use. Experience
and experiment alike show that yams can be readily prepared in
acceptable ways and are to be regarded as an important carbohydrate
food in regions where they are available. They are prepared for the

able in much the same way as potatoes and sweet potatoes.

tries as a breadstuff.. Like the flours and starches prepared from
other edible roots, these yam products are not used alone for making
yeast-raised bread, since they do not contain the gluten which is
characteristic of wheat flour and which gives the light, porous texture

to wheat bread. According to experimental evidence, 96 per cent of

the carbohydrates present 1n yams is assimilated on an average.
DASHEEN, TARO, AND YAUTIA.

Dasheen, taro, and yautia are closely related botanically and are
so much alike in general character and the uses to which they are
put that they may be grouped together for discussion. They belong
botanically to the Arum family, which includes also the large-leafed
ornamental plant called Caladium or “elephant’s ear,’ frequently
seen in gardens, as well as the calla lly and the Indian turnip or
jack-in-the-pulpit. Another member of the Arum family worthy of
mention is the tuckahoe or Virgina wake-robin (Pentandra vir-
ginica), which is closely. allied to the tropical America yautia. The
tuckahoe grows in marshy bottoms and river banks. Its roots, like
those of the yautia and Indian turnip, are very acrid when raw and
are full of needles of oxalate of lime, but when cooked are of a very
good flavor and much like the other aroid roots. The American
Indians are said to have made a kind of bread of the tuckahce, and,
as the earlier records show, tuckahce was of considerable importance
to the pioneer settlers of the United States.

The dasheen, taro, and yautia all form large underground root-
stocks or corms, in which starch is stored, and they are important
food plants in many tropical and subtropical countries. Taro is
an important crop in Hawaii and, indeed throughout Polynesia,
and from it the Hawaiians make the cooked and slightly fer-
mented paste called poi, a characteristic and very important article
of their diet. Taro, dasheen, and especially perhaps yautia, are
common in Porto Rico, and it was largely through the experiment

POTATOES AND OTHER STARCHY ROOTS AS FOOD. ON

station there that agriculturists in this country became interested
in them. They grow well in wet lands and make a profitable root
crop in soils too moist for potatoes or sweet potatoes, while the
dasheen also has proved itself well adapted for other soil conditions.
For this reason the Department of Agriculture and some of the
experiment stations of the South Atlantic and Gulf States have
been experimenting with them recently in the hope of developing
a profitable crop for the moist, rich soils of those coast-plain areas.
Particularly good results have been obtained with the dasheen.*
The Department of Agriculture has done much to make it known
in the United States, and it is quite generally liked by those who
have tried it. Though particularly useful in warm localities, where
white potatoes do not grow well, it can also be marketed elsewhere,
for it has good shipping and keeping qualities, and while it is not
expected to replace the potato crop it may well supplement it to
add variety to the list of starchy vegetables.

The dasheen root consists of a large stocky central rootstock or
corm, from which cormels or tubers branch out on all sides. The cen-
tral corm is nearly spherical, but slightly pointed toward the top,
and sometimes weighs as much as 6 pounds. It is firmer in texture
than the tubers which branch off from it.

Both corms and tubers are edible, though in some varieties the
tubers have a finer, more succulent flesh and a milder flavor. In gen-
eral their texture may be said to resemble that of white potatoes.
The flavor of dasheen is very much like that of the potato, being
starchy and mild, and has little if any of the characteristic acrid
taste which is common to nearly all the uncooked roots of this family
of plants but which is removed by cooking. The color of the roots
varies according to the variety, some being white or cream color, while
others run into orange, brown, or lavender, or even show a marbled
effect. The starch grains are very much smaller than those of
potatoes and most other common starchy food materials. The roots
also contain a gummy substance which sometimes interferes with
extracting the pure starch if ordinary methods are used. These
points, however, are more important in connection with starch manu-
facture than with the value of these roots as human food.

Recipes for cooking dasheen have appeared in earlier publications
of this department.? Their composition, as given in the table on page
27, shows that, like the other starchy roots described in this bulletin,
_ their nutritive value depends on carbohydrates and mineral matter
_ rather than on protein and fat.

1U. S. Dept. Agr., Bur. Plant Indus. Bul. 164 (1910); U. S. Dept. Agr., Bur. Plant
Indus. Doc. 1110 (1914), pp. 11.
2U. S. Dept. Agr., Bur. Plant Indus. 1110 (1914), p. 11.

26 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE,

POTATO DASHEEN

(EDIELE PORTION) (E021BLE PORTION)

IO, PROTEIN\

Nha hchedek Lhkdeddb iki itiitiiiiigii

Bhs PPROTEVIV
CAROOMY RATE,

)

SZ2O% CAPBOHYORATE 274%

O.7,%6 ASH LL 2AS/ |
CASSAVA SWEET POTATO
(E0IGLE PORTION) (E2/BLE PORTION)

Fic. 6.—Composition of common starehy root vegetables. These outline figures show
diagrammatically the proportion of nutrients present. Plain white indicates water
and the differently shaded portions protein, fat, carbohydrates, and ash, respectively.

POTATOES AND OTHER STARCHY ROOTS AS FOOD. 2

COMPOSITION AND ENERGY VALUE OF TROPICAL STARCHY ROOTS AS COMPARED
WITH POTATOES AND SWEET POTATOES.
Table III shows the composition of the tropical starchy roots as
compared with potatoes and sweet potatoes.

TABLE III1.—Average composition of edible portion of dasheen and other tropical
starch-bearing roots.

Total carbohy-
drates.
RADU IY ADT ee SEU Fuel

Kind of food. Water.| Protein.| Fat. g Ash. | value per

ugar, | a ound.

starch, | @uaoe p
te.

Per ct.| Perct. | Perct.| Peret.| Per ct.| Per ct.| Calories.
SW COlUCASSAVAM a wee ae sete ie oe els silt es Sees 66. 0 Nod 0.2 30. 2 1.8 0.7 610
WASSAas SPARC este ntere aye leels atoel oc ol a's as 10.5 a) 1 88.8 dil 1,625
WassavarOneaGe ns. see ae tae clea ce jac oes 10.5 9.1 3 79.0 1.1 1,610
Cassava cakes or wafers......-...---------+ 10.3 11 2 85. 2 1.6 1.6 1, 605
PRODI ec eae tes Sly= Can ag eae Boone 72.9 1.8 32, 23.3 .6 9 475
IDRS NGO I Ease sep cod cao Bse CORE See SEH ears 65.7 3.0 2 28.8 Be 1.3 605
SRAROP Mp e eres cone. Be nec Seine eclais s 70.9 1.8 2 23.2 8 12 475
SYANOUTITES 3 Sa es hes Ses elena Er a 70.0 2.2 .2 26.1 6 9 530
Potatoes for comparison......---.---------| 78.3 2.2 1 18.0 4 1.0 380
Sweet potatoes for comparison.........-... 69.0 1.8 ail 26.1 1.3 ules 560

The preceding diagram (fig. 6) shows in graphic form the com-
position of sweet potatoes, Irish potatoes, :
and other starchy roots, and perhaps ie COMPARISON
makes clearer data such as are recorded
in the table.

It is apparent from the diagram that
these typical starchy roots are very simi-
lar in general composition. Degree of
ripeness, length of storage, and other fac-
tors influence water content considerably.
Individual specimens of any one of them
would vary more or less in water content,
but on the average water makes up about
two-thirds to three-fourths of the total, ”“tggmmm—m
while carbohydrates constitute the greater :
part of the nutritive material. These
vary in the different groups, starch being
the characteristic carbohydrate of pota-
toes, cassava, and dasheen; sugar and aml in
starch of sweet potatoes; and inulin, lev- Ae]
ulin, and pectose bodies of Jerusalem
artichokes. ‘The proportion of protein in
these roots is small, but valuable in nutri- 570 CALOMES
tion, in part because of the vitamins F'6. 7—Hnergy value of some
believed to accompany the nitrogenous ~ eee
material. The proportion of ash is actually small, though relatively
large as compared with other foods. As a group, starchy roots are a

4000 CALORIES
POTATO CASSAVA

250 CALORIES 6/0 CALOFIES
DASHEEN

560 CILORIES 605 CALORIES

28 BULLETIN 468, U. S. DEPARTMENT OF AGRICULTURE.

wholesome, palatable, and useful food, and can be prepared for the
table in many acceptable forms without undue labor or fuel.

The starchy roots are important in nutrition as sources of energy.
Figure 7 shows in graphic form the energy value of some of the more
common of such vegetables.

As the diagram shows, the energy value varies from about 400 to
600 calories per pound. In general, the drier the root the higher the
energy value, which means that potatoes, for instance, which have
been harvested and dried out may have an energy value considerably
higher than the value here cited as an average.

CONCLUSION.

All these starchy tubers and roots—potato, sweet potato, Jerusalem
artichoke, cassava, yam, dasheen, yautia, and taro—yield the body
little protein to supply nitrogen needed for building body tissue
and little energy-producing fat, but on the other hand their fine-
grained starch and other carbohydrates supply easily digested energy-
yielding nutritive material and small quantities of valuable min-
eral matters which help to build the bones and are useful for other
physiological purposes. Thanks to the ease with which most of
them are cultivated, they are among the cheaper of our vegetables,
while their usually mild flavors and the variety of ways in which
they may be prepared make it possible to serve them in many com-
binations. They merit their extensive use because they make health-
ful supplements to other classes of food found in the usual mixed
diet, and because they are economical and agreeable sources of body
energy.

PUBLICATIONS OF THE DEPARTMENT OF AGRICULTURE OF IN-
TEREST IN CONNECTION WITH THIS BULLETIN.

Yearbook 1900, The value of potatoes as food.

Farmers’ Bul. 142, Principles of nutrition and nutritive value of food.

Farmers’ Bul. 167, Cassava.

Farmers’ Bul. 256, Preparation of vegetables for the table.

Farmers’ Bul. 295, Potatoes and other root crops used as food.

Farmers’ Bul. 324, Sweet potatoes.

Farmers’ Bul. 375, Care of food in the home.

Farmers’ Bul. 548, Storing and marketing sweet potatoes.

Bur. Chem. Bul. 106, Cassava: Its content of hydrocyanic acid and starch
and other properties.

Bur. Plant Indus. Bul. 164, Promising root crops for the South.

Bur. Plant Indus. Doc. 1110, The dasheen, a root crop for the South.

Bur. Plant Indus. Office Foreign Seed and Plant Introduction, Recipes for
the dasheen.

Office Expt. Stas. Bul. 43, Losses in boiling vegetables, and the composition
and digestibility of potatoes and eggs.

ADDITIONAL COPIES

OF THIS PUBLICATION MAY BE PROCURED FROM
THE SUPERINTENDENT OF DOCUMENTS
GOVERNMENT PRINTING OFFICE
WASHINGTON, D. C.

5 CENTS PER COPY

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