FRUIT AS FOOD 
indicates that all the sugar undergoes in- 
version during cooking, the acid present 
bringing about the inversion in the usual 
way. 
When fruits or fruit juices are cooked 
with sugar, the material very commonly 
solidifies or jellies on cooling, and this 
well-known property is taken advantage 
of in jelly making. In the case of some 
fruits, like the apple, the jelly-yielding 
material must be extracted from the 
fruit by cooking with hot water, while in 
the case of other fruits—the currant, for 
instance—this extraction with hot water 
is not necessary, as the expressed juice 
will produce a jelly. Heating the ex- 
tracted or expressed juice is commonly 
considered a necessary step in jelly mak- 
ing, but some fruit juices will, on stand- 
ing, jelly without heat, and laboratory 
tests have shown that jelly may also be 
obtained without the addition of sugar. 
Cooking and the addition of sugar are, 
however, important features in the prac- 
tical consideration of jelly making, as 
they have a decided effect upon the yield, 
flavor, and keeping qualities of the re- 
sulting product. 
Some fruits, like the ordinary var- 
ieties of pear, possess so little of the jel- 
ly-yielding material or possess it in such 
an unusual form that they do not yield 
a good jelly under ordinary household 
methods of treatment. The proportion 
of jelly-yielding material, like other con- 
stituents, varies with the stage of ma- 
turity, underripe rather than overripe 
fruit being best for the purpose. 
The jelly-yielding bodies are known to 
be carbohydrates and have been called 
pectin, pectose, pectin bodies, or some 
similar name. They have been commonly 
grouped with the plant gums and similar 
carbohydrates, and the true nature of 
these materials has been the subject of a 
great deal of study.* At the present time 
the consensus of opinion seems to be that 
* The Bureau of Chemistrv of the Department 
of Agriculture has reported a number of im- 
portant studies on the jelly-vielding constitu- 
ents of fruit and an extended summary of 
previous investigations of the chemical nature 
of pectins and related questions. U. S. Dept 
Agriculture, Bureau of Chemistry Bulletin No 
$4; gournal American Chemistry Society, 28 
1049 
the pectins are composed of seveial of 
the simpler carbohydrates united to 
form a complex carbohydrate. In some 
fruits, like the apple, where the jelly- 
yielding material must be extracted with 
hot water, the pectin is apparently united 
with cellulose as a part of the solid pulp 
As shown by the investigations of Bige- 
low and Gore at the Bureau of Chem- 
istry, 40 per cent of the solid material 
of apple pulp may be thus extracted with 
hot water, and consists of two carbo- 
hydrates, one of which is closely relat- 
ed to gum arabic. That such carbo- 
hydrates as these should yield a jelly is 
not surprising when we remember that 
they are similar to starch in their chem- 
ical nature, and, as every one knows, 
starch, though insoluble in cold water, 
yields when cooked with hot water a 
large proportion of paste which jellies on 
cooling. 
When fruits are used for making pies, 
puddings, etc, the nutritive value of the 
dish is, of course, increased by the ad- 
dition of flour, sugar, etc, and the dish 
as a whole may constitute a better bal- 
anced food than the fruit alone. It is 
commonly believed that dishes in which 
fruits are cooked with the addition of 
sugar, butter, and a flour crust of some 
sort are less easily digested than simple 
rations of bread, butter, and fruit hav- 
ing an equivalent nutritive value. The 
large number of digestion experiments 
which have been made with various 
mixed diets do not indicate that there is 
any special difference between the two 
rations as regards thoroughness of diges- 
tion, but additional experiments must be 
undertaken before it can be said with 
certainty whether or not there are actual 
dfferences in the ease and rapidity of 
digestion. 
In different countries opinions vary 
markedly regarding the relative whole- 
someness of raw and cooked fruit. Thus, 
as has often been pointed out, the Ger- 
mans use comparatively little raw fruit 
and consider it far less wholesome than 
cooked fruit. On the other hand, in the 
United States raw fruit of good quality 
is considered extremely wholesome, and 
