upon rich soils have appreciable amounts of nitrogen compounds, as
nitrates and nitrites, which have not been built up into proteids.
Vegetables have a unique value in the dietary, and while as a class they
contain small amounts of nutrients, they are indispensable for promoting
health and securing normal digestion of the food.

55. Canned Vegetables.--When sound vegetables are thoroughly cooked to
destroy ferments, and then sealed in cans while hot, they can be kept
for a long time without any material impairment of nutritive value.
During the cooking process there is lost a part of the essential oils,
which gives a slightly different flavor to the canned or tinned
goods.[17] In some canned vegetables preservatives are used, but the
enactment and enforcement of national and state laws have greatly
reduced their use. When the cans are made of a poor quality of tin, or
the vegetables are of high acidity, some of the metal is dissolved in
sufficient quantity to be objectionable from a sanitary point of
view.[18]

56. Edible Portion and Refuse of Vegetables.--Many vegetables have
appreciable amounts of refuse,[19] or non-edible parts, as skin, pods,
seeds, and pulp, and in determining the nutritive value, these must be
considered, as in some cases less than 50 per cent of the weight of the
material is edible portion, which proportionally increases the cost of
the nutrients. Ordinarily, the edible part is richer in protein than the
entire material as purchased. In some cases, however, the refuse is
richer in protein, but the protein is in a less available form. See
comparison of potatoes and potato skins.

CHAPTER IV

FRUITS, FLAVORS, AND EXTRACTS

57. General Composition.--Fruits are characterized by containing a
large amount of water and only a small amount of dry matter, which is
composed mainly of sugar and non-nitrogenous compounds. Fruits contain
but little fatty material and protein. A large portion of the total
nitrogen is in the form of amid compounds. Organic acids, as citric,
tartaric, and malic, are found in all fruits, and the essential oils
form a characteristic feature. The taste of fruits is due mainly to the
blending of the various organic acids, essential oils, and sugars.
Although fruits contain a high per cent of water, they are nevertheless
valuable as food.[20] The constituents present to the greatest extent
are sugars and acids. The sugar is not all like the common granulated
sugar, but