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Introduction
Corn or maize (Zea mays
L.) is the most important cereal in the world after wheat and rice; it is
also the most widely distributed. It is the most important crop in
the United States, occupying double the area of any other crop, which
produces half the world’s total corn.
Corn is used for three main purposes: (1) as a staple human food,
particularly in the tropics; (2) as feed for livestock, particularly in
temperate and advanced countries, providing over two-thirds of the total
trade in feed grains; (3) as a raw material for many industrial products.
Within a comparatively
short time of the discovery of America, corn had spread widely throughout the Old World, and became an important source of
carbohydrate food for the poorer classes in many tropical, subtropical and
warm temperate countries. The reasons for this adoption are many and
include: (1) it gives one of the highest yields per hour of labor spent;
(2) it provides nutrients in a compact form; (3) it is easily
transportable; (4) the husks give protection against birds and rain; (5)
it is easy to harvest and hull, and does not shatter; (6) it stores well
if properly dried; (7) it can be harvested over a long period, first as
immature cobs, and can be left standing in the field at maturity before
harvesting; (8) cultivars with different maturing periods are available;
(9) consumer preference, as many people prefer maize to their indigenous
cereals.
Corn on a dry weight basis, has approximately the same number of
calories as wheat or rice. It has less protein than wheat and is deficient
in two amino acids tryptophane and lysine, but has a higher oil content.
The grain is rich in thiamine, but low in niacin. The low content of
niacin and tryptophane can lead to pellagra, a deficiency disease, common
in South Africa. Corn is unsuitable for bread making as it is deficient in
gluten.
Corn is prepared and consumed in a multitude of ways.
It is usually
ground and pounded and the meal may be boiled, baked or fried. The whole
grain may be boiled or roasted and it may be fermented. Corn meal is
cooked with water to provide a thick mush or dough, or a thinner
consistency to provide gruel, porridge or soup. In North and Latin America
tortillas are made by baking thin flat cakes until they are crisp. Tamales
are produced by steaming the dough. Cornbread is made by mixing the meal
with wheat flour. Immature cobs, preferably sweet corn, are boiled and
eaten as corn on the cob, or the grain may be removed and eaten as a
vegetable, or it may be canned. More mature cobs are roasted.
Dry milling produces grits, consisting of coarsely ground endosperm
from which most of the bran and the germ have been separated. Cornflakes,
used as a breakfast cereal, are made by rolling grits after they have been
flavored. Hominy is produced by soaking whole grain in lye until the skin
has been loosened and can be washed free. Popcorn is made by heating the
small grains, which explode or pop, turning themselves inside out to
produce small fluffy white balls. Waxy corn is used for the production of
starch similar to tapioca.
Corn produces a number of important industrial products, which are
usually obtained by the wet-milling process, in which the grain is
steeped, after which the germ and bran are separated from the endosperm.
The main product is starch, which, when dried, can be used as such or
converted into dextrins. If not dried, it can be processed into syrup or
sugars. Oil, obtained from the germ, is made into soap or glycerine, but
can be refined to produce cooking or salad oil. The starch may be
used as human food or made into sizing, laundry starch, urethane plastics,
and other products.
Corn grain is an outstanding feed for livestock, high in energy, low in
fiber and easily digestible. It is an important forage crop, being
cut green, or dried for fodder, or made into silage. If the ears are
removed it is called stover.
Corn can be fermented and distilled to provide industrial products such
as ethyl, butyl or propyl alcohol, acetaldehyde, acetone, glycerol and
acetic, citric and lactic acids. Zein, the protein in corn, is used to
produce synthetic fibers of good tensile strength, and as a substitute for
shellac. The fiber in the stems has been used for making paper, and the
pith for explosives and light packing material. The cobs are used
for fuel, smoking pork products, pipes and are a source for charcoal.
The
leaves may be plaited into mats. Over 500 important products and
byproducts may be obtained from corn.
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