Biomedical Engineering Reference
In-Depth Information
Table 2.1
Cereal production in 2010 [
1
]
Cultivated area
(million ha)
Grain production
(million tons)
Species
Corn
162
844
Rice
154
672
Wheat
217
651
Barley
48
123
Sorghum + millet
76
85
Oats
9
20
Triticale
4
13
Rye
5
12
winter or spring varieties. The winter type requires vernalization by low temperatures;
it is sown in autumn and matures in early summer. Spring cereals are sensitive to
frost temperatures and are sown in springtime and mature in midsummer; they
require more irrigation and give lower yields than winter cereals.
Cereals produce dry, one-seeded fruits, called the “kernel” or “grain”, in the form
of a caryopsis, in which the fruit coat (pericarp) is strongly bound to the seed coat
(testa). Grain size and weight vary widely from rather big corn grains (~350 mg) to
small millet grains (~9 mg). The anatomy of cereal grains is fairly uniform: fruit and
seed coats (bran) enclose the germ and the endosperm, the latter consisting of the
starchy endosperm and the aleurone layer. In oats, barley, and rice the husk is fused
together with the fruit coat and cannot be simply removed by threshing as can be
done with common wheat and rye (
naked
cereals).
The chemical composition of cereal grains (moisture 11-14%) is characterized by
the high content of carbohydrates (Table
2.2
) [
2,
3
] . Available carbohydrates, mainly
starch deposited in the endosperm, amount to 56-74% and fiber, mainly located in
the bran, to 2-13%. The second important group of constituents is the proteins which
fall within an average range of about 8-11%. With the exception of oats (~7%),
cereal lipids belong to the minor constituents (2-4%) along with minerals (1-3%).
The relatively high content of B-vitamins is, in particular, of nutritional relevance.
With respect to structures and quantities of chemical constituents, notable differ-
ences exist between cereals and even between species and varieties within each
cereal. These differences strongly affect the quality of products made from cereal
grains. Because of the importance of the constituents, in the following we provide an
insight into the detailed chemical composition of cereal grains including carbohy-
drates, proteins, lipids, and the minor components (minerals and vitamins).
2.2
Carbohydrates
Cereal grains contain 66-76% carbohydrates (Table
2.2
), thus, this is by far the
most abundant group of constituents. The major carbohydrate is starch (55-70%)
followed by minor constituents such as arabinoxylans (1.5-8%), b -glucans (0.5-
7%), sugars (~3%), cellulose (~2.5%), and glucofructans (~1%).
