Biomedical Engineering Reference
In-Depth Information
Table 2.2
Chemical composition of cereal grains (average values) [
2,
3
]
Wheat
Rye
Corn
Barley
Oats
Rice
Millet
(g/100 g)
Moisture
12.6
13.6
11.3
12.1
13.1
13.0
12.0
Protein (N × 6.25)
11.3
9.4
8.8
11.1
10.8
7.7
10.5
Lipids
1.8
1.7
3.8
2.1
7.2
2.2
3.9
Available carbohydrates
59.4
60.3
65.0
62.7
56.2
73.7
68.2
Fiber
13.2
13.1
9.8
9.7
9.8
2.2
3.8
Minerals
1.7
1.9
1.3
2.3
2.9
1.2
1.6
(mg/kg)
Vitamin B
1
(thiamine)
4.6
3.7
3.6
4.3
6.7
4.1
4.3
Vitamin B
2
(ribo fl avin)
0.9
1.7
2.0
1.8
1.7
0.9
1.1
Nicotinamide
51.0
18.0
15.0
48.0
24.0
52.0
18.0
Panthothenic acid
12.0
15.0
6.5
6.8
7.1
17.0
14.0
Vitamin B
6
2.7
2.3
4.0
5.6
9.6
2.8
5.2
Folic acid
0.9
1.4
0.3
0.7
0.3
0.2
0.4
Total tocopherols
41.0
40.0
66.0
22.0
18.0
19.0
40.0
2.2.1
Starch
Starch is the major storage carbohydrate of cereals and an important part of our
nutrition. Because of its unique properties starch is important for the textural prop-
erties of many foods, in particular bread and other baked goods. Finally, starch is
nowadays also an important feedstock for bioethanol or biogas production (for
reviews see [
4,
5
] ).
2.2.1.1
Amylose and Amylopectin
Starch occurs only in the endosperm and is present in granular form. It consists of the
two water-insoluble homoglucans amylose and amylopectin. Cereal starches are typi-
cally composed of 25-28% amylose and 72-75% amylopectin [
6
] . Mutant genotypes
may have an altered amylose/amylopectin ratio. “Waxy” cultivars have a very high
amylopectin level (up to 100%), whereas “high amylose” or “amylostarch” cultivars
may contain up to 70% amylose. This altered ratio of amylose/amylopectin affects
the technological properties of these cultivars [
7,
8
]. High-amylose wheat has been
suggested as a raw material for the production of enzyme-resistant starch [
9
] .
Amylose consists of a -(1,4)-linked D-glucopyranosyl units and is almost linear.
Parts of the molecules also have a-(1,6)-linkages providing slightly branched struc-
tures [
10,
11
]. The degree of polymerization ranges from 500 to 6,000 glucose units
giving a molecular weight (MW) of 8 × 10
4
to 10
6
. Amylopectin is responsible for
the granular nature of starch. It contains 30,000-3,000,000 glucose units and, there-
fore, it has a considerably higher MW (10
7
-10
9
) than amylose [
12
] . Amylopectin is
a highly branched polysaccharide consisting of a -(1,4)-linked D -glucopyranosyl
