2009_Book_FoodChemistry

15.2 Individual Constituents 675
Table 15.6. Chemical composition of cereals (average values)
Wheat Rye Corn Barley Oats Rice Millet
weight %
Moisture 13.2 13.7 12.5 11.7 13.0 13.1 12.1
Protein (N × 6.25) 11.7 9.5 9.2 10.6 12.6 7.4 10.6
Lipids 2.2 1.7 3.8 2.1 7.1 2.4 a 4.05
Available carbohydrates 59.6 60.7 64.2 63.3 55.7 74.1 68.8
Fiber 13.3 13.2 9.7 9.8 9.7 2.2 3.8
Minerals 1.5 1.9 1.30 2.25 2.85 1.2 1.6
mg/kg
Thiamine 5.5 4.4 4.6 5.7 7.0 3.4 4.6
Niacin 63.6 15.0 26.6 64.5 17.8 54.1 48.4
Riboflavin 1.3 1.8 1.3 2.2 1.8 0.55 1.5
Pantothenic acid 13.6 7.7 5.9 7.3 14.5 7.0 12.5
a Polished rice: 0.8%.
Table 15.7. Fractions of various cereals separated by
milling (average weight-%)
Cereal variety Husk Bran Germ Endosperm
Wheat 0 15.0 2.0 83.0
Corn 0 7.2 11.0 81.8
Oats 20 8.0 2.0 70.0
Rice 20 8.0 2.0 70.0
Millet 0 7.9 9.8 82.3
15.2.1.2 A Review of the Osborne Fractions
of Cereals
In 1907 Osborne separated wheat proteins,
on the basis of their solubility, into four fractions.
Sequential extraction of a flour sample
yielded: water-soluble albumins, salt-soluble
(e. g., 0.4mol/l NaCl) globulins, and 70%
aqueous ethanol-soluble prolamins. The glutelins
remained in the flour residue. They can be
separated into two sub-fractions. For this purpose,
all the proteins remaining in the residue
are first dissolved in 50% aqueous 1-propanol
at 60 ◦ C with reduction of the disulfide bonds,
e. g., with dithioerythritol. The high-molecular
(HMW) subunits (cf. 15.2.1.3.1) precipitate out
on increasing the propanol concentration to 60%,
while the low-molecular (LMW) subunits
(cf. 15.2.1.3.3) remain in solution.
Further separation of the Osborne fractions and
subfractions into the components is possible
analytically with electrophoretic methods (cf.
Fig. 15.3, 15.4) and analytically and preparatively
with RP-HPLC (cf. Figs. 15.5–15.8).
Table 15.8. Chemical composition of anatomical parts of a wheat kernel (average weight-% on dry weight basis)
Ash Crude protein Lipids Crude fiber a Cellulose Pentosans Starch
(N × 6.25)
Longitudinal cells 1.3 3.9 1.0 27.7 32.1 50.1 –
Cross- and tube cells 10.6 10.7 0.5 20.7 22.9 38.9 –
Fruit and seed coatings 3.4 6.9 0.8 23.9 27.0 46.6 –
Aleurone cells b 10.9 31.7 9.1 6.6 5.3 28.3 –
Germ b 5.8 34.0 27.6 2.4 – – –
Starchy endosperm 0.6 12.6 1.6 0.3 0.3 3.3 80.4
a Crude fiber includes parts of cellulose and pentosans.
b Data for carbohydrates are incomplete.