2009_Book_FoodChemistry

676 15 Cereals and Cereal Products
Fig. 15.2. Longitudinal section of a wheat grain. I Pericarp, 1 epidermis (epicarp), 2 hypodermis, 3 tube cells,
4 seed coat (testa), 5 nucellar tissue, 6 aleurone layer, 7 outer starchy endosperm cells, 8 inner starchy endosperm
cells, 9 germ and 10 scutellum
Table 15.9. Mineral and vitamin distribution as % in kernel fractions of wheat
Pyridoxal Pantothenic
Fraction Minerals Thiamine Riboflavin Niacin phosphate acid
Fruit coat 7 1 5 4 12 9
Germ 12 64 26 2 21 7
Aleurone layer 61 32 37 82 61 41
Starchy endosperm 20 3 32 12 6 43
In the literature, Osborne fractions derived from
different cereals are often designated by special
names (cf. review Table 15.11). The various designations
may result in confusion and incorrect
conclusions with regard to protein homogeneity.
Therefore, it is better to preferentially use the
general designations of the Osborne fractions and
specify the protein source, e. g., wheat glutelin instead
of glutenin.
Albumins and globulins are derived mostly from
cytoplasmic residues and other subcellular fractions
which are part of the kernel. Thus, enzymes
are present in the first two Osborne fractions. Prolamins
and glutelins, on the other hand, are storage
proteins.
Cereals contain variable levels of Osborne fractions
(Table 15.12). Wheat has the highest content
of prolamin, corn has the second highest. The albumin
fraction is the highest in rye and the lowest
in corn. The content of albumin in oats is comparable
to that in rye. Oats and rice have a higher
content of glutelin than wheat, while rye, millet
and corn have a much lower glutelin content. The
amino acid composition of only the prolamins
(Table 15.13) can be correlated to the botanical
genealogy of cereals as shown in Fig. 15.1. In
general, the amino acid composition is similar for
wheat, of rye and barley. The prolamin composition
of oats is intermediate between Triticeae and
the other cereals. The amount of glutamic acid in