2009_Book_FoodChemistry

15.2 Individual Constituents 681
Fig. 15.4. Two-dimensional electrophoretic separation of glutenins a of the wheat cultivars Okapi (B4) and
Avalon (A6) b . (according to Krause et al., 1988)
1st. Dimension: isoelectric focussing in ultrathin (0.25 mm) layer (UTIEF), pH 3.5–9.5; 8 mol/lurea.
2nd. Dimension: polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and mercaptoethanol
(SDS-PAGE).
a Residue after extraction of defatted flour with water, salt solution, and aqueous ethanol.
b The baking quality class is given in brackets after the variety (bread volume yield for A6: average to high, for B4:
low to average)
(Fig. 15.7). This chromatogram also contains the
ω5-, ω1,2-, and γ-gliadins, which are not separated
during pre-fractionation because of varying
solubilities (cf. 15.2.1.2).
The high-molecular subunits of wheat glutelins
show a protein pattern typical of the cultivar
(Fig. 15.8).
Based on the data available on the structure
of gluten proteins, three main groups can be
formed which consist of several subunits. A highmolecular
group with the HMW subunits of
glutenins, a group of intermediate molecular
weights with the ω5- and ω1,2-gliadins, and
a low-molecular group with the α- andγ-gliadins
as well as the LMW subunits of the glutenins.
The properties of the protein groups mentioned
are summarized in Table 15.14 and the amino
acid composition is given in Table 15.15.
15.2.1.3.1 High-Molecular Group
(HMW Subunits of Glutenin)
As shown in Table 15.15, the HMW subunits of
glutenin are the only gluten proteins in which Gly
(ca. 19%), and not Pro (ca. 12%), takes second
place in the order of amino acids after Glx
(ca. 36%). Furthermore, the proteins are characterized
by the highest content of Tyr (ca. 6%)
and Thr (ca. 3.5%) and the lowest content of
Phe (ca. 0.3%) and Ile (ca. 0.8%). In the N-terminal
amino acid sequence presented in Table
15.16, the sequence EGEAS-RQLQC is valid
for all known HMW subunits and varies only in
position 6 (E, K, G). From the total sequences
known until now, it can be deduced that the
HMW subunits consist of three segments (A–C
in Table 15.17). The N- and C-terminal segments