Food Chemistry

15.2 Individual Constituents 681

Fig. 15.4.Two-dimensional electrophoretic separation of gluteninsaof the wheat cultivarsOkapi(B4) and
Avalon(A6)b. (according toKrauseet 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 mercap-
toethanol (SDS-PAGE).
aResidue after extraction of defatted flour with water, salt solution, and aqueous ethanol.
bThe 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-,ω 1 ,2-, andγ-gliadins, which are not sepa-
rated during pre-fractionation because of varying
solubilities (cf. 15.2.1.2).
Thehigh-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. Ahigh-
molecular group with the HMW subunits of
glutenins, a group of intermediate molecular
weightswith the ω5- andω 1 ,2-gliadins, and
alow-molecular groupwith theα-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 char-

acterized 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-ter-

minal 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