Agriculture Reference
In-Depth Information
Chapter 21
The Biochemical and Molecular Basis of
Wheat Quality
Colin Wrigley, Robert Asenstorfer, Ian Batey, Geoffrey Cornish,
Li Day, Daryl Mares, and Kolumbina Mrva
SUMMARY
(4) Starch pasting properties can be selected
on the basis of alleles relating to isoforms
of granule-bound starch synthase enzymes.
Thus grain quality (suitability for process-
ing) depends to a great extent on genotype
or cultivar (the combination of genes), but
also on the growth environment, especially
on whether the developing grain has been
subject to stress conditions.
(5) Lipid composition also affects processing
quality. Nonpolar lipids, embedded within
the gluten-protein matrix, may have a
lubrication role in dough rheology. The
polar glycolipids may be bound to the
gliadin proteins hydrophilically and to the
glutenin proteins hydrophobically, further
affecting dough properties.
(6) The color of wheat-based food products
depends on fl our color and on enzymic
reactions during mixing with water. For
example, polyphenol oxidases (PPOs) cause
darkening, especially of Asian noodles.
Amylases, produced by sprouting or genetic
defects, have adverse effects on the quality
of most end products, particularly bread
and noodles, causing stickiness, collapse of
product structure, and poor color.
(1) Wheat fl our goes into pastries, cakes,
cookies, breakfast cereals, confectionary,
thickening agents, custards and sauces in
western countries, and into a great diver-
sity of foods in Asian and Middle Eastern
countries—noodles, in their many forms,
fl at breads (pocket, Arabic, chapatti), and
Chinese steamed breads. Wheat is also
used in animal feeds. Starch and gluten
from wheat provide raw materials for the
manufacture of paper, adhesives, feed for
aquaculture and pets, and biofuels.
(2) Distinct quality specifi cations apply for
each of the diverse uses of wheat, involving
the hardness and protein content of the
grain, the water absorption of the milled
fl our, the viscosity of the starch, and the
strength and extensibility of the resulting
dough. Many of these specifi cations are
directly attributable to specifi c proteins,
which can be used to predict fl our
quality.
(3)
The subunits of glutenin may be ranked
according to their specifi c contributions to
dough quality, and certain combinations
are recommended as being suitable for
quality targets in breeding or for quality-
based segregation of grain at harvest. Spe-
cifi c puroindolines are suited to grain
hardness requirements of fl our milling.
(7)
New understanding of grain quality at the
molecular level offers a basis to test for the
causative compounds (or relevant genes),
thereby simplifying the quality-screening
process.
