Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
allow them to successfully replace two-phase separators in primary separation or as
middling separators. As a result, separation and refining steps can be performed
more effectively at a reduced cost.
The purified starch slurry leaves the washing section with about 23°Bé (equal
to about 40% dry substance) to intermediate storage for modification or saccharification
or finally to dewatering in discontinuously working peeler centrifuges or
vacuum drum filters. The minimum water content of starch cakes produced there
varies from 36 to 40%. To achieve storable starch powder with a maximum moisture
content of 14%, dewatered starch is dried in a pneumatic dryer, preferably a flash
dryer. Before being packed, dried starch is sifted in horizontally working sifters to
remove gritty particles that are ground for packing or readded to starch cakes.
8.3 WHEAT STARCH
8.3.1 GENERAL REMARKS
Wheat starch production was based both on wheat grains and wheat flours for a
long time. As with other starches, potential uses of by-products were decisive in
selecting the finally preferred technology. 10,11 The values of specific components in
wheat grain proteins are important, in particular those that constitute most of the
water-insoluble wheat protein fractions, the so-called gluten, and contribute to the
extraordinary property profile essential for forming a satisfying crumb in baking
wheat bread. When extraction and drying procedures for wheat gluten were developed
into technologies that maintained the valuable viscoelastic properties in the
dried product, wet milling processes were established exclusively in industrial practice,
which produced typical wheat starch together with high yields of the vital wheat
gluten. The principal characteristic of this gluten is to recover instantaneously viscoelastic
behavior when hydrated. 12 From an economical point of view, the valuable,
and as compared with the commodity product starch, high-priced by-product was
responsible for selecting the best-suited technique.
For a long time, the flour-based dough system was the most suitable substrate
for washing out starch. Because of the high flour quality needed for this process,
vital high-quality gluten was recovered at high levels too. Purification of the received
starch stream resulted then in the main product consisting of highly purified A-starch
and another rather impure starch fraction derived from tailings, called B-starch.
Other by-products such as fibers and pentosans, together with bran coming from the
milling process, are now mostly used as feed.
The dough-based Martin process dominated production for a long time. 13 The
main principle of this process was the formation of a dough similar to baker’s
dough, from which starch was washed out with rather high quantities of water.
The enormous water consumption of approximately 15 m 3 per tonne flour was the
main reason for the disuse of this process and replacement by procedures that
consumed less water. Later, however, a process was derived from the Martin
process. This technique, adapted to modern requirements and reestablished with
modern installations such as hydrocyclone systems, was called the modified Martin
process, and reduced water consumption to approximately 6 m 3 and even lesser