Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
FIGURE 8.1 The Westphalia three-phase decanter process.
it settles as a sediment around the bowl wall and gets transported to the concentrate
side by the decanter screw operating with a differential speed of approximately
60 rotation/min −1 . Depending on the decanter design, gluten, fibers, and process
water with pentosans are removed together with the overflow (two-phase decanter),
or process water and pentosans form the light phase and gluten and B starch the
middle phase (three-phase decanter).
8.3.4.3 A-Starch Purification and Gluten Recovery
As described previously, the recovered concentrate is further treated by screening,
multiple washing, and concentration. The A–starch, the starch fraction made up of
the big-size and more pure granules, is either washed in a combination of a centrifuge
and a multiple-stage hydrocyclone unit or a sequence of three-phase separators. The
commercial starch usually has a protein content below 0.3% dry basis (d.b).
Gluten is split off the middle phase and washed and dried as described for the
modified Martin process. The filtrate resulting after removal of gluten and its wash
water contains some small starch granules, a few gluten particles, and pentosans.
As far as possible, the small starch gets purified in a separate process line and is
finally added to the A-starch stream again to improve the starch recovery rate. 15 The
run-offs that contain fibers, B-starch, and pentosans are concentrated, dewatered,
and finally dried in application-oriented drying procedures. Pregelatinization via
drum drying is a preferred method in handling this highly unstable, and from a
microbiological point of view, critically loaded product used predominately as feed.