Food Lipids: Chemistry, Nutrition, and Biotechnology

using heat. Greater solvent holdup increases the energy required for desolventizing
the meal.
Toasting is often needed for feed meals to efficiently denature trypsin inhibitors
(protease inhibitors in soybeans affecting protein digestibility) and the enzyme urease
(soybeans), bind gossypol to protein (cottonseed), and improve protein digestibility.
Of course, none of these objectives can be achieved without considerable protein
denaturation and the accompanying loss of water solubility by the protein. However,
depending on the method used, meals with great differences in protein solubilities
or dispersibilities can be produced.
The preponderance of meal is used for feed, where extensive heat treatment is
necessary to maximize feed conversion efficiency by livestock. A conventional desolventizer/toaster
(DT) (Fig. 11) is usually composed of about six stacked trays, all
with indirect heating. The first two employ live steam injection through nozzles
within the sweep arms to evaporate the majority of the solvent. Meal advances down
through the trays, and a series of gates and floats control the levels in each tray. The
lower four trays are essentially toasting/drying sections, where the meal is held at a
minimum temperature of 100�C, and the meal is dried to a value suitable for dryers
Figure 11 Meal desolventizing/toasting equipment.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.