School of Graduate Study Department of Chemical Engineering

starch-lipid complex formed in the barrel may be more resistant to oxidation. Packaging
under nitrogen or vaccum in opaque containers may further protect extruded foods
(Camire, 2001).
Dietary Fiber
Dietary fiber is the edible part of plants or analogous carbohydrates that are resistant to
digestion and absorption in the human small intestine with complete or partial
fermentation in the large intestine. Dietary fiber includes polysaccharides,
oligosaccharides, lignin, and associated plant substances. Dietary fibers promote
beneficial physiological effects including laxation, and or blood cholesterol attenuation,
and or glucose attenuation (Camire, 2001)
A major difficulty in interpreting research involving fiber and extrusion in the variety of
analytical methods used to quantify and characterize different fiber components. For
example, measurement of total dietary fiber for food labeling does not detect changes in
fiber solubility induced by extrusion. As with starch fragments of larger molecules may
be sheared off during extrusion. These smaller molecules may be water soluble on the
other hand fragments could unite large insoluble complexes or maillard compounds that
may be analyses as lignin. Such physicochemical changes may influence profoundly the
health benefits of the extruded food. For example soluble forms of dietary fibers are
associated with reduce risks for heart diseases (Camire, 2001).
2.4.4 Extrusion cooking of soy products
In the extrusion cooking processes the raw material is converted in to viscous
-elastic fluid or “melts” where by the transport mechanism through the extruder changes
along the screw from solid flow to fluid flow. As a consequence, the pressure build up
during fluid flow, high shear stresses are developed which cause structural transformation
in the material. These transformations include loss of crystalline structure, destruction of
granular structure, rupture of glycoside bonds and new molecular interactions (Kebed
, 2006; Gonzalez et al., 1998).
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