Cereals processing technology

Biotechnology, cereal and cereal products quality 61
of starch (adjunct) added in the form of rice or maize is a key determinant of the
level of starch degrading enzyme required in the malt. The relative levels of
different starch degrading enzymes are important in determining the nature of
the substrate for fermentation and the sugar, alcohol and oligosaccharide content
of the beer. The alcohol and residual sugar content (sweetness) are influenced by
the levels of fermentable sugars and the non-fermentable oligosaccharides
contribute to the taste (mouthfeel).
Distilling
Distillation is a process where the product quality may be less dependent on the
raw materials than many other processes and may be a less important target for
biotechnology application in relation to the cereal raw material. However, the
quantity of starch available for fermentation might be enhanced.
Extrusion
Extrusion (production using high temperatures and pressures) of cereal products
is an increasingly important process in the production of a wide range of
products including snack foods, breakfast cereals and pet foods. The processing
properties required are complex but may be enhanced by the application of
biotechnology.
4.5.2 Cereal quality: the case of wheat
Wheat is used for a wide range of products with differing quality requirements
(Fig. 4.2). The importance of different wheat grain components and
characteristics depends on the ultimate end use product (Morris and Rose
1996). The protein quality is much more important for products such as breads
than for cakes and biscuits. Enhanced levels of desirable high molecular
weight glutenins may be desirable in wheat for use in breadmaking.
Manipulation of starch synthesis and starch properties may be more important
in products such as noodles. Colour may be controlled by a small number of
genes and has differing importance. For example, the yellow pigments in
durum wheat are considered highly desirable while some noodle products
require very white flour. The improvement of specific attributes using
biotechnology needs to target characters specific for particular end uses. Wheat
is used to produce the types of food products listed in Table 4.4 (Morris and
Rose 1996).
Improvement of the value of wheat for this wide diversity of uses requires the
matching of wheat characteristics to specific end product requirements. For
example, wheat with different combinations of protein and hardness are better
suited to particular end uses (Fig. 4.2). However, some combinations of
characteristics will not be optimal for any major end use.
Genetic improvement of wheat quality needs to address targets relevant to the
end use characteristics of wheat from a particular environment or region. For
example, selection for specific starch metabolism mutants or engineering of