Cereals processing technology

214 Cereals processing technology
In addition to effects from the protein content aspects of protein quality also
influence final product quality. Protein quality is most often judged by some
form of dough rheological test though in such cases the prediction of final
product quality is less certain because most dough rheological testing methods
are carried out using conditions which bear little relationship with the
breadmaking process in which the flour will be used. Protein quality testing
relies heavily on the interpretation of the rheological data by experts.
Bran does contain protein but this will not have the same functionality as the
proteins which are present in the endosperm. The particle size of the bran
fragments is important, with smaller sizes causing a greater reduction in bread
volume than larger particles for the same quantity of bran. The germ, like bran,
is high in less-functional proteins and in addition it contributes natural reducing
agents, which weaken dough systems (Cauvain, 1987).
The grade colour figure (GCF) of a flour is a measure of the amount of bran
that is present in a white flour. The higher the GCF the lower will be bread
volume (Cauvain et al., 1985), in part because of the dilution effect on the
functional protein content. With higher values for GCF the crumb colour will be
darker.
During the growing cycle for the wheat plant there are a large number of
enzymes at work. Of interest to us are the ones known collectively as amylases,
and especially -amylase. The term -amylase is used to describe a range of
enzymes which are capable of breaking down damaged starch granules (starch
granules become damaged during the flour milling process) into dextrins and in
combination with -amylase they will produce maltose. -amylase is produced
during the growing cycle and can achieve quite high levels if the period around
harvesting is wet. The level of amylase is measured using the Hagberg Falling
Number test, the lower the number the higher the -amylase level.
The dextrins which are produced by the action of -amylase on damaged
starch are sticky and if their level is high enough in the finished bread they build
up on the slicer blades and can reduce the blade efficiency to such an extent that
loaves can be crushed and damaged. Flour millers adjust the composition of the
wheats in the milling grist to deliver flours with known Falling Numbers and
usually the flour specification will be based on a minimum Falling Number.
Starch is an important component of the wheat endosperm and as the flour
milling process continues large numbers of the starch granules can become
damaged depending on the settings used on the roller mills. These damaged
starch granules absorb more water than the undamaged granules so that the
larger the proportion of damaged starch the higher the water absorption of the
flour (Stauffer, 1998).
10.7.2 Yeast
Bakers’ yeast (Saccharomyces Cerevisiae) comes in a number of different forms
(Williams and Pullen, 1998). The main ones in use are the compressed form
which comprises around 28–30% dry matter and cream (pumpable) yeast. The