Agriculture Reference
In-Depth Information
tions with fl our ash but this is not always so.
Unconvincing associations were observed between
fl our ash and brightness (L*) of dry fl our
(maximum 25% of the variation in fl our L*
explained by fl our ash) and between ash and L*
of a fl our slurry (maximum 16% of the variation
in slurry L* explained by fl our ash) (Zhang et al.,
2005).
ponent protein, direct measurement of starch can
be of value. Measurement of total starch essen-
tially involves its enzymatic digestion using
starch-specifi c enzymes (specifi c to glucose mol-
ecules linked α,1→4 or α,1→6) with subsequent
measurement of the glucose using a linked glucose
oxidase-peroxidase-chromogen assay (AACC
approved methods 76-11 and 76-13, AACC
2000).
Speckiness
Excessive numbers of visible bran specks in fl our
and semolina can lead to quality defi cits in noodles
and pasta. Therefore fl our (or semolina) specki-
ness is another element that can be important for
wheat to pass the test on end-use quality. Specks
can be assessed visually, or by machine vision in
fl our or semolina, or in dough or the fi nished
product. Machine vision need not always be asso-
ciated with complex image analysis systems.
Hatcher et al. (2004) described moving from a
CCD camera-based system to a system based on
a fl at-bed scanner for assessing speckiness of
noodle sheets. The scanner system was able to
count specks as well as monitor color shifts occur-
ring as noodle sheets aged and darkened. A CCD-
based laboratory-scale instrument was reported
by Evers (1998). The speck value from this instru-
ment has been used as part of a milling index (e.
g., Osborne et al., 2007). In-line industrial scale
versions are also available for monitoring fl our
streams in commercial mills. For particular appli-
cations, exploiting the fl uorescence of some bran
components may also be of value as mentioned
previously.
Starch damage
The water absorption capacity of damaged starch
is a major factor in the overall absorption capacity
of fl our. Starch damage can be controlled by
millers and therefore may require measurement.
A number of methods are available. Enzymatic
methods utilize the differential ability of damaged
starch granules to swell and become susceptible
to enzymatic hydrolysis at temperatures below
those required for gelatinization (Farrand 1964;
AACC approved methods 76-30A, 76-31, AACC
2000). An available amperometric method is
based on the greater absorption of iodine by
damaged starch and is effectively an extension of
earlier dye-binding methods (Morgan and Wil-
liams 1995; Boyaci et al., 2004). Attempts have
been made to increase the speed of existing tests.
For example, Boyaci et al. (2004) used a refrac-
tometer to measure degrees-Brix of the solution
resulting from an enzymatic digestion rather
than using a reducing sugar determination. Suc-
cessful NIRS calibrations have also been reported
for starch damage. Miralbés (2004) reported an
r
2
value of 0.94 and standard error of prediction
of 1.63 on a validation sample set when calibrated
against the amperometric SDMatic procedure
(Chopin, Triplette et Renauld, Paris, France).
Good agreement among the various starch-
damage tests has been reported (Gibson et al.,
1993; Morgan and Williams 1995; Lin and
Czuchajowska 1996).
STARCH AND FLOUR PROPERTIES
Total starch content
Starch can be analyzed simply as a component
although it is more common to require analysis
of its properties during thermal processing (see
“Starch and fl our paste viscosity and swelling
power” below). Although starch content of the
endosperm is negatively correlated with the
abundance of the other major endosperm com-
Starch and fl our paste viscosity and
swelling power
The viscoamylograph and its variants, and the
Rapid Visco-Analyzer series of instruments, are
