Agriculture Reference
In-Depth Information
sperm of kernels at equilibrium moisture (Song
et al., 1998). Other work has used MRI to monitor
the hydration of Japanese salted noodles during
boiling, resolving that water penetration was
faster in a lower protein sample compared to a
sample made with higher protein fl our (Kojima
et al., 2004). In a similar way Horigane et al.
(2006) monitored water penetration in dried and
fresh spaghetti and were able to resolve differ-
ences in moisture diffusion between the two
pasta types.
Wet (and dry) gluten determinations can also
be used as a rough guide to grain or fl our protein
content and quality. Wet gluten can be derived
manually or by machine (AACC approved
methods 38-10 and 38-12A, AACC 2000). These
methods are particularly useful as indicators of
relative protein or gluten abundance where more
sophisticated methods are unavailable. Wet gluten
has been highly correlated with protein content
determined as N × 5.7 (A.S. Ross, unpublished
data), but this relationship does not always hold
true (e.g., Pasha et al., 2007).
Near-infrared spectroscopy, in either trans-
mission or diffuse refl ectance modes, is a mature,
robust, and accurate method for estimating
protein contents in grain, meal, or fl our. It was
fi rst applied in a breeding context more than 30
years ago. As a secondary or derivative method,
NIRS is based on the correlation of sample spectra
with the concentration of the constituent of inter-
est as determined by a standard reference method
(AACC approved methods 39-00, 39-10, 39-11,
39-25; AACC 2000). The success of NIRS in
determining grain and fl our protein content, as a
result of its accuracy and precision, ease-of-use,
reliability, and relatively low operational cost, has
seen it become entrenched as a routine method
and unlikely to be supplanted in the foreseeable
future by other spectroscopic methods such as
midinfrared spectroscopy (Reeves and Delwiche
1997). One change that is occurring is in instru-
ment design, such as the new generation of diode-
array instruments, which can substantially reduce
analysis times and increase sample throughput
(Osborne 2006).
Protein content
Protein has been long considered the most impor-
tant functional constituent of wheat grain and
fl our. Protein content is a signifi cant factor in
price determination in wheat trading, once the
base price has been set through supply-and-
demand considerations. Higher protein hard
wheat, and lower protein soft wheat, generally
command moderately higher prices. Protein
content alone is only an approximate indicator of
overall wheat functionality, but it has profound
modifying effects on other functional properties.
For example, regardless of how appropriate the
gluten composition of a cultivar or grain lot is for
breadmaking, if grain and hence fl our protein
content is too low, then nothing will save it.
Two chemical methods of determining nitro-
gen are in common usage: the Kjeldahl digestion
method (AACC approved methods 46-09 to 46-
13, AACC 2000) and the Dumas combustion
method (AACC approved method 46-30, AACC
2000). The Dumas method is becoming ascen-
dant primarily because of its relative speed, ease,
and safety compared with the Kjeldahl method.
However, the nitrogen release by digestion in the
Kjeldahl method is less effi cient than the release
of nitrogen by pyrolysis in the Dumas method.
This leads to small, but signifi cantly higher,
nitrogen contents in samples tested by the com-
bustion method. Once converted to protein (in
the case of wheat and wheat fl our, as N × 5.7;
AACC approved method 46-19, AACC 2000) this
translates to an apparent increase in protein of
0.15%-0.25% in samples tested by combustion
(Williams et al., 1998).
Kernel texture
Kernel texture is another characteristic of wheat
that must be known before one can decide the
suitability of wheat for a given product sector.
Soft wheat mills with lower starch damage than
hard wheat (Williams 2000), and this difference
is fundamental to the profound divergence of
their optimal end uses. Though the distinction
between hard and soft wheat is controlled by a
pair of linked
Pin
(puroindoline) genes on chro-
mosome 5D in hexaploid wheat (Morris 2002),
