Agriculture Reference
In-Depth Information
among other phenomena. Information on the
amount of residual ungelatinized starch in fi n-
ished products, or the degree-of-cook of extruded
products and their process intermediates, can also
be analyzed using paste viscosity testing (Whalen
2007).
been extended to hard wheat, where it could show
some promise (Xiao et al., 2006) such as predic-
tion of water absorption capabilities in the absence
of gluten development.
The principle of SRC testing is that solvent
uptake is primarily associated with specifi c fl our
components: SC-SRC is an indicator of starch
damage and therefore, indirectly, kernel texture;
Su-SRC is an indicator of pentosan and gliadin
content; and W-SRC is a general indicator of
absorption capacity summed over all substances
in the fl our or meal (Bettge et al., 2002). The LA-
SRC uses absorption characteristics of glutenins
to predict dough or gluten strength and is corre-
lated with sodium dodecyl sulfate-sedimentation
volume (SDS-SV) in both hard (Xiao et al., 2006)
and soft wheat (Guttieri et al., 2004; Gaines et al.,
2006). Additionally in hard wheat LA-SRC has
been shown to have better predictive value than
SDS-SV over a narrow (1%) fl our protein range
than SDS-SV (Xiao et al., 2006), although con-
fi rmation of this result is required before it can be
applied widely and with confi dence. The correla-
tion between LA-SRC and SDS-SV has led some
researchers to adopt the practice of reporting
either SDS-SV or LA-SRC but not both, as they
tend to be redundant.
The absorptions determined by the four sol-
vents are highly correlated with each other, and
this is more evident for W-SRC, SC-SRC, and
Su-SRC (unpublished data). Clearly there is
overlap in what components are absorbing in each
solvent. The originators of the technique did not
suggest strict partitioning of the absorption to
specifi c components, rather that the solvents
emphasize absorption of the component of inter-
est (e.g., starch damage for SC-SRC). An example
is the anomalously high Su-SRC value of fl our
from the soft wheat cultivar Daws compared with
its overall water absorption capacity (Bettge et al.,
2002). This was considered to be a result of the
known higher pentosan content of Daws. Inter-
estingly wholemeal from this cultivar also had an
anomalously high SC-SRC, indicating the possi-
bility that the high pH of the sodium carbonate
solution also partitions some water-unextractable
pentosans into the aqueous phase. High pH is
employed routinely to extract non-water-soluble
SOLVENT RETENTION CAPACITY
As noted earlier, absorption capacity is a key indi-
cator of fl our utility. Water absorption can be
predicted using the farinograph to measure the
combined absorption of intrinsic fl our compo-
nents and gluten formation (see below) or by
observing the ability of fl our or wholemeal to
absorb water in the presence of a large excess.
This type of analysis can be further refi ned by
adding selected solutes to the water to partition
the absorption capacities of different fl our com-
ponents. The original test that measured absorp-
tion in an excess of solvent was the alkaline water
retention capacity (AWRC) test. This test used a
weak alkaline solution of 0.84% (w/v) sodium
bicarbonate (AACC approved method 56-10,
AACC 2000). High AWRC absorption is associ-
ated with poor cookie spread. The concept of this
test was modifi ed to the sugar water retention
capacity test (Saunders et al., 1989 as cited in
Slade and Levine 1994), which in turn was further
refi ned as the solvent retention capacity (SRC)
method (AACC approved method 56-11, AACC
2000).
In standard guise the SRC test uses four sol-
vents for the fl our: water (W-SRC) and three
aqueous solutions, 50% w/w sucrose (Su-SRC),
2% w/w sodium carbonate (SC-SRC), and 5%
w/w lactic acid (LA-SRC). The SRC is deter-
mined by measuring the weight increase of the
fl our pellet after suspension of the fl our or meal
in the solvent of interest and subsequent con-
trolled centrifugation. The SRC is reported as a
function of the original sample weight at 14% mb.
This test was designed originally for evaluating
soft wheat and has been adapted to smaller sample
size and the use of wholemeal to make it more
applicable in breeding programs (Bettge et al.,
2002). Investigations of the utility of SRC have
