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Background and Objective:
This project determined the
properties of buckwheat starch and other components that influence
noodle-making quality. The trait of “soft-starch” was transferred to
self-pollinating lines, as an increased content of soft starch allows
machine made noodles of much higher quality. Quality parameters and
such traits as green testa and low amylose were also transferred to
self-pollinating buckwheat lines. Finally, other unique starch
buckwheat varieties were developed. This work was conducted with input
from the Japanese Buckwheat Millers Association with the goal of
increasing the demand for and production of Manitoba buckwheat.
Results and
Discussion:
Starch was found to be the major
component of buckwheat seeds. Its content varied from 67.4% to 74.8%.
The protein content was found to vary from 13.1 to 14.5% in the
presently registered varieties. However, lines were developed that had
a protein content which ranged from 11.6% to 16.3 %. A wider range
would be desirable in the development of new buckwheat products. The
fat content of the seeds ranged from 3.0 to 3.8%. Dietary fiber content
varied from 7.6 to 10.3%. Due to its known health benefits, development
of lines with increased dietary fiber would be desirable in the market
place.
Buckwheat starches appeared to
have a normal distribution of the starch polymers, amylose and
amylopectin. The amylose content, however, varied from 21.4% to 27.9%
depending on the buckwheat variety. It was determined that up to 10% of
the amylose may be lipid-bound.
The molecular weight of
amylopectin and amylose polymers in buckwheat starches was determined.
The molecular weight of amylopectin ranged from 250 x 106 to
350 X 106. The molecular weight of amylose ranged from 7.2 x
106 to 16.1 x 106. These values are higher than
those for corn, potato and tapioca which indicate that these compounds
in buckwheat are composed of larger molecules.
Buckwheat has relatively small
starch granules, with the majority having a diameter between 2 and 8
μm. There were some differences if granule size distribution that
existed among the presently registered buckwheat varieties. The starch
granules are normally eight sided as they are packed closely together
before the seeds dry.
The gelatinization temperature
of buckwheat starches were determined and were found to be relatively
high compared to other starches with a similar amylopectin/amylose
ratio. The melting enthalpy of amylose-lipid complex in buckwheat
starches was found to be unusually low and might indicate a weak
complexation property of amylose in buckwheat starch.
Buckwheat starches were found to
form stiffer and harder gels than corn, rice or wheat starches as
indicated by significantly higher values of the elastic modulus of both
fresh and aged gels. The high elastic modulus values of amylose might
be responsible for the strong elastic properties of buckwheat starch.
The pasting properties of
buckwheat starches differed slightly from those of wheat and corn.
Buckwheat starches swelled faster and exhibited a greater paste
viscosity than corn or wheat starches. Some differences were also noted
between the presently registered varieties of buckwheat.
The swelling power and oil
absorption of buckwheat starches were comparable to those of rice but
were much greater than those of corn or wheat starches.
The swelling power of buckwheat
flours (white) was evaluated to determine whether there were any
differences in water uptake during cooking. The swelling power was
found to vary from 2.4 g H2O/20 mg to 2.05 g H2O/20
mg. As the quality of the finished buckwheat noodle has a high
correlation to increased starch swelling power it was decided to utilize
this character as a screening tool for the development of lines with
increased quality characteristics. A rapid screening method has been
developed and is now being utilized in the breeding program to identify
superior lines.
Mixograph evaluations of flours
from different buckwheat varieties showed that some varieties had a much
higher ‘peak height’ and ‘width at peak’ parameters. However, the dough
mixing parameter was comparable between the flours.
Rheological measurements
confirmed the mixograph studies. The elastic modulus from some
varieties was much higher than for other varieties. These differences
very well might be attributed to the much higher water absorption of
flour from these varieties. However, the reasons for the differences
have not yet been well understood. Some varieties form much stronger
and elastic dough than do other varieties. These differences might be
due to differences in protein properties among the different buckwheat
flours.
Buckwheat non-starch
polysaccharides consist mainly of galactose, glucose, and xylose with
much smaller quantities of arabinose and mannose. They also contain a
considerable amount of uronic acids. Buckwheat non-starch
polysaccharides have a very high intrinsic viscosity which indicated a
high molecular weight and exhibited strong viscelastic properties. It
was found that there were substantial differences in intrinsic viscosity
among the buckwheat varieties that were evaluated. Buckwheat non-starch
polysaccharides, when dissolved in water formed very viscous solutions.
At concentrations of greater than 4% they are capable of forming weak
gels. Buckwheat non-starch polysaccharides also strongly increase the
elastic properties of starch paste. They are likely to posses all the
health benefits associated with soluble dietary fiber.
Green Testa Development
The color of the testa layer is
the most important quality factor for buckwheat in the Japanese market.
The finding of a testa layer with increased green color in the
inter-specific cross between Fagopyrum esculentum and
F. homotropicum provided the opportunity to develop lines with
increased green color. The original material used had very poor
agronomic characteristics and therefore the green testa had to be
incorporated into lines with good agronomic and quality characteristics.
It was found that the green
color of the testa layer was due to chlorophyll. The lines with
increased green were found to have an increase in chlorophyll b but not
in chlorophyll a. The increased green color was found to be inherited
as a recessive gene, however, during the backcrossing program to
incorporate the color it was found that the intensity of the color could
also be increased. Lines with a 10 fold increase in the amount of
chlorophyll b were chosen as the best intensity for the Japanese market.
At the same time lines with an 18 fold increase of chlorophyll b were
also chosen for the development of lines for a specialty hand made
noodle market niche.
A lighter green color of the
testa was also developed and is referred to as ‘steam green’ due to its
color being similar to broccoli after it has been steamed. It is a very
bright color and was immediately chosen by the Japanese Buckwheat
Millers Association as being the most desirable color. This color
therefore was utilized in all green testa crosses.
Several thousand green testa
lines have now been developed, with the most promising being evaluated
for agronomic and quality characteristics. This character has now
become a standard character that will be placed into all new developing
lines as a very desirable trait. Approximately 50% of the entire
buckwheat breeding program now has this trait incorporated.
The development of the very dark
green testa layer has been slower than the development of the green
testa layer. This was because the dark color had to be developed over
several generations and backcrosses during which time only the dark
green color was selected for. Therefore, many of the seed, plant and
quality characteristics were very poor. As the dark green trait is now
stable, incorporation of the trait into lines with superior agronomic
and quality traits was initiated.
Seed Density
Studies were conducted to
determine the optimum seed shape and density for buckwheat. As the
buckwheat seed has to be dehulled the shape of the seed becomes very
important for groat recovery. The shape of the hull also affects the
ease with which dehulling can take place which has a direct effect on
groat recovery.
It was found that the best seed
shape for buckwheat was as close a possible to a round seed shape which
produced a round groat. The round groat has almost the same size of
embryo tissue as does the triangular seed but the endosperm tissue is
increased. This resulted in increased starch content in the flour which
is a desirable attribute in the Japanese market.
As approximately two thirds of
all the buckwheat milled is dehulled with stone dehulling equipment the
shape of the hull must accommodate this method. It was found that the
edges of the hull must project slightly out from the round shape to
allow them to be engaged with the stones and removed from the seed with
minimal damage to the groat. The extended edges of the hull, or
‘flanges’ must extend the entire length of the edge and are therefore
much different from ‘winged’ seeds which extend out much further and in
only one area of the edge. This seed shape has now become the standard
for the buckwheat breeding program.
The development of the round
seeds has progressed well with some lines having totally round seeds now
being produced. However, this appears to be a quantitative trait and
therefore progress on the incorporation of this trait into the breeding
program will be slower than it would have been if the trait was
conditioned by only a single gene or a few genes.
Seed density is an important
trait for quality in buckwheat. Increased seed density has always been
a desirable trait in the breeding program. However, increased seed size
has also been an important quality characteristic. As there is a high
negative correlation between the two traits it has been difficult to
increase seed density at the same time as increasing seed size. With
seed size now being stabilized at approximately 40 grams per thousand
seeds, selection for seed density can receive more emphasis. The
variety Mancan has a seed density of approximately 570 g/l. while the
variety Koto has a seed density of approximately 611 g/l. It was
determined that the optimum seed density of buckwheat is approximately
666 g/l. If the seed density is increased beyond this point the flanges
must be reduced which results in poorer dehulling characteristics and
more groat damage. Many lines with a seed density in excess of 630 g/l
were developed during this project and are now in initial evaluation
stages.
Hull Thickness
Hull thickness also affects
groat or flour recovery. However, if the hull is too thin then it can
split or be removed during harvest operations. As dehulled seeds are
classed as a dockage factor in the Japanese market this is an
undesirable characteristic. It was determined that Koto has a hull
thickness of 0.22 m while Mancan has a hull thickness of 0.19 m. Lines
with a hull thickness of varying from 0.10 to 0.25 m were developed. It
was decided that the optimal hull thickness is approximately 0.15 m.
Lines with this hull thickness were selected and are now incorporated
into the breeding program.
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