| Summary: | The ability of wheat flour to be processed into bread and other products is largely
determined by the gluten proteins, which confer unique visco-elastic properties to
dough. These proteins are influenced by genetic make up and the environment in
which the plants are grown. The objective of this study was to gain a better
understanding of the influence of extreme temperatures on the gluten proteins,
quality characteristics, starch and starch components. Two bread wheat cultivars,
a soft biscuit wheat and a durum wheat were grown two plants to a pot, with 12
pots for each replication, with three replications in a greenhouse for two
consecutive years. Cold and heat treatments were applied during grain filling.
Size exclusion and reverse phase HPLC were used to measure the different
protein fractions. Starch, amylose, amylopectin and various quality
characteristics were measured on all entries after harvest in both years.
The results from this study showed that in both years the softest cultivar, Snack
showed the largest reaction to low temperature stress specifically, where the
monomeric proteins were significantly increased, and the polymeric proteins
were significantly decreased. In the second year SST86 showed the same trend
as Snack under cold stress conditions. Oranje, the durum wheat cultivar, reacted
to both heat and cold stress in the second year, where the small polymeric
proteins (SDS soluble) were significantly reduced, and the small monomeric
proteins were increased with stress, and the SDS insoluble large monomeric
proteins were increased only under heat stress. The protein fractions of the
tetraploid Oranje were very different from that of the other three hexaploid
cultivars. The soft wheat Snack had significantly lower large polymeric protein,
and higher large monomeric protein fractions (SDS insoluble) than the bread
wheat cultivars for both years. Summed over cultivars, per treatment for the two
years, all the fractions, except for the small polymeric and small monomeric
proteins (SDS insoluble) were affected by the cold treatment. The monomeric
proteins were consistently increased, and the polymeric proteins decreased. Only the SDS soluble large polymeric proteins were significantly affected by the heat
treatment, where it was significantly decreased.
Both kernel weight and diameter were significantly decreased at both stress
treatments for the two bread wheat cultivars, indicating that their kernel
characteristics were sensitive to extreme temperatures. Across the two seasons,
the starch content in Kariega was significantly reduced by both heat and cold
temperatures, as is also reflected in the reduction of kernel weight and diameter.
Amylose content and the amylose:amylopectin ratio increased under heat and
cold treatment. There were highly significant positive and negative correlations
between certain RP-HPLC peaks and quality characteristics for all three the
temperature treatments in both years. The number of significant correlations was
reduced under the two stress conditions, but there is a possibility to use certain
peaks for quality selection. The profiles must, however, be standardised so that
peaks can be scored and compared on any gel according to their elution times.
Stepwise regression also emphasized the importance of some of the RP-HPLC
peaks in explaining variation in flour protein content and SDS sedimentation for
all three temperature treatments.
|
|---|
