THE INFLUENCE OF HEAT AND COLD STRESS ON GLUTEN PROTEIN AND STARCH IN WHEAT

• Main Author: Oskar, Elago
• Other Authors: Dr E Koen
• Format: Others
• Language: en-uk
• Published: University of the Free State 2009
• Subjects: Plant Sciences
• Online Access: http://etd.uovs.ac.za//theses/available/etd-02062009-141420/restricted/

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.