influence of atmospheric CO2 concentration on the protein, starch and mixing properties of wheat flour

Wheat (Triticum aestivum L.) cultivars Hartog and Rosella were grown at CO2 concentrations of 280 µL L-1 (representing the pre-industrial CO2 concentration), 350 µL L-1 (ambient) and 900 µL L-1 (an extreme projection of atmospheric CO2 concentration). The plants were grown in naturally lit glasshouses in 7 L pots containing soil to which basal nutrients had been added and the pH adjusted to 6.5. Hartog yielded 2.4 g of grain per plant when grown at 280 µL CO2 L-1. This yield was increased by 38% and 75% at CO2 concentrations of 350 µL L-1 and 900 µL L-1 respectively. These changes were due to increases in both grain number and individual grain weight as the level of CO2 was raised. The yield of Rosella was unaffected by altering the CO2 concentration. Increasing the CO2 concentration reduced grain protein concentration of cv. Hartog from 17.4% at 280 µL CO2 L-1 to 16.5% and 16% at CO2 concentrations of 350 µL L-1 and 900 µL L-1 respectively. The grain protein concentration of cv. Rosella was reduced from 10.7% to 10.2% by increasing the CO2 concentration from 280 µL L-1 to 350 µL L-1; however, an additional increase in the CO2 concentration to 900 µL L-1 had no effect on grain protein concentration. In Hartog flour, the highest proportion of polymeric protein in the flour (7.7%) occurred at 280 µL CO2 L-1. This was reduced to 6.3% at 350 µL CO2 L-1 but then increased again to 7.0% at 900 µL CO2 L-1. These changes in concentration of polymeric protein were correlated (r2=0.58) with changes in mixing properties. The mixing time required to produce optimum dough strength was greatest at 900 µL CO2 L-1 (181 s), then 141 s and 151 s at 350 µL CO2 L-1 and 280 µL CO2 L-1 respectively. These changes in mixing time could not be explained by changes in grain protein concentration. The proportion of ‘B’ starch granules (