THE INFLUENCE OF ATMOSPHERIC CO2 CONCENTRATION ON THE PROTEIN, STARCHAND MIXING PROPERTIES OF WHEAT-FLOUR

Wheat (Triticum aestivum L.) cultivars Hartog and Rosella were grown a t CO2 concentrations of 280 mu L L-1 (representing the pre-industrial CO2 concentration), 350 mu L L-1 (ambient) and 900 mu L L-1 tan extrem e projection of atmospheric CO2 concentration). The plants were grown in naturally lit glasshouses in 7 L pots containing soil to which basa l nutrients had been added and the pH adjusted to 6.5, Hartog yielded 2.4 g of grain per plant when grown at 280 mu L CO2 L-1. This yield wa s increased by 38% and 75% at CO2 concentrations of 350 mu L L-1 and 9 00 mu L L-1 respectively. These changes were due to increases in both grain number and individual grain weight as the level of CO2 was raise d. The yield of Rosella was unaffected by altering the CO2 concentrati on. Increasing the CO2 concentration reduced grain protein concentrati on of cv. Hartog from 17.4% at 280 mu L CO2 L-1 to 16.5% and 16% at CO 2 concentrations of 350 mu L L-1 and 900 mu L L-1 respectively. The gr ain protein concentration of cv. Rosella was reduced from 10.7% to 10. 2% by increasing the CO2 concentration from 280 mu L L-1 to 350 mu L L -1; however, an additional increase in the CO2 concentration to 900 mu L L-1 had no effect on grain protein concentration. In Hartog flour, the highest proportion of polymeric protein in the flour (7.7%) occurr ed at 280 mu L CO2 L-1. This was reduced to 6.3% at 350 mu L CO2 L-1 b ut then increased again to 7.0% at 900 mu L CO2 L-1. These changes in concentration of polymeric protein were correlated (r(2)=0.58) with ch anges in mixing properties, The mixing time required to produce optimu m dough strength was greatest at 900 mu L CO2 L-1 (181 s), then 141 s and 151 s at 350 mu L CO2 L-1 and 280 mu L CO2 L-1 respectively. These changes in mixing time could not be explained by changes in grain pro tein concentration. The proportion of 'B' starch granules (<10 mu m di ameter) increased from 25% of total weight of starch at 280 mu L CO2 L -1 to 30% at CO2 concentrations 350 and 900 mu L L-1. There were gener ally no effects of CO2 concentration on dough mixing properties or sta rch granule size distribution for Rosella.