Effect of elevated carbon dioxide concentration on rice quality: Nutritive value, color, milling, cooking, and eating qualities

Increase in the atmospheric carbon dioxide concentration ([CO2]) enhanced the concentration of carbohydrates in rice grains, according to results of a previous study. However, its impact on other quality traits is little known. To investigate the effect of CO2 levels (375 and 550 μmol/mol) on rice quality, a field experiment was conducted with open-top chambers. Elevated [CO2] affected several nutritional parameters of the grain. Whereas the concentration of α-linolenic acid increased, that of linoleic and γ-linolenic acids decreased. For example, reductions of 9 and 28% were observed for linoleic acid in the brown rice and for γ-linolenic acid in the husk, respectively. Phytic acid concentration and zinc bioavailability were unaffected. Whereas iron bioavailability decreased in the brown rice (22%), calcium bioavailability increased in the bran and husk (5–11%). The concentrations of essential amino acids were also reduced; for example, the amount of isoleucine in the white rice, tyrosine in the brown rice, and phenylalanine in the bran decreased by 40, 57, and 23%, respectively. In contrast, elevated [CO2] resulted in improved grain whiteness (3%) and starch viscosity (11%), with no effect on the milling quality. These data indicate that increased [CO2] has both positive and negative effects on quality, depending on the specific end use of the rice grain.