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Effect of Elevated Carbon Dioxide Concentration on Rice Quality: Nutritive Value, Color, Milling, Cooking, and Eating Qualities

¹CITAB – Centre for the Research and Technology of Agro-Environment and Biological Sciences, Universidade de Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal. ²CQVR – Centro de Quimica Vila Real, Universidade de Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal. ³Instituto Nacional de Investigação Agrária e Veterinária, Av. República, Nova Oeiras, 2784-505 Oeiras, Portugal. ⁴Department of Food Industries, ESAV, Polytechnic Institute of Viseu, CI&DETS, 3500-606 Viseu, Portugal. ⁵Institut für Pflanzenbau und Bodenkunde, Julius Kühn-Institut, Bundesforschungsinstitut für Kulturpflanzen, Bundesallee 50, D-38116 Braunschweig, Germany. ⁶Corresponding author. Phone: +351 259 350 751. Fax: +351 259 350 327. E-mail: htrindad@utad.pt

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.