Influence of free-air CO2 enrichment (FACE) on the eating quality of rice

Rice plants (Oryza sativa L cv Akitakomachi) were grown under free-air CO2 enrichment (FACE) in farmers' fields in Shizukuishi, Iwate, Japan during 1999 and 2000. The grains were harvested and subsequently analyzed for protein and amylose contents as well as the traits related to cooked-rice viscosity. The cooked rice was also subjected to sensory evaluation. The protein content of rice grains grown under elevated CO2 was significantly lower than that of rice grown under ambient conditions. In addition, CO2 enrichment increased the whiteness of the grains in both brown and milled rice and reduced their surface hardness. Although the amylose content of rice grains was unaffected, starch pasting properties demonstrated that rice grains in elevated CO2 had higher maximum viscosity and breakdown than those grown in ambient conditions. Sensory evaluation of cooked rice with respect to umami (deliciousness), appearance, aroma, hardness, stickiness and overall palatability index indicated that the sensory properties were not significantly altered by the CO2 enrichment treatment. Therefore, we conclude that the growth of the rice cultivar Akitakomachi under elevated CO2 concentration decreased the protein content, but did not change the palatability to a level that may be detected by sensory taste panel evaluation. (c) 2005 Society of Chemical Industry.