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

Abstract

Rice plants (Oryza sativa L cv Akitakomachi) were grown under free-air CO 2 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 CO 2 was significantly lower than that of rice grown under ambient conditions. In addition, CO 2 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 CO 2 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 CO 2 enrichment treatment. Therefore, we conclude that the growth of the rice cultivar Akitakomachi under elevated CO 2 concentration decreased the protein content, but did not change the palatability to a level that may be detected by sensory taste panel evaluation.

Rising atmospheric carbon dioxide on grain quality in crop plants

“…Seneweera et al (1994) reported CO 2 induced increase in amylose content in grains, under various levels of phosphorus application. However, Terao et al (2005) did not observe any change in the palatability of rice grains with the reduction in the protein content under elevated CO 2 condition. Seneweera et al (1994) observed 4% increase of amylose content due to elevated CO 2 under phosphorusdeficient conditions, which is much higher than the decrease in protein content that was less than 2.5%.…”

“…This increase in amylose content was not simply because of the decreased protein content, but also because of the change in the starch composition. Terao et al (2005) also reported that CO 2 enrichment changed the starch pasting properties affecting the texture and stickiness of cooked rice. However, CO 2 induced change in the amylose content did not affect the viscosity of starch.…”

“…Thus the overall protein yield may not be reduced by elevated CO 2 although the amount of protein on a consumption basis was reduced. Terao et al (2005) concluded that this change in protein content resulted in an increase in maximum viscosity and breakdown of starch that improves the eating quality of rice. In addition, they have also observed that elevated CO 2 reduced the milling degree and increased the whiteness of both brown and milled rice grains.…”

Grain growth of different rice cultivars under elevated CO2 concentrations affects yield and quality

“…In general, the projected increases in [CO 2 ] will promote photosynthesis and crop productivity in the future (Ziska et al, 2012;Tausz et al, 2013). On the other hand, elevated [CO 2 ] (E-[CO 2 ]) is known to reduce the protein content in rice grains (Lieffering et al, 2004;Terao et al, 2005;Taub et al, 2008;Myers et al, 2014), and also degrades grain appearance quality with increased occurrence of chalky grains which will affect the rice market price as well as the nutrient intake of hundreds of millions of people (Borrell et al, 1999). The mechanisms underlying the quality degradation are not well understood, however.…”

As carbon dioxide rises, food quality will decline without careful nitrogen management

“…At elevated carbon dioxide and standard fertilizer levels, wheat had 10% less grain protein (Fangmeier et al 1999;Kimball et al 2001). Similarly, grain protein in rice (Terao et al 2005) and tuber nitrogen in potato (Fangmeier et al 2002) declined by about 10% at elevated carbon dioxide concentrations. Several approaches could mitigate these declines in food quality under carbon dioxide enrichment.…”