Impact of free air ozone concentration enrichment on cooked rice (Wuyunjing 21) texture and palatability

Without appropriate control of ozone precursor emissions, tropospheric ozone concentration will be projected to increase significantly by the middle of this century. Rice (Oryza sativa L.), the most important food crop, has provided nutrition for more than half of the world's population over the centuries. Elevated ozone concentration has been noted to induce a series of physiological changes in rice crop. Such changes have included changes in the processes of photosynthesis, water relation, nutrient absorption/translocation and grain filling. Such altered physiological processes due to ozone exposure have likely affected the physical and chemical properties of rice grain and thus grain quality. To date, most studies on rice response to ozone stress have focused on growth and yield with little known issues on the effects of ozone on grain quality, especially the taste of edible crops. To investigate the effects of elevated ozone concentration on the texture and taste of cooked rice, a unique free air ozone concentration enrichment (ozone-FACE) experiment was conducted in two consecutive rice growing seasons (2009 and 2010). The FACE experiment was located in Xiaoji Town in Jiangdu County of Jiangsu Province, China (119°42′0′′E, 32°35′5′′N). A native Japonica rice cultivar "Wuyunjing 21" was exposed to ambient or elevated ozone concentration of 50% above ambient value. Texture analyzer measurements showed that the hardness of cooked rice increased by 13.6% (P < 0.05) under elevated ozone concentration. Sensory analyzer evaluation of taste also showed that elevated ozone concentration respectively decreased aroma, luster, flavor, taste and integrated value by 0.8% (P > 0.1), 6.2% (P < 0.1), 2.6% (P < 0.1), 5.1% (P < 0.05) and 4.3% (P < 0.05) and increased intactness by 2.0% (P < 0.05). While the yearly effect was significant for all texture and taste variables of cooked rice, the interaction between year and ozone was in the most cases not detected. The above results suggested that rice grown under future high ozone environments will have greater hardness and deteriorated taste properties after cooking.