With the ever-increasing global demand for high quality rice in both local production regions and with Western consumers, we have a strong desire to understand better the importance of the different traits that make up the quality of the rice grain and obtain a full picture of rice quality demographics. Rice is by no means a ‘one size fits all’ crop. Regional preferences are not only striking, they drive the market and hence are of major economic importance in any rice breeding / improvement strategy. In this analysis, we have engaged local experts across the world to perform a full assessment of all the major rice quality trait characteristics and importantly, to determine how these are combined in the most preferred varieties for each of their regions. Physical as well as biochemical characteristics have been monitored and this has resulted in the identification of no less than 18 quality trait combinations. This complexity immediately reveals the extent of the specificity of consumer preference. Nevertheless, further assessment of these combinations at the variety level reveals that several groups still comprise varieties which consumers can readily identify as being different. This emphasises the shortcomings in the current tools we have available to assess rice quality and raises the issue of how we might correct for this in the future. Only with additional tools and research will we be able to define directed strategies for rice breeding which are able to combine important agronomic features with the demands of local consumers for specific quality attributes and hence, design new, improved crop varieties which will be awarded success in the global market.

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To identify the chromosomal regions controlling the eating quality of cooked rice, we performed a quantitative trait locus (QTL) analysis using 93 backcross inbred lines (BILs) and 39 chromosome segment substitution lines (CSSLs) derived from crosses between a japonica rice cultivar Koshihikari (glossier appearance, tasty, sticky and soft eating quality of rice when cooked) and an indica cultivar Kasalath (less glossy appearance, less sticky and hard eating quality of rice when cooked). We evaluated the eating quality of rice including overall evaluation (OE), glossiness (GL), taste (TA), stickiness (ST) and hardness (HA) in each line based on the sensory test of cooked rice. Twenty-one QTLs for eating quality were mapped to eight regions on chromosomes 1, 2, 3 (two regions), 6, 7, 9 and 10. The Koshihikari alleles at 19 out of 21 QTLs increased the eating quality, while the Kasalath alleles at the other two QTLs increased the eating quality. We also mapped the QTLs for chemical properties, such as amylose content (AC) and protein content (PC), which affected the eating quality. Four QTLs in the terminal region of the short arm of chromosome 3 and five QTLs on chromosome 6 for eating quality were mapped to the same region as that of the QTLs for AC. Three QTLs on chromosome 1 for eating quality were also mapped to the same region as that of a QTL for PC. The chromosome positions of the other QTLs for eating quality did not coincide with those of the QTLs for AC and PC. Six out of 21 QTLs for eating quality, qTA3, qOE6, qGL6, qTA6, qST6 and qHA6, were commonly identified by analysis using both BILs and CSSLs. One QTL, qTA3, was not a locus of AC, PC or known eating genes. Thus the QTL was mapped in the interval between the SSR markers RM1332 and RM6676 in the middle region of the short arm of chromosome 3 by fine mapping of three sub-CSSLs. Five QTLs, qOE6, qGL6, qTA6, qST6 and qHA6, seemed to be associated with the Waxy (Wx) gene located on chromosome 6.

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Changes in the taste of japonica, hybrid, and indica brown and milled rice, stored for 10 months at low (5 degrees C, 65-70% relative humidity) and room temperatures were observed by physicochemical analyses and a novel method using a taste sensing system. During storage, some properties increased or decreased while others were fairly constant. The main taste components of cooked rice such as sweetness (sucrose) and umami tastes (glutamic acid and aspartic acid) were reduced during storage, whereas glucose and fructose increased. The increase of fat acidity and consequent decrease of the pH value of the cooking solution may contribute to the off-taste of cooked stored rice. A taste sensing system with 10 lipid membrane sensors was also used to classify new and old rice samples using principal component analysis. Fresh and room temperature stored japonica and indica rice could be clearly distinguished; however, it was not possible to differentiate the samples stored at low temperature.