Sensory evaluation of cooked rice in relation to water-to-rice ratio and physicochemical properties

The effects of cooking water-to-rice (W/R) ratio on the sensory characteristics of cooked rice eating quality of 14 varieties of Thai rice were investigated in relation to their physicochemical properties. Milled rice samples were cooked with five W/R ratios ranging from 1.3 to 2.5 on a weight basis and presented to 12 trained panelists for sensory evaluation. A three-way analysis of variance and a principal component analysis identified the intensity of sensory hardness as the main characteristic of cooked rice. It decreased with increasing W/R ratio whereas sensory stickiness decreased. The overall acceptability based on appearance, texture and flavor attributes reached peak levels corresponding to optimum W/R ratios for different rice varieties, and was highly correlated with sensory hardness and stickiness. Partial least squares regression models of optimum W/R ratio and peak overall acceptability gave coefficients of determination of 0.991 and 0.980, respectively, thus indicating that the optimum W/R ratio and the acceptability ratings of cooked rice could be reliably predicted from the physicochemical properties such as the apparent amylose content, protein content, gel consistency, alkali-spreading value and grain elongation ratio of milled rice. Sensory evaluation of cooked rice eating qualities is a difficult task to carry out routinely on a day-to-day basis. Presently, rice varieties are categorized according to grain dimensions and selective physicochemical traits that reflect on the eating quality of cooked rice. Though it has been long realized that the amount of water used for cooking and rice physicochemical properties highly influence the eating quality of cooked rice, no information is currently available on the quantitative evaluation of these factors. Results of this study showed that models could be developed to quantify the optimum amount of water for cooking rice of different varieties with the most desirable sensory eating qualities. The prediction of peak overall sensory acceptability scores that correspond to the optimum cooking water-to-rice ratio could be useful for categorizing rice varieties based on their impact on sensory eating quality and for the development of baseline information for consumers by the rice industry.