| Abstract | In general, two major methods are commonly employed for evaluating the texture of cooked rice comprise of instrumental and sensory tests. These tests play an important role in assessing the eating quality of new rice varieties and consumer preference. Instrumental or objective tests can be used for evaluating the quality of rice's in both raw and cooked form whereas sensory or subjective test can be used only for determining the eating quality of cooked rice. Instrumental tests are used to determine physico—chemical properties of raw milled rice, pasting characteristics of rice flour, and cooked rice attributes such as hardness and stickiness. The parameters obtained from various instrumental tests may correspond to the Specific textural characteristics of cooked rice. Subjective tests are limited to the sensory evaluation of the texture of cooked rice by a group of taste panelists. Although subjective testing is the most direct method for evaluating the eating quality of rice, it is time consuming and difficult to carry out properly, and require a large sample. Therefore, the overall objective of this study was to investigate both instrumental and subjective methods for evaluating the texture of cooked rice and to establish possible meaningful correlations between instrumental tests and sensory measurements in the form of predictive models for general application. Ten popular Thai rice varieties ranging from low to high amylose content were selected for testing. Cooked rice samples were prepared using seven different water-to- rice ratios ranging from 1.3 to 2.5. Physico-chemical properties of milled rice such as amylase content, gel consistency, alkali spreading value, and protein content were determined. Pasting characteristics of rice flour such as pasting temperature, peak viscosity, consistency, set back, and breakdown were also determined from Brabender amylograrn. The hardness and stickiness parameters of cooked rice were determined from three different instrumental tests, namely, Ottawa texture measuring system (OTMS), back extrusion (BE), and compress-hold—pull back (CI-HDB) tests. In addition, sensory texture attributes such as hardness and stickiness along with degree of preference of cooked rice were evaluated from subjective test by using nine-point Hedonic scale test. Correlations among parameters obtained in each test as well as those determined with different tests were investigated. ' It was observed that sensory hardness and stickiness of cooked rice could be highly correlated with the physico—chemical properties of raw rice in terms of amylose content, gel consistency, alkali spreading value, and water-to-rice ratio. In addition, sensory hardness and stickiness were also highly correlated with pasting characteristics of rice flour in terms of pasting temperature, peak viscosity, consistency, and water-to-rice ratio. It was found that sensory hardness was positively correlated with instrumental test ' parameters. namely. peak extrusion force in OTMS and BE tests, and residual compression force, negative peak force. and area under negative force-distance curve in iiiCHPB test. On the contrary, the stickiness of cooked rice was negatively correlated with instrumental test parameters indicating lower values of correlation coefficients than sensory hardness. It was possible to develop predictive models relating sensory and instrumental test parameters by considering water—to-rice ratio as an independent variable. However, the accuracy of predictive models increased when data were analyzed separately for different levels of water-to-rice ratio. The results of this study showed that overall acceptability or degree of preference of cooked rice texture could also be estimated from other sensory texture attributes such as hardness and stickiness, which in turn could be satisfactorily estimated from physico— chemical properties, pasting characteristics, and other instrumental test parameters. Finally, a numerical computation scheme was developed for predicting the acceptability score of cooked rice texture and Optimum water-to-rice ratio based on physico-chemical properties and pasting characteristics of milled rice. The developed procedure for textural characterization of cooked rice could find general application in predicting the degree of palatability of new rice varieties along with recommended water—to—rice ratio for cooking based on the information obtained from instrumental tests. |