Texture Evaluation of Cooked Rice Prepared from Japanese Cultivars Using Two‐Bite Instrumental Test and Electromyography

The objective of this study was to determine the effects of texture of cooked rice on the natural chewing behavior of people who habitually consume rice. Eight Japanese cultivars varying in amylose content and protein content were selected and cooked rice samples with various texture were prepared. Instrumentally measured textural parameters were highly correlated with the amylose content but not with protein content. Electromyography (EMG) from both masseter muscles was recorded during natural eating for 10 men. The number of chews, mastication time and sum of muscle activities were significantly higher in the harder rice samples from high amylose cultivars. The burst duration and muscle activities per chew were also high; however, the interburst duration was low in rice with a high amylose content. EMG variables per chew were compared in the early, middle and late stages of mastication. The amplitude and muscle activities decreased in the late stage, whereas the interburst duration and cycle time increased for all cultivars and the burst duration was similar. No significant correlations between EMG variables and protein content were found. Amylose content influences the texture of cooked rice and also chewing behavior, but the effects of amylose content were diminished at the late stage of mastication. EMG was useful for analyzing natural eating behavior as well as dynamic changes in texture during mastication of cooked rice. PRACTICAL APPLICATIONS: The texture of cooked rice is due to the amylose content in starch contained in rice grains. Many parameters obtained from instrumental and electromyography (EMG) measurements were significantly correlated with the amylose content. EMG is useful for analyzing eating behavior and dynamic changes in texture during mastication. Raw EMG variables analyzed through repeated‐measure analysis of variance (ANOVA) and standardized EMG variables using a control sample followed by ANOVA provided similar results for different cultivars. Both raw and standardized EMG variables correlated with instrumentally measured parameters. Standardization of EMGs is not necessary if the number of chews, time for oral processing, chewing cycle are of interest. These absolute values are useful for designing the texture of foods and optimizing the cooking method if there is not a good control material. The standardized EMGs clearly indicate degree of texture effects on each variable.