Department of Food Science and Biotechnology, Dongguk University-Seoul, Goyang-si, Republic of Korea.
J Texture Stud. 2018 Dec;49(6):639-645. doi: 10.1111/jtxs.12370. Epub 2018 Oct 15.
The cooked rice stickiness is conventionally measured as the maximum detachment force required to separate the probe from the sample, after compression on the platform of a texture analyzer. A corrected stickiness (the measured stickiness force divided by the contact area) was newly created to avoid the deviation of stickiness influenced by the contact area varying with the rice sample's irregularity, regarding shape and size. The contact area could be estimated from the volume, density, and thickness of the samples. The compression force triggering the stickiness was also converted to the corrected compression force (the force divided by the contact area). Two varieties of rice (short-grain rice and glutinous rice) were cooked with different amount of water to prepare the samples with various stickiness levels. The contact area was mostly higher in the glutinous rice than short-grain rice. The contact area increased with the cooking water amount. Three parameters were compared such as the stickiness (the measured force), the primarily corrected stickiness (the corrected stickiness at a fixed value of compression force), and the secondarily corrected stickiness (the corrected stickiness at a fixed value of the corrected compression force). The difference between the rice samples was the most pronounced in the secondarily corrected stickiness. The correlation between the instrumental and sensorial stickiness was also the highest in the secondarily corrected stickiness. Conclusively, the new corrected parameters enhanced the sample discrimination capability and the agreement with the sensorial stickiness than the uncorrected stickiness. PRACTICAL APPLICATIONS: Stickiness is the important quality factor associated with cooked rice preferences. Instrumental stickiness is a detaching force of the preliminarily compressed rice grain by cylindrical probe of texture testing equipment. When it comes to a force measurement, the contact area is usually considered to convert the force to stress. But, for the samples like cooked rice grain, with smaller contact area than that of probe, the contact area is not easy to know because it is not simply the probe bottom area. So the contact area had not been employed to measure cooked rice stickiness. In this study, an established method was devised to figure out the contact area. The corrected stickiness by considering the contact area proved to be more accurate than the original stickiness through sensory evaluation.
米饭的粘性通常通过质构仪平台对样品进行压缩后，测量探头与样品分离所需的最大分离力来衡量。为避免因米饭样品形状和大小不规则导致粘性受接触面积变化的影响，本研究创建了一个新的粘性校正值（测量粘性力除以接触面积）。接触面积可以通过样品的体积、密度和厚度来估算。将触发粘性的压缩力也转换为校正后的压缩力（力除以接触面积）。将两种不同的大米（短粒米和糯米）用不同量的水煮熟，制备粘性水平不同的样品。糯米的接触面积通常高于短粒米。接触面积随烹饪水量的增加而增加。比较了三个参数，即粘性（测量力）、初步校正粘性（在固定压缩力值下的校正粘性）和二次校正粘性（在固定校正压缩力值下的校正粘性）。在二次校正粘性中，不同大米样品之间的差异最为显著。仪器粘性和感官粘性之间的相关性在二次校正粘性中也最高。总之，与未校正的粘性相比，新的校正参数提高了样品的分辨能力和与感官粘性的一致性。
粘性是与米饭口感相关的重要质量因素。仪器粘性是质构仪圆柱形探头初步压缩米饭颗粒时的分离力。在力测量中，通常认为接触面积可以将力转换为应力。但是，对于像煮熟的米粒这样的样品，其接触面积比探头小，接触面积不容易知道，因为它不只是探头的底部面积。因此，接触面积并未用于测量煮熟的米饭粘性。在本研究中，设计了一种方法来确定接触面积。通过考虑接触面积得出的校正粘性比原始粘性通过感官评估更准确。
