New insights into cooked rice quality by measuring modulus, adhesion and cohesion at the level of an individual rice grain

Causal relationships between physical properties and structure/composition of cooked rice are difficult to quantify when mechanical measurements are performed on bulk samples using large deformations that alter the structure irreversibly. We demonstrate here methods involving small-deformation to characterise the elastic modulus (E), adhesion and cohesion at the individual grain level, and show distinct differences between freshly cooked rice and shelf-stable retorted rice. On average, retorted rice is harder and less adhesive and cohesive than freshly cooked rice, but their distributions in each of these mechanical properties overlap. E is independent of adhesion and weakly correlated with moisture content. In addition, a ring-shear tester is shown to distinguish the bulk cohesion and flowing ability between rice samples. Measuring the inherent physical properties of individual grains has the potential to enable a more sensitive evaluation of new processes and grain varieties, and development of quantitative structure-property-processing relationships for rational design of products to perform optimally at different stages, from manufacturing through to oral processing.