Rupture strength of brown rice varieties as affected by moisture content and loading rate

In this research, the mechanical strength of 12 varieties of brown rice grain was investigated. The brown rice grains at four levels of moisture content (8, 10, 12 and 14% w.b.) were quasi-statically loaded at two rates of 10 and 15 mm/min in horizontal orientation. The results revealed that the rupture force of brown rice grain decreased by increasing the moisture content and loading rate. For all varieties evaluated, the highest values of rupture force was obtained at the moisture content of 8% (w.b.) and loading rate of 10 mm/min; while the lowest rupture force corresponded to the moisture content of 14% (w.b.) and loading rate of 15 mm/min. The 12 varieties were divided into three groups based on the slenderness ratio of the grains, namely, local short grain varieties (LSGV), local long grain varieties (LLGV), and improved long grain varieties (ILGV). This classification is used in Iranian rice trade markets. The means groups were contrasted through the general linear model (GLM) procedure. It was observed that the rupture strength of the three groups were statistically different from each other ( P<0.01). It was revealed that the brown rice rupture at lower levels of moisture content was in the form of sudden failure with less deformation; while at higher levels of moisture content the grain rupture was in the form of gradually crushing with more deformation. The results proved that some other characteristics such as textural properties might exist in the grains which influence the rheological behaviour and mechanical strength of the grains. So, it is recommended that the design and adjustment of rice processing equipments must be performed based on the mechanical and textural properties of rice varieties.