Effect of extrusion parameters on physicochemical properties of hybrid indica rice (type 9718) extrudates

In order to improve the edible quality of hybrid indica rice (Type 9718) in China, extrusion technology might be considered to create the so-called “reformed rice.” Effects of extrusion parameters such as feed water content, barrel temperature and extruder screw speed on physicochemical properties of rice extrudates were investigated. Water-soluble carbohydrates and enzyme sensitivity (α-amylase) of extrudates were basically higher than those of parboiled rice. Water absorption index of all extrudates was lower than that of parboiled rice (4.95 g/g), which indicated that extrusion cooking was not only a heating procedure but also a process with shear force, degradation of rice starch. Through statistical analysis, it was found that both barrel temperature and feed water content could positively be correlated with physicochemical properties of extrudates excluding bulk density. Texture studies indicated that hardness of all hybrid indica rice (Type 9718) extrudates was lower than that of cooked raw rice and parboiled rice. The scanning electron microscope images demonstrated that there was indeed a granular gel network formed within the rice extrudates. PRACTICAL APPLICATIONS: Extrusion cooking technology is used for cereal and protein processing in the food. In the present study, this technology was employed to investigate the effects of feed water content, barrel temperature and extruder screw speed on the physicochemical properties of hybrid indica rice (Type 9718) extrudates. It was found that extrusion cooking was not only a heating procedure but also a process with shear force and pressure, destruction and degradation of rice starch, the most important constituent which could affect physicochemical properties in rice extrudates. Textural studies had shown that under proper extrusion parameters, the texture of hybrid indica rice (Type 9718) extrudates was in fact much better than that of cooked raw rice and parboiled rice.