EVALUATION OF VARIETAL PROPERTIES OF COOKED RICE GRAINS BY RHEOLOGICAL MEASUREMENT

Dynamic viscoelasticities of cooked rice grains were measured using an instrument for evaluating dynamic viscoelasticity of irregularly shap ed and small samples in the double-side shear mode. Viscoelastic param eters, modulus G', dynamic loss G'' and loss tangent tandelta were obt ained for five varieties of rice which had different amylose (17.5 app roximately 30.0%) and protein (6.5 approximately 11.6%) contents. Trea tments performed on these samples, included conductive heating by mean s of an electric rice cooker, steaming and microwave heating. For the coefficient of varience, these tandelta values were less than 5%, in c ontrast to both G' and G'' which were more than 10%. These tandelta va lues were not influenced very much by water content or polishing rate of grains, while they were substantially affected by the treatments an d aging at room temperature. Each variety treated by conductive heatin g could be classified with respect to tandelta values which were betwe en 0.175 and 0.335. In the case of equal value of tandelta, those vari eties could be classified by their dynamic modulus. On the other hand, it was found that tandelta related amylose content and the breakdown viscosity by amylography from chemical and rheological analyses. As a result, the use of tandelta as the index of the breakdown properties o f the starch granules upon heating was suggested.