Physicochemical and Thermal Properties of Non-Waxy Rice Flour as Affected by Waxy Rice Flour and Its Influence on Textural and Cooking Properties of Rice Spaghetti

In the present study, a dry milling method was applied to prepare rice flour from 2 rice varieties, Chai Nat 1 and Rice Division 6 (RD6), which were used to make rice spaghetti. The spaghetti samples were made from flours obtained by dry-milled Chai Nat 1 (DMCNT1; non waxy) rice flour and blending of drymilled RD6 (DMRD6; waxy) to dry-milled Chai Nat 1 (DMCNT1; non waxy) rice flour at three different ratios (5:95, 10:90, and 15:85). Amylose content, physicochemical, and thermal properties of flours were determined. The cooking properties of rice spaghetti samples were evaluated through textural properties, cooking qualities and microstructure. The amylose content of DMRD6 and DMCNT1 were 4.42 and 33.36 % dry basis, respectively. The blending ratios of DMRD6 to DMCNT1 from 5 to 15: 95 to 85 significantly decreased the amylose content of flours. The pasting and thermal properties of rice flours determined by using a rapid-visco analyser (RVA) and differential scanning calorimeter (DSC) indicated that blending of DMRD6 to DMCNT1 significantly decrease the pasting temperature, setback value and final viscosity. The retrogradation enthalpy of the blending of DMRD6 to DMCNT1 samples were also decreased with the increasing of DMRD6 rice flour level. The cooked rice spaghetti made from the blended flour of DMRD6 and DMCT1 at the ratio of 10:90 gave the highest tensile strength and the lowest cooking loss. From the study by a stereomicroscope, the cooked rice spaghetti made from DMCT1 had a uneven surface, in contrast to the surface of cooked rice spaghetti from blended flour (DMRD6 to DMCNT1; 10:90), which had smooth surface. Therefore, the blending of waxy rice flour to non waxy rice flour could improve rice spaghetti quality by reducing retrogradation value and improving the surface appearance of the rice spaghetti made from the optimum ratio of 10:90 (DMRD6:DMCNT1) rice flour.