A study of the pasting properties of rice flour and starch as affected by rice variety and physicochemical properties.

摘要

The cooking properties of rice and other grains are commonly characterized by the measurement of the viscosity of a flour or starch slurry during a programmed heating-holding-cooling cycle. A micro-method to measure the rheological properties of flour and starch during gelatinization, pasting and retrogradation using a controlled stress rheometer (CSR) was developed. The benefits of the CSR include precise control of shear rate and temperature, small sample size (100 mg), viscosity expressed in fundamental units and the possibility of continuous measurements throughout a simulated cooking process. The milligram scale sample size requirement of the micro-method allows its use to characterize samples from individual plants, typical of samples that may be found in cereal breeding programs.; The pasting properties of rice flours of California rice (Calmochi-101, L-202, L-204, M-202, M-401 and S-102) and waxy corn starch (Amioca) were measured by CSR and the Rapid Visco-Analyzer (RVA). A slurry concentration of 6–9% at a shear rate of 200s−1 was found to be optimum. The viscoamylographs were very reproducible as indicated by the 0–8% relative standard deviation of the peak viscosity for these samples. The CSR method and size exclusion chromatography with molar mass characterization by light scattering was also used to characterize waxy rice from California, Japan, China and Thailand from two crop years. The set of Japanese waxy rice had lower viscoamylographic viscosity parameters than the waxy rice from the other sources. Several methods were used to produce rice starch by removal of protein and/or fat from flour. There were considerable differences between the viscoamylographic profiles demonstrating the strong interaction between starch, protein and fat.; The effect of storage time on the pasting properties of rice flour and on the texture of cooked milled rice (Calmochi-101, Koshihikari, M-202 and L-204) grown in California from two crop years was evaluated by CSR. Viscoamylographic paste viscosity of all flours increased during 3, 6, and 12 months of storage. Hardness of long grain increased considerably, but hardness of other rice increased only slightly after 12 months of storage.