|Wood, Delilah - De|
|Yokoyama, Wallace - Wally|
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2007
Publication Date: 8/8/2007
Citation: Ibanez-Carranza, A.M., Wood, D.F., Yokoyama, W.H., Park, I.M., Tinoco, M.A., Hudson, C.A., McKenzie, K.S., Shoemaker, C.F. 2007. Viscoelastic Properties of Waxy and Non-Waxy Rice Flours, Their Fat and Protein-Free Starch, and the Microstructure of Their Cooked Kernels. Journal of Agricultural and Food Chemistry. 55(16):6761-6771. Interpretive Summary: The food textural properties of two important rices grown in California were evaluated by a combination of chemistry, enzymatic treatment and rheological measurements. Removal of fat or protein resulted in changes in the textural properties of rice as determined by changes in the viscoelastic properties during a standard temperature-controlled gelation treatment. The structural changes accompanying the textural changes were also related to scanning electron micrographs of cooked kernels.
Technical Abstract: Physicochemistry and structural studies of two types of japonica rice, low amylose Calmochi-101 (CM101) and intermediate amylose M-202 (M202), were conducted to determine similarities and differences between the rices perhaps attributable to amylose content differences. The rheological behavior of the gelation and pasting processes of flours and starches was determined with high accuracy and precision using a controlled stress rheometer. Fat and protein, although minor constituents of milled rice, were shown to have significant effects on the physicochemical and pasting properties of starches and flours. Removal of protein and lipids with aqueous alkaline or detergent solutions caused lower pasting temperatures and higher overall viscosity in both starches, compared with their respective flours. There was less viscosity difference between M202 flour and its starch when isolated by enzymatic hydrolysis of protein. The protease did not reduce internally bound lipids, suggesting that fats help to determine pasting properties of rice flours and their respective starches. Structural integrity differences in individual granules of waxy and nonwaxy rice flours, starches, and whole raw, soaked, and cooked milled grain were revealed by fracture analysis and scanning electron microscopy. Calmochi 101 and M202 did not differ in weight-averaged molar mass (Mw) and root-mean-square radii (Rz) between flours and starches, as determined by high-performance size exclusion chromatography (HPSEC) and multiple-angle laser light scattering (MALLS) (Park, I.; Ibanez, A. M.; Shoemaker, C. F. Starch 2007, 59, 69-77).