Effects of Compositional and Granular Properties on the Pasting Viscosity of Rice Starch Blends
| Main Authors: | , , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0038-9056 |
| Online Access: | http://www.viks.sk/chk/star_5_03_203_212.doc |
| Abstract: | Summaries. The changes in swelling power and pasting properties of suspensions of starch blends were studied in dependence on starch composition and at various isothermal temperatures (Tiso). Samples were prepared by mixing rice starches from Kaoshiung Sen 7 (KSS7, a high-amylose-content variety) and Taichung waxy 70 (TCW70, a waxy variety). Generally, mixing these starches at a comparable ratio caused significant decrements in overall swelling power, onset temperature of gelatinization or viscosity rise, and final viscosity of hot pastes after 30 min of isothermal stirring. Notable increases in the peak and conclusion temperatures of gelatinization and in the peak viscosity of the pastes were also observed. Generally, all viscosity parameters of the blends showed two linear dependencies on the starch composition, the graphs intersecting at a critical starch composition depending on the parameters concerned. The onset temperature of viscosity increase was related to the volume fraction of swollen granules when they were just closely packed in suspension. The volume fraction of KSS granules was smaller than that of TCW70. In addition, the rate of viscosity increase and the peak viscosity of the starch suspensions could be well described in terms of the swelling power (O) when Q <= ~27, and depending on the 7iS0 examined. From the photomicrographs of starch suspensions, the extensive shear-induced disintegration of TCW70 granules in the co-existence of rigid KSS7 granules was evident and in turn responsible for the reduced final viscosities of the hot pastes obtained from starch blends. Conclusion. When the restricted-swelling KSS7 starches were mixed with the easily swelling TCW70 starches at a comparable ratio, a significantly reduced swelling power and increased peak or conclusion temperature of gelatinization was observed. During pasting of the starch blends, the onset and peak temperatures of viscosity development were polynomial functions of starch composition, while the viscosities showed two linear dependencies on the starch composition. Mixing the starches resulted in an increased peak viscosity and degree of shear thinning but reduced final viscosity after 30 min of isothermal stirring. The rates of viscosity increase and the peak viscosities of the starch suspensions could be well described as a function of the swelling power for Q <= ~27, the other variables being the isothermal temperature and starch variety. The difference in swelling ability between the two starch species and the resultant shear-induced granular disintegration decisively determine the final viscosity of the starch blends. Generally, the influence of the granular properties on the pasting behavior of starch blends is higher than that of the soluble materials. The above results provide precise information about starch compositional and pasting conditions for native or pregelatinized starch blends. They would be quite valuable for preparation of real food systems such as soups, sauces, rice cakes, rice noodles, or instant starch mixes. More investigations on the formulation-paste property relationships of multiple starch or flour blends are required, in relation to the shear-induced changes in granular and soluble properties of starches. |
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| ISSN: | ISSN 0038-9056 |
