| Summary: | 碩士 === 國立臺灣大學 === 食品科技研究所 === 89 === The pasting, shear thinning, thermal and rheological properties of pure and mixed rice starches in the presence of guar gum (GG) or locust bean gum (LBG) (0.1 and 0.5%, w/w) were investigated. Two varieties of rice starches (TNuS19 and TCW70) with well-known molecular structures were used as samples and mixed at five blend ratios. The applicability and modification of Takayanagi polymer blending laws to describe the rheological changes of the starch or starch/galactomannan mixtures with the blending ratio were examined, in order to elucidate the roles of starch-starch and starch-galactomannan interactions in governing the whole physical properties of the mixed systems. Generally, the addition of galactomannans caused the increase in rapid viscosity, especially for the TNuS19 rather than TCW70 systems. The effectiveness of increasing rapid viscosities by GG was greater than by LBG. Shear thinning (%) varied significantly between different kind of galactomannan and added concentration. The onset temperature (To) and peak temperature (Tp) of starch composites/hydrocolloid mixtures did not show significant change compared with starch composites alone. Similar phenomena were also detected in retrogradation endotherm stored at 4oC for 14 days storage. The G¢, G¢¢ and tan ■ values of the starch composites varied significantly with the blend ratio of TCW70 to TNuS19 and the galactomannan concentration examined. The G'' increments caused by adding LBG were greater than those did by GG, but this situation was not observed for G'. The phase contrast light microscopy and iodine staining show that the TNuS19/galactomannan mixtures gave more granular form of swollen particles dispersed in macromolecular medium and less leaching-out amylose. The G'65 values of the starch composite-galactomannan (0.1%) system were close to the theoretical values derived by a modified isostress model of polymer blending laws. The G'25 and G'1h data of the above systems were intermediate values of the theoretical values based on isostrain and isostress models. However, when the GG or LBG concentration increased to 0.5 %, the above G' changes appeared to follow a modified isostress or isostrain laws, respectively. Generally, the modified blending laws could be used to describe the composition dependencies of starch composites and starch-galactomannan mixtures, which were also governed by the molecular property and concentration of the samples concerned.
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