| Summary: | 碩士 === 臺灣大學 === 農業化學研究所 === 98 === The purpose of this study was to investigate the effect of different amylose contents on the granular morphologies, molecular structures, pasting and thermal properties of ball-milled corn starches. Waxy, normal and Hylon VII corn starches were ball milled with a planetary ball mill. The surface appearance, granular morphologies, and crystallinities of the ball-milled starches were characterized with scanning electron microscopy (SEM), wide angle X-ray diffractometer (WXRD) and small angle X-ray scattering (SAXS). The weight-averaged molecular weight of amylose and amylopectin as well as the chain length distribution of isoamylase debranched amylopectin of the ball-milled starches were determined with high-performance size-exclusion chromatography (HPSEC). The thermal and pasting properties of the ball-milled starches were obtained respectively with modulated differential scanning calorimetry (MDSC) and rapid visco analyser (RVA). The SEM investigation revealed that after ball milling, the damage of Hylon VII corn starch was limited, while that of waxy and normal corn starch was significant. As ball milling time prolong the molecular weight of normal and waxy corn starch decreased gradually, while Hylon VII corn starch was remained the same. It suggests that ball milling was more effective in reducing the starch with lower amylose content than higher amylose content. However, in the sample of debranch ball-milled waxy and normal corn starches, the chain length for waxy corn starch didn’t have significant difference whether ball-milled or not, but normal corn starch did. The content of amylose of ball-milled normal corn starch was decreased, while the content of chain length with DP~18 was increased for 1 or 2 hr ball milling. It might be because of the ball milling will cleavage the amylose and the chains in amorphous region of amylopectin. For normal and waxy corn starch, the gelatinization enthalpies disappeared after ball milling for 2 hr, and the peak viscosity, final viscosity, breakdown viscosity, and set back decreased after ball milling. In addition, the WAXD and SAXS peaks of all these starches (conditioned at 54% RH) decreased while the ball milling time increased. These revealed that the ball milling was effective in reducing the crystallinity and the double helical order arrangements of all the starches, among which the waxy corn starch had the highest degree of disintegration.
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