| Summary: | 碩士 === 靜宜大學 === 食品營養學系 === 104 === Pyroconversion has been used to alter the physicochemical properties of starch and further increasing the utility of starch in food products. Dextrinization of starch will take times if the starch is heating without the presence of catalyst, therefore catalyst, such as hydrochloric acid, is used for shortening the reaction time. The presence of catalyst reduces not only the reaction time but also the reaction temperature used during pyrocoversion. In this study, pyrodextrins were prepared from normal corn starch under various temperature (140-180 oC) for 3 h by using of 0-2.5% (based of starch dry weight) acetic acid as catalyst. Recovery, color, morphology, solubility, reducing sugar content, molecular size distribution and available starch content of the prepared pyrodextrins were examined and compared for elucidating the feasibility and effect of acetic acid as a catalyst. Results indicated that the recovery was all above 93.5% for pyrodextrins prepared with various treatment conditions. Color changed from white of starch to light brown of pyrodextrins, granule intact, birefringence and iodine stained ability of starch decreased after pyroconversion. Molecular size of pyrodextrins shifted to small molecular fraction, available starch content of pyrodextrins significantly decreased (p˂0.0001), and cold-water-solubility of pyrodextrins significantly increased (p˂0.0001), while reducing sugar content of pyrodextrins slightly increased. Treatment temperature or acetic acid concentration showed significant effects (p˂0.0001) on solubility, molecular size and available starch content of pyrodextrins, while no effect (p>0.05) was found on reducing sugar content. The interaction of treatment temperature and acetic acid concentration showed no significant effect (p>0.05) on reducing sugar content and solubility measured at 25 or 50 oC. Results of contribution analysis indicated that treatment temperature had high contribution ratios on available starch content (49.1%) and solubility measured at 25 oC (81.0%) or 50 oC (81.2%), acetic acid concentration showed the highest contribution ratio (39.5%) on solubility measured at 90 oC, while the interaction of treatment temperature and acetic acid concentration showed the highest contribution ration (38.5%) on molecular size. In clusion, acetic acid, which is edible and safe in process, can be used as catalyst during pyroconversion of starch and controllably changes the properties of starch.
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