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Contents of Indigestible Fraction, Water Solubility, and Color of Pyrodextrins Made from Waxy Sorghum Starch

¹Graduate student, School of Bioresource, College of Natural Science, Andong National University. Current address: Daepyung Co., Ltd., Sangju, Korea. ²School of Bioresource, College of Natural Science, Andong National University, Andong, Kyungbuk 760-749, Korea. ³Corresponding author. Phone: 82 54 820 5492. Fax: 82 54 823 1627. E-mail: kmchung@andong.ac.kr ⁴Graduate student, Department of Food Science and Technology, School of Agricultural Biotechnology, Seoul National University, Korea. ⁵National Laboratory for Functional Food Carbohydrate, School of Agricultural Biotechnology, and Center for Agricultural Biomaterials, Seoul National University, Korea.

To investigate the effect of prethinning of starch by acid before pyrolysis on the formation of indigestible fraction (IF) in pyrodextrins, native and prethinned (50°C for 1, 4, and 24 hr) waxy sorghum starches were heated at 120–160°C with 20–60 μL of 9% HCl/g of starch. Pyrodextrin containing 14.6% IF, measured as total dietary fiber by enzymatic-gravimetric method, was produced at 120°C with 20 μL of HCl from native waxy sorghum starch. Prethinning before pyrolysis increased IF content by 0–68%, depending on the conditions for pyrolysis, compared with that of the native starch. Reduction in the molecular size of starch by prethinning might cause greater mobility during pyroconversion reaction and thus generate higher IF contents. Increasing temperature and acid concentration during pyroconversion also increased IF content of pyrodextrins. Pyrodextrin of 44.9% IF was produced at 160°C with 60 μL of HCl from prethinned starch (50°C for 24 hr). Solubility of pyrodextrins was inversely proportional to IF content (r = -0.87) and had a range of 62.7–98.3%. Color of pyrodextrins became brownish with more severe pyroconversion conditions.