Contents of indigestible fraction, water solubility, and color of pyrodextrins made from waxy sorghum starch

To investigate the effect of prethinning of starch by acid before pyrolysis on the formation of indigestible fraction (IF) in pyrodextrins, native and prethinned (50degreesC for 1, 4, and 24 hr) waxy sorghum starches were heated at 120-160degreesC with 20-60 muL of 9% HCl/g of starch. Pyrodextrin containing 14.6% IF, measured as total dietary fiber by enzymatic-gravimetric method, was produced at 120degreesC with 20 muL 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 160degreesC with 60 muL of HCl from prethinned starch (50degreesC 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.