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G. E. Babcock, R. Tobin, R. J. Dimler, and F. R. Senti. Copyright 1960 by the American Association of Cereal Chemists, Inc. Particle size in starch dispersions prepared by commonly used methods or by high-shear treatments was examined by ultracentrifugal and light-scattering methods. Heating at 98 or 120 C. in water left nearly 70% of the corn starch as relatively large, incompletely dispersed granule fragments which had sedimentation coefficients S20 greater than 1,500S (Svedberg units). About one-half the dispersed starch was free amylose, which sedimented as a separate component with S20 = 5--6S. Remaining dispersed particles had sedimentation coefficients up to 600S. Most marked effect of sodium hydroxide (1.0N) on autoclaved solutions was to free all the amylose component with little change in the degree of dispersion of the amylopectin residue. Ammonia pregelatinization weakened the granule structure of corn starch and doubled the extent to which it was dispersed in water at 98 degrees. High rate of mechanical shear was effective in dispersing granule fragments in starch pastes. Average particle size could be reduced readily to a narrow distribution with S20 = 80--150S and particle weights of 80--150 million. Little difference was found in the extent of dispersion of corn and wheat starch pastes under shear. Amount of free amylose in solution was relatively unaffected by reduction in particle size and comprised about 60 to 75% of the total amylose content of the starch. |
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