Role of hydrogen ion concentration in retrogradation of starch sols

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Abstract

Cornstarch sols were prepared with pH adjusted to various values both before and after gelatinization. Retrogradation was ascertained by measurement of crystallinity (x-ray), enzymatic digestibility, and cold water solubility. When the starch was gelatinized after pH adjustment, maximum retrogradation was at a pH value of about 5, with diminishing retrogradation at higher and lower values. When the starch was gelatinized before pH adjustment, maximal retrogradation occurred at pH values 1–2, with diminishing retrogradation at higher values. After an initial period of rapid retrogradation, retrogradation at all pH values studied follows first-order kinetics. The data are explained in terms of molecular size, role of pH in hydrogen bond rupture, the weakly acidic character of starch, and changes in the configurational entropy of starch molecules.

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