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Physical Properties and Enzymatic Digestibility of Phosphorylated ae, wx, and Normal Maize Starch Prepared at Different pH Levels1

November 1999 Volume 76 Number 6
Pages 938 — 943
Huijun Liu , 2 Lawrence Ramsden , 2 and Harold Corke 2 , 3

Presented in part at the AACC 83rd Annual Meeting, Minneapolis, MN, September 1998. Cereal Science Laboratory, Department of Botany, The University of Hong Kong, Pokfulam Road, Hong Kong. Corresponding author. Fax: +852 2857 8521. E-mail: harold@hku.hk

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Accepted August 30, 1999.

Phosphorylated starches were prepared with sodium tripolyphosphate (STPP) at pH 6, 8, and 10 from waxy (wx, 3.3% amylose), normal (22.4% amylose), and two high-amylose (ae, 47 and 66% amylose) maize starches. After phosphorylation, the gelatinization peak temperature (Tp) decreased and pasting peak viscosity (PV) increased for all the starches except wx, which showed a slight increase in gelatinization temperature. There was a substantial effect of phosphorylation pH on paste viscosity. More crosslinking was found in ae starches with phosphorylation at pH 10. Sodium ions apparently decreased PV of all the phosphorylated starches while only slightly affecting PV of native starches. Phosphorylation increased swelling power of some of the starches, with maximum swelling power at phosphorylation pH 8 and minimum at pH 10. Maximum swelling power for wx starch after preparation was at pH 8 and minimum at pH 6. After phosphorylation, the clarity and freeze-thaw stability of all the starches was greatly increased compared with the native starches. Phosphorylation increased digestibility of ae starches but had little effect on wx and normal starches. After phosphorylation, the adhesiveness, springiness, and cohesiveness of all starch gels generally increased, the hardness of 47% ae and wx starches increased, and that of normal starches decreased. Enthalpy of gelatinization decreased after phosphorylation with the greatest decrease observed for ae starches. When the phosphorylation pH increased from 6 to 10, the brightness (L*) of all the phosphorylated starches decreased, while a* and b* of all the phosphorylated starch increased. Scanning electron micrographs showed some erosion on the surface of starch granules after phosphorylation.

© 1999 American Association of Cereal Chemists, Inc.