2001 AACC Annual Meeting Charlotte, North Carolina October 14-18, 2001 Charlotte Convention Center

Although pulsed NMR (PNMR) has been used for qualitative study of starch retrogradation in selected systems, validation is necessary for its application to new systems. In this paper, PNMR was used to analyze the retrogradation of rice starches in purified form and in rice flour and whole rice grains. The standard curves between relative solid content (S%) of PNMR and the percentage of gelatinized starch (G%) were determined for common rice starch, waxy rice starch and common rice flour at different moisture contents. The coefficients of linear regression R(^2) were all above 0.997. Starches with different amylose contents were tested for their S% value at the stages of freshly gelatinized, retrograded (4°C, 18 days) and re-heated (90°C, 20min). The S% of re-heated starch was identical with S% of freshly gelatinized starch, so we concluded that the increase in S% during storage corresponded to amylopectin retrogradation. The effect of moisture content on retrogradation of rice starch, rice flour and cooked whole rice grains was studied by PNMR and the data were interpreted using the Avami equation. Decreasing the moisture content increased the rate of retrogradation, and led to a higher parameter k and a lower parameter n. For moisture content in the range studied, PNMR could be used to follow amylopectin retrogradation of different rice starch systems.