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Retrogradation of Amaranth Starch at Different Storage Temperatures and the Effects of Salt and Sugars¹

¹Published with the approval of the Director of the Agricultural Experiment Station, North Dakota State University, Fargo, ND 58105. ²Research assistant and associate professor, respectively, Department of Cereal Science, North Dakota State University, Fargo, ND 58105. ³Corresponding author. E-mail: rayasdu@okway.okstate.edu Phone: 405/744-6468. Fax: 405/744-6313. Present address: Food and Agricultural Products Research and Technology Center, Oklahoma State University, Stillwater, OK 74078-6055.

The retrogradation of amaranth, corn, wheat, and rice starches at different storage temperatures (-20, 4, and 25°C) was measured by differential scanning calorimetry (DSC). Sodium chloride (2 and 5%), glucose, sucrose, and fructose (10, 20, and 30%) were added to amaranth starch gels. The retrogradation was measured as the percent of gelatinization enthalpy (ΔH _g) of the retrograded gel when compared to the original nonretrograded sample. The data were analyzed fitting an exponential first-order equation by regression, assuming a first-order process. A modified equation was used for the data that showed several days of lag time before retrogradation was observed. Retrogradation percentage of amaranth gels at all three storage temperatures was lower than those of corn, wheat, or rice starches. Amaranth starch showed ≈2–9 times slower retrogradation rates than corn, wheat, and rice starches at 4 and -20°C, and up to ≈2.8 times lower maximum percent of retrogradation than the other starches at all three temperatures. After 21 days, amaranth, corn, and wheat starches exhibited the highest retrogradation (45, 77, and 67%, respectively) at 4°C, compared to 25 and -20°C. Rice starch had a higher retrogradation percentage (55%) at -20°C, compared to 25 and 4°C. The percent of retrogradation of gels with 5% NaCl addition decreased ≈2 and 1.7 times at 25 and 4°C, respectively, and increased ≈1.2 times at -20°C, compared to the control. The addition of sugars had similar effects in reducing retrogradation at 25 and 4°C and increasing retrogradation at -20°C when compared to samples with no sugar added.