33A-1 |
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A. M. BARTH, Dept. of Food Science, Purdue Univ., 745 Agriculture Mall Dr., West Lafayette, IN 47907-2009 and B. R. Hamaker, Whistler Center for Carbohydrate Research, Purdue Univ., Dept. of Food Science, 745 Agriculture Mall Dr., West Lafayette, IN 47907-2009. Sorghum grain is an important food source for people living in the semiarid zone of Africa as well as parts of China and India (Dendy 1995). One problem often associated with food products made from sorghum is texture. Porridges made from sorghum tend to be sticker and softer than porridges made from maize. Flat and composite breads made from sorghum tend to stale faster than breads made from wheat or maize. The objective of this research was to relate sorghum starch properties to sorghum food product quality. Starch was isolated and defatted from several varieties of sorghum, corn, and rice. Commercial corn starch was also defatted. Differential scanning calorimetry was performed on 1: 2 starch: water dispersions. Dispersions were gelatinized, subjected to temperature cycling, and rescanned after 4 days. Dynamic oscillatory rheometry was performed on 9.5% d.s.b. starch gels stored for 7 days at 4°C. Temperature sweep tests were performed on gels at 0 (1 hour after cooling), 1, 3, 5, and 7 days at 1% strain and 1 Hz in a closed cell rheometer. Increase in elastic modulus followed the following order from fastest to slowest: sorghum variety Mota Maradi, normal dent corn (lab isolated), sorghum variety SC283-14, sorghum variety P851171, commercial corn starch, and long grain rice variety Lbnt. Differential scanning calorimetry results showed that variety Mota Maradi had the highest retrograded enthalpy, and variety SC 283-14 had the lowest enthalpy. Rice variety Lbnt had the second highest retrograded enthalpy. The rate of retrogradation in sorghum based food products appears to be a function of variety, shear, and possibly concentration. Our results indicate that formation of retrograded crystals under conditions used for differential scanning calorimetry (i.e. concentrated starch dispersions and no shear) are not effective measures for predicting textural properties of less concentrated starch gels.
Session 33A, Carbohydrate: General
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