Amylose contents, rheological properties and gelatinization kinetics of yam (Dioscorea alata) and cassava (Manihot utilissima) starches

After defatting yam and cassava starches have amylose contents of 36.2 and 24.2%, respectively. Suspensions of these starches in water were analysed, in an oscillatory rheometer, using a heating rate of 4.0degreesC min(-1), deformation of 1% and a frequency of 1 Hz, the initial temperatures of gelatinization being 71 and 62degreesC for yam and cassava, respectively. A gelatinization study was also carried out by differential scanning calorimetry with different heating rates (2.5, 3.0, 4.0 and 5.0degreesC min(-1)), to give, by the Arrhenius equation, the activation Energy (E-a) of the process. Yam starch showed a more energetic gelatinization process of when compared to cassava starch and also had a lower rate constant (s(-1)), indicating, a relatively slow gelatinization process of at higher temperatures. Yam gels formed by autoclaving a suspension (50 g l(-1)) showed after 24 h of refrigeration, a stronger structure than for a cassava gel. (C) 2003 Published by Elsevier Ltd.