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 4.0 °C min−1, deformation of 1% and a frequency of 1 Hz, the initial temperatures of gelatinization being 71 and 62 °C 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 5.0 °C min−1), to give, by the Arrhenius equation, the activation Energy (Ea) 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.