Abstract
BACKGROUND: Changes in the properties of starch during postharvest hardening of trifoliate yam (Dioscorea dumetorum) tubers need to be investigated. In this work the starch gelatinisation kinetics of D. dumetorum cv. Yellow stored under prevailing tropical ambient conditions (0.98β2.32 kg vapour per 100 m^3^ airflow) for 0, 2, 7, 14, 21 and 28 days was studied using a 3 Γ 5 factorial experiment with three cooking temperature (75, 85 and 95 Β°C) and five cooking times (0, 5, 10, 20 and 40 min). Samples were also evaluated for starch properties and gelatinisation temperature.
RESULTS: Storage of D. dumetorum tubers caused starch damage. However, the starch gelatinisation temperature was between 70 and 75 Β°C irrespective of the tuber storage duration. The starch gelatinisation reaction followed firstβorder kinetics defined by the relationship ln(1 β Ξ±) = β k~G~t. The gelatinisation rate was significantly influenced (Pβ€0.05) by cooking temperature and increased with tuber storage duration. The activation energy also increased with tuber storage duration.
CONCLUSION: Although the gelatinisation temperature of D. dumetorum starch was not influenced by tuber storage, the starch gelatinisation process was affected by tuber storage duration, since tuber storage involved a greater need of energy for starch gelatinisation, which may be an effect of the postharvest hardening phenomenon. Copyright Β© 2008 Society of Chemical Industry