Rice pellets were prepared by single-screw extrusion cooking at an in-barre
l water content of 45 to 55 wt. %. The glass transition (T-g) and expansion
(T-e) temperature of rice pellets has been determined by differential scan
ning calorimetry (DSC) and non-contact infrared thermometer, respectively.
T-g and T-e had similar dependence on equilibrium moisture that acted as pl
asticiser. T-e increased linearly with T-g with a correlation coefficient (
r(2)) of 0.95. T-e was 20-100 degrees C higher than T-g, which indicated th
at the expansion of pellets occurred at the rubbery region. Maximum expansi
on occurred at 10% equilibrated moisture due to the transition of pellet fr
om brittle to ductile. The addition of dextrin reduced the average molecula
r weight as well as T-g, but increased the expansion ratio due to decreasin
g the viscosity. Gordon Taylor equation fitted well (r(2)=0.89) T-g of the
pellets without dextrin. A model has been developed to estimate T-g for the
pellet consisting of rice flour, water and dextrin. (C) 2000 Academic Pres
s.