A mathematical model to describe the change in moisture distribution in maize starch during hydrothermal treatment

Instantaneous Controlled Pressure Drop, ‘De´tente Instantanee Controˆlee' (DIC) was performed on standard maize starch at residual moisture content (~12%). Changes in moisture distribution were observed during the treatment and modelled through a phenomenological model based on gravimetric data. The model proposes an exponential variation in the moisture content with processing time at various pressures. The predicted data were found to be in good agreement with experimental data. The values of water activity coefficient (c) obtained from the model decrease, when processing pressure increases; 5.86, 3.71 and 3.36 (dry basis))1 for 1, 2 and 3 bar, respectively. The mass transfer coefficient decreases, when the pressure increases. Its value ranged from 5.89 · 10)5 m s)1 for 1 bar down to 0.92 · 10)5 m s)1 for 2 bar and 0.77 · 10)5 m s)1 for 3 bar. This coefficient is not only controlled by a simple resistance to the mass transfer, but also by gelatinisation phenomenon that progresses when temperature increases.