A study of water diffusion into a high-amylose starch blend: the effect of moisture content and temperature

The effect of moisture content and temperature on water diffusion into a modified high amylose (< or = 90%) maize thermoplastic starch blend was investigated. Gravimetric and magnetic resonance imaging (MRI) studies were conducted to elucidate the diffusion mechanism and diffusion coefficients for this system. The diffusion coefficient data demonstrated that the rate of water diffusion into this blend was significantly dependent upon temperature and moisture content. Water diffusion was faster at higher temperatures and generally for samples stored at higher relative humidity environments. It was revealed from the gravimetric data that water diffusion into this starch blend was Fickian; however, further analysis of the MRI images found that the water diffusion mechanism was exponentially dependent on the concentration. This result was determined by comparing experimental water concentration profiles to a theoretical model calculated using the implicit Crank-Nicolson finite difference method.