Radial NMR microimaging studies of the rehydration of extruded pasta

Abstract

A novel NMR radial microimaging technique is used to image the ingress of water into extruded pasta during rehydration. It is shown that the rehydration is a non-Fickian diffusion process where the diffusion coefficient is strongly dependent on the local moisture content and where diffusion is accompanied by radial and length expansion. The simultaneous diffusion and expansion are modelled numerically for three types of extruded pasta, differing in the amounts of their constituent hard and soft wheat. It is found that increasing the amount of hard wheat shifts the diffusion closer to the limit of Case II Fickian diffusion where there is a sharp moving boundary between the unhydrated glassy state and the rehydrated gel. The potential of NMR radial microimaging for monitoring mass and heat transport during the processing of other food materials is discussed.