NMR imaging of continuous and intermittent drying of pasta

An NMR imaging technique published in literature was adapted to investigate the role of glass transition on Fickian and non-Fickian modes of moisture transport in pasta. The modified technique allowed measuring the moisture distribution in samples with initial moisture content from 10% to 50% or higher. A change in slope in the signal intensity versus moisture content curves indicated different state or distribution of water in pasta samples below 16.9% moisture content for both 22 degrees C and 40 degrees C data. Sharp shape of moisture content profiles during continuous drying experiments indicated non-Fickian moisture transport near the glass transition regime. With progress of drying at 40 degrees C, the moisture profiles became more round, as pasta approached towards the glassy state, which indicated Fickian transport. A sharp change in pasta's moisture content during drying near glass transition caused a wide contrast in pasta's mechanical properties across its cross-section, which may make it prone to stress-cracking. During intermittent drying, a wet layer near the surface of pasta samples was clearly observed, which caused greater amount of moisture loss than during continuous drying. (c) 2005 Elsevier Ltd. All rights reserved.