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 °C and 40 °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 °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.