Original article: Characterisation of water species revealed in the drying operation of <i>Todarodes pacificus</i> Steenstrup using water proton NMR analysis

Abstract

Summary For the discrimination of water molecules during the squid‐drying process, the water distribution was characterised by water proton NMR and moisture diffusivity ( De ) analysis methods as a function of the water content ( W 0 ). The proton NMR spectrum showed three peaks indicating three different species (species‐A, ‐B, and ‐C) distributed in the squid muscle, each of which had a characteristic behaviour of the relaxation time ( T 2 ) as a function of the W 0 . The 1/ T 2 of species‐A was drastically varied at W 0 = 120%‐d.b., indicating two further categories, i.e., species‐A 1 and ‐A 2 . Species‐A 1 is available at W 0 &gt; 120%‐d.b. and was characterised as having De = 5.1 × 10 −10 m 2 s −1 , activation energy of moisture diffusivity ( E D ) = 17 kJ mol −1 , and relaxation rate 1/ T 2 = 74 s −1 , as evaluated by the proton NMR spectrum without depending on W 0 . Species‐A 2 is available at W 0 &lt; 120%‐d.b., indicating a distribution of De = 4.8 × 10 −10 –1.7 × 10 −10 m 2 s −1 , E D = 25–35 kJ mol −1 and 1/ T 2 = 1.8 × 10 3 –1.5 × 10 2 s −1 with increasing W 0 . Species‐A 1 and ‐A 2 were assigned as weakly restricted water and strongly restricted water, respectively.