Effect of moisture uptake on the texture of dried laver Porphyra. (Nori) studied by mechanical characterization and NMR measurements

Abstract Mechanical property measurements, 1H T2 measurement by low-field (LF) NMR and 13C T1 measurement by high-resolution cross polarization/magic angle spinning (CP/MAS) solid-state NMR were carried out to evaluate the structural changes of Nori upon moisture uptake. The texture of dry Nori changed to be tough and then soft upon moisture uptake. The increase of 1H T2 and decrease of 13C T1 were observed with an increase of moisture content indicating the increase of the molecular mobility of Nori components. The results of the LF-NMR suggested that the increase of mobility of the inert protons in rigid components is more dominated than that of the labile protons in soft components when Nori becomes the soggy state, whereas the mobility of the soft part increases more by moisture uptake when Nori becomes the wet state. The changes of molecular mobility of each main component (proteins and porphyran) were well depicted by the 13C T1 measurement, which represented the hydration of porphyran and proteins in the pulps and binder part. The change of mechanical properties of Nori was successfully elucidated with the NMR relaxation measurements.