NMR relaxometry and rheology of ionic and acid alginate gels

The relationship between NMR relaxometry and rheology of acid alginate gels has been investigated in vitro and compared to that of ionic alginate gels. The onset and early stages of the gelation process were characterized by the time dependent changes in the storage modulus G′ and transverse relaxation rate R2 of the water, demonstrating how this NMR parameter can be used as a non-invasive/non-destructive indicator of the formation of these gels. Compression tests on the final gels showed that the acid gels were much weaker. No direct correlation was observed between the final strength of these types of gels and the measured NMR R2 values. The results suggest that in MRI studies in vivo the R2 relaxation rate could provide valuable information on the rate of gelation (but not on the actual final gel strength) of alginate-containing foods in the human gastric lumen.