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.

The water content of larval and puparial cuticle of Calliphora vomitoria has been measured under differing conditions using nuclear magnetic resonance, differential scanning calorimetry and simple gravimetry. On average, 2.5 molecules of water are associated with each amino acid side chain. This water is not displaced by tanning, even though tanning reduces the overall content of freezable water, suggesting that tanning agents do not interact with polar groups on the protein but increase overall hydrophobicity. This refutes normally accepted concepts of tanning by covalent cross linking. Additionally, covalent cross linking cannot account for the reduction in swellability of the cuticle on tanning.

Measurements of the temperature dependences of the spin-spin relaxations of the water protons have been made in gels of kappa- and iota-carrageenan and of mixtures thereof as functions of gel concentration, and ionic content and character. A maximum and subsequent minimum are observed in the temperature dependence of the spin-spin relaxation time T 2 , with the minimum generally being related to the onset of gel melting. The temperature and the depth of the T 2 minimum are enhanced by a decrease in the sulphate content of the polysaccharide and an increase in ionic content, with differential cationic and anionic effects being observed. A model is applied in which it is assumed that, in the temperature region between the T 2 maximum and minimum, the relaxation is dominated by an increasingly effective contribution by a highly immobile proton species associated with the polysaccharide. The determination of the relaxation of the water protons by the mobility and rate of exchange of this immobile species allows the water relaxation to act as a sensitive probe of the polysaccharide dynamics and aggregation.