ISSN:
1750-3841
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
,
Process Engineering, Biotechnology, Nutrition Technology
Notes:
Pulsed NMR was applied to measure the spin-lattice (T1) and the spin-spin (T1) relaxation times of the water adsorbed on sodium alginate, pectin, corn starch, casein and cellulose. T1 was determined by means of repeated 90°-90° pulse sequences and T2 by the spin-echo method. T1 relaxation time curves for all the samples studied showed simple exponential, i.e., single phase, behavior. Plots of T1 as a function of moisture content showed minima at 0.15–0.258 water/g dry matter; plots of T1 vs water activity (Aw) yielded minima at Aw of 0.65. T2 relaxation time curves for corn starch containing more than 0.56g water/g DM exhibited two-phase behavior, indicating the existence of two water fractions of different mobility. The amount of water in the bound fraction showed a remarkable consistency (0.194 ± 0.011g water/g DM) among six samples of high moisture content. T2 was found to increase with moisture content for all the macromolecules. Cellulose showed exceptionally long T2 values compared to the other materials at the same moisture content, whereas pectin and sodium alginate showed short T2 values. These results indicated that T2 value is a measure of strength of water binding. Break points were observed in the T2-moisture curve. The moisture contents at these points corresponded to the bound water content determined by freezing and to the equilibrium moisture content at Aw of 0.9. T2 increased exponentially with Aw.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-2621.1976.tb00604.x
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