Side-by-side aggregation number of network-forming gellan aggregates as inferred from gradient NMR measurements

• Restriction on probe diffusion in gellan solutions decreased during cooling.
• A model was suggested to calculate aggregate-numbers from diffusion measurements.
• The model yields low aggregate-numbers, near independently of gellan concentration.
• The limitations and applicability of the model are discussed.

The gelation process of deacylated gellan gum was studied using gradient NMR. The concentration of semi-stiff coil solute (i.e., non-aggregated) gellan chains was estimated from the echo-signal intensity, and the self-diffusion coefficient of pullulan, which was added as a probe, was measured using pulsed-field-gradient stimulated-echo (PFG-STE) NMR. A model was suggested for the calculation of the relative side-by-side aggregation number of gellan. The model assumes that the restriction of diffusion in the gelling solution is hydrodynamic in nature, and that the same scaling of the dynamic correlation length holds for both helix-aggregates and (non-aggregated) semi-stiff coil gellan chains. With these assumptions, the gellan aggregation number's near-independence of gellan concentration (0.5–1.5%) for a fixed CaCl2 concentration was confirmed. The trends of increasing aggregation numbers with increasing salt concentration and higher aggregation numbers for Ca2+ than K+ were consistent with previous reports. Tentative estimates of the absolute aggregation number were in the range 8–34.

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