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^1H NMR and Rheological Studies of the Calcium Induced Gelation Process in Aqueous Low Methoxyl Pectin Solutions

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Dobies M., Kuśmia S., Jurga S.

Acta Physica Polonica A

2005

vol. 108

issue 1

33-46

The ^1H NMR relaxometry in combination with water proton spin-spin relaxation time measurements and rheometry have been applied to study the ionic gelation of 1% w/w aqueous low methoxyl pectin solution induced by divalent Ca^{2+} cations from a calcium chloride solution. The model-free approach to the analysis of ^1H NMR relaxometry data has been used to separate the information on the static (β) and dynamic (〈τ_c〉) behaviour of the systems tested. The ^1H NMR results confirm that the average mobility of both water and the pectin molecules is largely dependent on the concentration of the cross-linking agent. The character of this dependency (β,〈τ_c〉 and T_2 vs. CaCl_2 concentration) is consistent with the two-stage gelation process of low methoxyl pectin, in which the formation of strongly linked dimer associations (in the range of 0-2.5 mM CaCl_2) is followed by the appearance of weak inter-dimer aggregations (for CaCl_2 ≥ 3.5 mM). The presence of the weak gel structure for the sample with 3.5 mM CaCl_2 has been confirmed by rheological measurements. Apart from that, the T_1 and T_2 relaxation times have been found to be highly sensitive to the syneresis phenomenon, which can be useful to monitor the low methoxyl pectin gel network stability.

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1 Acta Physica Polonica A

1 2005

1 Dobies M.

1 Jurga S.

1 Kuśmia S.

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^1H NMR and Rheological Studies of the Calcium Induced Gelation Process in Aqueous Low Methoxyl Pectin Solutions