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Gelation of gellan gum aqueous solutions studied by polarization modulation spectroscopy
Author(s) -
Horinaka Junichi,
Kani Kohei,
Itokawa Yoshimi,
Ogawa Etsuyo,
Shindo Yohji
Publication year - 2004
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.20134
Subject(s) - chemistry , gellan gum , aqueous solution , salt (chemistry) , intermolecular force , intramolecular force , crystallography , analytical chemistry (journal) , polymer chemistry , chromatography , stereochemistry , organic chemistry , molecule , food science
Circular birefringence (CB, or optical rotation) and linear birefringence (LB) were measured for gellan gum aqueous solutions with and without salt to examine the gelling system in the helical structure as well as in the orientation. It was found that gelling samples with salt show nonzero LB values, whereas LB is zero for the samples without salt even in the gel state. This difference can be explained by the thermal deformation of the system containing anisotropic aggregations of helices formed with the shielding effect of the added salt on the intramolecular and intermolecular electrostatic repulsions. Considering that the presence of LB in the system affects the estimation of CB, we developed an original procedure of the CB measurement to eliminate the contribution of LB. It was shown that our methods for eliminating the contribution of LB can improve the CB measurement for the gellan gum gel. The temperature dependence of [α] for the samples with salt in the gel state is quite different from that for the samples without salt, suggesting that the aggregates of helices in the samples containing a high concentration of salt form a supramolecular structure that contributes to CB. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004