The jellifying capacity of some alginate gels excreted by Azotobacter vinelandii DSM 576 was studied by oscillatory tests at alginate concentrations (c) of 1.0% and 1.5% w/w. Frequency dependence of the complex shear modulus (G ) permitted these gels to be discriminated in terms of their different orders of the relaxation function (a) and ‘‘gel stiffness’’ (Aa ) values using Friedrich and Heymann theory [Journal of Rheology, 32 (1988) 235]. Of the samples tested that characterised by a guluronate content of 25% and a number-average molecular mass (Mn ) of 263.4 kDa exhibited a gel stiffness at c ¼ 1% w/w of the same order of magnitude of that pertaining to alginates extracted from Macrocystis pyrifera or Lessonia nigrescens with greater guluronate contents (35–40%) but smaller number-average molecular masses (70–110 kDa) with about half of a. Whereas a was found to depend exponentially on the ratio of guluronate to mannuronate monad frequencies (NG=M) only, Aa was expressed as a power function of c, Mn , NG=M, and average G-block length (NG ). The limited data available, as well as incomplete understanding of the real controlling factors for ionotropic gelation of alginates, made such empirical correlations just useful for a preliminary screening of alginates independently of their weed or microbial origin.

Viscoelastic properties of microbial alginate gels by oscillatory dynamic tests

PARENTE, Eugenio
2004-01-01

Abstract

The jellifying capacity of some alginate gels excreted by Azotobacter vinelandii DSM 576 was studied by oscillatory tests at alginate concentrations (c) of 1.0% and 1.5% w/w. Frequency dependence of the complex shear modulus (G ) permitted these gels to be discriminated in terms of their different orders of the relaxation function (a) and ‘‘gel stiffness’’ (Aa ) values using Friedrich and Heymann theory [Journal of Rheology, 32 (1988) 235]. Of the samples tested that characterised by a guluronate content of 25% and a number-average molecular mass (Mn ) of 263.4 kDa exhibited a gel stiffness at c ¼ 1% w/w of the same order of magnitude of that pertaining to alginates extracted from Macrocystis pyrifera or Lessonia nigrescens with greater guluronate contents (35–40%) but smaller number-average molecular masses (70–110 kDa) with about half of a. Whereas a was found to depend exponentially on the ratio of guluronate to mannuronate monad frequencies (NG=M) only, Aa was expressed as a power function of c, Mn , NG=M, and average G-block length (NG ). The limited data available, as well as incomplete understanding of the real controlling factors for ionotropic gelation of alginates, made such empirical correlations just useful for a preliminary screening of alginates independently of their weed or microbial origin.
2004
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11563/3032
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