Characterizing changes in levan physicochemical properties in different pH environments using asymmetric flow field-flow fractionation Field-Flow Fractionation

J. Ray Runyon, Lars Nilsson, Matilda Ulmius, Alejandra Castro, Ruxandra Ionescu, Claes Andersson, Christoph Schmidt

Research output: Contribution to journalArticlepeer-review

23 Scopus citations

Abstract

The purpose of this study was to assess the stability of the polyfructan levan under different pH solution conditions by monitoring changes in the levan physicochemical properties, such as molar mass (M), root mean square radius (r rms ), hydrodynamic radius (r h ), structure factor (r rms /r h ), and aggregation state with respect to solution pH and hydrolysis time. A commercial levan produced from Z. Mobilis was characterized using asymmetric flow field-flow fractionation (AF4) in combination with online multiangle light scattering (MALS) and differential refractive index (dRI) detection. Under neutral pH solution conditions the levan was found to have a M ranging from 105 to 5∈×∈ 107 g/mol, a r rms ranging from ~25 to 100 nm and a r h from ~3 to 151 nm. Two populations were observed in the sample. One population with a M less than 106 g/mol which represented ~60 % of the sample and a second population with an ultrahigh M up to 5∈×∈107 g/mol, which comprised ~40 % of the sample. The measured r rms /r h structure factor decreased from 1.8 to 0.65 across the AF4 fractogram indicating that early eluting low M levan species had a random coil configuration and late eluting high M species had more homogeneous spherical structures. The measured apparent density values decreased from 80 to 10 kg/m3 across the elution profile and suggest that the observed second population also contains aggregates. The stability of levan in different pH conditions ranging from 1.3 to 8.5 was assessed by tracking changes in the average M and r h, and monitoring the formation of fructose over 1 week. The onset of levan acid hydrolysis was observed to occur sooner at lower pH conditions and no hydrolysis was observed for pH 5.5 and higher.

Original languageEnglish (US)
Pages (from-to)1597-1605
Number of pages9
JournalAnalytical and bioanalytical chemistry
Volume406
Issue number6
DOIs
StatePublished - Feb 2014
Externally publishedYes

Keywords

  • Field flow-fractionation
  • Levan
  • Light scattering
  • Macromolecule separation
  • Polyfructose
  • Polysaccharide

ASJC Scopus subject areas

  • Analytical Chemistry
  • Biochemistry

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