Characterizing changes in levan physicochemical properties in different pH environments using asymmetric flow...

Area of Science:

• Biopolymers and Carbohydrate Chemistry
• Materials Science and Engineering
• Analytical Chemistry

Background:

• Levan, a polyfructan produced by bacteria like Zymomonas mobilis, is a complex polysaccharide with potential industrial applications.
• Understanding levan's stability under varying environmental conditions, particularly pH, is crucial for its effective utilization and storage.
• Physicochemical properties of levan, including molar mass and aggregation state, can be influenced by solution conditions.

Purpose of the Study:

• To evaluate the stability of bacterial levan under diverse pH conditions (1.3 to 8.5).
• To investigate the impact of pH and hydrolysis time on levan's molar mass, radius, structure factor, and aggregation state.
• To determine the threshold pH for levan hydrolysis and degradation.

Main Methods:

• Characterization of commercial levan using asymmetric flow field-flow fractionation (AF4).
• Online detection with multiangle light scattering (MALS) and differential refractive index (dRI) for molar mass and radius determination.
• Monitoring of physicochemical changes (molar mass, hydrodynamic radius) and fructose formation over one week at different pH levels.

Main Results:

• Levan exhibited a bimodal molar mass distribution, with populations below 10^6 g/mol (~60%) and ultrahigh molar mass up to 5x10^7 g/mol (~40%).
• Structure factor (r(rms)/r(h)) indicated random coil configurations for low molar mass levan and more spherical structures for high molar mass species, with evidence of aggregation.
• Acid hydrolysis of levan initiated rapidly at low pH (<5.5), with no significant degradation observed at pH 5.5 and above within the study period.

Conclusions:

• Levan stability is highly pH-dependent, with significant acid-catalyzed hydrolysis occurring below pH 5.5.
• Levan demonstrates good stability in neutral to alkaline conditions, suggesting suitability for applications in this pH range.
• The characterized levan possesses a complex structure with distinct populations and aggregation states, influencing its behavior in solution.