Structural analysis of fructans produced by acetic acid bacteria reveals a relation to hydrocolloid function

Some strains of acetic acid bacteria (Gluconobacter frateurii TMW 2.767, Gluconobacter cerinus DSM 9533T, Neoasaia chiangmaiensis NBRC 101099, Kozakia baliensis DSM 14400) produce high amounts of fructans, which can be exploited in food applications as previously demonstrated empirically for dough systems. In order to get insight into the structure and functionality of these polymers, we investigated the fructans isolated from these strains with respect to their linkage types and molecular weights/shapes using NMR spectroscopy and AF4-MALS-RI. Each fructan was identified as levan. The isolated levan fractions were highly similar according to their basic linearity and linkage types, but differed significantly in terms of their individual molecular weight distributions. In aqueous solutions the size of levan molecules present in all isolated levans continuously increased with their molecular weight and they tended to adopt a more compact molecular shape. Our data suggest that the increasing molecular weight of a levan particle enforces intramolecular interactions to reach the structural compactness of a microgel with hydrocolloid properties.