RATIONALE:Fructans are carbohydrates predominantly based on fructose which are generally considered to be soluble dietary fibers with health-promoting properties. It is known that the nutritional properties of fructans are affected by their structure. This study focused on structural determination of branched fructans, as the most important dietary fructans are branched graminan-type fructans. METHODSBranched fructans were synthesized enzymatically by incubation of a heterologously expressed sucrose:fructan 6-fructosyltransferase (6-SFT) from Pachysandra terminalis with native or 13C-labeled substrates. Liquid chromatography/mass spectrometry (LC/MS) was used for the structural identification of branched fructans. The MS2 fragmentation of these compounds is described for the first time. Analytes were charged by electrospray ionization in negative mode and a quadrupole mass analyzer was used for MS2 analysis. RESULTS:The MS2 fragmentation patterns of branched and linear fructans were shown to differ and distinctive ion formation allowed differentiation between all branched fructan isomers formed. P. terminalis 6-SFT preferred extending the existing fructan branch rather than creating a new branch. CONCLUSIONSThe MS2 fragmentation patterns described in the current paper now allow rapid screening of large sample sets for the presence of branched, graminan-type fructans. Furthermore, the data enables the characterization of fructan-metabolizing enzymes by identification of the fructan structures produced by in vitro reactions as described here for P. terminalis 6-SFT.
Rapid Communications in Mass Spectrometry, 2014, Vol 28, Issue 20, p. 2191-2200