Quantification of Sugar Epimers in Polygalactomannans by ESI-MS/MS

Erika Ponzini ,Greta Borgonovo ,Luca Merlini ,Yves M Galante ,Carlo Santambrogio ,Rita Grandori

doi:10.4172/2155-9872.1000281

Erika Ponzini , Greta Borgonovo + Show 4 more

Open Access

https://doi.org/10.4172/2155-9872.1000281

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Abstract

Polygalactomannans (PGMs) represent an important family of polysaccharides. They are obtained from the endosperm of leguminous plant seeds and are employed in a growing number of industrial applications as thickening agents and rheology modifiers. Each PGM has a typical mannose/galactose (M/G) ratio (from ~1 to ~5), which determines its solubility, viscosity and other physico-chemical properties. Complex polysaccharides are commonly characterized by proton nuclear magnetic resonance (1H-NMR), whereas mass spectrometry (MS) has not yet seen wide application. In this work, a new quantification method for sugar epimers in PGMs is presented, based on the characteristic fragmentation patterns of mannose and galactose in tandem MS (MS/MS) analyses. Standard galactose and mannose have been analyzed and fragmented in negative-ion mode on a hybrid quadrupole/time-of-flight (qTOF) mass spectrometer equipped with a nano electrospray ionization (ESI) source. The MS/MS spectra indicate accumulation of the same fragments for the two monosaccharides, but significant and reproducible differences in the relative intensities of the product ions. Known mixtures of mannose and galactose have been analyzed by the same procedure to test the applicability of the method for quantification purposes. The resulting peak intensities over the entire MS/MS spectrum can be deconvoluted as a linear combination of the signals from pure mannose and galactose standards, obtaining reliable and reproducible quantification of the epimers. The method has been applied to the characterization of hydrolysis products of PGMs from different species of leguminous plants, such as guar (Cyamopsis tetragonolobus), sesbania (Sesbania bispinosa) and tara (Caesalpinia spinosa), in order to assess specific susceptibility to hydrolysis conditions.

Highlights

Polysaccharides from animal, vegetal and microbial organisms are emerging as attractive materials in several industrial fields
Aqueous solutions of standard mannose and galactose were analyzed by electrospray ionization (ESI)-mass spectrometry (MS) in the two different ionization polarities
collision-induced dissociation (CID) experiments on sodium adducts do not lead to sugars fragmentation at any value of collision energy (CE), indicating a mere loss of the Na+ ion during the collisions with the inert gas, in agreement with previous reports on the MS/ MS behavior of pentoses and hexoses in positive ion-mode [46]

Summary

Introduction

Polysaccharides from animal (e.g., chitin, chitosan and hyaluronan), vegetal (e.g., cellulose, starch and pectin) and microbial (e.g., xanthan, gellan and curdlan) organisms are emerging as attractive materials in several industrial fields. They are employed as emulsion stabilizers, rheology modifiers, coating agents etc. PGMs are high-molecular weight polymers of about 1-2 MDa [12,13] They are normally composed of a β(1→4)-D-mannan backbone with several α(1→6) branches of single D-galactose units (Figure 1), more complex ramifications have been described [6]. The interest in these polymers is mainly due to the possibility of obtaining solutions with unique rheological properties, like extreme viscosities and non-

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