Neutral and acidic products derived from hydroxyl radical-induced oxidation of arabinotriose assessed by electrospray ionisation mass spectrometry

Abstract

The oxidation of α-(1 → 5)-L-arabinotriose (Ara3), an oligosaccharide structurally related to side chains of coffee arabinogalactans, was studied in reaction with hydroxyl radicals generated under conditions of Fenton reaction (Fe(2+)/H2O2). The acidic and neutral oxidation products were separated by ligand exchange/size-exclusion chromatography, subsequently identified by electrospray ionisation mass spectrometry (ESI-MS) and structurally characterised by tandem MS (ESI-MS/MS). In acidic fraction were identified several oxidation products containing an acidic residue at the corresponding reducing end of Ara3, namely arabinonic acid, and erythronic, glyceric and glycolic acids formed by oxidative scission of the furanose ring. In neutral fractions were identified derivatives containing keto, hydroxy and hydroperoxy moieties, as well as derivatives resulting from the ring scission at the reducing end of Ara3. In both acidic and neutral fractions, beyond the trisaccharide derivatives, the corresponding di- and monosaccharide derivatives were identified indicating the occurrence of oxidative depolymerisation. The structural characterisation of these oxidation products by ESI-MS/MS allowed the differentiation of isobaric and isomeric species of acidic and neutral character. The species identified in this study may help in detection of roasting products associated with the free radical-mediated oxidation of coffee arabinogalactans.

Evaluation of the photooxidation of galactosyl‐ and lactosylceramide by electrospray ionization mass spectrometry

“…These oxidation products are most probably formed due to oxidative cleavage of the lactosyl moiety. This result is in agreement with previous reports demonstrating oxidative cleavage of glycosidic bonds, after radical‐induced oxidation of small oligosaccharides due to the Fenton reaction …”

“…This result is in agreement with previous reports demonstrating oxidative cleavage of glycosidic bonds, after radical-induced oxidation of small oligosaccharides due to the Fenton reaction. [12,30] In order to confirm the structural features of the GSL oxidation products, accurate mass measurements and elemental composition determination were performed in a QTOF mass spectrometer (see Table 2). The structural assignments were made with a high degree of confidence, since deviations of the observed m/z values were between -4.3 and -7.9 ppm, thus confirming the proposed molecular formulae depicted in Table 2.…”

Effects of gamma irradiation and periodate oxidation on the structure of dextrin assessed by mass spectrometry

“…1. According to previous studies [38][39][40], the peak with the lowest elution time (10 min) was assigned to oligosaccharides bearing acidic residues, the one at 12 min was attributed to the enzyme, and the other peaks at 13-20 min were assigned to the neutral oligosaccharides.…”

“…This selective hydrolysis yields oligosaccharides of low molecular weight, allowing their separation by LEX/SEC and simplifying further MS spectra analyses. LEX/SEC provides an effective separation of acidic and neutral products, as well as the fractionation of neutral oligosaccharides according to their size [39,40,66].…”

“…For this, the samples were hydrolysed with α-amylase and further fractionated by semi-preparative ligand-exchange/size exclusion chromatography (LEX/SEC). MS has been used for the structural characterization of polysaccharides and oligosaccharides [35][36][37], including the oxidation of oligosaccharides [38][39][40]. Biomolecules, and namely polysaccharides (cellulose, dextran, dextrin, etc), are being increasingly used in the field of biomedicine.…”