Evaluation of glycosidic bond cleavage and formation of oxo groups in oxidized barley mixed-linkage β-glucans using tritium labelling

Iurlaro, Andrea; Dalessandro, Giuseppe; Piro, Gabriella; Miller, Janice G.; Fry, Stephen C.; Lenucci, Marcello Salvatore

doi:10.1016/j.foodres.2014.09.008

Cited by 8 publications

(7 citation statements)

References 47 publications

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“…However, new reducing termini in the case of polymeric materials such as BG originate exclusively from the non-reducing end portion of the molecule, and were observed by Iurlaro et al in the Fenton-induced degradation of barley BG and detected as [ 3 H]glucitol after reduction of formed carbonyls with NaB 3 H 4 and acid hydrolysis. 62 This is in agreement with the observations made in this study and is consistent with lytic C3/C4 oxidation.…”

Section: Identification Of Neutral Depolymerisation Productssupporting

confidence: 93%

UPLC-MS/MS investigation of β-glucan oligosaccharide oxidation

Boulos

Nyström

2016

Analyst

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Polysaccharide degradation mediated by hydroxyl radicals (HO˙) or lytic monooxygenases (LPMOs) is relevant in various biological and industrial processes. Thereby, the Fenton-induced (HO/Fe) oxidation of mixed-linkage (1→3,1→4)-β-d-glucan (BG), a cereal dietary fibre with several well-established health promoting properties, shows potential for modulating BG functionality. The precise identification of oxidation products, however, is impeded by their diversity due to the indiscriminate nature of HO˙, the large molecular weight, and the corresponding low frequency of discrete alterations along the polymer chain. In this paper, we studied the Fenton-induced degradation of several constitutionally isomeric glucotetraoses as BG model compounds by hydrophilic interaction UPLC-MS/MS in negative ion, high resolution mode. The influence of the β-(1→3)-linkage on the reaction was investigated with regard to degradation kinetics, formation of products, and MS/MS fragmentation patterns. The position and occurrence of a β-(1→3)-bond had no influence on the degradation kinetics. Classification into primary and secondary acidic oxidation products by monitoring their progress over time is also demonstrated, implying complexation of primary aldonic acid products by the catalytic iron and subsequently facilitated site-specific secondary oxidation, underlining the metal's importance beyond its role as HO˙-generating catalyst. Similarly to oxidations mediated by certain LPMOs, thorough MS/MS-analysis of selected products and comparison with synthesised standards confirmed two types of glycosidic cleavage cascades induced by HO˙-mediated H-atom abstraction at C1 and C3/C4, producing gluconic acids, native oligosaccharides, and oxo-oligomers (carbonyl at non-reducing end). Additionally, systematic study of other oxo-products from the different isomers and rationalisation of MS/MS fragmentation mechanisms allowed for the identification of potentially diagnostic fragment signals for oxidised cereal BG.

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Section: Identification Of Neutral Depolymerisation Productssupporting

confidence: 93%

UPLC-MS/MS investigation of β-glucan oligosaccharide oxidation

Boulos

Nyström

2016

Analyst

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“…Our results support previous studies, which suggest that hydroxyl radicals attack different carbons on glucosyl units of the β-glucan resulting in both degradation and formation of oxidised groups within the β-glucan chain. Iurlaro et al (2014) used tritium labelling to evaluate BBG oxidised with 1 μM CuSO4/10 mM H2O2/10 mM Asc. Based on their study, they suggested that more mid-chain carbonyl groups were formed compared to new reducing end carbonyl groups (ratio of 3:1) during oxidation.…”

Section: Formation Of Carbonyls Groups In the Oxidation Reactions Of mentioning

confidence: 99%

Reaction pathways during oxidation of cereal β-glucans

Mäkelä

Sontag‐Strohm

Schiehser

et al. 2017

Carbohydrate Polymers

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Oxidation of cereal β-glucans may affect their stability in food products. Generally, polysaccharides oxidise via different pathways leading to chain cleavage or formation of oxidised groups within the polymer chain. In this study, oxidation pathways of oat and barley β-glucans were assessed with different concentrations of hydrogen peroxide (HO) or ascorbic acid (Asc) with ferrous iron (Fe) as a catalyst. Degradation of β-glucans was evaluated using high performance size exclusion chromatography and formation of carbonyl groups using carbazole-9-carbonyloxyamine labelling. Furthermore, oxidative degradation of glucosyl residues was studied. Based on the results, the oxidation with Asc mainly resulted in glycosidic bond cleavage. With HO, both glycosidic bond cleavage and formation of carbonyl groups within the β-glucan chain was found. Moreover, HO oxidation led to production of formic acid, which was proposed to result from Ruff degradation where oxidised glucose (gluconic acid) is decarboxylated to form arabinose.

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“…Interestingly, lytic C5-oxidation has been largely overlooked as a pathway for direct cleavage of glycosidic linkages in HO • -mediated polysaccharide oxidation under formation of 5oxo Glc reducing ends (Faure et al, 2014 ; Iurlaro et al, 2014 ). This recent lack of reporting on C5-oxidation is especially puzzling in light of HO • -attack being somewhat favored at the C5-position as determined by EPR studies (Park et al, 1999 ) and pulsed γ-radiolysis of cellobiose (Sonntag et al, 1976 ).…”

Section: Resultsmentioning

confidence: 99%

“…Hence, cereal BG oxidation has been the focus of numerous studies employing various analytical techniques to investigate the radical reaction (ESR), to characterize the products (NMR/FT-IR), and monosaccharide composition (HPAEC-PAD), to quantify carbonyl or carboxylate groups (titration, fluorescent labeling), and to determine the change in bulk properties (rheology, M w distribution, aggregation; Kivelä et al, 2010 , 2011 , 2012 ; Faure et al, 2012 , 2013a , 2014 ; Mäkelä et al, 2015 , 2017 ). On a molecular level, indirect detection of oxo-products from HO • -mediated degradation of barley BG was reported by Iurlaro et al ( 2014 ), employing reductive tritium labeling followed by enzymatic or acid catalyzed hydrolysis and analysis by paper- and thin-layer chromatography. They confirmed the formation of new reducing ends and mid-chain oxo-groups, allowing to some extent the localization of the oxidative changes on monosaccharide units, but providing little information about their original connectivity prior to hydrolysis and no information about carboxylic acid products.…”

Section: Introductionmentioning

confidence: 99%

Complementary Sample Preparation Strategies for Analysis of Cereal β-Glucan Oxidation Products by UPLC-MS/MS

Boulos

Nyström

2017

Front. Chem.

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The oxidation of cereal (1→3,1→4)-β-D-glucan can influence the health promoting and technological properties of this linear, soluble homopolysaccharide by introduction of new functional groups or chain scission. Apart from deliberate oxidative modifications, oxidation of β-glucan can already occur during processing and storage, which is mediated by hydroxyl radicals (HO•) formed by the Fenton reaction. We present four complementary sample preparation strategies to investigate oat and barley β-glucan oxidation products by hydrophilic interaction ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), employing selective enzymatic digestion, graphitized carbon solid phase extraction (SPE), and functional group labeling techniques. The combination of these methods allows for detection of both lytic (C1, C3/4, C5) and non-lytic (C2, C4/3, C6) oxidation products resulting from HO•-attack at different glucose-carbons. By treating oxidized β-glucan with lichenase and β-glucosidase, only oxidized parts of the polymer remained in oligomeric form, which could be separated by SPE from the vast majority of non-oxidized glucose units. This allowed for the detection of oligomers with mid-chain glucuronic acids (C6) and carbonyls, as well as carbonyls at the non-reducing end from lytic C3/C4 oxidation. Neutral reducing ends were detected by reductive amination with anthranilic acid/amide as labeled glucose and cross-ring cleaved units (arabinose, erythrose) after enzyme treatment and SPE. New acidic chain termini were observed by carbodiimide-mediated amidation of carboxylic acids as anilides of gluconic, arabinonic, and erythronic acids. Hence, a full characterization of all types of oxidation products was possible by combining complementary sample preparation strategies. Differences in fine structure depending on source (oat vs. barley) translates to the ratio of observed oxidized oligomers, with in-depth analysis corroborating a random HO•-attack on glucose units irrespective of glycosidic linkage and neighborhood. The method was demonstrated to be (1) sufficiently sensitive to allow for the analysis of oxidation products also from a mild ascorbate-driven Fenton reaction, and (2) to be specific for cereal β-glucan even in the presence of other co-oxidized polysaccharides. This opens doors to applications in food processing to assess potential oxidations and provides the detailed structural basis to understand the effect oxidized functional groups have on β-glucan's health promoting and technological properties.

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Evaluation of glycosidic bond cleavage and formation of oxo groups in oxidized barley mixed-linkage β-glucans using tritium labelling

Cited by 8 publications

References 47 publications

UPLC-MS/MS investigation of β-glucan oligosaccharide oxidation

UPLC-MS/MS investigation of β-glucan oligosaccharide oxidation

Reaction pathways during oxidation of cereal β-glucans

Complementary Sample Preparation Strategies for Analysis of Cereal β-Glucan Oxidation Products by UPLC-MS/MS

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