Reaction pathways during oxidation of cereal β-glucans

Mäkelä, Noora; Sontag‐Strohm, Tuula; Schiehser, Sonja; Potthast, Antje; Maaheimo, Hannu; Maina, Ndegwa Henry

doi:10.1016/j.carbpol.2016.11.060

Cited by 11 publications

(7 citation statements)

References 30 publications

(31 reference statements)

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“…Interestingly, however, the two oxidation conditions exhibited different proportions regarding the more diagnostic cross-ring cleavage products such as Ara- and Ery-2AB (Figure 7B ). This contrasts results from Mäkelä et al ( 2017 ), who also observed arabinose from OBG and BBG oxidation with H 2 O 2 (10–70 mM) by HPAEC-PAD after hydrolysis with lichenase/β-glucosidase, but not for samples oxidized with AH 2 (10–70 mM). This underlines the sensitivity of our method with 2-AB labeling and UPLC-MS analysis that allowed detection of cross-ring cleavage products even from a very mild oxidation.…”

Section: Resultscontrasting

confidence: 98%

“…Apart from threatening the molecular integrity of BG and its health benefits (Wood et al, 2000 ; Wolever et al, 2010 ; Regand et al, 2011 ), deliberate incorporation of new functional groups through oxidation has also been reported to change BG's technological (Lee et al, 2011 ) and health promoting properties (Park et al, 2009 ), providing great potential to influence BG functionality. 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.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Resultscontrasting

confidence: 98%

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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“…This corresponds well with the results of Faure et al (2012), which showed faster formation of hydroxyl radicals in BBG than in OBG during the first 6 h of oxidation and similar contents of hydroxyl radicals in both BBG and OBG after 24 h of oxidation. The difference in the effectiveness of hydrogen peroxide to oxidatively degrade BBG85 and OBG85 was already shown in our former study (Mäkelä et al, 2016), where significantly higher Mw decrease was observed in BBG85 when the oxidative degradation of BBG and OBG were compared. According to Wang, Maina, Ekholm, Lampi, & Sontag-Strohm (2016), this difference was caused by a variation in the phytate content of these commercial β-glucans.…”

Section: Viscosities and Hysteresis Of Barley And Oat β-Glucans Dissosupporting

confidence: 62%

“…Besides enzymatic and acid hydrolysis, also oxidation has been shown to cause degradation of βglucan (Faure, Andersen, & Nyström, 2012;Kivelä, Gates, & Sontag-Strohm, 2009a;Kivelä, Nyström, Salovaara, & Sontag-Strohm, 2009b;Kivelä, Henniges, Sontag-Strohm, & Potthast, 2012;Mäkelä, Sontag-Strohm, & Maina, 2015, Mäkelä et al, 2016. The initiation of β-glucan oxidation can occur in the presence of reactive oxygen species (ROS), the hydroxyl radical (•OH) being the most reactive one.…”

Section: Introductionmentioning

confidence: 99%

Gelation of cereal β-glucan at low concentrations

et al. 2017

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Viscosity of cereal β-glucan during digestion is considered to be a vital factor for its health effects. Thus, studies on solution properties and gelation are essential for understanding the mechanisms of the β-glucan functionality. The aim of this study was to investigate the effect of the dissolution temperature on gelation of cereal β-glucan at low concentrations that are relevant for food products. The rheological properties of oat and barley β-glucans (OBG and BBG) using three dissolution temperatures (37 ˚C, 57 ˚C and 85 ˚C) at low concentration (1.5% and 1%, respectively) were studied for 7 days. Additionally, the β-glucans were oxidised with 70 mM H2O2 and 1 mM FeSO4×7H2O as a catalyst, to evaluate the consequence of oxidative degradation on the gelation properties. The study showed that dissolution at 85 ˚C did not result in gelation. The optimal dissolution temperature for gelation of OBG was 37 ˚C and for gelation of BBG 57 ˚C. At these temperatures, also the oxidised OBG and BBG gelled, although the gel strength was somewhat lower than in the non-oxidised ones. Gelation was suggested to require partial dissolution of βglucan, which depended on the molar mass and aggregation state of the β-glucan molecule. Therefore, the state of β-glucan in solution and its thermal treatment history may affect its technological and physiological functionality.

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“…They can be formed through various pathways such as Fenton reaction in the presence of endogenous hydrogen peroxide and ferrous iron (H 2 O 2 + Fe 2+ → Fe 3+ +·OH + OH − ). Hydroxyl radicals can attack the ␤-glucan leading to significant viscosity and molecular weight decrease, formation of carbonyl groups along the ␤-glucan chain and the release of formic acid (Kivelä, 2011;Mäkelä et al, 2017). Fenton reaction can be initiated by the presence of ascorbic acid which is a common additive in food.…”

Section: Introductionmentioning

confidence: 98%