Role of oxidative cleavage and acid hydrolysis of oat beta-glucan in modelled beverage conditions

Ascorbic acid-mediated reduction of arabinoxylan viscosity through free radical reactions

Arabinoxylan (AX) is a potential natural food additive that can enhance the textural properties of food. However, the addition of ascorbic acid (AA) can easily lead to a decrease in the viscosity of AX, which poses a challenge in the development of AX-rich foods. Therefore, the purpose of this study is to elucidate the mechanisms behind the reduction in AX viscosity in the presence of AA. The results indicated that AA could reduce the apparent viscosity and molecular weight of AX without significantly affecting the monosaccharide composition, suggesting a potential mechanism related to the cleavage of AX glycosidic bonds. Interestingly, free radicals were present in the reaction system, and the generation of free radicals under different conditions was consistent with the reduction in apparent viscosity of AX. Furthermore, the reduction in AX apparent viscosity by AA was influenced by various factors including AA concentration, reaction time, temperature, pH, and metal ions. These findings suggested that the mechanism of AX degradation may be due to AA-induced free radical generation, leading to non-selective attacks on glycosidic bonds. Therefore, this study revealed that the potential mechanism behind the reduction in AX viscosity induced by AA involved the generation of ascorbic acid radicals.

The importance of molecular weight in determining the minimum dose of oat β-glucan required to reduce the glycaemic response in healthy subjects without diabetes: a systematic review and meta-regression analysis

To determine the minimum amount of oat β-glucan (OBG) required to reduce glycaemic responses (MinDose), we conducted a systematic review and meta-regression analysis of acute, crossover, single-meal feeding trials that examined the effects of adding OBG or oat bran to a carbohydrate-containing test-meal versus a control test-meal containing an equivalent amount of available-carbohydrate (avCHO) from the same or similar source. Medline, Embase, and Cochrane Library were searched up to 18 August 2021. The primary outcome was glucose incremental-area-under-the-curve (iAUC). Secondary outcomes included insulin iAUC, and glucose and insulin incremental peak-rise (iPeak). Two independent reviewers extracted data. Results were expressed as ratio-of-means (RoM) with 95% confidence intervals (CIs). Linear associations were assessed by random effects meta-regression. MinDose was defined as the dose at which the upper 95% CI of the regression line cut the line of no effect (i.e., RoM = 1). Fifty-nine comparisons (n = 340) were included; 57 in healthy subjects without diabetes and two in subjects with diabetes; 24 high-MW (>1000 kg/mol), 22 medium-MW (300-1,000 kg/mol), and 13 low-MW (<300 kg/mol). In healthy subjects without diabetes the associations between OBG dose and glucose iAUC and iPeak were linear (non-linear p value >0.05). MinDoses for glucose iAUC for high-MW, medium-MW and low-MW OBG, respectively, were estimated to be 0.2 g, 2.2 g and 3.2 g per 30 g avCHO; MinDoses for glucose iPeak were less than those for iAUC. Insufficient data were available to assess MinDose for insulin, however, there was no evidence of a disproportionate increase in insulin. More high-quality trials are needed to establish MinDose in individuals with diabetes.

Impact of Enzymatic Hydrolysis and Microfluidization on the Techno-Functionality of Oat Bran in Suspension and Acid Milk Gel Models

Oat bran is a nutritionally rich ingredient, but it is underutilized in semi-moist and liquid foods due to technological issues such as high viscosity and sliminess. The aim of this work was to improve the technological properties of oat bran concentrate (OBC) in high-moisture food applications by enzymatic and mechanical treatments. OBC was hydrolyzed with β-glucanase (OBC-Hyd) and the water-soluble fraction (OBC-Sol) was separated. OBC, OBC-Hyd and OBC-Sol were further microfluidized at 5% dry matter content. Enzymatic treatment and microfluidization of OBC reduced the molecular weight (Mw) of β-glucan from 2748 kDa to 893 and 350 kDa, respectively, as well as the average particle size of OBC (3.4 and 35 times, respectively). Both treatments increased the extractability of the soluble compounds from the OBC samples (up to 80%) and affected their water retention capacity. OBC in suspension had very high viscosity (969 mPa·s) when heated, which decreased after both enzyme and microfluidization treatments. The colloidal stability of the OBC in suspension was improved, especially after microfluidization. The addition of OBC samples to acid milk gels decreased syneresis, improved the water holding capacity and softened the texture. The changes in the suspension and gel characteristics were linked with reduced β-glucan Mw and OBC particle size.

Valorization of cereal by-product hemicelluloses: Fractionation and purity considerations

The biomass from cereal side streams is rich in valuable components, such as hemicelluloses. Among the hemicelluloses, arabinoxylans and β-glucans are the most acknowledged for potential health benefits. Numerous publications discuss the potential to use purified forms of these hemicelluloses for various applications. However, as the purification of hemicelluloses may not be economically feasible to upscale, sustainable and cost-effective methods are needed to make their valorization more realistic for industrial applications. Co-components present in hemicellulose-rich fractions may also provide added functionality, such as flavonoid content and antioxidant capacity. This review provides an overview on the feasibility of sustainably upscaling hemicellulose extraction processes, focusing on by-products from different cereal streams. We describe the hemicelluloses' physicochemical properties and provide various possible applications of pure and impure fractions from small scale to pilot and industrial scale. Furthermore, real case examples on the industrial utilization of cereal side streams are enclosed. This review provides pathways for future research for developing the hemicellulose extraction methods to obtain fractions with optimized purity, and offers suggestions to valorize them.

An overview on interactions between natural product-derived β-glucan and small-molecule compounds

β-Glucans are widely found in plants and microorganisms, which has a variety of functional activities. During production and application, interactions with other components have a great influence on the structure and functional properties of β-glucan. In this paper, interactions (including non-covalent interaction and free-radical reaction) between natural product derived β-glucan and ascorbic acid, polyphenols, bile acids/salts, metal ion or other compounds were summarized. Besides, the mechanism and influence factors of interactions between β-glucan and small-molecule compounds, and their effects on the functional properties of β-glucan were detailed. This review aims to develop an understanding and practical suggestions on interactions between β-glucan and small-molecule compounds, which is expected to provide a useful reference for processing and application.

Cereal B-Glucans: The Impact of Processing and How It Affects Physiological Responses

Cereal β-glucans are dietary fibres primarily found in oats and barley, and have several positive effects on health, including lowering the postprandial glucose response and the improvement of blood cholesterol levels. Cereal β-glucans have a specific combination of β-(1→4) and β-(1→3) linkages into linear long-chain polysaccharides of high molecular weight. Due to their particular structure, cereal β-glucans generate viscosity within the intestinal tract, which is thought to be the main mechanism of action responsible for their positive health effects. However, cereal grains are rarely consumed raw; at least one cooking step is generally required before they can be safely eaten. Cooking and processing methods more generally will modify the physicochemical characteristics of β-glucans, such as molecular weight, extractability and the resulting viscosity. Therefore, the health impact of β-glucans will depend not only on the dose administered, but also on the ways they are processed or converted into food products. This review aims at summarizing the different parameters that can affect β-glucans efficacy to improve glucose and lipid metabolism in humans.

Lactic acid treatment of by-products and phosphorus level in the diet modulate bacterial microbiome and the predicted metagenome functions using the rumen simulation technique

This study used a rumen simulation technique to evaluate the effects of soaking of by-product-rich concentrate (BPC) in 5% lactic acid (LAC; vol/vol) on the rumen microbiota, predicted metagenome, fermentation characteristics, and nutrient degradation without or with supplemented P. The diet was supplemented with 1.6 g of P in the form of monocalcium phosphate per kilogram of dry matter in addition to 284 mg of inorganic P/d per fermentor via artificial saliva. Fermentor fluid was collected for analyses of short-chain fatty acids, fermentation gases, redox potential, and microbiota and feed residues for calculation of nutrient degradation. The microbiota composition was assessed using paired-end Illumina (Illumina Inc., San Diego, CA) MiSeq sequencing of the V3 to V5 region of the 16S rRNA gene. Soaking in LAC reduced the contents of crude protein, neutral and acid detergent fibers, and organic matter fractions as well as ash and P content of the BPC. Both the LAC treatment of BPC and the inorganic P modified the relative bacterial abundances mainly within the predominant orders Bacteroidales and Clostridiales. Supervised DIABLO N-integration networking supported that operational taxonomic units related to BS11, Ruminococcaceae, Christensenellaceae, Eubacterium, and Selenomonas were the most discriminant for the LAC-treated BPC, whereas other operational taxonomic units related to BS11, RFN20, Ruminococcus, and Succiniclasticum were best correlated with the inorganic P supplementation. Integration networking also showed that carbohydrate and pyruvate metabolism, biosynthesis of unsaturated fatty acids, and degradation of several xenobiotics were stimulated by the LAC treatment of BPC. Those data supported the enhanced fermentation activity as indicated by increased total short-chain fatty acid concentration, especially propionate and butyrate, and methane, but decreased ruminal crude protein degradation, with the LAC-treated compared with control-treated BPC. In contrast, despite an increased abundance of imputed functions, such as inositol phosphate metabolism, phosphatidylinositol signaling, and fructose and mannose metabolism, the reduced abundance of the imputed Kyoto Encyclopedia of Genes and Genomes pathway "transcription machinery" as well as the decrease in total short-chain fatty acids and nutrient degradation indicated reduced bacterial metabolic activity with the inorganic P supplementation. In conclusion, soaking of BPC in LAC may favor the proliferation of certain fibrolytic bacterial taxa and stimulate their metabolic activity, whereas the supplemented P to a diet already meeting ruminal P needs may impair ruminal nutrient utilization.

Use of β-glucan from spent brewer's yeast as a thickener in skimmed yogurt: Physicochemical, textural, and structural properties related to sensory perception

Powdered β-glucan extracted from brewer's yeast (Yestimun, Leiber GmbH, Bramsche, Germany) was incorporated into skimmed-milk yogurt at varying concentrations (0.2-0.8% wt/wt) to investigate its potential application as a thickener. The effect of β-glucan fortification on the nutritional profile, microstructure, physicochemical properties, and texture of freshly prepared yogurts was investigated. Sensory evaluation was also conducted and was correlated with instrumental analysis. The addition of Yestimun significantly reduced the fermentation time of the yogurt mix from 4 h to 3 h. Scanning electron microscopy revealed that β-glucan particles formed small spherical clusters within the yogurt matrix. The majority of the physicochemical properties (syneresis, viscosity, color, and titratable acidity) remained unaffected by the incorporation of Yestimun in the recipe. Textural properties showed a gradual increment with increasing β-glucan concentration. Hardness, total work done, adhesive force, and adhesiveness increased by 19.27, 23.3, 21.53, and 20.76%, respectively, when using the highest amount of Yestimun powder. Sensory analysis (n = 40) indicated that fortifying yogurt with Yestimun at 0.8% (wt/wt) concentration may affect overall acceptance ratings, which was attributed to adverse flavor and aftertaste effects. However, the overall liking score of the yogurt (5.0/9.0) shows potential for commercialization of the product.

Whole Tibetan Hull-Less Barley Exhibit Stronger Effect on Promoting Growth of Genus Bifidobacterium than Refined Barley In Vitro

The gut microbiota has recently become a new route for research at the intersection of diet and human health. The aim of this study was to investigate whether whole Tibetan hull-less barley (WHB) and refined Tibetan hull-less barley (RHB) caused differentiation of the fecal microbiota in vitro. The microbiota-accessible ingredients in the 2 barley samples were studied using an in vitro enzymatic digestion procedure. After in vitro digestion, insoluble dietary fiber, phenolic compounds, proteins, and β-glucans were 93.2%, 103.4%. 18.8%, and 10.2% higher provided by WHB flour as compared with RHB flour based on the same mass amount. However, due to the significantly higher content of insoluble dietary fiber, WHB digesta had lower percentage contents of fast fermentable substrates including dietary fiber and starch as compared with RHB digesta. The results of Next-generation sequencing of the bacterial 16SrRNA gene showed that both WHB and RHB fermentation had significantly promoted the growth of Bifidobacterium and inhibited the growth of pathogenic bacteria such as Dorea, Escherichia, Oscillopira, and Ruminococcus. Moreover, in response to WHB fermentation, the relative abundance of Bifidobacterium increased by 78.5% and 92.8% as compared with RHB and fructo-oligosaccharides (FOs). Both WHB and RHB are good sources of fermentable dietary fiber with the ability to yield high concentration of short chain fatty acids (SCFAs) as compared to FOs. However, the higher fraction of soluble fiber in RHB digesta increase higher amounts of SCFA compared with WHB digesta. Our findings shed light on the complex interactions of whole cereals with gut microbiota and the possible impact on host health.

PRACTICAL APPLICATION

Until now, only few reports have regarded the impact of in vitro digestion in components of whole grain with complex food matrix. Moreover, our findings shed light on the complex interactions of whole cereals with gut microbiota and the possible impact on host health.

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

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.

Oral mucositis caused by Candida glabrata biofilms: failure of the concomitant use of fluconazole and ascorbic acid

OBJECTIVES

Candida glabrata is becoming one of the most prevalent pathogenic yeasts in cases of oral diseases. Mucositis is an recurrent oral infection in immunocompromised patients, and the actual guidelines recommend the use of fluconazole (Flu) for many cases. However, the azole resistance by C. glabrata is renowned, causing a reduced therapeutic response, especially when it occurs in biofilms. In this study, we performed an in vitro evaluation of an alternative pharmacotherapy for C. glabrata biofilm infections, combining ascorbic acid (AA) with Flu. AA is recognized for degrading β-glucans, an important compound of the biofilm matrices, which prevent drug diffusion.

MATERIALS AND METHODS

Routine clinical 30 or 40 mg/l doses of Flu were applied to C. glabrata biofilms simultaneously with 200 or 300 mg/l of AA.

RESULTS

The results showed that this combination effectively promoted the degradation of the biofilm network, but unfortunately, also stimulated the growth of the yeasts population due to release of several glucose monomers during β-glucans hydrolysis.

DISCUSSION

AA lead to the hydrolysis of the β-glucans of the matrix, liberating glucose molecules which are used as carbon souce by the yeasts, thus suppressing the desired antifungal effect of the drug combination with Flu.

CONCLUSIONS

Unlike to what happens in treatment of bacterial infection, AA should not be used together with Flu in the treating oral mucositis caused by Candida.

Lytic Polysaccharide Monooxygenases: The Microbial Power Tool for Lignocellulose Degradation

Lytic polysaccharide monooxygenases (LPMOs) are copper-enzymes that catalyze oxidative cleavage of glycosidic bonds. These enzymes are secreted by many microorganisms to initiate infection and degradation processes. In particular, the concept of fungal degradation of lignocellulose has been revised in the light of this recent finding. LPMOs require a source of electrons for activity, and both enzymatic and plant-derived sources have been identified. Importantly, light-induced electron delivery from light-harvesting pigments can efficiently drive LPMO activity. The possible implications of LPMOs in plant-symbiont and -pathogen interactions are discussed in the context of the very powerful oxidative capacity of these enzymes.

Physicochemical and in vitro binding properties of barley β-glucan treated with hydrogen peroxide

This study investigated the changes in content, purity, physical properties, and in vitro binding properties of barley β-glucan by oxidation treatment. Barleys (Hordeum vulgare) were oxidized, using different concentrations of hydrogen peroxide (0.2-1.0% H2O2). The total and soluble β-glucan contents ranged from 8.41% and 4.81% in the control to 9.48% and 6.45% in the 0.6% H2O2 treatment. With increasing H2O2 concentration, the purity of β-glucan increased from 35% to 70%, whereas molecular weight (MW), viscosity, and water-binding capacities decreased to 2.0 × 10(4)Da, 3.9 cP, and 4.45 g water/g β-glucan, respectively. Oil binding capacities ranged from 8.29 g of oil/g in non-oxidized β-glucan to 9.42 g of oil/g in β-glucan oxidized with 0.6% H2O2. The MW, viscosity, and binding capacities of waxy barley β-glucan were higher than those of non-waxy barley β-glucan. Oxidation by hydrogen peroxide improved the physical properties and in vitro binding capacity of barley β-glucan.

Fingerprinting of hydroxyl radical-attacked polysaccharides by N-isopropyl-2-aminoacridone labelling

Hydroxyl radicals (^•OH) cause non-enzymic scission of polysaccharides in diverse biological systems. Such reactions can be detrimental (e.g. causing rheumatic and arthritic diseases in mammals) or beneficial (e.g. promoting the softening of ripening fruit, and biomass saccharification). Here we present a method for documenting ^•OH action, based on fluorescent labelling of the oxo groups that are introduced as glycosulose residues when ^•OH attacks polysaccharides. The method was tested on several polysaccharides, especially pectin, after treatment with Fenton reagents. 2-Aminoacridone plus cyanoborohydride reductively aminated the oxo groups in treated polysaccharides; the product was then reacted with acetone plus cyanoborohydride, forming a stable tertiary amine with the carbohydrate linked to N-isopropyl-2-aminoacridone (pAMAC). Digestion of labelled pectin with ‘Driselase’ yielded several fluorescent products which on electrophoresis and HPLC provided a useful ‘fingerprint’ indicating ^•OH attack. The most diagnostic product was a disaccharide conjugate of the type pAMAC·UA-GalA (UA=unspecified uronic acid), whose UA-GalA bond was Driselase-resistant (product 2A). 2A was clearly distinguishable from GalA-GalA–pAMAC (disaccharide labelled at its reducing end), which was digestible to GalA–pAMAC. The methodology is applicable, with appropriate enzymes in place of Driselase, for detecting natural and artificial ^•OH attack in diverse plant, animal and microbial polysaccharides.

Non-enzymic scission of polysaccharides by hydroxyl radicals (^•OH) may be biologically detrimental or beneficial. We present a ‘fingerprinting’ method for detecting polysaccharides that have been ^•OH-attacked. The method detects the glycosulose residues introduced by ^•OH action.

Modulating the structural properties of β-D-glucan degradation products by alternative reaction pathways

The aim of the present study was to compare the degradation of β-D-glucan induced by hydroxyl radical to the degradation induced by heat treatment. β-D-Glucan was quickly and widely degraded by the action of hydroxyl radicals produced by a Fenton system at 85 °C, while thermal hydrolysis at 85 °C induced slow β-D-glucan depolymerization. The hydroxyl radical-induced degradation of β-D-glucan was accompanied by the formation of peroxyl radicals and new oxidized functional groups (i.e. lactones, carboxylic acids, ketones and aldehydes), as detected by ESR and NMR, respectively. In contrast, no changes in the monomer chemical structure of β-D-glucan were observed upon thermal hydrolysis. Therefore, different mechanisms are proposed for the oxidative cleavage of β-D-glucan, which are initiated by the presence of an unpaired electron on the anomeric carbon.