β-Glucan (Oat; High Viscosity)

Fermentation of β-glucan fractions from barley [average molecular mass (MM), of 243, 172, and 137 kDa] and oats (average MM of 230 and 150 kDa) by the human faecal microbiota was investigated. Fractions were supplemented to pH-controlled anaerobic batch culture fermenters inoculated with human faecal samples from three donors, in triplicate, for each substrate. Microbiota changes were monitored by fluorescent in situ hybridization; groups enumerated were: Bifidobacterium genus, Bacteroides and Prevotella group, Clostridium histolyticum subgroup, Ruminococcus-Eubacterium-Clostridium (REC) cluster, Lactobacillus-Enterococcus group, Atopobium cluster, and clostridial cluster IX. Short-chain fatty acids and lactic acid were measured by HPLC. The C. histolyticum subgroup increased significantly in all vessels and clostridial cluster IX maintained high populations with all fractions. The Bacteroides-Prevotella group increased with all but the 243-kDa barley and 230-kDa oat substrates. In general β-glucans displayed no apparent prebiotic potential. The SCFA profile (51 : 32 : 17; acetate : propionate : butyrate) was considered propionate-rich. In a further study a β-glucan oligosaccharide fraction was produced with a degree of polymerization of 3-4. This fraction was supplemented to small-scale faecal batch cultures and gave significant increases in the Lactobacillus-Enterococcus group; however, the prebiotic potential of this fraction was marginal compared with that of inulin.

Trained immunity has been recently identified in innate immune cells, which undergo long-term epigenetic and metabolic reprogramming after exposure to pathogens for protection from secondary infections. (1, 3)/(1, 6)-β-glucan derived from fungi can induce potent trained immunity; however, the effect of (1, 3)/(1, 4)-β-glucan (rich in dietary fiber oat) on trained immunity has not been reported. In the present study, two cell culture systems for trained immunity induction were validated in monocytes/macrophages from mouse bone myeloid and human THP-1 cells exposed to positive inducers of trained immunity, including β-glucan from Trametes versicolor or human-oxidized low-density lipoprotein. Primed with oat β-glucan, the mRNA expression and production of TNF-α and IL-6 significantly increased in response to re-stimulation of TLR-4/2 ligands. Moreover, the expression of several key enzymes in glycolytic pathway and tricarboxylic acid cycle was significantly upregulated. In addition, inhibiting these enzymes decreased the production of TNF-α and IL-6 boosted by oat β-glucan. These results show that oat β-glucan induces trained immunity through metabolic reprogramming. This provides important evidence that dietary fiber can maintain the long-term responsiveness of the innate immune system, which may benefit for prevention of infectious diseases or cancers.

The shear and extensional rheology of β-glucan and mucin mixtures have been studied as to probe the functionality-related thickening effects of consumed β-glucan during food digestion. Mucins, the main viscosity-inducing components of oral and gastrointestinal fluids, can increase the shear viscosity of β-glucan solutions, e.g. when 3% mucin is added into 1% β-glucan, the shear viscosity increases from 0.4 Pa s (1% β-glucan) to 2 Pa s at a shear rate of 0.1 s^-1. The 3% mucin contributes 1.6 Pa s in the presence of β-glucan, which is nearly 16 times of the viscosity induced by 4% mucin alone at the same shear rate. Mucin affects the extensional viscosity in a similar way, e.g. incorporation of 2% mucin into a 2% β-glucan system increases the extensional viscosity from 4 Pa s to 8 Pa s. Substitution of β-glucan for an equal concentration of mucin results in the decrease of the shear and extensional viscosities: Α 4% β-glucan solution has a maximum extensional viscosity of 92 Pa s; substitution of 1% β-glucan for 1% mucin (1% mucin+3% β-glucan) reduces the maximum recorded extensional viscosity to 36 Pa s; this is further reduced down to 8 Pa s at 2% mucin+2% β-glucan, and then on to 4 Pa s at 3% mucin+1% β-glucan, and to 0.8 Pa s at 4% mucin. A similar trend is observed for the shear viscosities. The shear and extensional moduli and the extensional relaxation times also follow such patterns. The Trouton ratio values are lower than 100, that is they are not as high as in other food hydrocolloids; this strongly suggests a fine in vivo interplay between shear and extensional viscosities. The effect of mucin on β-glucan solutions rheology is primarily attributed to excluded-volume interactions, which increase the effective concentration of the glucans. The implications of the above on the rheology-related functionality of β-glucans are discussed.

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 (H₂O₂) or ascorbic acid (Asc) with ferrous iron (Fe²⁺) 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 H₂O₂, both glycosidic bond cleavage and formation of carbonyl groups within the β-glucan chain was found. Moreover, H₂O₂ 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.

This study investigated the role of phytate in the Fenton reaction induced oxidative degradation of cereal β-glucan. Viscosity analysis showed that the degradation rate was high in the beginning of oxidation, which fitted to the second order kinetic model. Oat β-glucan contained significant amount of residual phytate and after the residual phytate was removed, faster degradation was shown compared to the original oat β-glucan. Adding the same amount of phytic acid (PA) to the phytate removed β-glucan sample also retarded the degradation but not as efficiently as the residual phytate. Considerable retardation of viscosity loss was shown when the PA to iron ratio was high. The presence of ascorbic acid weakened the retardation effect of phytic acid. Thus, phytate can significantly improve the oxidative stability of β-glucan when the ratio of phytic acid to transition metals and the presence of ascorbic acid are taken into consideration.

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 β-glucan, 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.

The physicochemical properties of the oat beta-glucan powder (BG) and coenzyme Q10 (CoQ10)-loaded BG powder (L-BG) produced by the pressurized gas-expanded liquid (PGX) technology were studied. Helium ion microscope, differential scanning calorimeter, X-ray diffractometer, AutoSorb iQ and rheometer were used to determine the particle morphology, thermal properties, crystallinity, surface area and viscosity, respectively. Both BG (7.7 µm) and L-BG (6.1 µm) were produced as micrometer-scale particles, while CoQ10 nanoparticles (92 nm) were adsorbed on the porous structure of L-BG. CoQ10 was successfully loaded onto BG using the PGX process via adsorptive precipitation mainly in its amorphous form. Viscosity of BG and L-BG solutions (0.15%, 0.2%, 0.3% w/v) displayed Newtonian behavior with increasing shear rate but decreased with temperature. Detailed characterization of the physicochemical properties of combination ingredients like L-BG will lead to the development of novel functional food and natural health product applications.

Β-glucan is one of the components that differentiate oats from other cereals and that contribute to the health-related value of oats. However, so far oats cannot easily be applied in bread-like products without loss of product quality. Here we have studied how the content and viscosity of oat β-glucan affect the technological properties of oat dough in both a gluten-free and a gluten-containing system. In both systems, increasing the β-glucan concentration resulted in an increase of dough stiffness and in a reduction of dough extensibility. β-glucan negatively impacted the elastic properties that additional wheat gluten conferred to oat dough. This effect was smaller for medium-viscosity β-glucan than for high-viscosity β-glucan. Interestingly, dough made from low β-glucan flour (<2%) had increased gas retention capacity. Overall, the impact of β-glucan on the properties of oat dough systems was governed by concentration and viscosity, with or without additional wheat gluten. Our findings indicate that β-glucan is a key component that determines the rheology of oat-based dough systems and, with that, the technological functionality of oat in dough systems.

Novel oligomers that resist digestion in the upper gut were prepared from oat mixed-linked β-glucan and xylan by enzymatic hydrolysis with lichenase of Bacillus subtilis and xylanase of Trichoderma reesei respectively. The low-molecular-mass hydrolysis products of β-glucan and xylan were compared with fructooligomers and raffinose in their ability to provide growth substrates for probiotic (Lactobacillus and Bifidobacterium) and intestinal (Bacteroides, Clostridium and Escherichia coli) strains in vitro. A degradation profile of each carbohydrate and total sugar consumption were analysed with HPLC, and bacterial growth rate with an automatic turbidometer, the Bioscreen C system. β-Glucooligomers and xylooligomers both enhanced the growth of health-promoting probiotic strains as compared with intestinal bacterial growth, but not to a significant level. Raffinose stimulated the probiotic strains significantly, whereas fructooligomers induced high average growth for intestinal bacteria also.