Extracellular depolymerisation triggers fermentation of tamarind xyloglucan and wheat arabinoxylan by a porcine faecal inoculum

Potential prebiotic effects of soy by-products as novel dietary fibre: Structure, function, in vitro simulation of digestion and fermentation properties

This study aimed to prepare soybean dregs dietary fibre (DF) using physically assisted chemical (KHMSO) modification and study its structure, function and vitro simulation experiments. The soluble dietary fibre (SDF) content in KHMSO increased and insoluble dietary fibre (IDF) content decreased. The modified DF surface becomes irregular and rough, and the results of XPS fitting indicated that the DF structure had different peak-splitting groups. The KHMSO-treated group had the lowest digestion rate in gastric fluid and the highest digestibility in intestine fluid. The OD600 of fecal cultures was increased to 0.915, and the increased abundance of microbiota was associated with the metabolism of SCFAs, such as Lachnospiraceae, as well as the higher n-butyric acid in the KHMSO-treated group compared to the other groups and lower than the inulin, suggesting KHMSO might enhance the production of functional foods aimed at promoting intestinal health.

Cascade Microbial Metabolism of Ferulic Acid In Vitro Fermented by the Human Fecal Inoculum

Ferulic acid (FA), predominantly existing in most cereals, can modulate the gut microbiome, but the influences of its metabolites on the microbial population and FA-transforming microorganisms are still unclear. In this study, FA and its potential phenolic metabolites were fermented in vitro for 24 h with the human fecal inoculum. A comparable short chain fatty acid (SCFA) production trend was observed in the presence and absence of substrates, suggesting limited contribution of FA mechanism to SCFA formation. Dihydroferulic acid, 3-(3,4-dihydroxyphenyl)propionic acid, and 3-(3-hydroxyphenyl)propionic acid were ascertained to be successive metabolites of FA, by tracking the intermediate variation. FA remarkably promoted the absolute abundances of total bacteria, while different metabolites affected bacterial growth of selective genera. Specific genera were identified as quantitatively correlating to the content of FA and its metabolites. Ultimately, FA-mediated gut microbiota modulation involves both the action of metabolizing microbes and the regulation effects of metabolites on bacterial growth.

Unveiling the breadmaking transformation: Structural and functional insights into Arabinoxylan

To understand the changes in arabinoxylan (AX) during breadmaking, multi-step enzyme digestion was conducted to re-extract arabinoxylan (AX-B) from AX-fortified bread. Their structural changes were compared using HPSEC, HPAEC, FT-IR, methylation analysis, and 1H NMR analysis; their properties changes in terms of enzymatic inhibition activities and in vitro fermentability against gut microbiota were also compared. Results showed that AX-B contained a higher portion of covalently linked protein while the molecular weight was reduced significantly after breadmaking process (from 677.1 kDa to 15.6 kDa); the structural complexity of AX-B in terms of the degree of branching was increased; the inhibition activity against α-amylase (76.81 % vs 73.89 % at 4 mg/mL) and α-glucosidase (64.43 % vs 58.08 % at 4 mg/mL) was improved; the AX-B group produced a higher short-chain fatty acids concentration than AX (54.68 ± 7.86 mmol/L vs 44.03 ± 4.10 mmol/L). This study provides novel knowledge regarding the structural and properties changes of arabinoxylan throughout breadmaking, which help to predict the health benefits of fibre-fortified bread and achieve precision nutrition.

Interaction between β-glucans and gut microbiota: a comprehensive review

Gut microbiota (GMB) in humans plays a crucial role in health and diseases. Diet can regulate the composition and function of GMB which are associated with different human diseases. Dietary fibers can induce different health benefits through stimulation of beneficial GMB. β-glucans (BGs) as dietary fibers have gained much interest due to their various functional properties. They can have therapeutic roles on gut health based on modulation of GMB, intestinal fermentation, production of different metabolites, and so on. There is an increasing interest in food industries in commercial application of BG as a bioactive substance into food formulations. The aim of this review is considering the metabolizing of BGs by GMB, effects of BGs on the variation of GMB population, influence of BGs on the gut infections, prebiotic effects of BGs in the gut, in vivo and in vitro fermentation of BGs and effects of processing on BG fermentability.

Novel constituents of Salvia hispanica L. (chia) nutlet mucilage and the improved in vitro fermentation of nutlets when ground

Upon wetting, chia (Salvia hispanica L.) nutlets produce a gel-like capsule of polysaccharides called mucilage that comprises a significant part of their dietary fibre content. Seed/nutlet mucilage is often used as a texture modifying hydrocolloid and bulking dietary fibre due to its water-binding ability, though the utility of mucilage from different sources is highly structure-function dependent. The composition and structure of chia nutlet mucilage is poorly defined, and a better understanding will aid in exploiting its dietary fibre functionality, particularly if, and how, it is utilised by gut microbiota. In this study, microscopy, chromatography, mass spectrometry and glycome profiling techniques showed that chia nutlet mucilage is highly complex, layered, and contains several polymer types. The mucilage comprises a novel xyloamylose containing both β-linked-xylose and α-linked-glucose, a near-linear xylan that may be sparsely substituted, a modified cellulose domain, and abundant alcohol-soluble oligosaccharides. To assess the dietary fibre functionality of chia nutlet mucilage, an in vitro cumulative gas production technique was used to determine the fermentability of different chia nutlet preparations. The complex nature of chia nutlet mucilage led to poor fermentation where the oligosaccharides appeared to be the only fermentable substrate present in the mucilage. Of note, ground chia nutlets were better fermented than intact whole nutlets, as judged by short chain fatty acid production. Therefore, it is suggested that the benefits of eating chia as a "superfood", could be notably enhanced if the nutlets are ground rather than being consumed whole, improving the bioaccessibility of key nutrients including dietary fibre.

In Vitro Fermentation Characteristics and Fiber-Degrading Enzyme Kinetics of Cellulose, Arabinoxylan, β-Glucan and Glucomannan by Pig Fecal Microbiota

Non-digestible polysaccharides are of great significance to human and animal intestinal health. Cellulose, arabinoxylan, β-glucan and glucomannan were selected in the present study to investigate the fermentation characteristics and fiber-degrading enzyme kinetics by inoculating pig fecal microbiota in vitro. Our results showed that fermentation of arabinoxylan and β-glucan produced the highest amount of acetate and lactate, respectively. The abundance of Prevotella_9 was the highest in β-glucan group and positively correlated with lactate and acetate. Glucomannan fermentation produced the highest amount of butyrate, and the abundance of Lachnospiraceae_XPB_1014_group and Bacteroides were the lowest. A significant negative correlation was found between Lachnospiraceae_XPB_1014_group, Bacteroides and butyrate. Exo-β-1,4-xylanase had the highest activity at 24 h during arabinoxylan fermentation. The activity of β-glucosidase and β-mannosidase at 36 h were higher than those at 15 h in the glucomannan group. The abundance of Prevotella_9 was positively correlated with β-glucosidase while Lachnospiraceae_XPB_1014_group and Bacteroides were negatively correlated with β-xylosidase. Our findings demonstrated the β-glucan and arabinoxylan promote proliferation of Prevotella_9, with the preference to secret β-glucosidase, β-mannosidase and the potential to produce lactate and acetate. Butyrate production can be improved by inhibiting the proliferation of Lachnospiraceae_XPB_1014_group and Bacteroides, which have the lack of potential to secret β-xylosidase.

In vitro fermentation outcomes of arabinoxylan and galactoxyloglucan depend on fecal inoculum more than substrate chemistry

Using in vitro fermentation conditions, this study investigated the fermentation characteristics of arabinoxylan (AX) and xyloglucan (XG) with a fecal inoculum that was collected either from humans consuming unrestricted diets or pigs fed a semi-defined diet with cellulose being the sole non-starch polysaccharide for 10 days prior to fecal collection. Metagenomic analysis revealed that microbial communities in the two types of inoculum were distinctively different, which led to distinct fermentation characteristics with the polysaccharides. The microbial communities fermented with the porcine fecal inoculum were clustered according to the fermentation time, while those fermented with the human fecal inoculum were differentiated by the substrates. Using the porcine fecal inoculum, irrespective of the substrates, Prevotella copri and the unclassified lineage rc4-4 were the dominant operational taxonomic units (OTUs) promoted during fermentation. Fermentation of wheat AX (WAX) and galacto-XG (GXG) with the human fecal inoculum, however, promoted different OTUs, except for a shared OTU belonging to Lachnospiraceae. Specifically, WAX promoted the growth of Bacteroides plebeius and a Blautia sp., while GXG promoted an unclassified Bacteroidales, Parabacteroides distasonis, Bacteroides uniformis and Bacteroides sp. 2. These changes in bacterial communities were in accordance with the short chain fatty acid (SCFA) production, where comparable SCFA profiles were obtained from the porcine fecal fermentation while different amounts and proportions of SCFA were acquired from fermentation of WAX and GXG with the human fecal inoculum. Altogether, this study indicated that the starting inoculum composition had a greater effect than polysaccharide chemistry in driving fermentation outcomes.

Interaction of cellulose and xyloglucan influences in vitro fermentation outcomes

To investigate the effects of interactions between cellulose and xyloglucan (XG) on in vitro fermentation, a composite of bacterial cellulose (BC) incorporating XG during pellicle formation (BCXG), was fermented using a human faecal inoculum, and compared with BC, XG and a mixture (BC&XG) physically blended to have the same BC to XG ratio of BCXG. Compared to individual polysaccharides, the fermentation extent of BC and fermentation rate of XG were promoted in BC&XG. XG embedded in the BCXG composite was degraded less than in BC&XG, while more cellulose in BCXG was fermented than in BC&XG. This combination explains the similar amount of short chain fatty acid production noted throughout the fermentation process for BCXG and BC&XG. Microbial community dynamics for each substrate were consistent with the corresponding polysaccharide degradation. Thus, interactions between cellulose and XG are shown to influence their fermentability in multiple ways.

Catechin-grafted arabinoxylan conjugate: Preparation, structural characterization and property investigation

In this study, a high molecular weight arabinoxylan (AX, Mw: 694 kDa) from wheat bran was alkaline extracted and covalently linked with Catechin (CA) by free radical catalytic reaction. Comparing to AX, arabinoxylan-catechin (AX-CA) conjugates demonstrated an extra UV-vis absorption peak at 274 nm, a new FT-IR absorption band at 1516 cm^-1 and new proton signals at 6.5-7.5 ppm, which all confirmed the covalently linked structure. Grafting CA onto AX not only decreased the molecular weight, thermal stability and apparent viscosity of AX, but also enhanced its inhibition effects on starch digestibility in vitro. The in vitro fermentation test with pig feces showed that the degradation & utilization rate of AX, the total short-chain fatty acid (SCFA) and acetic acid levels produced all were significantly delayed after grafting. This study provided a novel approach to synthesize AX-CA conjugates that could be a novel dietary fiber of enhanced functional/bioactive properties using in the fields of functional foods and medicine.

Wheat cell walls and constituent polysaccharides induce similar microbiota profiles upon in vitro fermentation despite different short chain fatty acid end-product levels

Plant cell walls as well as their component polysaccharides in foods can be utilized to alter and maintain a beneficial human gut microbiota, but it is not known whether the architecture of the cell wall influences the gut microbiota population. In this study, wheat flour cell walls (WCW) were isolated and compared with their major constituents - arabinoxylan (AX), mixed linkage (1,3)(1,4)-β-glucan (MLG) and cellulose - both separately and as a physical mixture of polysaccharides (Mix) equivalent in composition to WCW. These samples underwent in vitro fermentation with a faecal inoculum from pigs fed a diet free of cereals and soluble-fibre to avoid prior adaptation to substrates. During fermentation, samples were collected for DNA extraction and 16S rRNA gene amplicon sequencing. Bioinformatics analyses revealed that the microbial communities promoted during fermentation by AX, MLG, Mix and WCW were similar at the genus level, but differed from the microbiota observed for the cellulose substrate. Differences in proportions of propionate and butyrate end-products were associated with differences in the relative levels of genera. These findings show that, in this experiment, the microbes that flourished were able to utilize diverse WCW polysaccharides alone, in mixtures or in intact cell walls in a similar way, but that different fermentation end-products were associated with AX (propionate) or MLG (butyrate) polysaccharides.

Nanoencapsulation of Saccharomycopsis fibuligera VIT-MN04 using electrospinning technique for easy gastrointestinal transit

In this study, probiotic yeast Saccharomycopsis fibuligera (S. fibuligera) VIT-MN04 was encapsulated with wheat bran fibre (WBF) and exopolysaccharide (EPS) along with 5% polyvinylpyrrolidone (PVP) using electrospinning technique for easy gastrointestinal transit (GIT). The electrospinning materials viz. WBF (10%), EPS (15%), PVP (5%) and electrospinning parameters viz. applied voltage (10 kV) and tip to collector distance (15 cm) were optimised using response surface methodology to produce fine nanofibres to achieve maximum encapsulation efficiency (100%) and GIT tolerance (97%). The probiotic yeast was successfully encapsulated in nanofibre and investigated for potential properties. The survival of encapsulated S. fibuligera VIT-MN04 was increased compared to the free cells during in vitro digestion. In addition, encapsulated yeast cells retained their viability during storage at 4°C for 56 days. The nanofibres were characterised using scanning electron microscopy, atomic force microscopy, X-ray diffraction, thermogravimetric analysis, zeta potential analysis and Fourier transform infrared spectroscopy followed by gas chromatography-mass spectrometry and nuclear magnetic resonance analysis. This work provides an efficient approach for encapsulation of probiotic yeast with the nanofibres which can also broaden the application of the prebiotic like WBF providing an idea for the efficient preparation of functional synbiotic supplements in the food industry.

"Dietary fibre": moving beyond the "soluble/insoluble" classification for monogastric nutrition, with an emphasis on humans and pigs

This review describes dietary fibres originating from a range of foods, particularly in relation to their plant cell walls. It explores the categorization of dietary fibres into “soluble” or “insoluble”. It also emphasizes dietary fibre fermentability, in terms of describing how the gastro-intestinal tract (GIT) microbiota respond to a selection of fibres from these categories. Food is categorized into cereals, legumes, fruits and vegetables. Mention is also made of example whole foods and why differences in physico-chemical characteristics between “purified” and “non-purified” food components are important in terms of health. Lastly, recommendations are made as to how dietary fibre could be classified differently, in relation to its functionality in terms of fermentability, rather than only its solubility.

Effects of the Starch Molecular Structures in Barley Malts and Rice Adjuncts on Brewing Performance

Background: Achieving optimal fermentation is challenging when the variation within malt starch structure and enzyme activities are not part of the standard malting specifications. This study explores how the variation of starch and starch amylolytic enzymes in both malts and rice adjuncts affect the mashing and the subsequent yeast fermentation in the laboratory-scale production of beer. Results: The addition of rice adjuncts significantly increased the maltose content whilst reducing the glucose content during mashing. The maltotriose content, released during mashing, was significantly negatively correlated with the total amylose content (r = −0.64, p < 0.05), and significantly negatively correlated with the number of amylopectin longer chains (degree of polymerization 37–100) (r = −0.75, p < 0.01). During fermentation, while the content of maltotriose significantly and positively correlated with both the rate and amount of ethanol production (r = 0.70, p < 0.05; r = 0.70, p < 0.05, respectively), the content of soluble nitrogen in the wort was significantly and positively correlated with both the rate and the amount of ethanol production (r = 0.63, p< 0.05; r = 0.62, p < 0.05, respectively). The amount of amylopectin with longer chains was; however, significantly negatively correlated with the ethanol production (r = −0.06, p < 0.05). Small variations among the ethanol concentration and the rate of ethanol production during fermentation were found with the addition of different rice varieties. Conclusions: The effects of the rice adjuncts on the performance of fermentation depends on the properties of the malt, including the protein modification and malt enzyme activities. This study provides data to improve standard malt specifications in order for brewers to acquire more efficient fermentation, and includes useful molecular structural characterisation.