Microwave treatment enhances human gut microbiota fermentability of isolated insoluble dietary fibers.

Most insoluble dietary fibers are known to be relatively poorly fermented by the human gut microbiota. Here, the potential of microwave (MW) treatment to enhance the susceptibility of insoluble fruit polysaccharides to fermentation by the human gut microbiota was evaluated. Insoluble fruits dietary fibers before (xylan A, xylan T, and arabinan) and after MW (xylan A-MW, xylan T-MW, and arabinan-MW) treatment were fermented using an in vitro fermentation model. Gas production, shifts in pH, and short chain fatty acids (SCFAs) production showed an increase in fermentability of all tested dietary fibers, with an average 4-fold increase in SCFAs production after microwaving with total SCFAs ranging from 17.1 mM in the arabinan-MW to 40.4 mM in the xylan T-MW. While arabinan-MW and xylan T-MW promoted all three SCFAs proportionally (acetate:propionate:butyrate), xylan A-MW led to a marked and slow increase in butyrate reaching 28.1% of total SCFAs at 24 h. Rearrangements in three-dimensional structure that potentially facilitate bacterial accessibility to the dietary fiber were observed by scanning electron microscopy in xylan A-MW, forming coin-like particles with ~1.1 µm diameter. 16S rRNA gene sequencing indicated that microbiota shifts were related to both treatment (native versus MW) and dietary fiber type with many butyrogenic species being promoted by xylan A-MW. Overall, MW treatment enhanced insoluble dietary fiber fermentability promoting increased SCFAs production and bacterial shifts which are related to health benefits.

Prebiotic potential of mushroom d-glucans: implications of physicochemical properties and structural features.

Mushroom d-glucans are recognized as dietary fibers and as biologically active natural polysaccharides, with the advantages of being quite inexpensive for production, tolerable, and having a range of possible structures and physicochemical properties. The prebiotic potential of mushroom d-glucans has been explored in recent years, but the relationship between their various structural features and activity is poorly understood. This review focuses on comprehensively evaluating the prebiotic potential of mushroom d-glucans in face of their structural variations. Overall, mushroom d-glucans provide a unique set of different structures and physicochemical properties with prebiotic potential, where linkage type and solubility degree seem to be associated with prebiotic activity outcomes. The understanding of the effects of distinct structures and physicochemical properties in mushroom d-glucans on the gut microbiota contributes to the design and selection of new prebiotics in a more predictable way.

Discrete Fiber Structures Dictate Human Gut Bacteria Outcomes.

Supplementation with resistant starches of different structures led to divergent shifts in key bacterial taxa abundance and distinct butyrate or propionate outcomes. A recent randomized controlled trial (RCT) reported by Deehan et al. showed similar responses within treatment groups and dose-response plateauing at 35 g/d. These results support a proposed alignment of discrete dietary fiber (DF) structures with gut bacteria.

Pectins from cashew apple fruit (Anacardium occidentale): Extraction and chemical characterization.

The cashew tree (Anacardium occidentale) is a tropical evergreen tree largely cultivated in Brazil, which produces the cashew apple, a peduncle rich in carbohydrates and considered an industrial waste of the nut production. Until now, there were no data available about the chemical structure of cell wall polysaccharides found in cashew apple. In this work, its pectic polysaccharides have been characterized through monosaccharide composition, HPSEC, methylation and 13C and 1H/13C HSQC-DEPT-NMR analyses. Highly methyl esterified homogalacturonan with a DE of 76% mixed with arabinogalactan were found. This latter was purified and presented a highly branched type II arabinogalactan (AG II) and small amounts of a type I rhamnogalacturonan in which the AG II could be anchored. These findings about the chemical structure of cashew apple pectins could contribute to develop future nutritional, biotechnological and pharmacological uses for this industrial waste from the cashew nut production.

In vitro fermentation of Cookeina speciosa glucans stimulates the growth of the butyrogenic Clostridium cluster XIVa in a targeted way.

Dietary fiber chemical and physical structures may be critical to the comprehension of how they may modulate gut bacterial composition. We purified insoluble polymers from Cookeina speciosa, and investigated its fermentation profile in an in vitro human fecal fermentation model. Two glucans, characterized as a (1 → 3),(1 → 6)-linked and a (1→3)-linked ß-D-glucans were obtained. Both glucans were highly butyrogenic and propiogenic, with low gas production, during in vitro fecal fermentation and led to distinct bacterial shifts if compared to fructooligosaccharides. Specific increases in Bacteroides uniformis and genera from the Clostridium cluster XIVa, such as butyrogenic Anaerostipes and Roseburia were observed. The (1 → 3)-linked ß-D-glucan presented a faster fermentation profile compared to the branched (1 → 3),(1 → 6)-linked ß-D-glucan. Our findings support the view that depending on its fine chemical structure, and likely its insoluble nature, these dietary fibers can be utilized to direct a targeted promotion of the intestinal microbiota to butyrogenic Clostridium cluster XIVa bacteria.

Structural diversity of alkali-soluble polysaccharides from the fruit cell walls of tucumã (Astrocaryum aculeatum), a commelinid monocotyledon from the family Arecaceae.

The polysaccharide compositions of primary and secondary cell walls of members of the family Arecaceae in the commelinid clade of monocotyledonous plants have previously been found to be distinguishable from other commelinid families, and to be more similar to those of non-commelinids. However, few studies have been conducted. We aimed to extract and characterize the main cell-wall polysaccharides in the fruit pulp of tucumã (Astrocaryum aculeatum), a member of Arecaceae family. Hemicellulosic polysaccharides extracted by alkali from the fruit pulp were present in greater proportions (6.4% yield) than water-extracted ones (3.0% yield). Thus, the former was analyzed using monosaccharide composition, methylation, molecular weight determination and 13C-NMR data. The tucumã alkaline extract presented a highly ramified acidic galactoarabinoxylan (53.7%), a linear (1 â†’ 5)-linked α-L-arabinan (27.8%), a low branched glucuronoxylan (14.1%) and small portions of a xyloglucan (4.4%). The major polysaccharide found in A. aculeatum (acidic galactoarabinoxylan) is similar to those found in other commelinid plants such as grasses and cereals.

Isolation and characterization of a xylan with industrial and biomedical applications from edible açaí berries (Euterpe oleraceae).

The chemical features of xylan largely determine its physical and biological properties and its use in the industry. In this work, we describe the occurrence, purification and partial characterization of a xylan in edible açaí berries (Euterpe oleraceae), using a fairly simple and inexpensive method of purification from alkaline açaí extract. A mainly linear (1→4)-ß-d-xylan was found as the majority (70%) of alkali extract and 4.2% of the dry matter açaí pulp. This represents the biggest source of xylan found so far in a fruit pulp and could be suitable for applications in the industry and biomedical field.

Extraction and characterization of pectins from primary cell walls of edible açaí (Euterpe oleraceae) berries, fruits of a monocotyledon palm.

Açaí berries (Euterpe oleracea) are greatly consumed in Brazil and exported to other countries as a nutritional supplement, due to health benefits attributed to its consumption. However, the complete chemical structure of bioactive polysaccharides was not fully elucidated yet. In this work, we characterize pectic polysaccharides from açaí berries through monosaccharide composition, HPSEC, methylation and 13C and 1H/13C HSQC-DEPT-NMR analyses. A highly methoxylated homogalacturonan with a DM of 88% and Mw of 22kDa together with small amounts of a mannoglucan were found. Moreover, a type II arabinogalactan (Mw=45kDa) containing a backbone with high portions of 6-O-linked and 3,6-O-linked Galp chains rather than 3-O-linked Galp was also isolated and structurally characterized. The type II arabinogalactan was found as a side chain of a type I rhamnogalacturonan. These findings contribute to correlate the fine chemical structure with the previously reported action of açaí polysaccharides on innate immune response. Moreover, from the taxonomic point of view, the results bring new information about polysaccharide composition of primary cell walls of palms (Arecaceae), that despite being commelinid monocots, have a distinct cell wall composition.

Arabinan-rich pectic polysaccharides from buriti (Mauritia flexuosa): an Amazonian edible palm fruit.

Primary cell wall polysaccharides from aqueous extract of buriti fruit pulp (Mauritia flexuosa, an exotic tropical palm) were isolated and characterized. After freeze-thaw and α-amylase treatments, extracted polysaccharides were purified by sequential ultrafiltration through membranes. Two homogeneous fractions were obtained, SBW-100R and SBW-30R (Mw of 126 kDa and 20 kDa, respectively). Monosaccharide composition, methylation and (13)C NMR analysis showed that fraction SBW-100R contained a (1 → 5)-linked arabinan, branched at O-3 and O-2 positions, linked to a type I rhamnogalacturonan. Low amounts of these polymers were also present in fraction SBW-30R according to (13)C NMR analysis and monosaccharide composition. However, a high methyl esterified homogalacturonan (HG) was present in higher proportions. These results reinforce previous findings present in literature data which indicate that pectic polysaccharides are found in high amounts in primary cell walls of palms, which are commelinid monocotyledons.

Polysaccharides from prunes: gastroprotective activity and structural elucidation of bioactive pectins.

Prunes are the dried fruits from Prunus domestica. After the purification steps, two homogeneous polysaccharides were characterised, SF-50R and SF-50E and contained Ara:Gal:Rha:GalA in 47.8:31.5:10.7:10.0 and 39.6:50.3:5.1:5.0 molar ratios, respectively. Methylation analysis and (13)C NMR spectroscopy indicated that both fractions are constituted by rhamnogalacturonans with type I arabinogalactans as side chains, differing mainly in the proportions of the rhamnogalacturonan backbone, in the length of the (1→4)-ß-galactan chain and in the proportion of the arabinan side chain. Crude water extract (PWH) and fraction SF-50E were evaluated for their gastroprotective properties against ethanol-induced acute gastric lesions in rats. Oral administration of PWH (3 and 10mg/kg) reduced the gastric lesion area by 67±11% and 60±12%, respectively, while fraction SF-50E (10 and 30mg/kg) inhibited the lesion area by 84±12% and 83±12%, respectively. These results indicated that prune's polysaccharides act as gastroprotective agents in rats.