Enzymatically synthesized α-glucans have attracted attention due to their limited digestibility; however, their technological potential in food systems remains underexplored. This study investigated the effects of two structurally distinct α-glucans (RoGBE 0.001X and RoGBE 0.1X), synthesized using amylosucrase from Neisseria polysaccharea and glycogen branching enzyme from Rhodothermus obamensis, on dough and bread quality. Structural characterization revealed that RoGBE 0.001X had a molecular size of 2.6 × 10⁴ Da and a branching ratio of 0.81

Dietary fibers are crucial in shaping gut microbial composition and functionality. Physical complexity and chemical interactions between fibers and the gut environment lead to diverse and specialized responses that involve entire food webs of gut bacteria; however, there is comparatively less emphasis on understanding ecological dynamics to predict these outcomes. These responses may potentially promote either a broader (less specific) or narrower (more specific) group of gut bacterial taxa, which may vary across individuals. This review examines fiber specificity at the organismal and community levels by exploring mechanistic interactions among dietary fibers and gut bacteria. We discuss the interplay of exogenous and endogenous factors and the structure-function relationships influencing fiber specificity. We establish a mathematical framework to describe specificity in fiber-microbiome interactions based on directionality, magnitude, and stochasticity of fiber-microbiome ecological responses. Finally, we identify research gaps to enhance fiber-microbiota predictions, with implications for strategies aimed at optimizing fiber design.

Individual variability in gut microbiota responses limits the consistency of health benefits from prebiotic fiber interventions. Building on our concept of fiber hierarchical specificity, defined as the selective alignment and use of fibers by a narrow subset of gut microbes, we evaluated new putative high-specificity fibers for their ability to promote predictable and intense microbial shifts across individuals. Here, six candidate fibers (Acacia gum, Fucogalactan, Gellan gum, Guar gum, Locust bean gum, and Xylooligosaccharides) were tested in vitro using fecal microbiota from ten donors and compared to low-specificity (Fructooligosaccharides) and high-specificity (an insoluble glucan) reference fibers. SCFA analysis showed that Fucogalactan and Guar were strongly propiogenic, while Acacia and Locust promoted balanced SCFA production. Gellan exhibited minimal fermentability. Acacia, Fucogalactan, Guar, and Locust consistently enriched putative beneficial genera (Eisenbergiella, Hungatella, Anaerotruncus, and Parabacteroides, respectively), with strong and consistent responses across individuals, features characteristic of high-specificity fibers. In contrast, Fructooligosaccharides and Xylooligosaccharides produced more variable, and less intense responses. Our findings support Acacia, Fucogalactan, Guar, and Locust as high-specificity fibers that induce consistent, taxon-targeted shifts in the gut microbiome. These expand the repertoire of high-specificity fibers-a promising prebiotic approach for predictable microbiota modulation and related health outcomes.

Dietary fibers within whole grains reach the large intestine where they shape the microbial composition. However, the bioavailability of these dietary nutrients to the microbiota is likely limited due to entrapment within the grain particle and requires liberation by microbial enzymes. Here, we used batch fecal fermentation from mixed donors on a range of sizes of wheat particles generated by cyclone milling from a single source to identify bacterial taxa and genomic signatures that are responsive to differences in wheat bran fine structures. We present evidence that different taxa within the same genus colonize wheat bran particles of different sizes. Further, neutral sugar content varied across wheat bran particles despite originating from the same batch, suggesting different polysaccharide structures and nutritional niches. In line with the taxonomic and compositional differences, specific short chain fatty acids varied across particle sizes; in fine wheat bran particle fermentations propionate was high and butyrate low. To identify relevant genomic features implicated in bran colonization, we took a metagenomic approach. From this, we linked genes associated with polysaccharide fermentation to wheat bran particles independent of size, however, within one well-distributed taxon, Lachnospiraceae , genes related to motility were linked to large and medium wheat bran particles. Overall, these results suggest that differences in fine structures and resource availability, as generated through milling, can drive compositional changes in the gut microbiota in an organism-specific manner, mediated through its genomic capacity. IMPORTANCE Cereal brans comprise a large fraction of the dietary fiber consumption. Although it is well-known that dietary fibers influence the metabolic output and taxonomic composition of the gut microbiota, relatively little is known regarding whether the fine structures and resource availability of milled whole grains exert any influence on the microbial makeup. Our data suggest that the sugar content varies across bran milled from a single source to different sizes. These differences in composition may result in colonization differences by related, but unique, taxa, mediated by genes related to polysaccharide fermentation, thus leading to differences in metabolic output. Furthermore, our data suggest that genes related to motility might influence the capacity of microorganisms to colonize particles. Taken together, our data suggest that physical context can influence gut microbiota composition in turn impacting metabolic output. ![Figure][1] [1]: pending:yes

BACKGROUND:The aim of this study was to evaluate and compare the gut microbiome modulatory effects of dietary fibers (DFs) of different Turkish apricot (Prunus armeniaca L.) varieties dried using different techniques. Three different sun-dried apricots belonging to Şekerpare, Iğdır Şalağı, and Hasanbey varieties from Erzincan region; and sun-dried, and sulfurized apricots belonging to Şekerpare variety from Malatya region were obtained. Neutral and acidic monosaccharide compositions were analyzed using gas chromatography-mass spectroscopy (GC-MS) and spectrophotometry, respectively. In vitro fecal fermentation analyses were applied and changes in microbiota composition and short-chain fatty acids were determined using 16S rRNA sequencing technique and GC, respectively. RESULTS:Dried apricot DFs were dominated with pectin- and cellulose/hemicellulose-related monosaccharide units, and the DF compositions showed only slight differences from variety to variety. Dried apricot DFs were found to influence the β- and α-diversities of microbial communities in variety and drying techniques independent-ways. Although the degrees of promotions were slightly impacted by the apricot-variety and drying technology, dried apricot DFs were generally capable of promoting the beneficial microbial taxa, including Coprococcus eutactus, Lachnospiraceae, and Ruminococcus flavefaciens related operational taxonomic units (OTUs). CONCLUSION:Overall, this study demonstrates that dried apricots can modulate colonic microbiota composition and function, with the effect being subtly impacted by variety, location, and drying techniques. These findings also suggest that gut microbiome modulation ability of DFs of dried appricot could be an important contribution factor to its health promoting properties. Thus, dried apricots have potential to be utilized for the development of functional foods aimed at promoting colonic health. © 2025 Society of Chemical Industry.

The interplay between maternal microRNAs (miRNAs) and human milk oligosaccharides (HMOs) in influencing infant gut bacteria remains poorly understood. This study investigated how milk miRNAs impact the growth dynamics and gene expression of Bifidobacterium infantis cultured on HMOs and lactose as substrates (1 % w/v). The strain was cultured in vitro with either human milk miRNAs or synthetic mimics (500 ng/mL). B. infantis grew significantly faster on HMOs (plateau at 11.23 h) than lactose (12.75 h), but miRNAs showed minimal effects on growth in both substrates. Transcriptome analysis further showed limited differential gene expression upon miRNA treatments, with only 11 overexpressed genes in the HMO-miRNA group, none likely affecting metabolism. In contrast, substrate type drove expression changes in 1986 genes, involving in ABC transporters, amino acid biosynthesis, purine, and carbohydrate metabolism. This research highlighted the stronger effects of HMOs than miRNAs on B. infantis biology, despite both being abundant in milk.

The human colonic microbiota exerts a profound influence on health, mediated by highly specific relationships among dietary fiber structures and microbial degraders. Systematic control of fiber structure offers opportunities to engineer microbiota-targeted interventions with increasing precision. Here, we examine the evolution of designed dietary fibers — biotechnologically produced oligosaccharides or polysaccharides synthesized de novo or naturally occurring polysaccharides intentionally modified post-extraction for their fine physical or chemical structures to influence gut microbiome. We propose a hierarchical framework to classify these fibers based on the degree of fine structure control, highlight current strategies for carbohydrate modification approaches, and discuss emerging directions for the field. Despite recent advances, much potential remains unrealized for the rational, reproducible design of microbiome-targeted fibers.

This study investigated the dietary fiber composition, monosaccharide profile, and prebiotic potential of fruit pomaces (apple, apricot, peach, and grape). Insoluble fiber (IF) was predominant in all samples, with apple (74.37%) and grape pomace (74.06%) having the highest IF contents. The highest soluble fiber (SF) was detected in peach pomace (18.71%), while grape pomace had the lowest (6.55%). Monosaccharide analysis showed that glucose was the major sugar in both SF and IF fractions, followed by arabinose, galactose, mannose, xylose, and rhamnose. Fucose was not detected. Apricot and apple pomaces exhibited the highest levels of neutral sugars and uronic acids, suggesting a richer presence of pectic substances and hemicelluloses. Despite grape pomace having the highest phenolic content and antioxidant capacity, its low SF content limited SCFA (short-chain fatty acid) production during in-vitro fecal fermentation. In contrast, apple pomace—with a more balanced SF/IF profile and richer monosaccharide diversity—induced significantly higher acetate, propionate, and butyrate levels (P<0.05). These results highlight the importance of not just fiber quantity, but also solubility and sugar composition, in determining the prebiotic efficacy of fruit pomace fibers. Among the pomaces evaluated, apple pomace displayed compositional characteristics that may warrant further investigation for potential prebiotic applications.

ABSTRACT To reveal the functional properties of hazelnut dietary fibers (DFs) in different colonic segments (cecum, proximal, and distal colon), a diet enriched with natural hazelnut, roasted hazelnut, or hazelnut skin DFs was applied to mice for 6 weeks; microbial metabolites, microbial composition, and tissue morphology were determined segmentally using gas chromatography, 16S rRNA sequencing technology, and microscopy, respectively. Roasted hazelnut DFs revealed significantly ( p < 0.05) higher propionate in the cecum of female mice, while hazelnut skin DFs significantly increased the butyrate level in the distal colon of male counterparts. 16S rRNA sequencing revealed hazelnut DFs promoted the Lactobacillus animalis , L. gasseri , and Akkermansia muciniphila related OTUs, especially in the proximal colon, but the degrees of promotions were hazelnut type‐, segment‐ and sex‐dependent. Interestingly, hazelnut skin DFs significantly ( p < 0.05) stimulated Prevotella related OTUs in the distal colon regardless of sex, which is known to have great ability to utilize dietary polysaccharides. Furthermore, hazelnut skin DF group had higher crypt height values, suggesting that hazelnut skin DFs have ability to maintain saccharolytic activity in more distal region of the colon. Overall, our results demonstrate that hazelnut DFs differentially impact microbial metabolite formation, microbiota composition and tissue morphology in different segments of the colon.

Alternative flours can reveal beneficial health effects. The aim of this study was to evaluate and compare the effects of dietary fibers (DFs) of coconut and carob flours on colonic microbiota compositions and function. Coconut flour DFs were found to be dominated by mannose-containing polysaccharides by gas chromatography (GC)/MS and spectrophotometer, whereas glucose and uronic acid were the main monosaccharide moieties in carob flour DFs. In vitro fecal fermentation analysis revealed that coconut flour DFs result in the generation of microbial butyrate as much as inulin does, which is known to be a butyrogenic prebiotic, but at a slower rate. Supportingly, coconut flour DFs promoted butyrate-producing bacteria including Roseburia and Coprococcus, whereas carob flour DFs stimulated Prevotella-related OTUs. In addition, higher microbial diversity was achieved at the end of the fermentation of coconut flour DFs by the fecal microbiota. This study clearly shows that alternative flours have distinct functionalities in terms of colonic microbiota composition and function, and coconut flour could be used as an alternative flour for the development of functional food products targeting colonic health.

The aim of this study was to evaluate the impacts of enzymatically synthesized α-glucans possessing α-1,4- and α-1,6-glucose linkages, and varying in branching ratio, on colonic microbiota composition and metabolic function. Four different α-glucans varying in branching ratio were synthesized by amylosucrase from Neisseria polysaccharea and glycogen branching enzyme from Rhodothermus obamensis. The branching ratios were found to range from 0 % to 2.8 % using GC/MS. In vitro fecal fermentation analyses (n = 8) revealed that the branching ratio dictates the short-chain fatty acid (SCFA) generation by fecal microbiota. Specifically, slightly branched (0.49 %) α-glucan resulted in generation of significantly (P < 0.05) higher amounts of propionate, compared to more-branched counterparts. In addition, the amount of butyrate generated from this α-glucan was statistically (P > 0.05) indistinguishable than those observed in resistant starches. 16S rRNA sequencing revealed that enzymatically synthesized α-glucans stimulated Lachnospiraceae and Ruminococcus related OTUs. Overall, the results demonstrated metabolic function of colonic microbiota can be manipulated by altering the branching ratio of enzymatically synthesized α-glucans, providing insights into specific structure-function relationships between dietary fibers and the colonic microbiome. Furthermore, the slightly branched α-glucans could be used as functional carbohydrates to stimulate the beneficial microbiota and SCFAs in the colon.

Structurally complex corn bran arabinoxylan (CAX) was used as a model glycan to investigate gut bacteria growth and competition on different AX-based fine structures. Nine hydrolyzate segments of the CAX polymer varying in chemical structure (sugars and linkages), CAX, five less complex non-corn arabinoxylans, and xylose and glucose were ranked from structurally complex to simple. The substrate panel promoted different overall growth and rates of growth of eight Bacteroides xylan-degrading strains. For example, Bacteroides cellulosilyticus DSM 14838 (Bacteroides cellulosilyticus) grew well on an array of complex and simple structures, while Bacteroides ovatus 3-1-23 grew well only on the simple structures. In a competition experiment, B. cellulosilyticus growth was favored over B. ovatus on the complex AX-based structure. On the other hand, on the simple structure, B. ovatus strongly outcompeted B. cellulosilyticus, which was eliminated from the competitive environment by Day 11. This adaptation to fine structure and resulting competition dynamics indicate that dietary fiber chemical structures, whether complex or simple, favor certain gut bacteria. Overall, this work supports a concept that fiber degraders diversify their competitive abilities to access substrates across the spectrum of heterogeneity of fine structural features of dietary fibers.

The aim of this study was to evaluate and compare the in vitro protein digestibility, phenolic contents, and antioxidant capacities of commercially important tree-nut species (almond, cashew, hazelnut, pistachio, and walnut). To evaluate the protein digestibility, upper gastrointestinal digestion was simulated in vitro in which tree-nuts were treated with pepsin and pancreatin. After the simulation, protein digestibility was calculated by measuring the remaining (undigestible) protein using Kjeltec nitrogen analyzer and by quantifying the primary amino acids formed through TNBS (2,4,6 trinitrobenzene sulfonic acid) method. Total phenolic contents and antioxidant capacities of tree-nuts were assessed spectrophotometrically. Our results revealed that that tree-nuts differ in their protein digestiblities in vitro . Based on the remaining protein calculations, cashew nut had the highest in vitro %protein digestibility (%91.79), followed by almond nut (%87.71), hazelnut (%86.10), pistachio nut (%81.15), and walnut (%44.75). TNBS results also partially agree with this that the lowest primary amino acid content after the digestion was found in walnut samples. The highest phenolic content was obtained in walnut (6.8 mg GAE/g), while cashew nut exhibited the lowest phenolic content (1.3 mg GAE/g). Both antioxidant capacity assays correlated with the total phenolic content; the samples possessing higher phenolic content revealed the higher antioxidant capacity. This study shows that in vitro protein digestibility, total phenolic contents, and antioxidant capacities of commercially important tree-nuts show variations from species to species, with walnut possessing the lowest protein digestibility, the highest phenolic content and antioxidant capacity, but the opposite was true for cashew nut.

Exopolysaccharide (EPS) producing Lactic Acid Bacteria (LAB) species can be presented in distinct environments. In this study, Turkish fermented sausage (sucuk) was tested for the presence of EPS producer LAB strains and slimy-mucoid colonies were selected for further tests. Among the isolates, Weissella confusa strain S6 was identified and tested for the physicochemical characterisation of its EPS. This strain was found to produce 0.74 g L-1 of EPS in modified BHI medium conditions. Structural characterisation of EPS S6 by 1H and 13C NMR demonstrated that EPS S6 was a highly branched dextran type glucan formed by mainly (1 -* 2)-linked alpha-D- glucose units together with low levels of (1 -* 3)-linked alpha-D-glucose units as branching points. This structure was further confirmed by methylation analysis detected by GC-MS. An average molecular weight of 8 x 106 Da was detected for dextran S6. The FTIR analysis supported the dextran structure and revealed the presence of distinct functional groups within dextran S6 structure. A strong thermal profile was observed for dextran S6 detected by DSC and TGA analysis and dextran S6 revealed a degradation temperature of 289 degrees C. In terms of physical status, dextran S6 showed amorphous nature detected by XRD analysis. SEM analysis of dextran S6 demonstrated its rough, compact and porous morphology whereas AFM analysis of dextran S6 detected in its water solution showed the irregularity with no clear cross -link within the dextran chains. These technological features of dextran S6 suggests its potential to be used for in situ or ex situ application during meat fermentations.

The aim of this study was to extract water-soluble dietary fibers (WSDFskin), pectin (PECskin), and xyloglucan (XGskin) from hazelnut skin and to determine their impacts on colonic microbiota and metabolic function. WSDFskin, PECskin, and XGskin were extracted by water, acid, and alkali treatments, respectively. Monosaccharide analysis revealed WSDFskin and PECskin were dominated by uronic acids, while the XGskin was found to contain xyloglucan- and pectin-associated sugars. In vitro fecal fermentation analysis showed that WSDFskin, PECskin, and XGskin are fermented to different microbial short-chain fatty acid profiles by identical microbiota. 16S rRNA sequencing demonstrated that PECskin promoted Faecalibacterium prausnitzii and Lachnospiraceae related operational taxonomic units (OTUs), which are recognized as beneficial members of the human gut, whereas WSDFskin and XGskin stimulated Bacteroides OTUs. Interestingly, increased abundances of F. prausnitzii and Lachnospiraceae OTUs in PECskin were higher than those in commercially available pectin. Finally, PECskin and XGskin were tested in a biscuit model and the results showed that either PECskin or XGskin can be incorporated into biscuit formulations without impacting physical, textural, and sensory properties of the final product. Overall, our results demonstrated that hazelnut skin, an industrial byproduct, can be utilized for the production of functional dietary fibers, especially pectin, to improve colonic health.

Glucansucrase AP-37 was extracted from the culture supernatant of Lactobacillus kunkeei AP-37 and characteristics of the glucan produced by the active glucansucrase in terms of structural and functional roles were determined in this study. A molecular weight around 300 kDa was observed for glucansucrase AP-37 and its acceptor reactions with maltose, melibiose and mannose were also conducted to unveil the prebiotic potential of the poly-oligosaccharides formed via these reactions. The core structure of glucan AP-37 was determined by 1H and 13C NMR and GC/MS analysis which revealed that glucan AP-37 was a highly branched dextran composing of high levels of (1 → 3)-linked α-d-glucose units with low levels of (1 → 2)-linked α-d-glucose units. The structural features of the glucan formed, demonstrated that glucansucrase AP-37 was an α-(1 → 3) branching sucrase. Dextran AP-37 was further characterised by FTIR analysis and XRD analysis demonstrated its amorphous nature. A fibrous compact morphology was observed for dextran AP-37 with SEM analysis whereas TGA and DSC analysis revealed its high stability as no degradation was observed up to 312 °C. Finally, the prebiotic potential of the dextran AP-37 and the gluco-oligosaccharides produced with the acceptor reaction of α-(1 → 3) branching sucrase AP-37 were determined and promising results were found for the gluco-oligosaccharides to act as prebiotics.

This study aimed to evaluate and compare the effects of dietary fibers (DFs) of commercially important tree nuts (almond, cashew, hazelnut, pistachio, and walnut) on gut microbiota in vitro. Microbial compositions and short-chain fatty acids were determined using 16S rRNA sequencing and gas chromatography (GC), respectively. Neutral and acidic monosaccharides were analyzed using GC/MS and spectrophotometry, respectively. Our results revealed that cashew fibers exhibit higher butyrate formation compared to others. Accordingly, cashew fiber promoted butyric acid-producing bacteria-related operational taxonomic units (OTUs; Butyricimonas and Collinsella) at higher relative abundances. The higher butyrogenic capacity of cashew fiber is mainly attributed to its higher soluble/total DF ratio and remarkably distinct monosaccharide composition. Additionally, nut fibers stimulated family Lachnospiraceae- and Ruminococcaceae-related OTUs. These findings show that although the degree of promotion is nut type-dependent, nut fibers are generally capable of promoting beneficial microbes in the colon, further suggesting that DFs of tree nuts are contributing factors to their health-promoting effects.

Although many efforts have been made to characterize the functional properties of hazelnut constituents (mainly its oil, protein, and phenolics), those of its dietary fiber (DF) have not been elucidated yet. Here, we aimed to investigate the impact of DF of natural and roasted hazelnuts, and hazelnut skin on the colonic microbiota in vivo (C57BL/6J mouse models) by determining their composition through 16S rRNA sequencing and microbial short-chain fatty acids (SCFAs) using gas chromatography. Our results revealed that hazelnut DF generally showed an acetogenic effect in male mice, whereas the same trend was not observed in the female counterparts. The 16S rRNA sequencing results showed that hazelnut DF, especially that of natural hazelnuts, increased the relative abundances of Lactobacillus-related OTUs that have probiotic potential. LEfSe analysis indicated that, for female mice, Lachnospiraceae, Prevotella, Ruminococcaceae, and Lactobacillus were found to be discriminators for DF of natural hazelnuts, roasted hazelnuts, hazelnut skin, and control, respectively, whereas Bacteroides, Lactobacillus, Prevotella, and Lactococcus were the discriminators for the male counterparts, respectively. This study clearly indicates that, although the roasting process slightly alters the functionalities, hazelnut DF favors beneficial microbes and stimulates beneficial microbial metabolites in the colon in a sex-dependent way, which could be a contributing factor to the health-promoting effects of hazelnuts. Furthermore, hazelnut skin, a byproduct of the hazelnut industry, was found to have potential to be utilized to produce functional DF targeting colonic health.

EDITORIAL article Front. Microbiol., 23 February 2023Sec. Food Microbiology Volume 14 - 2023 | https://doi.org/10.3389/fmicb.2023.1160746

Summary Due to its high antioxidant capacity, hazelnut ( Corylus avellana L.) skin oil has recently gained great attention. However, its thermal and oxidative characteristics have not been elucidated yet. Here, we determined the thermal and oxidative properties, antioxidant activity and fatty acid composition of hazelnut skin oil (HSO) using differential scanning calorimetry (DSC), spectrophotometry and gas chromatography/mass spectrometry, respectively, and compared those with the oils from natural and roasted hazelnuts. HSO was found to have significantly higher proportions of polyunsaturated fatty acid, compared with oils from natural and roasted hazelnut. HSO had the lowest melting point. Moreover, HSO revealed higher oxidative stability, which can be attributed to its greater antioxidant capacity. These findings indicate that hazelnut skin, a by‐product of hazelnut industry, has potential to be utilised in hazelnut oil industry to produce oil possessing high oxidative and thermal stability.