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Carbohydrate Structure Database (CSDB) is a curated glycan data collection and a glycoinformatic platform. In this report, its database, analytical, and other components that have appeared for the recent years are reviewed. The major improvements were achieving close-to-full coverage on glycans from microorganisms, launching modules for glycosyltransferases and saccharide conformations, online glycan builder and 3D modeler, NMR simulator, NMR-based structure predictor, and other tools. Graphical Abstract

We investigate how host mucus glycan composition interacts with dietary carbohydrate content to influence the composition and expressed functions of a human gut community. The humanized gnotobiotic mice mimic humans with a nonsecretor phenotype due to knockout of their α1–2 fucosyltransferase (Fut2) gene. The fecal microbiota of Fut2 ⁻ mice that lack fucosylated host glycans show decreased alpha diversity relative to Fut2 ⁺ mice and exhibit significant differences in community composition. A glucose-rich plant polysaccharide-deficient (PD) diet exerted a strong effect on the microbiota membership but eliminated the effect of Fut2 genotype. Additionally fecal metabolites predicted host genotype in mice on a polysaccharide-rich standard diet but not on a PD diet. A more detailed mechanistic analysis of these interactions involved colonization of gnotobiotic Fut2 ⁺ and Fut2 ⁻ mice with Bacteroides thetaiotaomicron , a prominent member of the human gut microbiota known to adaptively forage host mucosal glycans when dietary polysaccharides are absent. Within Fut2 ⁻ mice, the B. thetaiotaomicron fucose catabolic pathway was markedly down-regulated, whereas BT4241–4247, an operon responsive to terminal β-galactose, the precursor that accumulates in the Fut2 ⁻ mice, was significantly up-regulated. These changes in B. thetaiotaomicron gene expression were only evident in mice fed a PD diet, wherein B. thetaiotaomicron relies on host mucus consumption. Furthermore, up-regulation of the BT4241–4247 operon was also seen in humanized Fut2 ⁻ mice. Together, these data demonstrate that differences in host genotype that affect the carbohydrate landscape of the distal gut interact with diet to alter the composition and function of resident microbes in a diet-dependent manner.

Starch is a major food supply for humanity. It is produced in seeds, rhizomes, roots and tubers in the form of semi-crystalline granules with unique properties for each plant. Though the size and morphology of the granules is specific for each plant species, their internal structures have remarkably similar architecture, consisting of growth rings, blocklets, and crystalline and amorphous lamellae. The basic components of starch granules are two polyglucans, namely amylose and amylopectin. The molecular structure of amylose is comparatively simple as it consists of glucose residues connected through α-(1,4)-linkages to long chains with a few α-(1,6)-branches. Amylopectin, which is the major component, has the same basic structure, but it has considerably shorter chains and a lot of α-(1,6)-branches. This results in a very complex, three-dimensional structure, the nature of which remains uncertain. Several models of the amylopectin structure have been suggested through the years, and in this review two models are described, namely the “cluster model” and the “building block backbone model”. The structure of the starch granules is discussed in light of both models.

This paper explores the multifaceted nature of β-glucan, a notable dietary fiber (DF) with extensive applications. Beginning with an in-depth examination of its intricate polysaccharide structure, the discussion extends to diverse sources like oats, barley, mushrooms, and yeast, emphasizing their unique compositions. The absorption and metabolism of β-glucan in the human body are scrutinized, emphasizing its potential health benefits. Extraction and purification processes for high-quality β-glucan in food, pharmaceuticals, and cosmetics are outlined. The paper underscores β-glucan’s biofunctional roles in immune modulation, cholesterol regulation, and gastrointestinal health, supported by clinical studies. The review discusses global trade dynamics by tracing its evolution from a niche ingredient to a global commodity. In summary, it offers a comprehensive scientific perspective on β-glucan, serving as a valuable resource for researchers, professionals, and industries exploring its potential in the dietary fiber landscape.

Dietary fibers are major substrates for maintaining and shaping gut microbiota, but the structural specificity of these fibers for the diversity, structure and function of gut microbiota are poorly understood. Here, we employed an in vitro sequential batch fecal culture approach to address two ecological questions: (i) whether the chemical complexity of a carbohydrate influences its ability to maintain microbial diversity against high dilution pressure (ii) whether substrate structuring or obligate microbe-microbe metabolic interactions (e.g. exchange of amino acids or vitamins) exert more influence on maintained diversity. Sorghum arabinoxylan (SAX, a complex polysaccharide), inulin (a low-complexity oligosaccharide) and their corresponding monosaccharide controls were selected as model carbohydrates. Our results demonstrate that complex carbohydrates stably sustain diverse microbial consortia. Furthermore, other metabolic interactions were less influential in structuring microbial consortia consuming SAX than inulin. Finally, very similar final consortia were enriched on SAX from the same individual's fecal microbiota one month later, suggesting that polysaccharide structure is more influential than stochastic alterations in microbiome composition in governing the outcomes of sequential batch cultivation experiments. These data suggest that carbohydrate structural complexity affords independent niches that structure fermenting microbial consortia, whereas other metabolic interactions govern the composition of communities fermenting simpler carbohydrates.

Diet, especially with respect to consumption of dietary fibers, is well recognized as one of the most important factors shaping the colonic microbiota composition. Accordingly, many studies have been conducted to explore dietary fiber types that could predictably manipulate the colonic microbiota for improved health. However, the majority of these studies underappreciate the vastness of fiber structures in terms of their microbial utilization and omit detailed carbohydrate structural analysis. In some cases, this causes conflicting results to arise between studies using (theoretically) the same fibers. In this investigation, by performing in vitro fecal fermentation studies using bran arabinoxylans obtained from different classes of wheat, we showed that even subtle changes in the structure of a dietary fiber result in divergent microbial communities and metabolic outputs. This underscores the need for much higher structural resolution in studies investigating interactions of dietary fibers with gut microbiota, both in vitro and in vivo . The chemical structures of soluble fiber carbohydrates vary from source to source due to numerous possible linkage configurations among monomers. However, it has not been elucidated whether subtle structural variations might impact soluble fiber fermentation by colonic microbiota. In this study, we tested the hypothesis that subtle structural variations in a soluble polysaccharide govern the community structure and metabolic output of fermenting microbiota. We performed in vitro fecal fermentation studies using arabinoxylans (AXs) from different classes of wheat (hard red spring [AX HRS ], hard red winter [AX HRW ], and spring red winter [AX SRW ]) with identical initial microbiota. Carbohydrate analyses revealed that AX SRW was characterized by a significantly shorter backbone and increased branching compared with those of the hard varieties. Amplicon sequencing demonstrated that fermentation of AX SRW resulted in a distinct community structure of significantly higher richness and evenness than those of hard-AX-fermenting cultures. AX SRW favored OTUs within Bacteroides , whereas AX HRW and AX HRS favored Prevotella . Accordingly, metabolic output varied between hard and soft varieties; higher propionate production was observed with AX SRW and higher butyrate and acetate with AX HRW and AX HRS . This study showed that subtle changes in the structure of a dietary fiber may strongly influence the composition and function of colonic microbiota, further suggesting that physiological functions of dietary fibers are highly structure dependent. Thus, studies focusing on interactions among dietary fiber, gut microbiota, and health outcomes should better characterize the structures of the carbohydrates employed. IMPORTANCE Diet, especially with respect to consumption of dietary fibers, is well recognized as one of the most important factors shaping the colonic microbiota composition. Accordingly, many studies have been conducted to explore dietary fiber types that could predictably manipulate the colonic microbiota for improved health. However, the majority of these studies underappreciate the vastness of fiber structures in terms of their microbial utilization and omit detailed carbohydrate structural analysis. In some cases, this causes conflicting results to arise between studies using (theoretically) the same fibers. In this investigation, by performing in vitro fecal fermentation studies using bran arabinoxylans obtained from different classes of wheat, we showed that even subtle changes in the structure of a dietary fiber result in divergent microbial communities and metabolic outputs. This underscores the need for much higher structural resolution in studies investigating interactions of dietary fibers with gut microbiota, both in vitro and in vivo .

Plants use the insoluble polyglucan starch as their primary glucose storage molecule. Reversible phosphorylation, at the C6 and C3 positions of glucose moieties, is the only known natural modification of starch and is the key regulatory mechanism controlling its diurnal breakdown in plant leaves. The glucan phosphatase Starch Excess4 (SEX4) is a position-specific starch phosphatase that is essential for reversible starch phosphorylation; its absence leads to a dramatic accumulation of starch in Arabidopsis, but the basis for its function is unknown. Here we describe the crystal structure of SEX4 bound to maltoheptaose and phosphate to a resolution of 1.65 Å. SEX4 binds maltoheptaose via a continuous binding pocket and active site that spans both the carbohydrate-binding module (CBM) and the dual-specificity phosphatase (DSP) domain. This extended interface is composed of aromatic and hydrophilic residues that form a specific glucan-interacting platform. SEX4 contains a uniquely adapted DSP active site that accommodates a glucan polymer and is responsible for positioning maltoheptaose in a C6-specific orientation. We identified two DSP domain residues that are responsible for SEX4 site-specific activity and, using these insights, we engineered a SEX4 double mutant that completely reversed specificity from the C6 to the C3 position. Our data demonstrate that the two domains act in consort, with the CBM primarily responsible for engaging glucan chains, whereas the DSP integrates them in the catalytic site for position-specific dephosphorylation. These data provide important insights into the structural basis of glucan phosphatase site-specific activity and open new avenues for their biotechnological utilization.

This study was designed to investigate the effects of dietary starch structure on muscle protein synthesis and gastrointestinal amino acid (AA) transport and metabolism of goats. Twenty-seven Xiangdong black female goats (average body weight = 9·00 ± 1·12 kg) were randomly assigned to three treatments, i.e., fed a T1 (normal maize 100 %, high amylose maize 0 %), T2 (normal maize 50 %, high amylose maize 50 %) and T3 (normal maize 0 %, high amylose maize 100 %) diet for 35 d. All AA in the ileal mucosa were decreased linearly as amylose:amylopectin increased in diets (P < 0·05). The plasma valine (linear, P = 0·03), leucine (linear, P = 0·04) and total AA content (linear, P = 0·03) increased linearly with the increase in the ratio of amylose in the diet. The relative mRNA levels of solute carrier family 38 member 1 (linear, P = 0·01), solute carrier family 3 member 2 (linear, P = 0·02) and solute carrier family 38 member 9 (linear, P = 0·02) in the ileum increased linearly with the increase in the ratio of amylose in the diet. With the increase in the ratio of amylose:amylopectin in the diet, the mRNA levels of acetyl-CoA dehydrogenase B (linear, P = 0·04), branched-chain amino acid transferase 1 (linear, P = 0·02) and branched-chain α-keto acid dehydrogenase complex B (linear, P = 0·01) in the ileum decreased linearly. Our results revealed that the protein abundances of phosphorylated mammalian target of rapamycin (p-mTOR) (P < 0·001), phosphorylated 4E-binding protein 1 (P < 0·001) and phosphorylated ribosomal protein S6 kinases 1 (P < 0·001) of T2 and T3 were significantly higher than that of T1. In general, a diet with a high amylose ratio could reduce the consumption of AA in the intestine, allowing more AA to enter the blood to maintain higher muscle protein synthesis through the mTOR pathway.

Starch, as a primary component of wheat, plays a crucial role in determining the quality of noodles and pasta. A deep understanding of the impact of starch on the quality of noodles and pasta is fundamentally important for the industrial progression of these products. The starch structure exerts an influence on the quality of noodles and pasta by affecting its functional attributes and the interaction of starch–gluten proteins. The effects of starch structure (amylopectin structure, amylose content, granules size, damaged starch content) on the quality of noodles and pasta is discussed. The relationship between the functional properties of starch, particularly its swelling power and pasting properties, and the texture of noodles and pasta is discussed. It is important to note that the functional properties of starch can be modified during the processing of noodles and pasta, potentially impacting the quality of the end product, However, this aspect is often overlooked. Additionally, the interaction between starch and gluten is addressed in relation to its impact on the quality of noodles and pasta. Finally, the application of exogenous starch in improving the quality of noodles and pasta is highlighted.

Delayed sowing (DS) is an important measure for adapting to global warming, but its effect on rice quality is poorly understood. To evaluate the influence of DS on the starch structure and quality of rice, this study conducted field experiments by sowing two indica rice cultivars on two different sowing dates in both Hanyuan and Chongzhou, Sichuan Province, China, from 2017 to 2018. The delayed sowing period experienced a mean temperature reduction of 1.87–2.99℃ during the grain-filling stage compared to the conventional sowing period. The amylose content (AC), starch content (SC), branching degree (BD), proportion of amylopectin A chain (DP 6–12), 1022/995 cm –1 ratio, Z-average molecular weight (Mz)/ number average molecular weight (Mn), and weight average molecular weight (Mw)/Mn were significantly ( p  < 0.05) and negatively correlated with both chalky rice rate (CRR) and chalkiness degree (CD) but positively correlated with appearance value (AV), taste value (TV), and comprehensive score (CS) of cooked rice. Meanwhile, starch granule average diameter (SGAD), volume-based percentage of large starch granules (D > 8 μm) (VPLSG), average amylopectin chain length (AACL), 1045/1022 cm –1 ratio, proportions of amylopectin B2 (DP 25–36) and B3 (DP ≥ 37) chains, and crystallinity degree (CRD) significantly ( p  < 0.05) reduced with eating quality of rice but positively associated with rice chalkiness. Compared to conventional sowing, the 1022/995 cm –1 ratio, amylose content (AC), BD, A chain proportion, Mw/Mn, and Mz/Mn were significantly ( p  < 0.05) increased by delayed sowing treatment in both study sites. DS also reduced the VPLSG, AACL, CRD, B2 and B3 chains proportions, and 1045/1022 cm –1 ratio. This contributed to reductions in CRR and CD, as well as increases in the AV, TV, and CS of cooked rice across study sites. No significance was observed in milling quality of rice. Therefore, delayed sowing improved the appearance and eating qualities of rice by altering its components and structural characteristics of starch.