Touching the High Complexity of Prebiotic Vivinal Galacto-oligosaccharides Using Porous Graphitic Carbon Ultra-High-Performance Liquid Chromatography Coupled to Mass Spectrometry

Distinguishing α/β-linkages and linkage positions of disaccharides in galactooligosaccharides through mass fragmentation and liquid retention behaviour

Galactooligosaccharides (GOS) are important prebiotics with function closely related to their structure. However, a comprehensive overview of the structure-function relationship is still limited due to the challenge in characterizing multiple isomers in GOS. This study presents a strategy of combining both hydrophilic interaction liquid chromatography (HILIC) retention time and tandem mass spectrometry (MS/MS) fragmentation pattern to distinguish α/β-linkages and linkage positions of disaccharide isomers in GOS through HILIC-MS/MS analysis. The results indicated that the ratio of m/z 203.0524 to m/z 365.1054 could distinguish α/β-linkages, while the ratios of m/z 347.0947 to m/z 365.1054, m/z 245.0642 to m/z 365.1054 and HILIC retention time could distinguish (1 → 2), (1 → 3), (1 → 4) and (1 → 6) linkages. The above rules enabled effective characterization of disaccharides in GOS-containing food samples, including milk powder, rice flour, drink, yogurt. This method can be used in the quality control of GOS and future research on the structure-specific health effects of GOS.

Galactooligosaccharides: Synthesis, metabolism, bioactivities and food applications

Prebiotics are non-digestible ingredients that exert significant health-promoting effects on hosts. Galactooligosaccharides (GOS) have remarkable prebiotic effects and structural similarity to human milk oligosaccharides. They generally comprise two to eight sugar units, including galactose and glucose, which are synthesized from substrate lactose by microbial β-galactosidase. Enzyme sources from probiotics have received particular interest because of their safety and potential to synthesize specific structures that are particularly metabolized by intestinal probiotics. Owing to advancements in modern analytical techniques, many GOS structures have been identified, which vary in degree of polymerization, glycosidic linkage, and branch location. After intake, GOS adjust gut microbiota which produce short chain fatty acids, and exhibit excellent biological activities. They selectively stimulate the proliferation of probiotics, inhibit the growth and adhesion of pathogenic bacteria, alleviate gastrointestinal, neurological, metabolic and allergic diseases, modulate metabolites production, and adjust ion storage and absorption. Additionally, GOS are safe and stable, with high solubility and clean taste, and thus are widely used as food additives. GOS can improve the appearance, flavor, taste, texture, viscosity, rheological properties, shelf life, and health benefits of food products. This review systemically covers GOS synthesis, structure identifications, metabolism mechanisms, prebiotic bioactivities and wide applications, focusing on recent advances.

Structural Characterization of Disaccharides Using Cyclic Ion Mobility Spectrometry and Monosaccharide Standards

To understand the mode of action of bioactive oligosaccharides, such as prebiotics, in-depth knowledge about all structural features, including monosaccharide composition, linkage type, and anomeric configuration, is necessary. Current analytical techniques provide limited information about structural features within complex mixtures unless preceded by extensive purification. In this study, we propose an approach employing cyclic ion mobility spectrometry (cIMS) for the in-depth characterization of oligosaccharides, here demonstrated for disaccharides. We were able to separate galactose and glucose anomers by exploiting the high ion mobility resolution of cIMS. Using the obtained monosaccharide mobilograms as references, we determined the composition and anomeric configuration of 4β-galactobiose by studying the monosaccharide fragments generated by collision-induced dissociation (CID) before the ion mobility separation. Drift times and individual MS2 spectra of partially resolved reducing-end anomers of 4β-galactobiose, 4β-galactosylglucose (lactose), and 4β-glucosylglucose (cellobiose) were obtained by deconvolution using CID fragmentation induced in the transfer region between the cIMS cell and TOF analyzer. The composition and anomeric configuration of the reducing end anomers of these disaccharides were identified using cIMS2 approaches, where first each anomer was isolated using cIMS and individually fragmented, and the monosaccharide fragments were again separated by cIMS for comparison with monosaccharide standards. With these results we demonstrate the promising application of cIMS for the structural characterization of isomeric oligosaccharides.

Effects of nondigestible oligosaccharides on inflammation, lung health, and performance of calves

Our objective was to determine the effects of nondigestible oligosaccharides (NDO) on lung health and performance. Three hundred male Holstein-Friesian calves aged 18.0 ± 3.6 d received 1 of 6 treatments for 8.5 wk (period 1). Treatments included a negative control (CON), galacto-oligosaccharides (GOS) administered as a spray via the nose once daily (SPR), GOS administered via the milk replacer (MR) at 1% (GOS-L) and 2% (GOS-H), fructo-oligosaccharides administered via the MR at 0.25% (FOS) and a combination of GOS and fructo-oligosaccharides administered via the MR at 1% and 0.25%, respectively (GOS-FOS). Milk replacer was fed twice daily. Feeding levels were equal between calves and increased progressively in time. Body weight was measured every 4 wk and clinical health was scored weekly. Blood and broncho-alveolar lavage fluid (BALF) samples were collected bi-weekly from a subset of calves (n = 120). After period 1, all calves received the same control MR for 18 wk until slaughter (period 2), during which general performance and clinical health were measured. Generally, infection pressure was high, with clinical scores and BALF proinflammatory TNFα concentrations increasing with time in period 1, which resulted in a high number of required group antimicrobial treatments (6 group antimicrobial treatments in 13 wk, supplied to all calves). Average daily gain adjusted to equal solid feed intake was increased for GOS-L (+61 g/d) compared with CON calves from experimental wk 1 to 5. Plasma white blood cell concentration tended to be lowered by GOS-L, plasma IL-8 concentration was reduced by all orally supplemented NDO, plasma IL-6 was reduced by all NDO treatments except GOS-FOS and plasma IL-1β was reduced by all NDO treatments compared with CON, although this differed per time point for SPR. The neutrophil percentage in BALF was reduced by GOS-L in wk 6, which was associated with a relative increase in macrophages. The BALF concentration of TNFα and IL-8 was reduced or tended to be reduced by GOS-L and GOS-H, while IL-6 was or tended to be reduced by SPR, GOS-L, GOS-H, and GOS-FOS, and IL-1β was reduced by SPR, GOS-L, GOS-H, and FOS. Generally, feeding the combination of GOS and FOS was not more effective than feeding GOS or FOS alone, because feeding GOS-FOS resulted in higher concentrations of plasma and BALF cytokine and chemokine concentrations compared with feeding GOS-L alone, and resulted in higher plasma cytokine concentrations compared with feeding FOS alone. None of the BALF and plasma cytokine or chemokine concentrations differed between the GOS-L and GOS-H treatment. Performance and clinical scores in period 2 did not differ among treatments. Altogether, all tested NDO reduced systemic and lung inflammation in calves under high natural infection pressure and for GOS-fed calves, this increased performance during the first 4 wk. Combining GOS and FOS did not have a synergistic effect. The intranasal administration of GOS also lowered systemic and lung inflammation, but tended to negatively affect performance. Overall, this study demonstrates the potential of NDO to alleviate systemic and respiratory inflammation in calves.

Evaluation of Prebiotic Glycan Composition in Human Milk and Infant Formula: Profile of Galacto-Oligosaccharides and Absolute Quantification of Major Milk Oligosaccharides by UPLC-Cyclic IM-MS and UPLC-MS/MS

Prebiotic oligosaccharides have attracted immense interest in the infant formula (IF) industry due to their unique health benefits for infants. There is a need for the reasonable supplementation of prebiotics in premium IF products. Herein, we characterized the profile of galacto-oligosaccharides (GOS) in human milk (HM) and IF using ultrahigh-performance liquid chromatography-cyclic ion mobility-mass spectrometry (UPLC-cIM-MS) technique. Additionally, we further performed a targeted quantitative analysis of five essential HM oligosaccharides (HMOs) in HM (n = 196), IF (n = 50), and raw milk of IF (n = 10) by the high-sensitivity UPLC-MS/MS method. HM exhibited a more abundant and variable HMO composition (1183.19 to 2892.91 mg/L) than IF (32.91 to 56.31 mg/L), whereas IF contained extra GOS species and non-negligible endogenous 3'-sialyllactose. This also facilitated the discovery of secretor features within the Chinese population. Our study illustrated the real disparity in the prebiotic glycome between HM and IF and provided crucial reference for formula improvement.

Gram-scale chemical synthesis of galactosyllactoses and their impact on infant gut microbiota in vitro

Galactooligosaccharides (GOS) are widely used as a supplement in infant nutrition to mimic the beneficial effects found in prebiotic human milk oligosaccharides (HMOs). However, the complexity of the GOS mixture makes it challenging to ascertain which of the GOS components contribute most to their health benefits. Galactosyllactoses (GLs) are lactose-based trisaccharides containing a β-galactopyranosyl residue at the 3'-position (3'galactosyllactose, 3'-GL), 4'-position (4'-galactosyllactose, 4'-GL), or the 6'-position (6'-galactosyllactose, 6'-GL). These GLs are of particular interest as they are present in both GOS mixtures and human milk at early stages of lactation. However, research on the potential health benefits of these individual GLs has been limited. Gram quantities are needed to assess their health benefits but these GLs are not readily available at this scale. In this study, we report the gram-scale chemical synthesis of 3'-GL, 4'-GL, and 6'-GL. All three galactosyllactoses were obtained on a gram scale in good purity from cheap and commercially available lactose. Furthermore, in vitro incubation of GLs with infant faecal microbiota demonstrates that the GLs were able to increase the abundance of Bifidobacterium and stimulate short chain fatty acid production.

The European Polysaccharide Network of Excellence (EPNOE) research roadmap 2040: Advanced strategies for exploiting the vast potential of polysaccharides as renewable bioresources

Polysaccharides are among the most abundant bioresources on earth and consequently need to play a pivotal role when addressing existential scientific challenges like climate change and the shift from fossil-based to sustainable biobased materials. The Research Roadmap 2040 of the European Polysaccharide Network of Excellence (EPNOE) provides an expert's view on how future research and development strategies need to evolve to fully exploit the vast potential of polysaccharides as renewable bioresources. It is addressed to academic researchers, companies, as well as policymakers and covers five strategic areas that are of great importance in the context of polysaccharide related research: (I) Materials & Engineering, (II) Food & Nutrition, (III) Biomedical Applications, (IV) Chemistry, Biology & Physics, and (V) Skills & Education. Each section summarizes the state of research, identifies challenges that are currently faced, project achievements and developments that are expected in the upcoming 20 years, and finally provides outlines on how future research activities need to evolve.

Application of chromatography in purification and structural analysis of natural polysaccharides: A review

Polysaccharides are widely distributed in natural sources from monocytic microorganisms to higher animals, and are found in a variety of biological activities in recent decades. Natural polysaccharides have the characteristics of large molecular weight, diverse composition, and complex structure, so their purification and structural analysis are difficult issues in research. Chromatography as a powerful separation technique, plays an irreplaceable role in the separation and structural analysis of natural polysaccharides, especially in the purification of polysaccharides, the separation of hydrolysates, and the analysis of monosaccharide composition. The separation mechanisms and application of different chromatographic methods in the studies of polysaccharides were summarized in this review. Moreover, the advantages and drawbacks of various chromatography methods were discussed as well.

Microbiota-dependent influence of prebiotics on the resilience of infant gut microbiota to amoxicillin/clavulanate perturbation in an in vitro colon model

Antibiotic exposure disturbs the developing infant gut microbiota. The capacity of the gut microbiota to recover from this disturbance (resilience) depends on the type of antibiotic. In this study, infant gut microbiota was exposed to a combination of amoxicillin and clavulanate (amoxicillin/clavulanate) in an in vitro colon model (TIM-2) with fecal-derived microbiota from 1-month-old (1-M; a mixed-taxa community type) as well as 3-month-old (3-M; Bifidobacterium dominated community type) breastfed infants. We investigated the effect of two common infant prebiotics, 2'-fucosyllactose (2'-FL) or galacto-oligosaccharides (GOS), on the resilience of infant gut microbiota to amoxicillin/clavulanate-induced changes in microbiota composition and activity. Amoxicillin/clavulanate treatment decreased alpha diversity and induced a temporary shift of microbiota to a community dominated by enterobacteria. Moreover, antibiotic treatment increased succinate and lactate in both 1- and 3-M colon models, while decreasing the production of short-chain (SCFA) and branched-chain fatty acids (BFCA). The prebiotic effect on the microbiota recovery depended on the fermenting capacity of antibiotic-exposed microbiota. In the 1-M colon model, the supplementation of 2'-FL supported the recovery of microbiota and restored the production of propionate and butyrate. In the 3-M colon model, GOS supplementation supported the recovery of microbiota and increased the production of acetate and butyrate.

Infant Fecal Fermentations with Galacto-Oligosaccharides and 2′-Fucosyllactose Show Differential Bifidobacterium longum Stimulation at Subspecies Level

The objective of the current study was to evaluate the potential of 2′-FL and GOS, individually and combined, in beneficially modulating the microbial composition of infant and toddler (12–18 months) feces using the micro-Matrix bioreactor. In addition, the impacts of GOS and 2′-FL, individually and combined, on the outgrowth of fecal bifidobacteria at (sub)species level was investigated using the baby M-SHIME® model. For young toddlers, significant increases in the genera Bifidobacterium, Veillonella, and Streptococcus, and decreases in Enterobacteriaceae, Clostridium XIVa, and Roseburia were observed in all supplemented fermentations. In addition, GOS, and combinations of GOS and 2′-FL, increased Collinsella and decreased Salmonella, whereas 2′-FL, and combined GOS and 2′-FL, decreased Dorea. Alpha diversity increased significantly in infants with GOS and/or 2′-FL, as well as the relative abundances of the genera Veillonella and Akkermansia with 2′-FL, and Lactobacillus with GOS. Combinations of GOS and 2′-FL significantly stimulated Veillonella, Lactobacillus, Bifidobacterium, and Streptococcus. In all supplemented fermentations, Proteobacteria decreased, with the most profound decreases accomplished by the combination of GOS and 2′-FL. When zooming in on the different (sub)species of Bifidobacterium, GOS and 2’-FL were shown to be complementary in stimulating breast-fed infant-associated subspecies of Bifidobacterium longum in a dose-dependent manner: GOS stimulated Bifidobacterium longum subsp. longum, whereas 2′-FL supported outgrowth of Bifidobacterium longum subsp. infantis.

Antibiotics in avian care and husbandry-status and alternative antimicrobials

Undoubtedly, the discovery of antibiotics was one of the greatest milestones in the treatment of human and animal diseases. Due to their over-use mainly as antibiotic growth promoters (AGP) in livestock farming, antimicrobial resistance has been reported with increasing intensity, especially in the last decades. In order to reduce the scale of this phenomenon, initially in the Scandinavian countries and then throughout the entire European Union, a total ban on the use of AGP was introduced, moreover, a significant limitation in the use of these feed additives is now observed almost all over the world. The withdrawal of AGP from widespread use has prompted investigators to search for alternative strategies to maintain and stabilize the composition of the gut microbiota. These strategies include substances that are used in an attempt to stimulate the growth and activity of symbiotic bacteria living in the digestive tract of animals, as well as living microorganisms capable of colonizing the host’s gastrointestinal tract, which can positively affect the composition of the intestinal microbiota by exerting a number of pro-health effects, i.e., prebiotics and probiotics, respectively. In this review we also focused on plants/herbs derived products that are collectively known as phytobiotic.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

Combining galacto-oligosaccharides and 2'-fucosyllactose alters their fermentation kinetics by infant fecal microbiota and influences AhR-receptor dependent cytokine responses in immature dendritic cells

Galacto-oligosaccharides (GOS) and 2′-fucosyllactose (2′-FL) are non-digestible carbohydrates (NDCs) that are often added to infant formula to replace the functionalities of human milk oligosaccharides (HMOs). It is not known if combining GOS and 2′-FL will affect their fermentation kinetics and subsequent immune-modulatory effects such as AhR-receptor stimulation. Here, we used an in vitro set-up for the fermentation of 2′-FL and GOS, either individually or combined, by fecal microbiota of 8-week-old infants. We found that GOS was fermented two times faster by the infant fecal microbiota when combined with 2′-FL, while the combination of GOS and 2′-FL did not result in a complete degradation of 2′-FL. Fermentation of both GOS and 2′-FL increased the relative abundance of Bifidobacterium, which coincided with the production of acetate and lactate. Digesta of the fermentations influenced dendritic cell cytokine secretion differently under normal conditions and in the presence of the AhR-receptor blocker CH223191. We show that, combining GOS and 2′-FL accelerates GOS fermentation by the infant fecal microbiota of 8-week-old infants. In addition, we show that the fermentation digesta of GOS and 2′-FL, either fermented individually or combined, can attenuate DC cytokine responses in a similar and in an AhR-receptor dependent way.

Galacto-oligosaccharides (GOS) and 2′-fucosyllactose (2′-FL) are non-digestible carbohydrates (NDCs) that are often added to infant formula to replace the functionalities of human milk oligosaccharides (HMOs).

Structure and function of non-digestible carbohydrates in the gut microbiome

Together with proteins and fats, carbohydrates are one of the macronutrients in the human diet. Digestible carbohydrates, such as starch, starch-based products, sucrose, lactose, glucose and some sugar alcohols and unusual (and fairly rare) α-linked glucans, directly provide us with energy while other carbohydrates including high molecular weight polysaccharides, mainly from plant cell walls, provide us with dietary fibre. Carbohydrates which are efficiently digested in the small intestine are not available in appreciable quantities to act as substrates for gut bacteria. Some oligo- and polysaccharides, many of which are also dietary fibres, are resistant to digestion in the small intestines and enter the colon where they provide substrates for the complex bacterial ecosystem that resides there. This review will focus on these non-digestible carbohydrates (NDC) and examine their impact on the gut microbiota and their physiological impact. Of particular focus will be the potential of non-digestible carbohydrates to act as prebiotics, but the review will also evaluate direct effects of NDC on human cells and systems.

Partial acid-hydrolysis of TEMPO-oxidized arabinoxylans generates arabinoxylan-structure resembling oligosaccharides

Arabinoxylans (AXs) display biological activities that depend on their chemical structures. To structurally characterize and distinguish AXs using a non-enzymatic approach, various TEMPO-oxidized AXs were partially acid-hydrolysed to obtain diagnostic oligosaccharides (OS). Arabinurono-xylo-oligomer alditols (AUXOS-A) with degree of polymerization 2-5, comprising one and two arabinuronic acid (AraA) substituents were identified in the UHPLC-PGC-MS profiles of three TEMPO-oxidized AXs, namely wheat (ox-WAX), partially-debranched WAX (ox-pD-WAX), and rye (ox-RAX). Characterization of these AUXOS-A highlighted that single-substitution of the Xyl unit preferably occurs at position O-3 for these samples, and that ox-WAX has both more single substituted and more double-substituted xylose residues in its backbone than the other AXs. Characteristic UHPLC-PGC-MS OS profiles, differing in OS abundance and composition, were obtained for each AX. Thus, partial acid-hydrolysis of TEMPO-oxidized AXs with analysis of the released OS by UHPLC-PGC-MS is a promising novel non-enzymatic approach to distinguish AXs and obtain insights into their structures.

Structure-Specific Fermentation of Galacto-Oligosaccharides, Isomalto-Oligosaccharides and Isomalto/Malto-Polysaccharides by Infant Fecal Microbiota and Impact on Dendritic Cell Cytokine Responses

SCOPE

Next to galacto-oligosaccharides (GOS), starch-derived isomalto-oligosaccharide preparation (IMO) and isomalto/malto-polysaccharides (IMMP) could potentially be used as prebiotics in infant formulas. However, it remains largely unknown how the specific molecular structures of these non-digestible carbohydrates (NDCs) impact fermentability and immune responses in infants.

METHODS AND RESULTS

In vitro fermentation of GOS, IMO and IMMP using infant fecal inoculum of 2- and 8-week-old infants shows that only GOS and IMO are fermented by infant fecal microbiota. The degradation of GOS and IMO coincides with an increase in Bifidobacterium and production of acetate and lactate, which is more pronounced with GOS. Individual isomers with an (1↔1)-linkage or di-substituted reducing terminal glucose residue are more resistant to fermentation. GOS, IMO, and IMMP fermentation digesta attenuates cytokine profiles in immature dendritic cells (DCs), but the extent is dependent on the infants age and NDC structure.

CONCLUSION

The IMO preparation, containing reducing and non-reducing isomers, shows similar fermentation patterns as GOS in fecal microbiota of 2-week-old infants. Knowledge obtained on the substrate specificities of infant fecal microbiota and the subsequent regulatory effects of GOS, IMO and IMMP on DC responses might contribute to the design of tailored NDC mixtures for infants of different age groups.

Novel Class of Human Milk Oligosaccharides Based on 6'-Galactosyllactose Containing N-Acetylglucosamine Branches Extended by Oligogalactoses

Human milk oligosaccharides (HMOs) have attracted much attention in recent years not only as a prebiotic factor but also in particular as an essential component of infant nutrition in relation to their impact on innate immunity. The backbone structures of complex HMOs generally contain single or repetitive lacto-N-biose (type 1) or lactosamine (type 2) units in either linear or branched chains extending from a lactose core. While all known branched structures originate from the 3,6-substitution of the lactosyl core galactose, we here describe a new class of HMOs that tentatively branch at the terminal galactose of 6'-galactosyllactose. Another novel feature of this class of HMOs was found in linear oligo-galactosyl chains linked to one of the N-acetylglucosamine (GlcNAc) branches. The novel structures exhibit general formulas with hexose versus hexosamine contents of 5/2 to 8/2 and can be designated as high-galactose (HG)-HMOs. In addition, up to three fucosyl residues are linked to the octa- to dodecasaccharides, which were detected in two human milk samples from the Lewis blood-group-defined donors. Structural analyses of methylated glycans and their alditols comprised matrix-assisted laser desorption ionization mass spectrometry, electrospray-(collision-induced dissociation) mass spectrometry and linkage analyses by gas chromatography-mass spectrometry of the derived partially methylated alditol acetates. Enzymatic degradation by the application of β1-3,4-specific galactosidase supported the presence of terminal galactose-linked β1-6 to one of the two GlcNAc branches. The mass spectrometry glycomic data have been deposited at the GlycoPOST archive with the data set identifier GPST000191 (Username: franz.hanisch@uni-koeln.de; Password: Soma1Dita2Carb. Watanabe, Y. GlycoPOST realizes FAIR principles for glycomics mass spectrometry data. Nucleic Acids Res. 2021, 49, D1523-D1528).