An efficient protocol for the preparation of linear arabino-oligosaccharides

Application of an α-galactosidase from Bacteroides fragilis on structural analysis of raffinose family oligosaccharides

Raffinose family oligosaccharides (RFOs) have diverse structures and exhibit various biological activities. When using RFOs as prebiotics, their structures need to be identified. If we first knew whether an RFO was classical or non-classical, structural identification would become much easier. Here, we cloned and expressed an α-galactosidase (BF0224) from Bacteroides fragilis which showed strict specificity for hydrolyzing α-Gal-(1 → 6)-Gal linkages in RFOs. BF0224 efficiently distinguished classical from non-classical RFOs by identifying the resulting hydrolyzed oligo- and mono-saccharides with HPAEC-PAD-MS. Using this strategy, we identified a non-classical RFO from Pseudostellaria heterophylla (Miquel) Pax with DP6 (termed PHO-6), as well as a classical RFO from Lycopus lucidus Turcz. with DP7 (termed LTO-7). To characterize these RFO structures, we employed four other commercial or reported α-galactosidases in combination with NMR and methylation analysis. Using this approach, we elucidated the accurate chemical structure of PHO-6 and LTO-7. Our study provides an efficient analytical approach to structurally analyze RFOs. This enzyme-based strategy also can be applied to structural analysis of other glycans.

Valorization of citrus peel industrial wastes for facile extraction of extractives, pectin, and cellulose nanocrystals through ultrasonication: An in-depth investigation

In this work we developed an eco-friendly valorisation of Citrus wastes (CWs), through a solvent-assisted ultrasonication extraction technique, thus having access to a wide range of bio-active compounds and polysaccharides, extremely useful in different industrial sectors (food, cosmetics, nutraceutical). Water-based low-amplitude ultrasonication was examined as a potential method for pectin extraction as well as polar and non-polar citrus extractives (CEs), among which hesperidin and triglycerides of 18 carbon fatty acids were found to be the most representative ones. In addition, citric acid:glycerol (1:4)-based deep eutectic solvent (DES) in combination with ultrasonic extraction was utilized to extract microcellulose (CMC), from which stable cellulose nanocrystals (CNCs) with glycerol-assisted high amplitude ultrasonication were obtained. The physical and chemical properties of the extracted polysaccharides (pectin, micro and nanocellulose) were analysed through DLS, ζ-potential, XRD, HP-SEC, SEM, AFM, TGA-DSC, FTIR, NMR, and PMP-HPLC analyses. The putative structure of the extracted citrus pectin (CP) was analysed and elucidated through enzyme-assisted hydrolysis in correlation with ESI-MS and monosaccharide composition. The developed extraction methods are expected to influence the industrial process for the valorisation of CWs and implement the circular bio-economy.

Preparation of β-galacto-oligosaccharides using a novel endo-1,4-β-galactanase from Penicillium oxalicum

Endo-1,4-β-galactanase is an indispensable tool for preparing prebiotic β-galacto-oligosaccharides (β-GOS) from pectic galactan resources. In the present study, a novel endo-1,4-β-galactanase (PoβGal53) belonging to glycoside hydrolase family 53 from Penicillium oxalicum sp. 68 was cloned and expressed in Pichia pastoris GS115. Upon purification by affinity chromatography, recombinant PoβGal53 exhibited a single band on SDS-PAGE with a molecular weight of 45.0 kDa. Using potato galactan as substrate, PoβGal53 showed optimal reaction conditions of pH 4.0, 40 °C, and was thermostable, retaining >80 % activity after incubating below 45 °C for 12 h. Significantly, PoβGal53 exhibited relatively conserved substrate specificity for (1 → 4)-β-D-galactan with an activity of 6244 ± 282 U/mg. In this regard, the enzyme is in effect the most efficient endo-1,4-β-galactanase identified to date. By using PoβGal53, β-GOS monomers were prepared from potato galactan and separated using medium pressure liquid chromatography. HPAEC-PAD, MALDI-TOF-MS and ESI-MS/MS analyses demonstrated that these β-GOS species ranged from 1,4-β-D-galactobiose to 1,4-β-D-galactooctaose (DP 2-8) with high purity. This work provides not only a highly active tool for enzymatic degradation of pectic galactan, but an efficient protocol for preparing β-GOS.

An efficient protocol for preparing linear β-manno-oligosaccharides

Linear β-manno-oligosaccharides (l-β-MOS) are widely used to investigate oligo- and poly-saccharide structures and mannanolytic enzyme activities. l-β-MOS are also being used as prebiotic agents with potential bio-active properties. In this study, we developed an efficient protocol to prepare a series of l-β-MOS by hydrolyzing cassia gum (CG) using mannanolytic enzymes (endo-1,4-β-mannanase, α-galactosidases and β-glucosidases). By using medium pressure liquid chromatography (MPLC), we purified l-β-MOS with different degrees of polymerization (DPs). HPAEC-PAD, MALDI-TOF-MS and NMR studies confirmed that these l-β-MOS species ranged from 1,4-β-d-mannobiose to 1,4-β-d-mannononaose (DP 2-9) with >95% purity. Our results provide a robust approach to preparing l-β-MOS, thus enabling l-β-MOS to be further used in the fields of chemistry, life science, and nutritional food.

Purification and identification of oligosaccharides from Cimicifuga heracleifolia Kom. rhizomes

Even though Cimicifuga sp. is widely used in functional foods around the world, the content and structure of its oligosaccharides remain unclear. Here, we isolated a mixture of oligosaccharides from Cimicifuga heracleifolia Kom. rhizomes with a yield of 9.5% w/w. Twenty-six oligosaccharide monomers from the mixture were purified using optimized SEC and HILIC techniques. The oligosaccharides were identified as belonging to two groups by using HPAEC-PAD, MALDI-TOF-MS, NMR and GC-MS methylation analyses. One group belongs to sucrose and inulin type fructo-oligosaccharides (FOS) {β-d-Fruf-(2 → 1)-[β-d-Fruf-(2 ↔ 1)]_n=1-12-α-d-Glcp} with a 3-14 degree of polymerization (DP). Oligosaccharides in the other group belong to the inulo-n-ose type FOS {β-d-Fruf-(2 → 1)-[β-d-Fruf-(2 → 1)]_m=0-12-β-d-Frup} with a DP of 2-14. This appears to be the first time that these oligosaccharides have been purified from Cimicifuga heracleifolia Kom., thus providing useful information concerning the utilization of Cimicifuga heracleifolia Kom. in functional foods.

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.

Size matters: TLR4-mediated effects of α-(1,5)-linear arabino-oligosaccharides in macrophage-like cells depend on their degree of polymerization

Linear arabino-oligosaccharides (LAOS) produced from controlled enzymatic hydrolysis of arabinans from sugar beet are well-known because of their chain-length dependent prebiotic effects. However, it is not clear if these α-(1,5)-linked arabinose oligosaccharides can interact directly with immune system cells, as well as if its degree of polymerization (DP) influences possible biological effects. Four high purity LAOS with distinct DP were tested in macrophage-like cells exposed or not to LPS. Results shown that LAOS interact with Toll-like receptor (TLR) 4 in a chain length-dependent manner. LAOS with higher DP induce stimulatory effects mainly through the TLR4/MyD88 pathway, thereby enhancing the release of tumor necrosis factor alpha (TNF-α), interleukin (IL-) 1β, 6, 12, and chemokines including MCP-1, RANTES, IL-8, and IP-10. Notably, LAOS with lower DP appears to have an opposite effect to those counterparts with higher DP, as they does not induce the secretion of cytokines and chemokines in macrophages-like cells, while also inhibit TLR4-mediated effects induced by both lipopolysaccharide and LAOS with higher DP. These findings provide not only insights into potential biological effects of LAOS, but also reveal that controlled enzymatic hydrolysis of sugar beet arabinans may lead to dietary oligosaccharides with desired biological properties.