Search Results (5)

Fungal arabinofuranosidases (ABFs) catalyze the hydrolysis of arabinosyl substituents (Ara) and are key in the interplay with other glycosyl hydrolases to saccharify arabinoxylans (AXs). Most characterized ABFs belong to GH51 and GH62 and are known to hydrolyze the linkage of α-(1→2)-Ara and α-(1→3)-Ara in monosubstituted xylosyl residues (Xyl) (ABF-m2,3). Nevertheless, in AX a substantial number of Xyls have two Aras (i.e., disubstituted), which are unaffected by ABFs from GH51 and GH62. To date, only two fungal enzymes have been identified (in GH43_36) that specifically release the α-(1→3)-Ara from disubstituted Xyls (ABF-d3). In our research, phylogenetic analysis of available GH43_36 sequences revealed two major clades (GH43_36a and GH43_36b) with an expected substrate specificity difference. The characterized fungal ABF-d3 enzymes aligned with GH43_36a, including the GH43_36 from Humicola insolens (HiABF43_36a). Hereto, the first fungal GH43_36b (from Talaromyces pinophilus) was cloned, purified, and characterized (TpABF43_36b). Surprisingly, TpABF43_36b was found to be active as ABF-m2,3, albeit with a relatively low rate compared to other ABFs tested, and showed minor xylanase activity. Novel specificities were also discovered for the HiABF43_36a, as it also released α-(1→2)-Ara from a disubstitution on the non-reducing end of an arabinoxylooligosaccharide (AXOS), and it was active to a lesser extent as an ABF-m2,3 towards AXOS when the Ara was on the second xylosyl from the non-reducing end. In essence, this work adds new insights into the biorefinery of agricultural residues. Full article

Although sugar beets are primarily treated as a source of sucrose, due to their rich chemical composition, they can also be a source of other carbohydrates, e.g., mono- and oligosaccharides. The study focused on both fresh beet roots and those stored in mounds. Our studies have shown that, in addition to sucrose, sugar beet tissue also comprises other carbohydrates: kestose (3.39%) and galactose (0.65%) and, in smaller amounts, glucose, trehalose and raffinose. The acidic hydrolysis of the watery carbohydrates extracts resulted in obtaining significant amounts of glucose (8.37%) and arabinose (3.11%) as well as xylose and galactose and, in smaller amounts, mannose. An HPSEC liquid chromatography study of the molecular mass profile of the carbohydrate compounds present in the beet roots showed alongside the highest percentage (96.53–97.43%) of sucrose (0.34 kDa) the presence of pectin compounds from the araban group and arabinoxylooligosaccharides (5–9 kDa) with a percentage share of 0.61 to 1.87%. On the basis of our research, beet roots can be considered a potential source of carbohydrates, such as kestose, which is classified as fructooligosaccharide (FOS). The results of this study may be helpful in evaluating sugar beets as a direct source of various carbohydrates, or as a raw material for the biosynthesis of fructooligosaccharides (FOS) or galactooligosaccharides (GOS). Full article

Arabinofuranosidases are important accessory enzymes involved in the degradation of arabinose-containing poly- and oligosaccharides. Two arabinofuranosidases from the recently described novel anaerobic cellulolytic bacterium Acetivibrio mesophilus, designated AmAraf51 and AmAraf43, were heterologously expressed in Escherichia coli and biochemically characterized. AmAraf51 not only removed arabinose moieties at O-3, O-2 and terminal O-5 positions of arabinose-containing oligosaccharides, but also exhibited exo-β-xylosidase side activity. In comparison, AmAraf43 preferably cleaved 1,3-linkages from arabinosyl disubstitutions. AmAraf51 and AmAraf43 demonstrated maximum activity at 70 °C and 57 °C, respectively. Judging from the genetic context and substrate specificity, AmAraf51 may decompose internalized arabino/xylo-oligosaccharides. The embedding of the AmAraf43 gene between genes for several putative xylanolytic enzymes, along with its enzymatic properties suggests that AmAraf43 cleaves arabinose decorations from heteroxylans extracellularly. The enzymes revealed completely converse activity profiles towards arabinan/arabinoxylan: AmAraf51 displayed strong activity on arabinan, while AmAraf43 prefers arabinoxylan. AmAraf51 dramatically stimulated the saccharification level of wheat arabinoxylan (WAX-RS) and sugar beet arabinan when administered along with xylanase M_Xyn10 or arabinanase PpAbn43, respectively. For WAX-RS degradation, the yield of arabinose and xylose was boosted 13.77-fold and 4.96-fold, respectively. The bifunctional activity, thermostability and high catalytic efficiency make AmAraf51 an interesting candidate for industrial applications. Full article

Hazelnuts are one of the most widely consumed nuts, but their production creates large quantities of by-products, especially shells, that could be upcycled into much more valuable products. Recent studies have shown that hazelnut shell hemicellulose is particularly rich in compounds that are potential precursors of xylooligosaccharides and arabino-xylooligosaccharides ((A)XOS), previously defined as emerging prebiotics very beneficial for human health. The production of these compounds on an industrial scale-up could have big consequences on the functional foods market. However, to produce (A)XOS from a lignocellulosic biomass, such as hazelnut shell, is not easy. Many methods for the extraction and the purification of these prebiotics have been developed, but they all have different efficiencies and consequences, including on the chemical structure of the obtained (A)XOS. The latter, in turn, is strongly correlated to the nutritional effects they have on health, which is why the optimization of the structural characterization process is also necessary. Therefore, this review aims to summarize the progress made by research in this field, so as to contribute to the exploitation of hazelnut waste streams through a circular economy approach, increasing the value of this biomass through the production of new functional ingredients. Full article

Brewer’s spent grain (BSG) is the main by-product of the beer brewing process. It has a huge potential as a feedstock for bio-based manufacturing processes to produce high-value bio-products, biofuels, and platform chemicals. For the valorisation of BSG in a biorefinery process, efficient fractionation and bio-conversion processes are required. The aim of our study was to develop a novel fractionation of BSG for the production of arabinose, arabino-xylooligomers, xylose, and bioethanol. A fractionation process including two-step acidic and enzymatic hydrolysis steps was investigated and optimised by a response surface methodology and a desirability function approach to fractionate the carbohydrate content of BSG. In the first acidic hydrolysis, high arabinose yield (76%) was achieved under the optimised conditions (90 °C, 1.85 w/w% sulphuric acid, 19.5 min) and an arabinose- and arabino-xylooligomer-rich supernatant was obtained. In the second acidic hydrolysis, the remaining xylan was solubilised (90% xylose yield) resulting in a xylose-rich hydrolysate. The last, enzymatic hydrolysis step resulted in a glucose-rich supernatant (46 g/L) under optimised conditions (15 w/w% solids loading, 0.04 g/g enzyme dosage). The glucose-rich fraction was successfully used for bioethanol production (72% ethanol yield by commercial baker’s yeast). The developed and optimised process offers an efficient way for the value-added utilisation of BSG. Based on the validated models, the amounts of the produced sugars, the composition of the sugar streams and solubilised oligo-saccharides are predictable and variable by changing the reaction conditions of the process. Full article