Antioxidant activity of xylooligosaccharides prepared fromThermotoga maritimausing recombinant enzyme cocktail of β-xylanase and α-glucuronidase

The Potential of Xylooligosaccharides as Prebiotics and Their Sustainable Production from Agro-Industrial by-Products

In recent years, concerns about a good-quality diet have increased. Food supplements such as prebiotics have great nutritional and health benefits. Within the diverse range of prebiotics, xylooligosaccharides (XOs) show high potential, presenting exceptional properties for the prevention of systemic disorders. XOs can be found in different natural sources; however, their production is limited. Lignocellulosic biomasses present a high potential as a source of raw material for the production of XOs, making the agro-industrial by-products the perfect candidates for production on an industrial scale. However, these biomasses require the application of physicochemical pretreatments to obtain XOs. Different pretreatment methodologies are discussed in terms of increasing the production of XOs and limiting the coproduction of toxic compounds. The advance in new technologies for XOs production could decrease their real cost (USD 25-50/kg) on an industrial scale and would increase the volume of market transactions in the prebiotic sector (USD 4.5 billion). In this sense, new patents and innovations are being strategically developed to expand the use of XOs as daily prebiotics.

Fusion of Oligopeptide to the C Terminus of α-Glucuronidase from Thermotoga maritima Improves the Catalytic Efficiency for Hemicellulose Biotransformation

Fusion protein combined the oligopeptide (HQAFFHA) with the C terminus of α-glucuronidase from Thermotoga maritima was produced in E. coli and purified for characterization and applications of glucuronic and glucaric acid production. The fusion protein with oligopeptide exhibited a 2.97-fold higher specific activity than individual protein. Their catalytic efficiency k_cat/K_m and k_cat increased from 469.3 ± 2.6 s^-1 (g mL^-1)^-1 and 62.4 ± 0.9 s^-1 to 2209.5 ± 26.3 s^-1 (g mL^-1)^-1 and 293.9 ± 4.9 s^-1, respectively. Fusion protein had similar temperature and pH profiles to those without oligopeptide, but the thermal stability decreases and the pH stability shifts to alkaline. Using beech xylan hydrolysate as a substrate, the glucuronic acid yield of fusion enzyme increased by 9.94% compared with its parent at 65 °C pH 8.5 for 10 h, and can hydrolyze corn cob xylan with xylanase to obtain glucuronic acid, and can be combined with uronate dehydrogenase to obtain high-added value glucaric acid. Homologous modeling analysis revealed the factors contributing to the high catalytic efficiency of fusion enzyme. These results show that the peptide fusion strategy described here may be useful for improving the catalytic efficiency and stability of other industrial enzymes, and has great potential for producing high value-added products from agricultural waste.

Molecular modification, structural characterization, and biological activity of xylans

The differences in the source and structure of xylans make them have various biological activities. However, due to their inherent structural limitations, the various biological activities of xylans are far lower than those of commercial drugs. Currently, several types of molecular modification methods have been developed to address these limitations, and many derivatives with specific biological activity have been obtained. Further research on structural characteristics, structure-activity relationship and mechanism of action is of great significance for the development of xylan derivatives. Therefore, the major molecular modification methods of xylans are introduced in this paper, and the primary structure and conformation characteristics of xylans and their derivatives are summarized. In addition, the biological activity and structure-activity relationship of the modified xylans are also discussed.

Xylanases of glycoside hydrolase family 30 - An overview

Xylan is the most abundant hemicellulose in nature and as such it is a huge source of renewable carbon. Its bioconversion requires a battery of xylanolytic enzymes. Of them the most important are the endo-β-1,4-xylanases which depolymerize the polysaccharide into smaller fragments. Most of the xylanases are members of glycoside hydrolase (GH) families 10 and 11, although they are classified in some other GH families. The relatively new xylanases of GH30 are of special interest. Initially, they appeared to be specific glucuronoxylanases, however, other specificities were found later among prokaryotic and in particular eukaryotic enzymes. This review gives an overview of the substrate and product specificities observed for the GH30 xylanases characterized to date. An emphasis is given to the structure-activity relationship in order to explain how minor differences in catalytic centre and its vicinity can alter catalytic properties from the endoxylanase into the reducing end xylose releasing exoxylanase or into the non-reducing end xylobiohydrolase. Biotechnological potential of the GH30 xylanases is also considered.

Evaluation of nutraceutical application of xylooligosaccharide enzymatically produced from cauliflower stalk for its value addition through a sustainable approach

There is increasing attention on the exploration of waste feedstocks as economically viable substrates for the production of prebiotic oligosaccharides, especially xylooligosaccharides, as excellent candidates for the maintenance and promotion of gut microbiota. XOS, an emerging prebiotic that has several functional attributes and beneficial health effects, is mainly produced by different processes, especially enzymatic hydrolysis through the valorisation of xylan enriched lignocellulosic materials. The present study deals with the enzymatic production of xylooligosaccharide (XOS) from xylan rich cauliflower stalk, a novel source. Delignification with alkali (NaOH) was found to be more efficient than acid and autohydrolysis, resulting in a higher extraction yield of xylan (18.42%). Alkaline extraction for 120 minutes at 1.25 M alkali concentration produced maximum xylan yield. FTIR analysis of xylan extracted from cauliflower stalk by an alkaline (NaOH) pretreatment method showed typical absorption bands at 1729 cm-1 that correspond to acetyl groups exhibiting the typical xylan specific band. Enzymatic hydrolysis was carried out with indigenously produced crude endoxylanase obtained from Aspergillus niger MTCC 9687 and the effects of substrate concentration, enzyme concentration, pH, time and temperature were investigated. High resolution MS analysis showed the presence of xylobiose as the major XOS. The major 1H spectral signals of XOS liberated from enzymatically hydrolysed alkali extracted cauliflower stalk xylan showed the presence of β-anomeric protons in the spectral region of 4.0-4.7 ppm. Prebiotic efficacy of cauliflower stalk derived XOS alone and synbiotic combinations with known probiotic strains (Lactiplantibacillus plantarum, Bifidobacterium bifidum, Lactobacillus delbrueckii ssp. Helveticus) were evaluated. Butyrate was found to be the major short chain fatty acid produced by XOS supplemented fermentation media. All the synbiotic combinations showed significantly higher antioxidant and antimicrobial activities and reduced the viability of human bone cancer MG-63 cells. The individual profiles of antimicrobial components of XOS were identified as dihydroxy benzoic acid and aspartic acid by HPLC coupled to a photodiode array detector.