Добірка наукової літератури з теми "Arabinoxylan distribution"

This research was to explore the distribution and some molecular characterization of arabinoxylan in wheat beer (B), beer foam (BF) and defoamed beer (DB) because of the crucial influences of arabinoxylan on wheat beer and its foam. The purified arabinoxylan from B, BF, and DB were fractionated by ethanol of 50%, 67%, 75%, and 80%. The monosaccharide composition, substitution degree (Ara/Xyl ratio, A/X), and average degrees of polymerization (avDP) of arabinoxylan were investigated. Molecular weight and microstructure were also involved in this study by GPC-LLS and SEM, respectively. Under the same ethanol concentration, the arabinoxylan content in the BF was higher than the other two, respectively, and it was precipitated in BF fraction with 50% ethanol which accounted for 80.84% of the total polysaccharides. Meanwhile, the greatest substitution degree (A/X) and highest value of avDP of the arabinoxylan was found in all beer foam fractions regardless of the concentration of ethanol used. The average degrees of polymerization (avDP) of arabinoxylan displayed a significant difference (p < 0.05) among B, BF, and DB. Furthermore, arabinoxylan presented varied microstructure with irregular lamellas and spherical structures and the weight-average molecular weight (Mw) of arabinoxylan showed the lowest values in BF, while the largest values were shown in DB. Therefore, arabinoxylan was more accumulated in beer foam, especially in 50% ethanol, characterised by greater value of A/X and avDP, as well as lower Mw. It was suggested that the arabinoxylan played important roles in maintaining wheat beer foam characteristics.

ABSTRACTDue to their potential prebiotic properties, arabinoxylan-derived oligosaccharides [(A)XOS] are of great interest as functional food and feed ingredients. While the (A)XOS metabolism ofBifidobacteriaceaehas been extensively studied, information regarding lactic acid bacteria (LAB) is still limited in this context. The aim of the present study was to fill this important gap by characterizing candidate (A)XOS hydrolyzing glycoside hydrolases (GHs) identified in the genome ofLactobacillus brevisDSM 20054. Two putative GH family 43 xylosidases (XynB1 and XynB2) and a GH family 43 arabinofuranosidase (Abf3) were heterologously expressed and characterized. While the function of XynB1 remains unclear, XynB2 could efficiently hydrolyze xylooligosaccharides. Abf3 displayed high specific activity for arabinobiose but could not release arabinose from an (A)XOS preparation. However, two previously reported GH 51 arabinofuranosidases fromLb. breviswere able to specifically remove α-1,3-linked arabinofuranosyl residues from arabino-xylooligosaccharides (AXHm3 specificity). These results imply thatLb. brevisis at least genetically equipped with functional enzymes in order to hydrolyze the depolymerization products of (arabino)xylans and arabinans. The distribution of related genes inLactobacillalesgenomes indicates that GH 43 and, especially, GH 51 glycosidase genes are rare among LAB and mainly occur in obligately heterofermentativeLactobacillusspp.,Pediococcusspp., members of theLeuconostoc/Weissellabranch, andEnterococcusspp. Apart from the prebiotic viewpoint, this information also adds new perspectives on the carbohydrate (i.e., pentose-oligomer) metabolism of LAB species involved in the fermentation of hemicellulose-containing substrates.

Insoluble-bound phenolics (IBPs) are extensively found in the cell wall and distributed in various tissues/organs of plants, mainly cereals, legumes, and pulses. In particular, IBPs are mainly distributed in the protective tissues, such as seed coat, pericarp, and hull, and are also available in nutritional tissues, including germ, epicotyl, hypocotyl radicle, and endosperm, among others. IBPs account for 20–60% of the total phenolics in food matrices and can exceed 70% in leaves, flowers, peels, pulps, seeds, and other counterparts of fruits and vegetables, and up to 99% in cereal brans. These phenolics are mostly covalently bound to various macromolecules such as hemicellulose, cellulose, structural protein, arabinoxylan, and pectin, which can be extracted by acid, alkali, or enzymatic hydrolysis along with various thermal and non-thermal treatments. IBPs obtained from various sources exhibited a wide range of biological activities, including antioxidant, anti-inflammatory, antihypertensive, anticancer, anti-obesity, and anti-diabetic properties. In this contribution, the chemistry, distribution, biological activities, metabolism, and extraction methods of IBPs, and how they are affected by various treatments, are summarized. In particular, the effect of thermal and non-thermal processing on the release of IBPs and their antioxidant potential is discussed.

The interactions between cell-wall polysaccharides and polyphenols in the gastrointestinal tract have attracted extensive attention. We hypothesized that dietary fiber modulates the fermentation patterns of cyanidin-3-O-glucoside (C3G) in a fiber-type-dependent manner. In the present study, the effects of four dietary fibers (fructose-oligosaccharides, pectin, β-glucan and arabinoxylan) on the modulation of C3G fermentation patterns were investigated through in vitro fermentation inoculated with human feces. The changes in gas volume, pH, total carbohydrate content, metabolites of C3G, antioxidant activity, and microbial community distribution during in vitro fermentation were analyzed. After 24 h of fermentation, the gas volume and total carbohydrate contents of the four dietary-fiber-supplemented groups respectively increased and decreased to varying degrees. The results showed that the C3G metabolites after in vitro fermentation mainly included cyanidin, protocatechuic acid, 2,4,6-trihydroxybenzoic acid, and 2,4,6-trihydroxybenzaldehyde. Supplementation of dietary fibers changed the proportions of C3G metabolites depending on the structures. Dietary fibers increased the production of short-chain fatty acids and the relative abundance of gut microbiota Bifidobacterium and Lactobacillus, thus potentially maintaining colonic health to a certain extent. In conclusion, the used dietary fibers modulate the fermentation patterns of C3G in a fiber-type-dependent manner.

Barley (Hordeum vulgare) is a widely grown, valuable cereal crop that is affected by various pests including nematodes. The cereal cyst nematode (CCN) Heterodera avenae is the most widely distributed and damaging species of nematodes to cereal crops grown in temperate regions, including Australia, and is estimated to cause global annual losses of around $160 billion. The use of cultivars resistant to H. avenae is the preferred approach for nematode management and four resistance loci, Rha1, Rha2, Rha3 and Rha4, have been mapped. The Rha4 locus was mapped in the Galleon/Haruna Nijo population to chromosome 5H and since Rha2 and Rha4 provide the most effective resistance against the Australian H. avenae pathotype Ha13 they have been widely used in barley breeding. Despite CCN resistance loci having been mapped in barley and other cereals, no resistance genes have been isolated and characterized. Recently both Rha2 and Rha4 have been fine-mapped and near-diagnostic markers have been developed to provide simple tools for selection. Fine-mapping indicates that approximately 105 genes are linked to the Rha4 locus, including cell wall-related genes predicted to encode (1-4)-β-xylan endohydrolases, also known as xylanases. This thesis reports on experiments that were undertaken to better understand the resistance conferred by Rha4 and to investigate the functions of the xylanases as prime candidate genes. The xylanase genes at the Rha4 locus were cloned and analysed for allelic differences between sequences from the cultivars Sloop (susceptible) and Flagship (Rha4-resistant). Although genes X1 and X2 have been characterised, the X3 gene has not been well described previously. The genomic sequences were used in reciprocal transformation experiments where, under the control of the 35S promoter, the genes from Sloop were transformed into a Flagship background, and vice versa. Tube tests were used to investigate any changes in nematode infection responses, and therefore resistance status, but no significant alterations were detected. However, overexpression of the xylanase genes proved to be detrimental to the overall health of the plant. The xylanases were concomitantly heterologously expressed in Escherichia coli and the X2 protein was characterized in terms of substrate preference and catalytic rate. In more general approaches not directly linked to Rha4 genotype, the natural variation in root polysaccharide amount and distribution, with a focus on (1,3;1,4)-β-glucan and arabinoxylan, was surveyed in a selection of susceptible and resistant barley cultivars. The effect of changes in amount of (1,3;1,4)-β-glucan was also examined through infection of the betaglucanless mutant and transgenic lines carrying either the overexpressed or silenced (1,3;1,4)-β-glucan synthase CslF6 gene. Variable amounts of (1,3;1,4)-β-glucan did not correlate to rates of nematode infection and no clear patterns of polysaccharide profiles could be linked to susceptible or resistant cultivar status. Finally, RNA sequencing was used to profile transcript changes in nematode infected and control Sloop and Flagship roots up to 24 days post inoculation. The patterns of the 105 genes linked to the Rha4 locus were extracted and a set of 27 genes which showed significant fold changes across the time course were profiled. Of these, three strong candidate genes were selected which are differentially expressed in the two cultivars and are involved in biochemical pathways that are feasibly linked to resistance mechanisms. Their putative roles in conferring resistance and how this might be tested were discussed.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food & Wine, 2019