Enriched arabinoxylan in corn fiber for value-added products

A two-step process is evaluated to separate the hexose component in wet milling corn fibers from the pentose component for production of value-added products. Corn fibers were first pretreated with hot water at 121°C for 1 h followed by glucoamylase hydrolysis to remove starch. The remaining solid was then treated with hot water at 140–170°C followed by an enzymatic hydrolysis to further separate the hexose and pentose components. After the second pretreatment, the enzymatic digestibility of cellulose was much better than that of arabinoxylan. As a result, up to 90% arabinoxylan in corn fibers was retained in a solid form after the enzyme hydrolysis, while most of the hexose components were removed.     

Microbial lipid production from pretreated and hydrolyzed corn fiber

With its high content of carbohydrates and low percentage of lignin, corn fiber represents a renewable feedstock that can be processed to produce biofuels. Through a combination of pretreatment by lime and enzymatic hydrolysis, total reducing sugars of 700 mg/g corn fiber were released. This amount is equivalent to 92.7% of theoretically available sugars in corn fiber. The resulting hydrolysate itself did not support any growth of Cryptococcus curvatus. But with addition of minerals, C. curvatus grew to a cell density of 6.6 g/L in 6 days. Using the adapted cells, rapid sugar consumption and cell growth were observed. This study demonstrated that it is feasible to produce microbial lipids from corn fiber through pretreatment, enzymatic hydrolysis, and fermentation. In addition, C. curvatus is an excellent candidate for this application since it can utilize all major sugars, glucose, xylose, and arabinose with yield of cells and lipids as 0.55 and 0.27 g/g sugars, respectively. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:945–951, 2014     

Evidence of the presence of 2-O-beta-D-xylopyranosyl-alpha-l-arabinofuranose side chains in barley husk arabinoxylan

(Glucurono)arabinoxylans were extracted from barley husks and degraded with endo-beta-xylanase or subjected to periodate oxidation. The released oligosaccharide fragments were separated and isolated on Biogel-P2, and their structures were determined by NMR spectroscopy. The oligosaccharides identified consisted of beta-d-(1-->4)-linked xylopyranosyl residues, of which some were substituted at O-3 with alpha-l-arabinofuranosyl groups or at O-2 with 4-O-methylglucuronic acid. In addition to these substituents, a disaccharide side chain, 2-O-beta-d-xylopyranosyl-alpha-l-arabinofuranose, attached at position O-3 of the main chain, was proved to exist in arabinoxylan from barley husks. The compound was fully characterized with NMR, and all (1)H and (13)C NMR signals were assigned. The arabinose to xylose ratio was low (approximately 0.2) and no 2,3-disubstitution existed. No blocks of substituted xylose residues could be observed along the main chain.     

Functional analysis of corn husk photosynthesis

The husk surrounding the ear of corn/maize (Zea mays) has widely spaced veins with a number of interveinal mesophyll (M) cells and has been described as operating a partial C(3) photosynthetic pathway, in contrast to its leaves, which use the C(4) photosynthetic pathway. Here, we characterized photosynthesis in maize husk and leaf by measuring combined gas exchange and carbon isotope discrimination, the oxygen dependence of the CO(2) compensation point, and photosynthetic enzyme activity and localization together with anatomy. The CO(2) assimilation rate in the husk was less than that in the leaves and did not saturate at high CO(2), indicating CO(2) diffusion limitations. However, maximal photosynthetic rates were similar between the leaf and husk when expressed on a chlorophyll basis. The CO(2) compensation points of the husk were high compared with the leaf but did not vary with oxygen concentration. This and the low carbon isotope discrimination measured concurrently with gas exchange in the husk and leaf suggested C(4)-like photosynthesis in the husk. However, both Rubisco activity and the ratio of phosphoenolpyruvate carboxylase to Rubisco activity were reduced in the husk. Immunolocalization studies showed that phosphoenolpyruvate carboxylase is specifically localized in the layer of M cells surrounding the bundle sheath cells, while Rubisco and glycine decarboxylase were enriched in bundle sheath cells but also present in M cells. We conclude that maize husk operates C(4) photosynthesis dispersed around the widely spaced veins (analogous to leaves) in a diffusion-limited manner due to low M surface area exposed to intercellular air space, with the functional role of Rubisco and glycine decarboxylase in distant M yet to be explained.     

On the production of food yeast from partially hydrolyzed cereal straw

Summary 1. Cereal straw was partially hydrolyzed with dilute sulphuric or hydrochloric acid at elevated temperatures, yielding about 20% of matter assimilable byTorulopsis utilis (calculated on oven-dry straw), which consisted chiefly of xylose, with small amounts of glucose and acetic acid.2. Experiments on a laboratory scale with non-fermentable substrates like ethanol and acetic acid showed that also in these cases an ample aeration is an essential condition for a good yield.3. Acetic acid is harmful to the yeast, even in small concentrations, when the pH is lower than 5.0.4. Small quantities of glucose or acetic acid stimulate the conversion of xylose byTorulopsis utilis.5. With an adequate aeration and an initial pH of 5.5–6.0 (maintained at this level until the acetic acid has disappeared and then lowered to 4.0–4.5) satisfactory conversion rates and yields could be obtained on straw extracts as mentioned sub 1.6. The results of the laboratory experiments mentioned sub 5 could be reproduced in a semi-technical installation with a capacity of 200 l straw extract.7. Good results were obtained in this installation with aVogelbusch aeration device, while foaming could be adequately controlled by means of a rotating wire screen.     

Structure characterization and carboxymethylation of arabinoxylan isolated from Ispaghula (Plantago ovata) seed husk

As revealed by NMR spectroscopy (after ultrasonic degradation) and HPLC (after total hydrolysis) an arabinoxylan (AX) containing 74.8% Xylp and 23.2% Araf was isolated from Ispaghula (Plantago ovata) by soaking the seed husk with water, extraction with aqueous sodium hydroxide and coagulation with acetic acid. The AX with a molar mass of 364,470 g/mol shows high swelling ability in water. The carboxymethylation of AX was carried out heterogeneously with sodium monochloroacetate in the presence of aqueous sodium hydroxide. The reaction parameters were varied in terms of slurry medium, molar ratio, temperature, time, and sodium hydroxide concentration. For comparative studies, carboxymethylation of arabinan was carried out. In order to determine the total degree of substitution (DS) and mole fractions of the repeating units of carboxymethyl arabinoxylan (CMAX) and of carboxymethyl arabinan, HPLC and ¹H NMR spectroscopic investigations after total hydrolysis were carried out. DS values for CMAX as high as 1.81 were achieved. CMAX is water soluble starting at DS of 0.33.     

Immobilization of proteins on partially hydrolyzed agarose beads

Treatment of agarose beads with mild acid (0.2 M HCl, 55 degrees C, several hours) hydrolyzes some of the glycosidic bonds between D-galactosyl residues and 3,6-anhydro-L-galactosyl residues, and thus produces aldehydo-groups useful for immobilization of amino compounds by reductive amination with NaCNBH3. More than 20 mg (0.3 mumol) of bovine serum albumin could be coupled per gram of partially hydrolyzed agarose beads. Arthrobacter neuraminidase immobilized by this method was useful for desialylation of sialyl glycoconjugates, and was found not to leach from the gel and to be much more thermostable than the free enzyme.     

pH catalyzed pretreatment of corn bran for enhanced enzymatic arabinoxylan degradation

Corn bran is mainly made up of the pericarp of corn kernels and is a byproduct stream resulting from the wet milling step in corn starch processing. Through statistic modeling this study examined the optimization of pretreatment of corn bran for enzymatic hydrolysis. A low pH pretreatment (pH 2, 150 °C, 65 min) boosted the enzymatic release of xylose and glucose and maximized biomass solubilization. With more acidic pretreatment followed by enzymatic hydrolysis the total xylose release was maximized (at pH 1.3) reaching ～ 50% by weight of the original amount present in destarched corn bran, but the enzyme catalyzed xylose release was maximal after pretreatment at approx. pH 2. The total glucose release peaked after pretreatment of approx. pH 1.5 with an enzymatic release of approx. 68% by weight of the original amounts present in destarched corn bran. For arabinose the enzymatic release was negatively affected by the acidic pretreatment as labile arabinosyl-linkages were presumably hydrolysed directly during the pretreatment. A maximum of 60% arabinose release was achieved directly from the optimal (acidic) pretreatment. The total content of diferulic acids, supposedly involved in the cross-linking of the arabinoxylan polymers, decreased by both alkaline and acidic pretreatment pH, with the loss by alkaline pretreatments being highest. No direct correlation between the enzymatic release of xylose and the content of diferulic acids in the substrate could be verified. On the contrary the enzymatic release of xylose was significantly correlated to the total release of arabinose, indicating that the degree of arabinosyl-substitutions on the xylan backbone is an essential parameter for enzymatic hydrolysis of corn bran arabinoxylan.     

Similar bifidogenic effects of prebiotic-supplemented partially hydrolyzed infant formula and breastfeeding on infant gut microbiota

The aim of the study was to assess the quantitative and qualitative differences of the gut microbiota in infants. We evaluated gut microbiota at the age of 6 months in 32 infants who were either exclusively breast-fed, formula-fed, nursed by a formula supplemented with prebiotics (a mixture of fructo- and galacto-oligosaccharides) or breast-fed by mothers who had been given probiotics. The Bifidobacterium, Bacteroides, Clostridium and Lactobacillus/Enterococcus microbiota were assessed by the fluorescence in situ hybridization, and Bifidobacterium species were further characterized by PCR. Total number of bifidobacteria was lower among the formula-fed group than in other groups (P=0.044). Total amounts of the other bacteria were comparable between the groups. The specific Bifidobacterium microbiota composition of the breast-fed infants was achieved in infants receiving prebiotic supplemented formula. This would suggest that early gut Bifidobacterium microbiota can be modified by special diets up to the age of 6 months.     

Temperature-Induced conformational transition in xanthans with partially hydrolyzed side chains

The conformational properties of xanthans with partially hydrolyzed side chains were in vestigated by optical rotation, CD, and differential scanning calorimetry (DSC). All variants displayed the well-known temperature-driven, cooperative order–disorder transition, and both optical rotation and DSC showed that the transition temperature was essentially independent of the content of terminal β-mannose. It was found that up to 80% of the changes in the specific optical rotation accompanying the transition reflects conformational changes linked to the terminal β-mannose in the side chains. Modification of the sidechains also affected the CD when xanthan was in the ordered state, but in this case the data suggest that the glucuronic acid is the major component determining the magnitude of the CD signal. DSC measurements showed that the transition enthalpy (ΔH_cal) increased linearly with the fraction of β-mannose, again indicating that a significant part (up to 80%) of ΔH_cal reflects conformational changes in the side chains. The conformational transition of the xanthan variants generally showed a higher degree of cooperativity (sharper transition) than unmodified, pyruvated xanthan. Calculation of the cooperativity parameter σ by means of the Zimm–Bragg theory (OR data) or from the ratio between ΔH_cal and the van't Hoff enthalpy (ΔH_vH) using DSC data showed a correlation between σ and the content of β-mannose, but the two methods gave different results when the content of β-mannose approached 100%. The ionic strength dependence of the transition temperature, expressed as d (log I)/d(T^?1_m), was nearly identical for intact xanthan and a sample containing only 6% of the terminal β-mannose. Application of the Manning polyelectrolyte theory does not readily account for the observed ΔH_cal values, neither does it provide new information on the nature of the ordered and disordered conformations in xanthan. © 1993 John Wiley & Sons, Inc.     

Post-training reward partially restores chronic stress induced effects in mice

Reduced responsiveness to positive stimuli is a core symptom of depression, known as anhedonia. In the present study, we assessed the expression of anhedonia in our chronic stress mouse model using a subset of read-out parameters. In line with this, we investigated in how far chronic stress would affect the facilitating effect of post-training self-administration of sugar, as we previously observed in na?ve mice. Male C57BL/6J mice were repeatedly and at unpredictable times exposed to rats (no physical contact) over the course of two weeks. Following novelty exploration, (non-) spatial learning and memory processes with and without post-training sugar acting as reinforcer, emotionality, reward sensitivity and corticosterone levels were determined. We found that (1) the effects of chronic stress persisted beyond the period of the actual rat exposure. (2) Post-training self-administration of sugar as reinforcer improved spatial performance in na?ve mice, whereas (3) in stressed mice sugar partially "normalized" the impaired performance to the level of controls without sugar. Chronic stress (4) increased behavioral inhibition in response to novelty; (5) induced dynamic changes in the pattern of circadian corticosterone secretion during the first week after rat stress and (6) increased the intake of sucrose and water. (7) Chronic stress and sugar consumed during spatial training facilitated the memory for the location of the sucrose bottle weeks later. Concluding, our chronic stress paradigm induces the expression of anhedonia in mice, at different levels of behavior. The behavioral inhibition appears to be long lasting in stressed mice. Interestingly, sugar consumed in close context with spatial learning partially rescued the stress-induced emotional and cognitive impairments. This suggests that reward can ameliorate part of the negative consequences of chronic stress on memory.     

Production of carboxylic acids from hydrolyzed corn meal by immobilized cell fermentation in a fibrous-bed bioreactor

Corn meal hydrolyzed with amylases was used as the carbon source for producing acetic, propionic, and butyric acids via anaerobic fermentations. In this study, corn meal, containing 75% (w/w) starch, 20% (w/w) fibers, and 1.5% (w/w) protein, was first hydrolyzed using amylases at 60 degrees C. The hydrolysis yielded approximately 100% recovery of starch converted to glucose and 17.9% recovery of protein. The resulting corn meal hydrolyzate was then used, after sterilization, for fermentation studies. A co-culture of Lactococcus lactis and Clostridium formicoaceticum was used to produce acetic acid from glucose. Propionibacterium acidipropionici was used for propionic acid fermentation, and Clostridium tyrobutylicum was used for butyric acid production. These cells were immobilized on a spirally wound fibrous matrix packed in a fibrous-bed bioreactor (FBB) developed for multi-phase biological reactions or fermentation. The bioreactor was connected to a stirred-tank fermentor that provided pH and temperature controls via medium circulation. The fermentation system was operated at the recycle batch mode. Temperature and pH were controlled at 37 degrees C and 7.6, respectively, for acetic acid fermentation, 32 degrees C and 6.0, respectively, for propionic acid fermentation, and 37 degrees C and 6.0, respectively, for butyric acid production. The fermentation demonstrated a yield of approximately 100% and a volumetric productivity of approximately 1 g/(1 h) for acetic acid production. The propionic acid fermentation achieved an approximately 60% yield and a productivity of 2.12 g/(1 h), whereas the butyric acid fermentation obtained an approximately 50% yield and a productivity of 6.78 g/(1 h). These results were comparable to, or better than those fermentations using chemically defined media containing glucose as the substrate, suggesting that these carboxylic acids can be efficiently produced from direct fermentation of corn meal hydrolyzate. The corn fiber present as suspended solids in the corn meal hydrolyzate did not cause operating problem to the immobilized cell bioreactor as is usually encountered by conventional immobilized cell bioreactor systems. It is concluded that the FBB technology is suitable for producing value-added biochemicals directly from agricultural residues or commodities such as corn meal.     

Physicochemical parameters of partially hydrolyzed S. salivarius levan fractions

The fractions obtained from the partially hydrolyzed branched Streptococcus salivarius levan were examined in solution. Sedimentation coefficients, S⁰, intrinsic viscosities, [η], weight-average molecular weights, M _w, and radii of gyration were obtained from sedimentation velocity, viscosity, and light-scattering measurements. Double logarithmic plots of [η] vs M _w and S⁰ vs M _w each yielded two linear segments intersecting at M _w ≈ 10⁵. Hydrodynamic data suggest that fractions of M _w > 10⁵ behave as compact spheres, whereas for M _w < 10⁵, the particles are best characterized as linear random coils. Calculations based on theories of random coils and spheres support the above observations.     

Immunological properties of partially purified material with monocytosis-producing activity from Listeria monocytogenes.

A fraction rich in a monocytosis-producing activity (MPA) has been obtained by a two-stage chromatographic separation from a saline extract (SE) of Listeria monocytogenes. Like SE, the purified material elicits monocytosis and decreases the halftime of circulating monocytes. The purification of MPA eliminates the following found in SE: the in vitro mitogenic activity, the in vitro adjuvant activity, the immunosuppressive activity, and the granulocytosis-promoting and the lymphopenia-inducing activities.     

Immunological function of kidney-infiltrating lymphocytes from aged NZB mice

A striking aspect of autoimmune kidney disease in the NZB mouse strain is the perivascular infiltration of lymphoid cells. Upon release by enzymatic digestion of kidney tissue from animals 6 months of age or older, these cells have been found to exhibit a high level of immunologic activity not seen in younger mice or in nonautoimmune strains. Kidney-derived cells were found to respond to T and B cell mitogens at levels ranging up to those observed for peripheral blood, and in some cases splenic lymphocytes, from the same animals. An enhanced proliferative response to autologous and allogeneic stimulation was observed compared to these other lymphoid sources. Both spontaneous and LPS-stimulated immunoglobulin synthesis were noted with all three populations, which could be totally or partially blocked by cycloheximide. Selective localization of autoantibody-producing cell populations was observed, with anti-erythrocyte antibody restricted to splenocytes and PBL, and the anti-dsDNA implicated in immune complex formation found only in kidney-derived cell culture supernatants.     

Prebiotic effects of wheat arabinoxylan related to the increase in bifidobacteria, Roseburia and Bacteroides/Prevotella in diet-induced obese mice

Background

Alterations in the composition of gut microbiota - known as dysbiosis - has been proposed to contribute to the development of obesity, thereby supporting the potential interest of nutrients targeting the gut with beneficial effect for host adiposity. We test the ability of a specific concentrate of water-extractable high molecular weight arabinoxylans (AX) from wheat to modulate both the gut microbiota and lipid metabolism in high-fat (HF) diet-induced obese mice.

Methodology/Principal Findings

Mice were fed either a control diet (CT) or a HF diet, or a HF diet supplemented with AX (10% w/w) during 4 weeks. AX supplementation restored the number of bacteria that were decreased upon HF feeding, i.e. Bacteroides-Prevotella spp. and Roseburia spp. Importantly, AX treatment markedly increased caecal bifidobacteria content, in particular Bifidobacterium animalis lactis. This effect was accompanied by improvement of gut barrier function and by a lower circulating inflammatory marker. Interestingly, rumenic acid (C18:2 c9,t11) was increased in white adipose tissue due to AX treatment, suggesting the influence of gut bacterial metabolism on host tissue. In parallel, AX treatment decreased adipocyte size and HF diet-induced expression of genes mediating differentiation, fatty acid uptake, fatty acid oxidation and inflammation, and decreased a key lipogenic enzyme activity in the subcutaneous adipose tissue. Furthermore, AX treatment significantly decreased HF-induced adiposity, body weight gain, serum and hepatic cholesterol accumulation and insulin resistance. Correlation analysis reveals that Roseburia spp. and Bacteroides/Prevotella levels inversely correlate with these host metabolic parameters.

Conclusions/Significance

Supplementation of a concentrate of water-extractable high molecular weight AX in the diet counteracted HF-induced gut dysbiosis together with an improvement of obesity and lipid-lowering effects. We postulate that hypocholesterolemic, anti-inflammatory and anti-obesity effects are related to changes in gut microbiota. These data support a role for wheat AX as interesting nutrients with prebiotic properties related to obesity prevention.     

Purification of xylanase from alkaliphilic Bacillus sp. K-8 by using corn husk column

The objective of this work was to apply low cost materials, agricultural residues, to the purification of xylanase. The results showed that crude extracellular, cellulase-free xylanase of an alkaliphilic Bacillus sp. strain K-8 could be purified in a single step by affinity adsorption–desorption on a corn husk column using a high flow rate, under the conditions 25 mM acetate buffer, pH 4.0, 4 °C, which prevented the hydrolysis of xylan by xylanase. After adsorption, the xylanase was eluted from the enzyme–corn husk complex with 500 mM Urea. The enzyme was purified 5.3-fold to homogeneity from culture supernatant. The molecular weight of the purified enzyme was 24 kDa as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The specific activity and recovery yield after purification were 25.4 U/mg protein and 42.3%, respectively.