Alkali-soluble Fractions Research Articles

Structure of Brewer's Spent Grain Lignin and Its Interactions with Gut Microbiota in Vitro.

Lignin is part of dietary fiber, but its conversion in the gastrointestinal tract is not well understood. The aim of this work was to obtain structural information on brewer's spent grain (BSG) lignin and to understand the behavior of the polymeric part of lignin exposed to fecal microbiota. The original BSG and different lignin fractions were characterized by pyrolysis-GC/MS with and without methylation. Methylation pyrolysis proved that the ratio between guaiacyl and syringyl units was similar in all lignin samples, but the ratio between p-coumaric and ferulic acids varied by the isolation method. Combined pyrolysis results indicated higher acylation of γ-OH groups in syringyl than in guaiacyl lignin units. The polymeric lignin structure in the alkali-soluble fraction after enzymatic hydrolysis was slightly altered in the in vitro colon fermentation, whereas lignin in the insoluble residue after enzymatic treatments remained intact.

Polyphosphates and Polyphosphatase Activity in the Yeast Saccharomyces cerevisiae during Overexpression of the DDP1 Gene.

The effects of overexpression of yeast diphosphoinositol polyphosphate phosphohydrolase (DDP1) having endopolyphosphatase activity on inorganic polyphosphate metabolism in Saccharomyces cerevisiae were studied. The endopolyphosphatase activity in the transformed strain significantly increased compared to the parent strain. This activity was observed with polyphosphates of different chain length, being suppressed by 2mM tripolyphosphate or ATP. The content of acid-soluble and acid-insoluble polyphosphates under DDP1 overexpression decreased by 9 and 28%, respectively. The average chain length of salt-soluble and alkali-soluble fractions did not change in the overexpressing strain, and that of acid-soluble polyphosphate increased under phosphate excess. At the initial stage of polyphosphate recovery after phosphorus starvation, the chain length of the acid-soluble fraction in transformed cells was lower compared to the recipient strain. This observation suggests the complex nature of DDP1 involvement in the regulation of polyphosphate content and chain length in yeasts.

Enzymatic Production of a Soluble Fiber Hydrolyzate from Chinese Cabbage Waste and Its Health-Related Properties

A feasibility study on the potential use of Chinese cabbage waste as a raw material for the production of soluble dietary fiber was performed. The alkali-soluble fraction obtained by extracting Chinese cabbage waste was hydrolyzed by two commercial xylanase preparations to produce soluble fiber hydrolyzates. The freeze-dried soluble fiber was treated with 85% ethanol and separated into the alcohol-soluble dietary fiber (ASF) and alcohol-insoluble dietary fiber (AIF) fractions. ASF had a significantly greater promoting effect on the growth of lactic acid bacteria. AIF effectively hindered the diffusion of glucose and bile acid from dialysis membranes and displayed a significantly greater bile acid retarding effect than carboxymethylcellulose and pectin. Thus, the water-soluble dietary fiber obtained from Chinese cabbage waste by enzymatic hydrolysis has potential use as a fiber source with prebiotic, hypoglycemic and hypolipidemic effects. Practical Applications Dietary fiber, which has many health-related benefits, is added to various food products as a functional ingredient or acceptability factor. The aim of this study was to produce soluble dietary fiber from Chinese cabbage waste by enzymatic hydrolysis. Our results indicated that soluble fiber hydrolyzate from Chinese cabbage is a practical new resource for preparing functional drinks and nutraceutical products for use in the food industry. The use of agro-industrial waste to produce bioactive ingredients could improve the economic value of such waste.

Lignin deposition during earlywood and latewood formation in Scots pine stems

Lignin deposition at consecutive secondary wall thickening stages of early and late xylem cells during annual ring wood formation in Scots pine (Pinus sylvestris L.) stems was studied. Lignin patterns, isolated by thioglycolic acid method, consisted of alcohol-soluble (LTGA-I) and alkali-soluble (LTGA-II) fractions. The sum of two fractions, being the total lignin content, gradually increased in the course of lignification. However, the increments of lignin amount at each development stage of early and late tracheids were different. The intensity of lignin deposition increased in the course of earlywood tracheid maturation and decreased toward the end of latewood cell differentiation. The deposition of two lignin fractions in each layer of forming wood also occurred oppositely. The increment of LTGA-I descended, whereas that of LTGA-II increased from the beginning to the end of early xylem lignification. In contrast, LTGA-I increment dropped, whereas LTGA-II rose during late xylem lignification. Gel permeation chromatography showed that the lignins, formed at the beginning of lignification, were more homogeneous and had higher molecular weight compared with the lignins at the end of cell differentiation. Besides, the content of cellulose, estimated as the residue after lignin isolation, and of cell wall substances, presented as cell wall cross-section areas, at consecutive maturation stages of early and late xylem cells have been found to be different. The data show that lignin deposition occurred in different conditions and with opposite dynamics during early and late xylem formation.

The self-assembled network and physiological degradation of pectins in carrot cell walls

The pectin structure determines cell wall properties, such as their stiffness, diffusivity and intercellular integrity, and this, in turn, determines the macro-properties that are important for consumers and industry. However, due to complex and dynamic physiological changes, the pectin molecular structure and their assemblies in cell walls are still not well described. In this study we characterise the pectin molecular structures of cell walls at different ripening stages using an atomic force microscope. The pectins used in this study were isolated from carrot cell walls as water soluble (WSP), chelator soluble (CSP) and diluted alkali soluble (DASP) pectin fractions. New structural features of pectins in the WSP and DASP fractions were obtained. WSP contained a high proportion of small pectic polymers, whereas DASP molecules on mica were organized into a regular network in early matured tissue. The CSP fraction contained a mixture of both chains and also contained short polymeric structures. The pectin network in the DASP fraction on mica formed 50–70 nm spaces, which contained cellulose and hemicellulose fibrils. The length of the molecules in CSP and DASP decreased and the network structure observed in DASP was lost during postharvest storage. This provides evidence that pectin enzymatic degradation, which occurs in the network and to individual molecules, is one of the mechanisms responsible for softening fruits and vegetables.

Mushroom Dietary Fiber from the Fruiting Body of Pleurotus tuber-regium: Fractionation and Structural Elucidation of Nondigestible Cell Wall Components

The cell wall of mushroom fruiting body is constituted of nondigestible macromolecules that are a rich source of dietary fiber with biological functions that are beneficial to human health. The cell wall components of an edible mushroom fruiting body from Pleurotus tuber-regium (PTR) were fractionated, and their chemical structures were investigated by chemical, physicochemical, and microscopic analyses. The present results suggest that the cell wall of the PTR mushroom fruiting body contains four main fractions: an outer fraction of polysaccharide and protein complex, which can be extracted using boiling water; a cold alkali-soluble fraction of heteropolysaccharides associated with a small amount of proteins; a hot alkali-soluble fraction of hyper-branched glucans; and an alkali-insoluble fraction of glucan-chitin complex with a normalized relative percentage of 3.6:21.9:55.7:18.8. The anomeric linkage of all the glucans was revealed by infrared spectroscopy to be β type. The structure of the major mushroom fruiting body cell wall polysaccharide (the hot alkali-soluble one, FHA-I) was elucidated by the methylation analysis to be composed of →1)-Glcp-(4→ linkages as the backbone with a 52% degree of branching consisting of →1)-Glcp-(6→ linkages in the side chains, whereas some →1)-Glcp-(3→ linkages might exist in the backbone or side chains. Size exclusion chromatography coupled with multiangle laser light scattering analysis revealed that FHA-I had a molecular weight of 4.224 × 10(6) g/mol and a root-mean-square radius of 30.4 nm. Both scanning electron and atomic force microscopy further showed the highly branched microstructure of FHA-I when dispersed in an aqueous sodium dodecyl sulfate solution.

Effect of cell wall integrity stress and RlmA transcription factor on asexual development and autolysis in Aspergillus nidulans

The cell wall integrity (CWI) signaling pathway is responsible for cell wall remodeling and reinforcement upon cell wall stress, which is proposed to be universal in fungal cultures. In Aspergillus nidulans, both the deletion of rlmA encoding the RlmA transcription factor in CWI signaling and low concentrations of the cell wall polymer intercalating agent Congo Red caused significant physiological changes. The gene deletion mutant ΔrlmA strain showed decreased CWI and oxidative stress resistances, which indicated the connection between the CWI pathway and the oxidative stress response system. The Congo Red stress resulted in alterations in the cell wall polymer composition in submerged cultures due to the induction of the biosynthesis of the alkali soluble fraction as well as the hydrolysis of cell wall biopolymers. Both RlmA and RlmA-independent factors induced by Congo Red stress regulated the expression of glucanase (ANID_00245, engA) and chitinase (chiB, chiA) genes, which promoted the autolysis of the cultures and also modulated the pellet sizes. CWI stress and rlmA deletion affected the expression of brlA encoding the early conidiophore development regulator transcription factor BrlA and, as a consequence, the formation of conidiophores was significantly changed in submerged cultures. Interestingly, the number of conidiospores increased in surface cultures of the ΔrlmA strain. The in silico analysis of genes putatively regulated by RlmA and the CWI transcription factors AnSwi4/AnSwi6 in the SBF complex revealed only a few jointly regulated genes, including ugmA and srrA coding for UgmA UDP-galactopyranose mutase and SrrA stress response regulator, respectively.

Isolation of structurally distinct lignin–carbohydrate fractions from maize stem by sequential alkaline extractions and endoglucanase treatment

Sequential fractionation of extractive-free maize stems was carried out using two mild alkaline extractions (0.5 and 2M NaOH, 20°C, 24h) before and after endoglucanase treatment. This procedure provided two lignin–carbohydrate fractions (LC1 and LC2) recovered after each alkali treatment. LC1 and LC2 contained 39% and 8% of the total lignin amount, respectively. These two fractions contained structurally distinct lignin molecules. While the content of resistant interunit bonds in lignin was 77% in LC1, it was increased up to 98% in LC2. Not unexpectedly, both alkali-soluble fractions contained substantial amount of p-coumaric and ferulic acids ether-linked to lignins. These results outline heterogeneity of maize stem lignins related to fractionation of grass materials.

Functional Analysis of the α-1,3-Glucan Synthase Genes agsA and agsB in Aspergillus nidulans: AgsB Is the Major α-1,3-Glucan Synthase in This Fungus

Although α-1,3-glucan is one of the major cell wall polysaccharides in filamentous fungi, the physiological roles of α-1,3-glucan remain unclear. The model fungus Aspergillus nidulans possesses two α-1,3-glucan synthase (AGS) genes, agsA and agsB. For functional analysis of these genes, we constructed several mutant strains in A. nidulans: agsA disruption, agsB disruption, and double-disruption strains. We also constructed several CagsB strains in which agsB expression was controlled by the inducible alcA promoter, with or without the agsA-disrupting mutation. The agsA disruption strains did not show markedly different phenotypes from those of the wild-type strain. The agsB disruption strains formed dispersed hyphal cells under liquid culture conditions, regardless of the agsA genetic background. Dispersed hyphal cells were also observed in liquid culture of the CagsB strains when agsB expression was repressed, whereas these strains grew normally in plate culture even under the agsB-repressed conditions. Fractionation of the cell wall based on the alkali solubility of its components, quantification of sugars, and 13C-NMR spectroscopic analysis revealed that α-1,3-glucan was the main component of the alkali-soluble fraction in the wild-type and agsA disruption strains, but almost no α-1,3-glucan was found in the alkali-soluble fraction derived from either the agsB disruption strain or the CagsB strain under the agsB-repressed conditions, regardless of the agsA genetic background. Taken together, our data demonstrate that the two AGS genes are dispensable in A. nidulans, but that AgsB is required for normal growth characteristics under liquid culture conditions and is the major AGS in this species.

Total fractionation of green tea residue by microwave-assisted alkaline pretreatment and enzymatic hydrolysis

Total refinery of constituents of green tea residue was achieved by combination of microwave-assisted alkaline pretreatment and enzymatic hydrolysis. Alkaline pretreatment was effective at separating pectic polysaccharides, protein, phenolic compounds and aliphatic compounds (probably originating from cuticular components), and the solubilization rate was attained 64–74% by heating at 120–200°C. The higher heating value (HHV) of alkali-soluble fraction attained 20.1MJ/kg, indicating its usability as black-liquor-like biofuel. Successive cellulolytic enzymatic hydrolysis mainly converted cellulose into glucose and attained the maximum solubilization rate of 89%. Final residue was predominantly composed of aliphatic cuticular components with high proportion in 9,10,18-trihydroxyoctadecanoic acid (30.1–48.6%). These cuticular components are potential alternative feedstock for aliphatic compounds commonly found in oil plants.

Horticultural and Floricultural Applications of Urban Wastes Originated Fertilizers

Different origin composts and a digestate from a biogas plant and their respective alkali soluble (SBO) and insoluble (IOR) fractions have been tested as organic fertilizers in growth media. The materials have been characterized by determination of pH, salinity, C, N, P, and K content. A preliminary evaluation of the possible phytoxicity has been performed by determination of the germination indexes of cress (Lepidium sativum), white mustard (Sinapsis alba) and radish (Raphanus sativus). Most of the materials did not promote the germination of the seeds. Notwithstanding these negative results, the materials were also used as partial peat substitute in a commercial substrate to test the growth of marigold (Tagetes patula), radish (Raphanus sativus), and spinach (Spinacia oleracea). The dimension and dry weight of the plants grown on the substrate mixed with the composts, the digestate or the SBOs were similar to those observed on the substrate. Moreover, most of the SOBs provoked the increase of the dry weight of the roots of the radishes, therefore an increase of the quality. The insoluble fractions (IOR) from the composts allowed a growth of the plants similar to that obtained with a commercial substrate. In contrast, the IOR obtained from the digestate was phytotoxic.

Molecular weight distribution of polysaccharides from edible seaweeds by high-performance size-exclusion chromatography (HPSEC)

Biological properties of polysaccharides from seaweeds are related to their composition and structure. Many factors such as the kind of sugar, type of linkage or sulfate content of algal biopolymers exert an influence in the relationship between structure and function. Besides, the molecular weight (MW) also plays an important role. Thus, a simple, reliable and fast HPSEC method with refractive index detection was developed and optimized for the MW estimation of soluble algal polysaccharides. Chromatogram shape and repeatability of retention time was considerably improved when sodium nitrate was used instead of ultrapure water as mobile phase. Pullulan and dextran standards of different MW were used for method calibration and validation. Also, main polysaccharide standards from brown (alginate, fucoidan, laminaran) and red seaweeds (kappa- and iota-carrageenan) were used for quantification and method precision and accuracy. Relative standard deviation (RSD) of repeatability for retention time, peak areas and inter-day precision was below 0.7%, 2.5% and 2.6%, respectively, which indicated good repeatability and precision. Recoveries (96.3–109.8%) also showed its fairly good accuracy. Regarding linearity, main polysaccharide standards from brown or red seaweeds showed a highly satisfactory correlation coefficient (r>0.999). Moreover, a good sensitivity was shown, with corresponding limits of detection and quantitation in mg/mL of 0.05–0.21 and 0.16–0.31, respectively. The method was applied to the MW estimation of standard algal polysaccharides, as well as to the soluble polysaccharide fractions from the brown seaweed Saccharina latissima and the red Mastocarpus stellatus, respectively. Although distribution of molecular weight was broad, the good repeatability for retention time provided a good precision in MW estimation of polysaccharides. Water- and alkali-soluble fractions from S. latissima ranged from very high (>2400kDa) to low MW compounds (<6kDa); this high heterogeneity could be attributable to the complex polysaccharide composition of brown algae. Regarding M. stellatus, sulfated galactans followed a descending order of MW (>1400kDa to <10kDa), related to the different solubility of carrageenans in red seaweeds. In summary, the method developed allows for the molecular weight analysis of seaweed polysaccharides with very good precision, accuracy, linearity and sensitivity within a short time.

Fractionation and thermal characterization of hemicelluloses from bamboo (Phyllostachys pubescens Mazel) culm

Water-soluble hemicelluloses and eight alkali-soluble hemicelluloses were fractionated from bamboo (Phyllostachys pubescens Mazel) culm with hot distilled water, 2% NaOH, 2% KOH, 5% NaOH, and 5% KOH aqueous solution. The chemical structures, as analyzed employing FTIR spectrometry, suggested that all the hemicelluloses were likely to be comprised of arabinoxylans associated with lignin more or less. Thermal analysis for hemicelluloses was carried out using TG-DTG method under nitrogen atmosphere at a heating rate of 10 °C/min, and first-order kinetics was evaluated. The major pyrolysis was focused at 187-346 °C, with activation energy ranging from 23.77 to 45.02 kJ/mol. The alkali-soluble fractions, being soluble in solution only at pH higher than 5.5, presented lower thermal stability and higher values of activation energy and pre-exponential factor than the alkali-soluble fractions remaining soluble in alkaline solution at pH lower than 5.5 and insoluble in ethanol. The chemical property of the hemicellulose fractions may greatly influence the thermal characteristics.

Structural and thermal characterization of hemicelluloses isolated by organic solvents and alkaline solutions from Tamarix austromongolica

Three organosolv and three alkaline hemicellulosic fractions were prepared from lignocellulosic biomass of the fast-growing shrub Tamarix austromongolica ( Tamarix Linn.). Sugar analysis revealed that the organosolv-soluble fractions contained a higher content of glucose (33.7–6.5%) and arabinose (14.8–5.6%), and a lower content of xylose (62.2–54.8%) than the hemicellulosic fractions isolated with aqueous alkali solutions. A relatively high concentration of alkali resulted in a decreasing trend of the xylose/4- O-methyl- d-glucuronic acid ratio in the alkali-soluble fractions. The results of NMR analysis supported a major substituted structure based on a linear polymer of β-(1 → 4)-linked d-xylopyranosyl residues, having ramifications of α- l-arabinofuranose and 4- O-methyl- d-glucuronic acid residues monosubstituted at O-3 and O-2, respectively. Thermogravimetric analysis revealed that one step of major mass loss occurred between 200–400 °C, as hemicelluloses devolatilized with total volatile yield of about 55%. It was found that organosolv-soluble fractions are more highly ramified, and showed a higher thermal stability than the alkali-soluble fractions.

β(1 → 3)-glucan aerosols in different occupational environments

The aim of this preliminary study was to assess exposure to β(1 → 3)-glucan as well as inhalable dust and viable fungi in different occupational environments. The study was conducted in three different industrial plants: metal plant where metalworking fluids were applied, wastewater treatment plant, and waste composting plant. In selected points simultaneously the stationary air sampling was performed to evaluate the levels of inhalable dust, β(1 → 3)-glucan, and to make a quantitative analysis of airborne fungi. All variables describing the exposure were characterized by a wide range of concentrations. The results were as follows: β(1 → 3)-glucan (1.38–65.1 ng/m3), inhalable dust (0.03–2.93 mg/m3), and fungi (0.16–285 × 102 CFU/m3). The highest concentrations for all parameters were found in the composting plant. In the composting plant, a statistically significant correlation was found between β(1 → 3)-glucan and fungal levels (r = 0.89; p < 0.05). In the metal industry and composting plant, the participation of alkali-soluble fraction was stable, exceeding 90% of all β(1 → 3)-glucan. However, in the wastewater treatment plant, its average amount was much lower—73.6%. The study showed that β(1 → 3)-glucan was present in different occupational environments and it should be taken into consideration as an important part of bioaerosols. However, more studies are required to assess the concentration levels as well as all determinants of exposure.

Multifunctional antioxidant activity of polysaccharide fractions from the soybean byproduct okara

An alcohol insoluble residue (AIR) from okara, a byproduct from soymilk, was mainly composed by indigestible carbohydrate (55.7%). After sequential extraction, three alkali-soluble fractions (12.7% yield) and an insoluble residue (RES, 58.7% yield) were obtained. Soluble polysaccharide fractions showed in vitro reduction power (11–26 μmol Trolox Equivalent (TE)/g dry weight (dw)) and free radical scavenging activity (63–78 μmol TE/g dw). The highest antioxidant activity was exhibited by 0.05 M NaOH-soluble fraction, rich in pectins. The 1 M KOH-soluble fraction had a mixture of hemicellulosic and pectic polysaccharides, and 4 M KOH-soluble fraction contained the bulk of xyloglucans, although some pectins could also be present. RES contained cellulose along with residual pectins. FT-IR spectra of okara and AIR exhibited an absorption band at 1740 cm −1 of carboxylic ester from pectins, which lacked in the fractions. Moreover, they showed absorption bands at 1650 and 1550 cm −1 of proteins, and at 900–890 cm −1 of β-glycosidic linkages. Potential antioxidant activity of okara cell-wall polysaccharides could be attributed to pectins, although the contribution of residual proteins cannot be ruled out.

Inorganic polyphosphates of different fractions in the mutant yeast Saccharomyces cerevisiae with impaired mitochondrial ATP synthesis

Impaired synthetase function of the mitochondrial ATPase induced by mutation in the ATP22 gene results in decreased accumulation of inorganic polyphosphates in the stationary growth phase of the yeast Saccharomyces cerevisiae grown on glucose. The content of polyphosphates in the mutant strain in this phase is 2.5 times lower than in the parent strain. This difference is most pronounced for the acid-soluble polyP1 fraction and the alkali-soluble polyP3 fraction. Polyphosphate chain length in mutant cells is less than in the parent cells in both the acid-soluble polyP1 and in the salt-soluble polyP2 fractions. The mutation had no effect on polyphosphates content in the mitochondria.

The fractionation of phosphorus in some modern and late-Holocene calcareous tufas in North Yorkshire, UK

Abstract Phosphorus fractionation studies were undertaken on seven UK tufas: three modern, and four old. The phosphorus in the carbonate fraction of the tufa averaged 19% of the total phosphorus in the modern material, and from 48–64% in the 4000 year-old deposits and the increase attributed to the mineralization of the contained organic matter. Two further phosphorus fractions contained significant amounts of P. The dithionite fraction ranged from 10–27% of the total, and most of this fraction was probably associated with detrital iron minerals. The alkali-soluble fraction which removed most of the organically-bound P was highest in the modern bryophyte tufas. Total P levels in the tufas ranged from 33–119 ppm. These are low values for stream sediments. Phosphorus uptake rates into tufa were estimated for these sites. They were less than 5% of the incoming P and deemed to have a negligible effect on the aquatic biota.

Structural Differences among Alkali-Soluble Arabinoxylans from Maize (Zea mays), Rice (Oryza sativa), and Wheat (Triticum aestivum) Brans Influence Human Fecal Fermentation Profiles

Human fecal fermentation profiles of maize, rice, and wheat bran and their dietary fiber fractions released by alkaline-hydrogen peroxide treatment (principally arabinoxylan) were obtained with the aim of identifying and characterizing fractions associated with high production of short chain fatty acids and a linear fermentation profile for possible application as a slowly fermentable dietary fiber. The alkali-soluble fraction from maize bran resulted in the highest short chain fatty acid production among all samples tested, and was linear over the 24 h fermentation period. Size-exclusion chromatography and (1)H NMR suggested that higher molecular weight and uniquely substituted arabinose side chains may contribute to these properties. Monosaccharide disappearance data suggest that maize and rice bran arabinoxylans are fermented by a debranching mechanism, while wheat bran arabinoxylans likely contain large unsubstituted xylose regions that are fermented preferentially, followed by poor fermentation of the remaining, highly branched oligosaccharides.

Contribution by different organic fractions to triazines sorption in Calcaric Regosol amended with raw and biotransformed olive cake

A soil, olive cake, compost and vermicompost of olive cake, were subjected to sequential laboratory extraction to progressively remove water-soluble, lipid and alkali-soluble (humic-type) fractions. Sorption experiments with triazines were carried out with non-amended and amended soil and with soil residues in the intermediate stages during the laboratory removal of the different organic fractions. Herbicide sorption in soil amended with olive cake was between two and three times higher than sorption in composted substrates. In non-amended soil, the removal of humic and fulvic acids led to a decrease of triazines sorption indicating the importance of these fractions in the sorption of these pesticides. The greater triazines sorption in soil amended with olive cake could be associated with the high concentration of water-soluble substances. In contrast, olive cake lipids did not favour the sorption of the more hydrophobic herbicides as indicated by the fact that the sorbed amount increased 30–40% when this fraction was removed. No significant ( P > 0.05) differences in K oc values were found in soils amended with compost and vermicompost in the course of the progressive removal of the different organic fractions, indicating triazine sorption was related more with the total amount of organic matter than with its chemical composition.