Neutral Sugar Composition Research Articles

Distribution of carboxy groups in TEMPO-oxidized cellulose nanofibrils prepared from never-dried Japanese cedar holocellulose, Japanese cedar-callus, and bacterial cellulose

We prepared 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized samples from never-dried Japanese cedar (JC) holocellulose, JC-callus, and bacterial cellulose (BC). The original never-dried samples and their TEMPO-oxidized products were characterized by neutral sugar composition analysis. TEMPO-oxidized cellulose nanofibrils (TEMPO-CNFs) were prepared from the TEMPO-oxidized samples by ultrasonication in water. The carboxy groups in TEMPO-CNFs were position-selectively esterified with 9-anthryl diazomethane (ADAM) to prepare TEMPO-CNF-COOCH2-C14H9 samples, which had UV absorption peak at 365 nm. The mass-average degree of polymerization (DPw) values of 1% lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) solutions of the original samples were determined by size-exclusion chromatography in combination with multi-angle laser-light scattering, ultraviolet absorption, and refractive index detection (SEC/MALLS/UV/RI), and were 5490, 2660, and 2380 for the JC holocellulose, JC-callus, and BC samples, respectively. The TEMPO-CNF-COOCH2-C14H9 sample solutions in 1% LiCl/DMAc were analyzed by SEC/MALLS/UV/RI to obtain SEC elution patterns. The patterns corresponded to the molar mass and carboxy group distributions of the samples, which were detected by RI and UV absorption of anthryl groups, respectively. The carboxy groups existed in the entire molar mass distribution regions of all the TEMPO-CNF samples, although their lower molar mass regions contained higher carboxy group densities. The obtained results indicate that random depolymerization occurred on the cellulose microfibril surfaces at the initial stage of TEMPO-catalyzed oxidation and/or ultrasonication in water. This depolymerization mechanism can explain all the obtained SEC-elution patterns of the TEMPO-CNFs, without considering the presence of periodically disordered regions in the cellulose microfibrils of the never-dried cellulose samples.Graphical abstract

Enzymatic de-esterification and depolymerization of apple pomace (Malus domestica var. Blanca de Asturias) pectin impacts lipid digestion invitro

Different degree of esterification (DE) and molecular weight (Mw) of apple pomace pectin (APP) were evaluated for the effect on lipid digestibility. APP was isolated from variety “Blanca de Asturias” by acidic extraction to obtain pectin with 66% of DE, and 348 kDa Mw. APP was de-esterified with pectinmethylesterase (PME) obtaining APP with DE of 57, 42, and 39%. APP was depolymerized by endo-polygalacturonase (PG) or pectate lyase (PL), and three modified APP fractions were obtained with Mw of 309, 166, and 162 kDa or 241, 205, and 184 kDa for PG-APP or PL-APP fractions, respectively. A considerable reduction in the composition of neutral sugars was observed in the modified samples, which is related to the reduction of the branched region of the pectin. Oil-in-water emulsions prepared with 2% (w/w) of different APP samples were shear thinning and viscosity was 2–20 times higher in pectin added emulsions. Inhibition of lipid digestibility measured in a multiple stage in vitro model showed that APP and modified APP with higher DE significantly reduced lipid digestibility by 25%. The results contribute to the design of higher fat foods and putative higher consumer acceptability. The addition of pectin with certain structural characteristics, can reduce the degree of lipid digestibility, that may help mitigate public health problems such as obesity.

Changes in chemical structures and molar mass parameters of birch wood powder by ethylene diamine treatment

It is necessary to delignify wood samples and treat them with ethylene diamine (EDA) before they are dissolved in 8% (w/v) lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) prior to size-exclusion chromatography (SEC) analysis. In the present study, the effects of delignifying birch wood powder 0–3 times with NaClO2 and subsequently treating it with EDA on its solubility in 8% (w/v) LiCl/DMAc and its SEC data. The neutral sugar composition of the birch powder was almost unaffected by either delignification or treatment with EDA. Treatment of the birch powder with EDA resulted in 28% solubilities in 8% (w/v) LiCl/DMAc. Approximately 11% of cellulose molecules in the birch wood powder was dissolved, and detected as a high-molar-mass (HMM) fraction in the SEC elution pattern. Each single delignification treatment increased the solubility in 8% (w/v) LiCl/DMAc to 68–74% after EDA treatment. Based on the glucose contents of the delignified samples, almost all cellulose molecules in the delignified samples were dissolved in 8% (w/v) LiCl/DMAc after EDA treatment, and detected as the HMM fractions in the SEC elution patterns. The HMM cellulose molecules in the EDA-treated birch powder had linear random-coil conformations in 1% (w/v) LiCl/DMAc. However, the SEC data suggest that there probably were some chemical linkages between the HMM cellulose molecules and lignin or NaClO2-treated lignin fragments in the HMM fractions.

Changes in Cell Wall Sugar Neutral Composition Contribute to Apple Texture Loss during Storage among Cultivars

Fruit texture affects apples’ quality, consumer preference, and shelf life. The cell wall neutral sugar composition was reported to contribute to apples’ mechanical properties at harvest. However, the contributions of cell wall neutral sugar composition to apple texture loss during storage among different cultivars are still unclear. In this study, six cultivars of the apple fruit were stored at 25 °C for 60 days (i.e., rapid loss of texture: ‘Jiguan’, ‘Yindu’, and ‘Qinguan’; slow loss of texture: ‘Fuji’, ‘Huaguan’, and ‘Cripps pink’). The texture properties, physiological indicators, and expression of cell wall-related genes were investigated every 20 d. The results showed that apple cultivars with rapid texture loss showed a faster loss in flesh hardness and crispness, and a higher level of flesh tightness and pericarp break distance, than the cultivars with slow texture loss. Galactose content showed the closest association with the texture properties among the cell wall neutral sugar compositions. The rapid loss of galacturonic acid content and the expression of MdPG1 were higher in the cultivars with rapid texture loss than in those with slow texture loss. These results indicated that changes in cell wall neutral sugar composition contribute to apple texture loss during storage among cultivars.

Valorisation Potential of Invasive Acacia dealbata, A. longifolia and A. melanoxylon from Land Clearings.

Acacia spp. are invasive in Southern Europe, and their high propagation rates produce excessive biomass, exacerbating wildfire risk. However, lignocellulosic biomass from Acacia spp. may be utilised for diverse biorefinery applications. In this study, attenuated total reflectance Fourier transform infrared spectroscopy (FTIR-ATR), high-performance anion-exchange chromatography pulsed amperometric detection (HPAEC-PAD) and lignin content determinations were used for a comparative compositional characterisation of A. dealbata, A. longifolia and A. melanoxylon. Additionally, biomass was treated with three white-rot fungi species (Ganoderma lucidum, Pleurotus ostreatus and Trametes versicolor), which preferentially degrade lignin. Our results showed that the pre-treatments do not significantly alter neutral sugar composition while reducing lignin content. Sugar release from enzymatic saccharification was enhanced, in some cases possibly due to a synergy between white-rot fungi and mild alkali pretreatments. For example, in A. dealbata stems treated with alkali and P. ostreatus, saccharification yield was 702.3 nmol mg−1, which is higher than the samples treated only with alkali (608.1 nmol mg−1), and 2.9-fold higher than the non-pretreated controls (243.9 nmol mg−1). By characterising biomass and pretreatments, generated data creates value for unused biomass resources, contributing to the implementation of sustainable biorefining systems. In due course, the generated value will lead to economic incentives for landowners to cut back invasive Acacia spp. more frequently, thus reducing excess biomass, which exacerbates wildfire risk.

Enhancive effect of instant controlled pressure drop (DIC) pre-treatment on pectin extractability from peach pomace

This study aimed to investigate if instant controlled pressure drop (DIC) processing can enhance pectin extractability from plant material. Peach pomace was treated by 0-, 1-, or 3-cycle of DIC processing at 90 or 105 °C. Pectin fractions including water soluble pectin and insoluble pectin were isolated from dried peach pomace and characterized by degree of methoxylation, neutral sugar composition, and molecular weight distribution. The results demonstrated that the thermomechanical effect of DIC processing induced a strong solubilization of in situ pectic polysaccharides of peach pomace, especially for water insoluble pectin fractions. This solubilization effect resulted in a more than 10% increasing ratio of extractable pectin yield from peach pomace over the maximum yield without the thermomechanical effect of DIC processing. Meanwhile, DIC processing conducted at 90 °C with 1-cycle affected pectin structure and property insignificantly. • DIC process induced solubilization of in situ pectic polysaccharides of peach pomace. • DIC treatment increased the pectin extractive yield of peach pomace by more than 10%. • 1-cycle DIC treatment at 90 °C affected slightly on pectin structure and properties.

Physico-chemical properties of maize (Zea mays L.) mucilage differ with the collection system and corresponding root type and developmental stage of the plant

PurposeMucilage plays crucial roles in root-soil interactions. Collection systems for maize (Zea mays L.) use primary and seminal roots of aeroponically-grown seedlings (CSA), or brace roots of soil-grown plants (CSB). While each method represents specific plant developmental stages, and root types growing in specific (micro-)environments, these factors are rarely considered. It is unclear whether mucilage exhibits distinct physico-chemical properties related to collection system-inherent factors.MethodsMucilage of maize genotype B73 was collected from systems CSA and CSB. Chemical composition was assessed by pH, nutrient contents, neutral sugar composition, and polysaccharide polymer length. Viscosity, surface tension and contact angle represented physical properties.ResultsThe share of hexoses among total polysaccharides was 11% higher in CSB than in CSA, whereas pentoses were predominant in CSA, together with higher nutrient concentrations and pH values. Mannose was detected only in CSB, which also exhibited higher surface tension, viscosity and contact angle compared to CSA.ConclusionsPhysico-chemical differences between the two mucilages are related to root type functions, environmental root growth conditions, and plant developmental state. Higher fractions of pentoses in CSA mucilage seem related to semi-sterile system conditions. Higher viscosity of CSB mucilage might reflect the need for enhanced water holding capacity of brace roots growing in drier conditions. A strong influence of environmental factors on mucilage properties even for a single genotype might play additional roles e.g. in the attraction of microbiomes. These aspects are relevant when assessing the role of mucilage in the rhizosphere, or when developing models of rhizosphere processes.

Changes in neutral sugar composition, molar mass and molar mass distribution, and solid-state structures of birch and Douglas fir by repeated sodium chlorite delignification

Changes in neutral sugar composition, molar mass and molar mass distribution, and solid-state structures of birch and Douglas fir by repeated sodium chlorite delignification

Neutral Sugar Content and Composition as a Sensitive Indicator of Fire Severity in the Andisols of an Araucaria–Nothofagus Forest in Southern Chile

Wildfire induces soil alterations that have a long-term impact on soil organic matter (SOM) quality. We postulated that after different fire severities, the neutral sugars in soils can be used as an indicator of soil organic matter quality after fire. The aim of this study was to determine the contribution of neutral sugar, bulk and occluded particulate organic matter (oPOM) affected by wildfire, at different soil depths in an Araucaria–Nothofagus Forest, four years post-after fire. The concentration and composition of the neutral sugars in the soils clearly comprised the major fraction in the unburned soil. Medium- and high-severity fires caused a drastic reduction in soil sugars in the bulk soil as well as in the oPOM fractions. The 13C-CPMAS NMR spectroscopy analysis revealed a high contribution of recalcitrant carbon to the decomposition such as aryl–C and aryl–O derived from charred material, whereas the abundance of O–alkyl C and alkyl C functional groups were decreased. The neutral sugars (Galactose+Mannose/Xilose+Arabinose) revealed a major microbial origin in fire affected areas as the ratio was >2. Therefore. Therefore, we suggest that the neutral sugar content of soil should be used for monitoring both short- and long-term changes in SOM altered by fires.

Physical and Chemical Properties of Red-Flesh Guava Pectin and Its Lipid-Lowering Effect in Vitro

Water-soluble pectin was extracted from red-flesh guava peel and pulp by ultrasonic-assisted citric acid extraction. The functional group characteristics, monosaccharide composition, thermal stability, rheological properties, and microstructure of guava pectin were studied. The combination of guava peel pectin and pulp pectin with fat, cholesterol micelle, and cholate were studied in vitro. The esterification degree of guava peel pectin was 56.29%. The average molecular weight had two grades, which were 618.40 kDa (43.4%) and 93.90 kDa (56.6%) individually. Neutral sugar composition: 0.58%±0.02% rhamnose, 0.02%±0.01% petrolatose, 88.48%±0.07% arabinose, 0.78%±0.06% xylose, 0.07%±0.02% mannose, 0.40%±0.03% glucose, 9.68%±0.03% galactose. The esterification degree of guava pulp pectin was 48.57%, and the average molecular weight was 1168.00 kDa (11.0%), 120.30 kDa (53.9%) and 64.94 kDa (35.1%), individually. Neutral sugar composition: 0.47%±0.03% rhamnose, 0.03%±0.01% norvoose, 83.86%±0.04% arabinose, 0.76%±0.05% xylose, 0.08%±0.01% mannose, 0.43%±0.02% glucose, 14.37%±0.05% galactose. The particle size of peel pectin solution was significantly smaller than that of pulp pectin (P<0.05). Both kinds of pectin showed the characteristics of pseudoplastic fluid. At the same concentration, the apparent viscosity of pulp pectin solution was higher than that of peel pectin. There were differences between the two types of pectin, with more tentacle filaments at the edge of the peel pectin and deeper folds in the pulp pectin based on the results from the scanning electron microscope (SEM). The absorption of fat, binding amount of cholesterol micelle and cholic acid by pulp pectin were significantly better than that of peel pectin (P<0.05). These results indicated that both of them had lipid-lowering functions in vitro, and the effect of pulp pectin was better than that of peel pectin. The difference in biological activity resulted from the different molecular structure of the two.

Purification and structural characterization of calcium hydroxide isolated arabinoxylans derived from bran, spent grain and sorghum grains

The calcium hydroxide extractable polysaccharides isolated from bran, spent grain and sorghum grains were separated on diethylaminoethyl-cellulose column into five sub-fractions each, by eluting successively with different eluents. These fractions differed in their yield, uronic acid contents and composition of neutral sugars as well as phenolic acids. The major fractions (0.1 M ammonium carbonate eluted) were resolved into a single peak each on Sephacryl S-400 and their homogeneity was ascertained by HPSEC. Ferulic acid was the major phenolic acid (19.84–29.32 mg/100 g) bound to arabinoxylan-(AX) type polysaccharides. The molecular weights were found to be 126.6 kDa for bran and spent grain, and 223.9 kDa for sorghum grains AX. The structural characterization of the purified polysaccharides, carried out by 13C NMR, 1H NMR, FTIR, periodate oxidation, Smith degradation and optical rotation analysis, indicated their backbone to be 1,4-β-D-xylan (optical rotation ranged from – 4.0 to – 7.8), substituted mainly at O-2 or O-3 and/or both by α-L-arabinose residues. As evident from the determination of colour characteristics and high thermostability (T0 > 200 °C), these polysaccharides can be used in the preparation of fibre-rich foods including bakery products.

Linear and branched structures present in high-molar-mass fractions in holocelluloses prepared from chara, haircap moss, adiantum, ginkgo, Japanese cedar, and eucalyptus

The land plants evolved from a salt-water algal ancestor, diversifying on land into fresh-water algae, mosses, ferns, gymnosperms, and finally the angiosperms that dominate land today. In this study, the structures of high-molar-mass fractions in holocelluloses prepared from chara (a freshwater alga), haircap moss, adiantum, ginkgo, Japanese cedar, and eucalyptus were investigated using size-exclusion chromatography with multi-angle laser-light scattering, ultraviolet, and refractive index detection (SEC/MALLS/UV/RI). 4% NaOH-extracted holocelluloses prepared from the above algal and land plants were dissolved in 8% (w/w) lithium chloride/N,N-dimethylacetamide and subjected to SEC/MALLS/UV/RI analysis. The neutral sugar compositions of the samples were also measured. The holocelluloses prepared from chara, haircap moss, and adiantum had the same crystalline microfibril structures (~ 3 nm in width) as those prepared from ginkgo, Japanese cedar, and eucalyptus. However, SEC/MALLS/UV/RI analysis gave different results among samples. Haircap moss, adiantum, Japanese cedar, and ginkgo had cellulose/glucomannan branched structures linked through degraded fragments of residual lignin or lignin-like phenolic compounds. In contrast, 4% NaOH-extracted chara holocellulose had no such branched structures, but contained the same linear structure as found in eucalyptus. The results obtained in this study, therefore, showed the possibility that land plant cellulose fibers, have branched structures with glucomannan in the HMM fractions, even though the cellulose fibers are prepared by repeated delignification and successive 4% NaOH extraction.

Structural conversion of pectin fractions during heat processing in relation to the ability of inhibiting lipid digestion: A case study of hawthorn pectin

This study used hawthorn as object to investigate the relation of structural conversion of pectin fractions during heat processing to the ability of inhibiting lipid digestion. Pectin fractions including water-soluble pectin (WSP), chelator-soluble pectin (CSP), and Na2CO3-soluble pectin (NSP) were isolated from hawthorn tissue after heat processing with different time, as well as the dissolved pectin (DSP) in the heating aqueous phase. The structural features of pectin fractions were characterized by degree of methoxylation, neutral sugar composition, and molecular weight (MW) distribution. After 30-min heat processing, the amount of WSP increased from 78 to 111 mg/g dry basis, while those of CSP and NSP decreased, meanwhile certain amount of DSP (68 mg/g dry basis) was generated. During heat processing, a dynamic alteration of pectin fractions involving solubilization and depolymerization occurred. The solubilization mainly happened in CSP and NSP, inducing a shift from water-insoluble pectin to WSP. The depolymerization occurred in homogalacturonan region of WSP, resulting in a formation of DSP. With the increasing heat time, a more pronounced depolymerization appeared in DSP, which resulted in forming a large amount of pectic polysaccharide fragments with small MW. The WSP showed a good rheological behavior and an ability to inhibit lipid digestion, which was higher than those of DSP. The inhibition rate of WSP (0.1% (w/w)) on lipid digestion decreased from 48.5% to 11.2% after 30-min heat processing. The results can provide novel knowledge to better understand the relation between structure and function of pectin in heat processing.

Impact of pectin characteristics on lipid digestion under simulated gastrointestinal conditions: Comparison of water-soluble pectins extracted from different sources

Four kinds of water-soluble pectin (WSP) extracted from hawthorn (HWSP), apple (AWSP), peach (PWSP), and carrot (CWSP) were mixed with oil-in-water emulsion to investigate pectin characteristics on lipid digestion under simulated gastrointestinal conditions. All WSPs were comprehensively characterized by the degree of methoxylation, neutral sugar composition, molecular weight and conformational parameters, intrinsic viscosity, the degree of linearity and branching, as well as molecular morphology observation by atomic force microscopy. The results demonstrated these WSPs possessed different structural characteristics. The molecules of HWSP were of small size with extended short and linear main chain, forming a certain amount of aggregations in the solution, while the molecules of PWSP were of large size with long and branched chains, forming intensive network structure. The molecular chains of AWSP and CWSP were both of medium size and tended to be flexible random coils in solution forming extensive entangled structures. The apparent viscosity of HWSP and PWSP solutions were both higher than those of AWSP and CWSP due to the aggregations or network structure. And the solution of PWSP showed better anti-shear ability than that of HWSP due to the strong cross-linking between molecule chains. The inhibitory effect of WSPs on lipid digestion decreased with the following order: PWSP, HWSP, CWSP, AWSP, which can be well related with their rheological property. The pectin with large molecular weight and highly branched chains that resulted in strong intermolecular interaction will possess good inhibitory effect on lipid digestion.

Changes in cell wall neutral sugar composition related to pectinolytic enzyme activities and intra-flesh textural property during ripening of ten apricot clones

The changes of texture and cell wall characteristics of apricot were investigated in ten clones at two maturity stages. Fruit firmness, cell wall composition and enzyme activity of three apricot flesh zones were analysed. The AIS (alcohol-insoluble solids) were characterised by high amounts of uronic acid (179–300 mg g−1 AIS) and relatively high amounts of cellulosic glucose (118–214 mg g−1 AIS). The methylesterification degree varied significantly among the different clones ranging from 58 to 97 in Ab 5 and Mans 15 respectively. Conversely to zones firmness, enzymatic activity was higher in pistil followed by equatorial and peduncle zones. The ripening effect has been observed in firmness evolution according to enzymatic activity. This correlation allowed a classification of clones depending on softening. Among studied clones, Ab 5, Marouch 16, Mans 15 and Cg 2 were less influenced by softening and have the advantage of a technological valorisation for the processing industry.

Effect of ionic liquid pretreatment on the physicochemical properties of hemicellulose from bamboo

Ionic liquid (IL) pretreatment of lignocellulosic biomass has been the focus of attention due to its numerous advantages compared with conventional methods. The change in the physicochemical properties of the three main components of this biomass during IL pretreatment is the key factor for their further utilization and conversion. In this study, hemicellulose extracted from bamboo was dissolved in three ILs with different imidazolium cations and the same anion of acetate, including 1-ethyl-3-methylimidazolium acetate (EmimAc), 1-butyl-3-methylimidazolium acetate (BmimAc), and 1-allyl-3-methylimidazolium acetate (AmimAc). The solubility of hemicellulose in the ILs was measured as a function of temperature from 120 °C to 150 °C. Hemicelluloses regenerated from the saturated IL solutions were characterized by using Fourier transform infrared spectroscopy, gel permeation chromatography, gas chromatography–mass spectrometry, 13C–1H heteronuclear single-quantum correlation nuclear magnetic resonance, and thermogravimetry. The solubility of hemicellulose in the three ILs was greatly affected by temperature, and the solubility increased with increasing temperature. The highest solubilities per 100 g of IL were 15.56, 15.09, and 6.73 g in BmimAc, EmimAc, and AmimAc, respectively. Hemicelluloses regenerated from saturated IL solutions showed similar physicochemical features with that of the original hemicellulose before being pretreated with ILs. These features included molecular weight, relative neutral sugar composition, structural feature, and thermal stability. Hence, hemicellulose was litter degraded during IL solving. In addition, the recovered EmimAc was analyzed after dissolving hemicellulose to a saturated state at 150 °C by using 13C and 1H NMR. The recovered IL contained minimal amounts of ethanol and other impurities.

Origin and significance of saccharides during initial pedogenesis in a temperate climate region

Saccharides are common constituents of soils, but their role and origin in the initial phases of pedogenesis remain unclear. Here we show the detailed composition of neutral sugars extracted from arenosols at different development stages, combined with additional lipids of diverse origins using gas chromatography-mass spectrometry (GC–MS). During the first stage (I) of development sucrose is the most abundant saccharide in the soil crust at up to 45,000 µg/g TOC. Sucrose is also the predominant compound in the second and third development stages, but its concentration decreased to the range of 1600 to 16,000 µg/g TOC. Stages II and III of soil development were characterized by a gradual increase in arabitol, mannitol and trehalose, compounds typical for fungi and lichen. Their abundances increased from several percent (compared to the major sucrose) to 10–32% for mannitol and 34–54% for trehalose. Moreover, in stage III there was a considerable increase in the contents of the saccharides: pinitol, myo-inositol, scyllo-inositol, arabinose, together with non-sugar compounds: dehydroabietic acid, p-hydroxybenzoic acid, gallic acid and sitosterol. All these latter compounds are higher plant markers, mainly derived from conifer detritus. The relationships between the ratios of trehalose/sucrose vs. (mannitol + arabitol)/sucrose and TOC vs. (mannitol + arabitol)/sucrose differentiated precisely the top soil layer of arenosols which are covered by different stages of biological soil crust. Our study shows that free sugars, supplemented by lipid biomarkers and total organic carbon contents, are good indicators of soil in the initial phase of pedogenesis.

Dissolved organic carbon content is lower in warm seasons and neutral sugar composition indicates its degradation in a large subtropical river (Nantong Section), China

Riverine organic carbon export plays a major role in the global carbon cycle. The biodegradability of riverine dissolved organic carbon (DOC) determines both greenhouse gas emissions and the amount of refractory DOC. However, seasonal changes in organic carbon and factors controlling DOC biodegradation are still not well understood in large rivers. Here, we examined the monthly changes in concentrations of particulate organic carbon (POC) and DOC in a large subtropical river (Changjiang River, Nantong Section, China) in 2017. We also measured biodegradable DOC (BDOC), specific UV absorbance (SUVA254), neutral sugar concentrations and their compositions. The results showed that POC had no significant relationship with water temperature, precipitation, and discharge. DOC concentrations were significantly negatively correlated with all these parameters, and water temperature explained 61% of the variance in DOC. BDOC concentrations varied between 0 and 14.01 ± 1.22 mg C/L and were closely associated with DOC (R2 = 0.85, p < 0.001). The negative correlation between BDOC% and SUVA254 (R2 = 0.63, p < 0.01) suggested that high aromaticity was associated with low bioavailability. Water temperature was positively correlated with total neutral sugar yield (R2 = 0.43, p < 0.001), which was mainly composed of glucose and deoxysugars in the warm season; thus, neutral sugar composition is a useful indicator of DOC decomposition. Taken together, our study showed that POC has no clear seasonal change, while DOC exhibits a strong seasonal change, and high water temperature leads to low BDOC in a large subtropical river.

Potential of Pectins to Beneficially Modulate the Gut Microbiota Depends on Their Structural Properties.

Pectins are plant cell-wall polysaccharides which can be utilized by commensal bacteria in the gut, exhibiting beneficial properties for the host. Knowledge of the impact of pectins on intestinal bacterial communities is insufficient and limited to a few types of pectins. This study characterized the relationship between the structural properties of pectins and their potential to modulate composition and activity of the gut microbiota in a beneficial way. For this purpose we performed in vitro fermentations of nine structurally diverse pectins from citrus fruits and sugar beet, and a pectic derivative, rhamnogalacturonan I (RGI), using a TIM-2 colon model. The composition of microbiota during TIM-2 fermentations was assessed by 16S rRNA gene amplicon sequencing. Both general and pectin-specific changes were observed in relative abundances of numerous bacterial taxa in a time-dependent way. Bacterial populations associated with human health, such as Faecalibacterium prausnitzii, Coprococcus, Ruminococcus, Dorea, Blautia, Oscillospira, Sutterella, Bifidobacterium, Christensenellaceae, Prevotella copri, and Bacteroides spp. were either increased or decreased depending on the substrate, suggesting that these bacteria can be controlled using structurally different pectins. The main structural features linked to the pectin-mediated shifts in microbiota included degree of esterification, composition of neutral sugars, distribution of homogalacturonan and rhamnogalacturonan fractions, degree of branching, and the presence of amide groups. Cumulative production of the total short chain fatty acids and propionate was largest in fermentations of the high methoxyl pectins. Thus, this study indicates that microbial communities in the gut can be specifically modulated by pectins and identifies the features in pectin molecules linked to microbial alterations. This knowledge can be used to define preferred dietary pectins, targeting beneficial bacteria, and favoring more balanced microbiota communities in the gut.

In Vitro Fecal Fermentation of High Pressure-Treated Fruit Peels Used as Dietary Fiber Sources.

Fruit by-products are being investigated as non-conventional alternative sources of dietary fiber (DF). High hydrostatic pressure (HHP) treatments have been used to modify DF content as well as its technological and physiological functionality. Orange, mango and prickly pear peels untreated (OU, MU and PPU) and HHP-treated at 600 MPa (OP/55 °C and 20 min, MP/22 °C and 10 min, PPP/55 °C and 10 min) were evaluated. Untreated and treated fruit peels were subjected to fecal in vitro fermentations. The neutral sugar composition and linkage glycosidic positions were related to the production of short chain fatty acids (SCFA) resulting from the fermentation of the materials. After HHP-treatments, changes from multibranched sugars to linear sugars were observed. After 24 h of fermentation, OP yielded the highest amount of SCFA followed by PPU and MP (389.4, 282.0 and 204.6 μmol/10 mg DF, respectively). HHP treatment increased the SCFA concentration of orange and mango peel by 7 and 10.3% respectively, compared with the untreated samples after 24 h of fermentation. The results presented herein suggest that fruit peels could be used as good fermentable fiber sources, because they yielded high amounts of SCFA during in vitro fermentations.