Simultaneous determination of neutral and amino sugars in biological materials

Galactosamine and mannosamine are integral parts of bacterial and fungal extracellular polymeric substances

Extracellular polymeric substances (EPS) are produced by microorganisms and interact to form a complex matrix called biofilm. In soils, EPS are important contributors to the microbial necromass and, thus, to soil organic carbon (SOC). Amino sugars (AS) are used as indicators for microbial necromass in soil, although the origin of galactosamine and mannosamine is largely unknown. However, indications exist that they are part of EPS. In this study, two bacteria and two fungi were grown in starch medium either with or without a quartz matrix to induce EPS production. Each culture was separated in two fractions: one that directly underwent AS extraction (containing AS from both biomass and EPS), and another that first had EPS extracted, followed then by AS determination (exclusively containing AS from EPS). We did not observe a general effect of the quartz matrix neither of microbial type on AS production. The quantified amounts of galactosamine and mannosamine in the EPS fraction represented on average 100% of the total amounts of these two AS quantified in cell cultures, revealing they are integral parts of the biofilm. In contrast, muramic acid and glucosamine were also quantified in the EPS, but with much lower contribution rates to total AS production, of 18% and 33%, respectively, indicating they are not necessarily part of EPS. Our results allow a meaningful ecological interpretation of mannosamine and galactosamine data in the future as indicators of microbial EPS, and also attract interest of future studies to investigate the role of EPS to SOC and its dynamics.

Relationships between feeding and microbial faeces indices in dairy cows at different milk yield levels

A study was carried out to gain quantitative information on the diet-dependent faecal microbial biomass of dairy cows, especially on the biomass fractions of fungi, Gram-positive (G+) and Gram-negative (G-) bacteria. Groups of high-yield, low-yield and non-lactating cows were investigated at four different farms. A mean faecal microbial biomass C (MBC) concentration of 33.5 mg g-1 DM was obtained by the chloroform fumigation extraction method. This is similar to a mean microbial C concentration of 31.8 mg g-1 DM, which is the sum of bacterial C and fungal C, estimated by cell-wall derived muramic acid (MurN) and fungal glucosamine (GlcN), respectively. However, the response of these two approaches to the feeding regime was contradictory, due to feeding effects on the conversion values. The higher neutral detergent fibre (NDF) and acid detergent fibre (ADF) concentrations in the non-lactating group led to higher (P < 0.05) concentrations of cellulose and lignin in their faeces in comparison with the lactating cows. This change in faecal chemical composition in the non-lactating group was accompanied by usually higher ratios of G+/G- phospholipid fatty acids (PLFA), ergosterol/MBC and fungal C/bacterial C. Although bacteria dominate the faecal microbial biomass, fungi contribute a considerable mean percentage of roughly 20% to the faecal microbiome, according to PLFA and amino sugar data, which requires more attention in the future. Near-infra red spectroscopic estimates of organic N and C fractions of cow faeces were able to model microbial biomarkers successfully, which might be useful in the future to predict its N2O emission potential and fertilizer value.

Methods for mucin analysis: a comparative study

The aim was to compare five techniques commonly used to quantify mucin concentrations in ileal digesta collected from three growing pigs that had been fed a diet in which the sole protein was casein. Ileal mucin output was estimated by the periodic acid-Schiff, ethanol precipitation, and phenol-sulfuric acid methods as 25.1, 19.3, and 20.7 g kg-1 of dry matter intake (DMI), respectively. The mucin concentration estimated from sialic acid was only 5.9 g kg-1 of DMI. On the basis of the concentrations of the hexosamines N-acetylglucosamine and N-acetylgalactosamine, mucin output was estimated as 44.9 g kg-1 pf DMI. Of the five assays studied, the ethanol precipitation, periodic acid-Schiff, phenol-sulfuric acid, and sialic acid methods may considerably underestimate mucin in the digesta, which calls into question the accuracy of all of these approaches. In contrast, the gas chromatography method for the determination of hexosamines gave more information on the type and state of the mucin present.

Characterization of cyanidin- and quercetin-derived flavonoids and other phenolics in mature saskatoon fruits (Amelanchier alnifolia Nutt.)

In order to further characterize the anthocyanins, flavonols, and other phenolics present in mature saskatoon ( Amelanchier alnifolia Nutt.) fruit, extracts were characterized using high-performance liquid chromatography, gas chromatography, and liquid chromatography-mass spectrometry. Cyanidin 3-O-galactoside, cyanidin 3-O-glucoside, cyanidin 3-O-arabinoside, and cyanidin 3-O-xyloside were identified as the four major anthocyanins in the mature fruit. The quercetin-derived flavonols, quercetin 3-O-glucoside, quercetin 3-O-galactoside, quercetin 3-O-arabinoside, quercetin 3-O-xyloside, quercetin 3-O-arabinoglucoside, quercetin 3-O-robinobioside, and quercetin 3-O-rutinoside were also identified in mature fruit extracts. In addition, two chlorogenic acid isomers (hydroxycinnamates), 3-O-caffeoylquinic acid and 5-O-caffeoylquinic acid were detected. The total content of the anthocyanin-, flavonol-, and hydroxycinnamate-type phenolics detected in mature 'Smoky' saskatoon fruit was 140, 25, and 96 mg/100 g fresh weight, respectively. These data further our knowledge of the phenolic composition of mature saskatoon fruit, and as anthocyanins, flavonols, and hydroxycinnamates exhibit antioxidant activities, the presence and levels of these classes of phenolics will aid in the understanding of the potential health-beneficial effects of saskatoon fruits in the human diet.

Supplementation of xylanase and phospholipase to wheat-based diets for weaner pigs

The effects of supplementing a wheat-based diet for weaner pigs with exogenous xylanase and phospholipase on ileal and faecal nutrient digestibilities and on the level of microbial metabolites in ileal digesta were examined. Fourteen piglets, weaned at 11 days, were fitted with a simple T-cannula at the distal ileum. The pigs were offered a control diet or diets supplemented with xylanase and phospholipase individually or in combination, in a two period crossover design. The combination of xylanase and phospholipase tended to increase the ileal recovery of the amino sugar galactosamine, whereas the concentration expressed in mg/kg dry matter intake of glucosamine was slightly decreased (p < 0.10). There was neither an effect of enzyme supplementation on ileal and faecal digestibility of the other nutrients and energy, nor was there an effect on pH and on the level of microbial metabolites in ileal digesta. However, an increase in ileal and faecal nutrient and energy digestibility with increasing age was observed. The ileal and faecal digestibility coefficients (except for ether extract) were significantly (p < 0.05) higher in experimental period I than in period II. These higher values may be attributed to a lower feed intake during period I. Since a lower level of feed intake is generally associated with a slower rate of passage and a longer retention time of digesta, a positive impact on digestion and absorption of nutrients can be assumed, which, on the other hand, limits the potential of additional enzyme effects.

The gel-forming polysaccharide of psyllium husk (Plantago ovata Forsk)

The physiologically active, gel-forming fraction of the alkali-extractable polysaccharides of Plantago ovata Forsk seed husk (psyllium seed) and some derived partial hydrolysis products were studied by compositional and methylation analysis and NMR spectroscopy. Resolving the conflicting claims of previous investigators, the material was found to be a neutral arabinoxylan (arabinose 22.6%, xylose 74.6%, molar basis; only traces of other sugars). With about 35% of nonreducing terminal residues, the polysaccharide is highly branched. The data are compatible with a structure consisting of a densely substituted main chain of beta-(1-->4)-linked D-xylopyranosyl residues, some carrying single xylopyranosyl side chains at position 2, others bearing, at position 3, trisaccharide branches having the sequence L-Araf-alpha-(1-->3)-D-Xylp-beta-(1-->3)-l-Araf. The presence of this sequence is supported by methylation and NMR data, and by the isolation of the disaccharide 3-O-beta-D-xylopyranosyl-L-arabinose as a product of partial acid hydrolysis of the polysaccharide.

A poorly fermented gel from psyllium seed husk increases excreta moisture and bile acid excretion in rats

Psyllium seed husk (PSH) increases stool output and lowers blood cholesterol levels in humans. PSH and three fractions isolated from it were meal-fed to colectomized rats and fermented in vitro to test the hypothesis that viscous, gel-forming fraction B was responsible for these physiological actions. Control rats were fed 50 g/kg cellulose. The concentration of each PSH fraction in the test meals was equivalent to its concentration in PSH. Yields of the fractions were: A, 171; B, 575; and C, 129 g/kg of PSH. The wet weight and moisture content of ileal excreta (IE) from rats fed test meals containing PSH or fraction B were greater than those measured in excreta from rats fed meals containing cellulose or the other two PSH fractions. Total bile acids in IE did not differ between rats fed PSH or fraction B and were greater in these groups than in the other groups. Fraction A was not fermented during 3 d of incubation; fraction B was poorly fermented, with approximately 30% of the constituent sugars disappearing; and fraction C was rapidly and nearly completely fermented. These results indicate that the gel-forming fraction we isolated from PSH is the physiologically active component of the husks.

An unfermented gel component of psyllium seed husk promotes laxation as a lubricant in humans

BACKGROUND

In addition to increasing stool weight, supplements of psyllium seed husk produce stools that are slick and gelatinous.

OBJECTIVE

Our purpose was to test the hypothesis that a gel-forming fraction of psyllium escapes microbial fermentation and is responsible for the characteristics that enhance laxation.

DESIGN

Fifteen healthy adults consumed controlled diets for two 7-d periods, one of which included 8.8 g dietary fiber provided by 15 g/d of a psyllium seed husk preparation. All stools were collected and evaluated and diet was monitored throughout.

RESULTS

Psyllium significantly increased the apparent viscosity of an aqueous stool extract, stool moisture, and wet and dry stool weights. A very viscous fraction, not present in low-fiber stool and containing predominantly 2 sugars that are also found in abundance in psyllium husk, was isolated from psyllium stool.

CONCLUSIONS

In contrast with other viscous fibers that are fermented completely in the colon, a component of psyllium is not fermented. This gel provided lubrication that facilitated propulsion of colon contents and produced a stool that was bulkier and more moist than were stools resulting with use of comparable amounts of other bowel-regulating fiber sources.

Plant residue and bacteria as bases for increased stool weight accompanying consumption of higher dietary fiber diets

OBJECTIVE

Stool diluting effects of relatively inert material, such as unfermentable dietary fiber, has been proposed as an effect of fiber beneficial to the colon. Stool dilution by increasing bacterial mass may be beneficial or deleterious, depending on bacterial metabolic products. The purpose of this study was to determine the basis for stool weight when two stepwise increases of fiber from all classes of fiber-containing foods were consumed.

METHODS

Stool from five men consuming three constant diets containing 15, 30 and 42 g/d of dietary fiber were fractionated into plant material and bacteria and analyzed for neutral and amino sugar content. Fecal nitrogen, fat and ash were measured.

RESULTS

Daily gravimetric yield and sugar content of the plant fraction from stool increased with each fiber addition. Compared to the low fiber diet, the medium fiber diet decreased the concentration of the bacterial mass in wet stool by 11% and the high fiber diet by an additional 32%. The high fiber diet decreased stool fat concentration; the medium and high fiber diets decreased stool nitrogen concentration to the same extent. Apparent digestibility of plant-derived neutral sugars decreased with each fiber addition.

CONCLUSIONS

Inherently less fermentable plant material modulates the colon environment in three beneficial ways: it is a relatively unreactive diluent of lumenal contents; it adds mass to promote distal movement of waste; it does not promote a large bacterial mass.

Mucin output in ileal digesta of pigs fed a protein-free diet

Daily outputs of mucin in ileal digesta were estimated in three barrows fed a protein-free diet while administered either saline (SAI) or a complete amino acid mixture (AAI) intravenously. The water soluble-ethanol precipitable fraction of ileal digesta (crude mucin; CM) was used to estimate the composition of mucin in ileal digesta. This fraction exhibited a carbohydrate composition characteristic of mucin and had a high threonine, serine and proline content (40 mol/100 mol). The proportions of soluble gastric and intestinal mucins, approximately 27 and 73%, respectively, were estimated from the N-acetylglucosamine (GlcNAc)/N-acetylgalactosamine (GalNAc) ratio in CM. The daily outputs of soluble mucin, 2.75 and 3.41 g/day from SAI and AAI pigs (p = 0.13), respectively, were determined from the GalNAc outputs in CM, assuming the above contributions of gastric and intestinal mucins. The estimated soluble mucin outputs accounted for more than 99% of the fucose, galactose, GalNAc and GlcNAc in CM. Total mucin outputs in ileal digesta, 5.32 and 5.65 g/day from SAI and AAI Pigs (p = 0.24), respectively, were determined from the total GalNAc output in digesta, assuming soluble and insoluble mucin had similar compositions. Based on these outputs, mucin represented approximately 30, 7 to 22, 15 and 11% of the endogenous threonine, proline, serine and protein, respectively, in ileal digesta. Approximately 74, 76, 100 and 53% of the fucose, galactose GalNAc and GlcNAc, respectively, in ileal digesta from pigs in this study was attributed to mucin. The results from this study demonstrate the importance of mucin as a source of some endogenous amino acids and carbohydrates.

Ileal recovery of nutrients and mucin in humans fed total enteral formulas supplemented with soy fiber

The objective of this study was to determine whether soy fiber supplementation of total enteral nutrition formulas affected small intestinal recovery of nitrogen, amino acids, and carbohydrates or mucin output in eight human subjects (four males, four females) with ileostomies. The subjects ingested five test diets to provide 1.0-16.5 g soy fiber/L for 2 consecutive days each. The five test diets, each with a different soy fiber content were formulated by varying the relative proportion (1:0, 0.75:0.25, 0.5:0.5, 0.25:0.75, and 0:1) of two commercially available formulas. Effluent dry matter increased with soy fiber intake as a result of the quantitative recovery of soy fiber nonstarch polysaccharide. Nitrogen and amino acid digestibilities were unchanged by the ingestion of soy fiber. Nutrients from the total enteral nutrition formulas were well digested in the small intestine with true nitrogen and amino acid digestibilities in excess of 90% and starch digestibilities approaching 100%. Ileal mucin output was higher in male subjects and was unaffected by soy fiber intake. In summary, soy fiber supplementation does not compromise protein and carbohydrate absorption from the small intestine of humans.

Fermentation of carbohydrate in rat ileal excreta is enhanced with cecal inocula compared with fecal inocula

The differential fermentative capacities of microflora from two regions of the large bowel and how fermentation was altered by prior exposure of the microflora to the substrate to be fermented were studied using an in vitro fermentation system. Bacterial inocula were prepared from cecal contents and feces from three groups of rats fed purified diets containing 100 g/kg dietary fiber from canned peas or psyllium seed husk, or a nonpurified diet containing 170 g/kg dietary fiber. The substrate for all fermentations was ileal excreta from colectomized rats fed a purified diet containing 100 g/kg dietary fiber from canned peas. Anaerobic fermentations were conducted for 0, 3, 6, 12, 24, 48 and 96 h. Sugars of the unfermented polysaccharides were measured by gas chromatography following acid hydrolysis; disappearance was the measure of fermentation. Independent of inoculum source, > 90% of the starch and arabinose and 75% of the uronic acids, but < 30% of non-starch glucose (the measure of cellulose), were fermented by 24 h. Cecal inocula fermented arabinose and uronic acids more quickly (P < 0.05) and fermented more (P < 0.05) non-starch glucose than fecal inocula. Inocula adapted to psyllium seed husk fermented starch faster (P < 0.05) and non-starch glucose, arabinose and uronic acids more slowly (P < 0.05) than inocula adapted to peas or nonpurified diet. Bacterial efficiency of carbohydrate utilization, the increase in muramic acid/mole carbohydrate fermented, was greatest (P < 0.05) with cecal inocula adapted to peas. We conclude that using cecal microflora as the inoculum source provides a more accurate index of fermentation during transit through the large bowel and that noncellulosic and storage polysaccharides of the plant cell wall are utilized before cellulose.

Mucin secretion in germfree rats fed fiber-free and psyllium diets and bacterial mass and carbohydrate fermentation after colonization

The effect of psyllium on mucin secretion was determined by comparing water-soluble and -insoluble fractions of excreta from germfree rats fed a fiber-free (FF) diet or a diet containing psyllium seed husk (PS). Excreta from the same rats after colonization with a rat mixed cecal culture were separated into water-soluble, plant, and bacterial fractions to compare the remaining carbohydrate and the mass of bacteria. The sugar composition and water solubility of carbohydrate in excreta from germfree rats fed FF diets indicated that a primary fermentable substrate was mucin. PS increased fecal excretion of mucin-derived sugars almost threefold in germfree rats. Fecal carbohydrate was reduced from 619 to 237 mumol/g of dry feces and mostly in the bacterial fraction when rats fed an FF diet were colonized. The total sugar content and the amount of muramic acid, but not bacterial counts and mass, indicated that PS increased fecal bacteria. Fractionation of excreta from PS-fed rats was complicated by a gel which, based on sugar composition, was PS. Sugar composition of the water-soluble fraction from excreta from PS-fed rats suggested that it contained some bacterial component, possibly exopolysaccharides and some of the PS, but not mucin. PS digestibility ranged from 60 to 80%, depending on what fecal fraction was used for output. Because of the presence of PS-derived sugars in the gel and soluble fraction, it was not possible to determine which, if any, of the PS digestibilities was correct.

Determination of fermentable carbohydrate from the upper gastrointestinal tract by using colectomized rats

The primary aim of this study was to characterize the carbohydrate that would be supplied to the colon for fermentation under physiological conditions. Colectomized rats were fed fiber-free diets or diets containing 5% (wt/wt) gum arabic. Four (fucose, galactose, glucosamine, and galactosamine) of 11 analyzed sugars accounted for 77% of the total sugar in ileal excreta from colectomized rats fed fiber-free diets. The three sugars in gum arabic, rhamnose, arabinose, and galactose, accounted for 84% of the total sugars in gum arabic ileal excreta. Comparisons of the sugar compositions of the ileal excreta, the water-soluble fractions of the excreta, and three gel filtration fractions of the water-soluble material with those of the water-soluble fraction of rat mucosa, the acetone-soluble fraction of pancreas, and pancreatin suggested that the major source of endogenous carbohydrate is mucin. Gum arabic increased the daily excretion of the four mucin-derived sugars (fucose, galactose, glucosamine, and galactosamine) by the colectomized rats from 473 mumol per day to 634 mumol per day. We conclude that mucin is the major endogenous carbohydrate excreted from the upper gut and that gum arabic increases the amount of this endogenous carbohydrate.

Liquid chromatographic method for the determination of the carbohydrate moiety of glycoproteins. Application to alpha 1-acid glycoprotein and tissue plasminogen activator

A rapid procedure is described for the qualitative and quantitative analysis of the carbohydrate composition of glycoproteins by liquid chromatography with light-scattering detection. The analysis was carried out in three steps. First, the glycoprotein samples were purified by a two-step purification on a Sephadex G-25 column with a 90% yield. Second, the selectivity of the separation and the sensitivity of detection of monosaccharides, as methyl glycosides obtained by direct methanolysis of glycoproteins, were improved by modified simplex optimization of the methanolysis parameters (temperature, methanolic hydrochloric acid strength and reaction time) determined at 66 degrees C, 1.2 M and 8.1 h for alpha 1-acid glycoprotein (alpha-AGP) and 73 degrees C, 1.5 M and 12.5 h for tissue plasminogen activator (tPA). Finally, the method was applied to the determination of the carbohydrate moiety of the two N-glycosylated glycoproteins alpha-AGP and tPA.