Determination of saturated and unsaturated oligogalacturonic acids by means of thin-later chromatography

Prebiotic potential and chemical characterization of the poly and oligosaccharides present in the mucilage of Opuntia ficus-indica and Opuntia joconostle

The mucilage extracted from the convection-dried cladodes of O. ficus-indica and O. joconostle, two species of economic importance, delivered three fractions after methanol precipitation. Two were composed of high molar mass polysaccharides, and one included water-soluble mono-, di-, and oligosaccharides. The large polysaccharides have a molar mass range of 4.0 × 10³ to 8.0 × 10⁵ g·mol^-1 and are consistently composed of galactose, arabinose, xylose, and rhamnose; however, the content of galacturonic acid was different between both fractions and species. Their fermentability by selected probiotics was relatively low, 11-27 % compared to glucose, and decreased with increasing levels of galacturonic acid in the molecules. In the third fraction, previously unreported oligosaccharides were found. These include simple- and complex-structured galactooligosaccharides with arabinosyl-, xylosyl- and galacturonosyl acid residues. Their fermentability by prebiotic species can be ascribed more to their structural characteristics and monosaccharide composition than their molecular dimensions.

High-performance liquid chromatographic separation and on-line mass spectrometric detection of saturated and unsaturated oligogalacturonic acids

A method for the simultaneous determination of saturated and unsaturated oligogalacturonic acids up to degree of polymerization (dp) of 7 by high-performance liquid chromatography (HPLC) is presented. For this purpose, a Cyclobond I 2000 column and a volatile mobile phase consisting of ammonium formate and methanol were used, allowing direct coupling of HPLC to a mass spectrometer via an electrospray interface (ESI-MS) without additional desalting. The analytical system was used for the characterization of digests obtained by incubation of polygalacturonic acid with commercial enzyme preparations.

Characterization of PG2, an early endoPG produced by Sclerotinia sclerotiorum, expressed in yeast

Sclerotinia sclerotiorum, a plant pathogenic ascomycete, contains a neutral endopolygalacturonase (endoPG) subfamily of genes that was previously isolated. We report here that pg2, a member of this subfamily, is early and strongly expressed during the first steps of pathogenesis of sunflower cotyledons. The corresponding protein, PG2, was produced in the heterologous Kluyveromyces lactis system and purified. Characterization of the recombinant enzyme revealed a narrow pH activity curve with an optimal pH of 4.5. Hydrolysis of polygalacturonic acid by PG2 resulted in the accumulation of oligomers ranging from 2- to 9-mer. This degradation profile indicates a random attack on the polymer and demonstrates an endo-mode of action. These results provide evidence that pg2 contributes to the infection process during the early phase of host colonization.

Large-scale preparation of α-D-(14)-oligogalacturonic acids from pectic acid

An efficient and inexpensive method for large-scale preparation of α-D-(1[Formula: see text]4)-oligogalacturonic acids (oligo-GalA), up to DP 5, from pectic acid is described. Pectic acid was digested with a commercially available pectinase to yield a mixture of oligo-GalA, which was effectively separated by a combination of low-pressure – size-exclusion chromatography based on ion-exchange chromatography to obtain pure oligo-GalA of DP 2-5. Key words: pectic acid, galacturonic acid, galabiose, galatriose, pectinase.

The degree of methylation influences the degradation of pectin in the intestinal tract of rats and in vitro

We investigated the degradation, metabolism, fate, and selected effects of pectin in the intestinal tract of rats. Conventional and germfree rats were fed for 3 wk diets containing 6.5% pectin (degree of methylation 34.5, 70.8 and 92.6%, respectively) or pectin-free diets. Pectin passes the small intestine as a macromolecule. The molecular weight distribution of pectins isolated from intestinal contents of germfree rats were unaffected by diet. No or very little galacturonan was found in cecum, colon or feces of most of the conventional rats. In colon contents of some conventional rats, di- and trigalacturonic acid were present. Total anaerobic and Bacteroides counts were greater in groups fed pectin. The concentration of short-chain fatty acids (SCFA) was higher in cecum and feces in all pectin-fed groups. With increasing degree of methylation, the formation rate of SCFA decreased in the cecum of conventional rats. During in vitro fermentation of pectin with fecal flora from rats, unsaturated oligogalacturonic acids appeared as intermediate products. Low-methoxyl pectin was fermented faster than high-methoxyl pectins in vivo and in vitro. Pectin-fed rats had greater ileum, cecum and colon weights. We conclude that structural parameters of pectin influence its microbial degradation in the intestinal tract.

Degradation of pectins with different degrees of esterification by Bacteroides thetaiotaomicron isolated from human gut flora

A complete human fecal flora and cultures of defined species obtained from fecal flora were investigated in vitro to determine their ability to ferment the dietary fiber pectin. Bacteroides thetaiotaomicron was tested as a pectin-degrading microorganism alone and in coculture with Escherichia coli. Macromolecular pectins with different degrees of esterification were used as substrates in microbial degradation studies. The levels of oligogalacturonic acids formed in batch cultures were estimated during a 24- or 48-h incubation period by using high-performance thin-layer chromatography and high-performance anion-exchange chromatography. The spectrum and the amount of unsaturated oligogalacturonic acids formed as intermediate products of pectin fermentation changed permanently in the culture media during incubation with the complete fecal flora. After 24 h, no oligogalacturonic acids were detected. The pectin-degrading activities of pure cultures of B. thetaiotaomicron were lower than the pectin-degrading activity of a complete fecal flora. Cocultures of B. thetaiotaomicron and E. coli exhibited intermediate levels of degradation activity. In pure cultures of E. coli no pectin-degrading activity was found. Additionally, the rate of pectin degradation was affected by the degree of esterification of the substrate. Saturated oligogalacturonic acids were not found during pectin fermentation. The disappearance of oligogalacturonic acids in the later stages of fermentation with both the complete fecal flora and B. thetaiotaomicron was accompanied by increased formation of short-chain fatty acids.

Unsaturated oligogalacturonic acids are generated by in vitro treatment of pectin with human faecal flora

Pectins with a degree of esterification (DE) of 95, 66, 34 and 0%, respectively, were incubated in vitro with human faecal flora (pH 7.8). The concentration and composition of oligogalacturonic acids (oligoGalA) generated were determined using high-performance thin-layer chromatography (HPTLC) with UV and colorimetric detection. In the first period of the anaerobic degradation, the pectin macromolecules were fragmented into unsaturated oligoGalA as intermediate products by the action of bacterial pectate lyases. Depending on the incubation time and the DE of pectin, the amount of unsaturated oligoGalA having different degrees of polymerization changed continuously. These oligoGalA were present in the cultures for some hours. Mixtures of unsaturated di-, tri- and tetraGalA were the end products of a pectate lyase action. Later, the oligoGalA disappear as a result of their further fermentation by the gastrointestinal microflora under formation of short-chain fatty acids (SCFA). Low-esterified pectins were depolymerized and fermented faster than the highly esterified by the human faecal flora in vitro. Furthermore, a mixture of unsaturated oligoGalA prepared from pectic acid by the action of pectate lyase from Erwinia carotovora was completely fermented by human faecal flora.