Determination of the degrees of methylation and acetylation of pectins using a C18 column and internal standards

Remodeling of pectin and hemicelluloses in tomato pericarp during fruit growth

Tomato fruit texture depends on histology and cell wall architecture, both under genetic and developmental controls. If ripening related cell wall modifications have been well documented with regard to softening, little is known about cell wall construction during early fruit development. Identification of key events and their kinetics with regard to tissue architecture and cell wall development can provide new insights on early phases of texture elaboration. In this study, changes in pectin and hemicellulose chemical characteristics and location were investigated in the pericarp tissue of tomato (Solanum lycopersicon var Levovil) at four stages of development (7, 14 and 21day after anthesis (DPA) and mature green stages). Analysis of cell wall composition and polysaccharide structure revealed that both are continuously modified during fruit development. At early stages, the relative high rhamnose content in cell walls indicates a high synthesis of rhamnogalacturonan I next to homogalacturonan. Fine tuning of rhamnogalacturonan I side chains appears to occur from the cell expansion phase until prior to the mature green stage. Cell wall polysaccharide remodelling also concerns xyloglucans and (galacto)glucomannans, the major hemicelluloses in tomato cell walls. In situ localization of cell wall polysaccharides in pericarp tissue revealed non-ramified RG-I rich pectin and XyG at cellular junctions and in the middle lamella of young fruit. Blocks of non-methyl esterified homogalacturonan are detected as soon as 14 DPA in the mesocarp and remained restricted to cell corner and middle lamella whatever the stages. These results point to new questions about the role of pectin RGI and XyG in cell adhesion and its maintenance during cell expansion.

Extraction optimization and physicochemical properties of pectin from melon peel

In this study, acidic extraction (citric acid) was used for the extraction of pectin from melon peel. A central composite design (CCD) was applied to study the effect of temperature (35-95°C), time (40-200min), pH (1-3) and solvent to sample ratio (10-50v/w) on the yield and degree of esterification (DE). The results showed that the yield and DE ranged from 2.87 to 28.98% and 1.33-29.33%, respectively. Also, the highest extraction yield (29.48±1.7%) was obtained under optimal conditions (pH of 1, temperature of 95°C and ratio of 10v/w after 200min). The protein, ash, carbohydrate and galacturonic acid content of pectin obtained under optimal conditions were about 1.5, 3.5, 10 and 48%, respectively. Rheological experiments determined that melon peel pectin dispersions behaved as a weak gel at concentrations of 1%w/v. The emulsifying activity was 35% and also, the emulsion stability was higher at 4°C than at 23°C.

Cell wall dynamics during apple development and storage involves hemicellulose modifications and related expressed genes

BACKGROUND

Fruit quality depends on a series of biochemical events that modify appearance, flavour and texture throughout fruit development and ripening. Cell wall polysaccharide remodelling largely contributes to the elaboration of fleshy fruit texture. Although several genes and enzymes involved in cell wall polysaccharide biosynthesis and modifications are known, their coordinated activity in these processes is yet to be discovered.

RESULTS

Combined transcriptomic and biochemical analyses allowed the identification of putative enzymes and related annotated members of gene families involved in cell wall polysaccharide composition and structural changes during apple fruit growth and ripening. The early development genes were mainly related to cell wall biosynthesis and degradation with a particular target on hemicelluloses. Fine structural evolutions of galactoglucomannan were strongly correlated with mannan synthase, glucanase (GH9) and β-galactosidase gene expression. In contrast, fewer genes related to pectin metabolism and cell expansion (expansin genes) were observed in ripening fruit combined with expected changes in cell wall polysaccharide composition.

CONCLUSIONS

Hemicelluloses undergo major structural changes particularly during early fruit development. The high number of early expressed β-galactosidase genes questions their function on galactosylated structures during fruit development and storage. Their activity and cell wall substrate remains to be identified. Moreover, new insights into the potential role of peroxidases and transporters, along with cell wall metabolism open the way to further studies on concomitant mechanisms involved in cell wall assembly/disassembly during fruit development and storage.

Structure characterization, chemical and enzymatic degradation, and chain conformation of an acidic polysaccharide from Lycium barbarum L

An acidic polysaccharide, named as p-LBP, was isolated from Lycium barbarum L. by water extraction and purified by decoloration, ion exchange chromatography, dialysis and gel chromatography, successively. The primary structure analysis was determined by HPAEC-PAD, HPSEC, FT-IR, GC-MS, and NMR. The results showed p-LBP was a homogeneous heteropolysaccharide as a pectin molecule with an average molecular weight of 64kDa p-LBP was an approximately 87nm hollow sphere in 0.05mol/L sodium sulfate solution determined by HPSEC-MALLS, DLS and TEM. A discussion of degradation patterns gave the detailed structural information of p-LBP. Therefore, the results from degraded fragments elucidated that the backbone of p-LBP was formed by →4-α-GalpA-(1→, repeatedly. Partial region was connected by →4-α-GalpA-(1→ and →2-α-Rhap-(1→, alternatively. On the C-4 of partial →2-α-Rhap-(1→ residues existed branches forming by →4-β-Galp-(1→, →3-β-Galp-(1→ or →5-α-Araf-(1→, while on the C-6 of partial →3-β-Galp-(1→ residues existed secondary branches forming by terminal-α-Araf, terminal-β-Galp or →3-α-Araf-(1→.

Pectin content and composition from different food waste streams

In the present paper, 26 food waste streams were selected according to their exploitation potential and investigated in terms of pectin content. The isolated pectin, subdivided into calcium bound and alkaline extractable pectin, was fully characterized in terms of uronic acid and other sugar composition, methylation and acetylation degree. It was shown that many waste streams can be a valuable source of pectin, but also that pectin structures present a huge structural diversity, resulting in a broad range of pectin structures. These can have different physicochemical and biological properties, which are useful in a wide range of applications. Even if the data could not cover all the possible batch by batch and country variabilities, to date this represents the most complete pectin characterization from food waste streams ever reported in the literature with a homogeneous methodology.

Induced mutations in tomato SlExp1 alter cell wall metabolism and delay fruit softening

Fruit ripening and softening are key traits for many fleshy fruit. Since cell walls play a key role in the softening process, expansins have been investigated to control fruit over ripening and deterioration. In tomato, expression of Expansin 1 gene, SlExp1, during fruit ripening was associated with fruit softening. To engineer tomato plants with long shelf life, we screened for mutant plants impaired in SlExp1 function. Characterization of two induced mutations, Slexp1-6_W211S, and Slexp1-7_Q213Stop, showed that SlExp1 loss of function leads to enhanced fruit firmness and delayed fruit ripening. Analysis of cell wall polysaccharide composition of Slexp1-7_Q213Stop mutant pointed out significant differences for uronic acid, neutral sugar and total sugar contents. Hemicelluloses chemistry analysis by endo-β-1,4-d-glucanase hydrolysis and MALDI-TOF spectrometry revealed that xyloglucan structures were affected in the fruit pericarp of Slexp1-7_Q213Stop mutant. Altogether, these results demonstrated that SlExp1 loss of function mutants yield firmer and late ripening fruits through modification of hemicellulose structure. These SlExp1 mutants represent good tools for breeding long shelf life tomato lines with contrasted fruit texture as well as for the understanding of the cell wall polysaccharide assembly dynamics in fleshy fruits.

Application of Celluclast 1.5L in apple pectin extraction

Pectins were extracted from apple pomace with Celluclast 1.5L at a dose of 25, 50 and 75 μl per 1g of material. In obtained pectin, the galacturonic acid (GalA) content, the neutral sugars (NS) profile, the degree of methylation (DM) and acetylation (DAc), the molecular mass, protein, ash and polyphenol levels as well as antioxidant and antitumor activity were determined. The lowest dose of enzymatic preparation resulted in the yield of pectin isolation comparable with acidic treatment (15.3%). Application of higher dose caused further, almost 4% increase in polymer recovery. Enzymatically isolated pectin was characterised by larger molecular mass and contained more GalA of higher DM and DAc than polymer extracted with acid. It was also richer in protein and polyphenols, and had different NS profile, which resulted in higher antiradical activity as well as the ability to inhibit the proliferation and invasion of Caco-2 adenocarcinoma cells.

Simple and validated quantitative ¹H NMR method for the determination of methylation, acetylation, and feruloylation degree of pectin

The knowledge of pectin esterification degree is of primary importance to predict gelling and other properties of pectin from different sources. This paper reports the development of a simple and rapid (1)H NMR-based method for the simultaneous quantitative determination of methylation, acetylation, and feruloylation degree of pectin isolated from various food sources. Pectin esters are hydrolyzed in NaOH/D2O, and the obtained methanol, acetic acid, and ferulic acid are directly measured by (1)H NMR. High accuracy, repeatability, and reproducibility of the method were obtained, and the analysis time is reduced as compared to conventional chromatography- or titration-based methods.

Novel and diverse fine structures in LiCl-DMSO extracted apple hemicelluloses

Hemicelluloses are key polysaccharides in the regulation of the mechanical properties of plant cell walls during organ development and in fruit texture. Their diverse compositions and structures are partially known, in particular with regard to their function in cell walls. To that end, apple hemicelluloses were sequentially extracted by DMSO doped by LiCl followed by potassium hydroxide. The weakly bounded hemicelluloses in the LiCl-DMSO soluble extract were fractionated by ion exchange (AEC) and size exclusion (SEC) chromatographies. The structure of all the extracts and fractions was established by enzymatic fingerprinting using β-glucanase, β-mannanase and β-xylanase. Molecular weight of the fraction was established by HPSEC. MS as well as HPAEC analyses of the enzyme digests revealed the remarkable diversity of apple hemicelluloses. Different xyloglucan (XyG), galactoglucomannan (GgM) and glucuronoarabinoxylan were isolated along the extraction and fractionation process. All LiCl-DMSO soluble fractions were acetyl-esterified. Besides, the LiCl-DMSO soluble XyG differed from the 4M KOH extracted one essentially on the basis of its molecular weight. At least two populations differing in their content and distribution of glucose and mannose composed GgM. Moreover, galactose ramifications occurred on mannose blocks in the glucose rich fraction. These results open the way for future studies on the complex structure-function relationship of hemicelluloses in plant cell walls.

Determination of degree of methylation of food pectins by chromatography

BACKGROUND

In Florida, 90% of citrus is processed into juice, leaving large amounts of peel waste that could be processed into food ingredients such as pectins for other applications. Pectins of low degree of methylation (DM < 50) have important functional properties for use in foods and pharmaceuticals. Thus determination of DM is important, but DM analyses are difficult to perform and assays can have interference due to the presence of salts or neutral sugars.

RESULTS

A chromatography method has been developed for determination of DM of food pectin using alkaline hydrolysis followed by pectin digestion with a commercial pectinase. Analysis was performed by ion exclusion chromatography (IEC) to obtain methanol (MeOH) concentrations and by anion exchange chromatography (AEC) to obtain galacturonic acid (GalA) concentrations. Data were compared with values obtained using other DM analysis procedures. For example, a 55-75 DM pectin assayed as 55.5, 59.6, 60.1 and 57.0 DM by IEC, AEC, colorimetric and conductivity detection methods respectively.

CONCLUSION

The chromatography procedure described in this paper provides an alternative method for determination of DM of food pectins for accurate and efficient analysis when confronted with limited quantities or large numbers of samples.

Effect of extraction conditions on the yield and chemical properties of pectin from cocoa husks

Different extraction conditions were applied to investigate the effect of temperature, extraction time and substrate-extractant ratio on pectin extraction from cocoa husks. Pectin was extracted from cocoa husks using water, citric acid at pH 2.5 or 4.0, or hydrochloric acid at pH 2.5 or 4.0. Temperature, extraction time and substrate-extractant ratio affected the yields, uronic acid contents, degrees of methylation (DM) and degrees of acetylation (DA) of the extracted pectins using the five extractants differently. The yields and uronic acid contents of the extracted pectins ranged from 3.38-7.62% to 31.19-65.20%, respectively. The DM and DA of the extracted pectins ranged from 7.17-57.86% to 1.01-3.48%, respectively. The highest yield of pectin (7.62%) was obtained using citric acid at pH 2.5 [1:25 (w/v)] at 95 °C for 3.0 h. The highest uronic acid content (65.20%) in the pectin was obtained using water [1:25 (w/v)] at 95 °C for 3.0 h.

Pectin extraction from quince (Cydonia oblonga) pomace applying alternative methods: effect of process variables and preliminary optimization

The objectives of this study were to introduce alternative methods in the process of pectin extraction from quince pomace, to determine the effect of selected process variables (factors) on the obtained pectin, and to perform a preliminary optimization of the process. A fractional factorial experimental design was applied, where the factors considered were six: quince pomace pretreatment (washing vs blanching), drying method (hot air vs LPSSD), acid extraction conditions (pH, temperature, and time), and pectin extract concentration method (vacuum evaporation vs ultrafiltration). The effects of these factors and their interactions on pectin yield (Y: 0.2-34.2 mg/g), GalA content (44.5-76.2%), and DM (47.5-90.9%), were determined. For these three responses, extraction pH was the main effect, but it was involved in two and three factors interactions. Regarding alternative methods, LPSSD was required for maximum Y and GalA, and ultrafiltration for maximum GalA and DM. Response models were used to predict optimum process conditions (quince blanching, pomace drying by LPSSD, acid extraction at pH 2.20, 80 , 3 h, and concentration under vacuum) to simultaneously maximize Y (25.2 mg/g), GalA (66.3%), and DM (66.4%).

Pectina: da matéria-prima ao produto final

A pectina, provavelmente a mais complexa macromolécula natural, é um heteropolissacarídeo contendo predominantemente resíduos de ácido galacturônico. Este polímero, do grupo das fibras dietéticas, é amplamente utilizado como geleificante e estabilizante na indústria de alimentos. O principal processo industrial para obtenção de pectina está baseado na solubilização da protopectina do bagaço de maçã e casca de frutos cítricos, realizada em condições levemente ácidas sob aquecimento. Estudos recentes têm reportado a extração de pectina de novas matérias-primas sob diferentes condições, com influência sobre a qualidade e sobre o rendimento do produto final, para aumentar sua qualidade reológica. Esta revisão descreve a estrutura, as fontes, as aplicações, o processo de extração industrial assim como as principais técnicas de caracterização da pectina.

Purification, characterization, and mode of action of a rhamnogalacturonan hydrolase from Irpex lacteus, tolerant to an acetylated substrate

A novel rhamnogalacturonase (RGase) acting on an acetylated substrate was detected in the commercial preparation Driselase, an enzymatic mixture derived from the basidiomycete Irpex lacteus. The activity was isolated by hydrophobic interaction chromatography, gel filtration, and preparative isoelectric focusing, resulting in the isolation of five different rhamnogalacturonan hydrolases exhibiting various isoelectric points from 6.2 to 7.7. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and mass spectrometry analyses after trypsin cleavage of the five fractions revealed that the five rhamnogalacturonases have a molar mass of 55 kDa without any divergences in the identified peptides. The RGase with a pI of 7.2 exhibited a pH optimum between 4.5 and 5 and a temperature optimum between 40 degrees C and 50 degrees C. Its mode of action was analyzed by mass spectrometry of the oligosaccharides produced after hydrolysis of acetylated and nonacetylated rhamnogalacturonan. Oligomers esterified by an acetyl group on the reducing galacturonic acid residue or fully acetylated were detected in the hydrolysate showing that the novel enzyme is able to bind acetylated galacturonic acid in its active site.

Extraction of green labeled pectins and pectic oligosaccharides from plant byproducts

Green labeled pectins were extracted by an environmentally friendly way using proteases and cellulases being able to act on proteins and cellulose present in cell walls. Pectins were isolated from different plant byproducts, i.e., chicory roots, citrus peel, cauliflower florets and leaves, endive, and sugar beet pulps. Enzymatic extraction was performed at 50 degrees C for 4 h, in order to fulfill the conditions required for microbiological safety of extracted products. High methoxy (HM) pectins of high molar mass were extracted with three different enzyme mixtures. These pectins were subsequently demethylated with two pectin methyl esterases (PMEs), either the fungal PME from Aspergillus aculeatus or the orange PME. It was further demonstrated that high molar mass low methoxy (LM) pectins could also be extracted directly from cell walls by adding the fungal PME to the mixture of protease and cellulase. Moreover, health benefit pectic oligosaccharides, the so-called modified hairy regions, were obtained after enzymatic treatment of the residue recovered after pectin extraction. The enzymatic method demonstrates that it is possible to convert vegetable byproducts into high-added value compounds, such as pectins and pectic oligosaccharides, and thus considerably reduce the amount of these residues generated by food industries.

Evidence for a blockwise distribution of acetyl groups onto homogalacturonans from a commercial sugar beet (Beta vulgaris) pectin

Commercial acid-extracted sugar beet pectin was extensively hydrolysed using an endo-polygalacturonase (AnPGI from Aspergillus niger or AnPGII from A. niger or FmPG from Fusarium moniliforme) in combination with Aspergillus aculeatus pectin methyl-esterase (AaPME). The homogalacturonan-derived oligogalacturonates released were quantified by high-performance anion-exchange chromatography and their structure determined by mass spectrometry. The different endo-polygalacturonases exhibited variable tolerance towards acetyl groups. AnPGI was the most active and FmPG the less. A hypothetical homogalacturonan was constructed using the AnPGI-recovered oligogalacturonates as building blocks and the validity of the model was checked taking into account FmPG observed requirements and hydrolysis products. A blockwise repartition of the acetyl groups onto sugar beet pectin homogalacturonan is proposed.

Immunological and Structural Properties of a Pectic Polymer from Glinus Oppositifolius

The aim of this paper was to further elucidate the structure and the immunomodulating properties of the pectic polymer GOA2, previously isolated from Glinus oppositifolius. Enzymatic treatment of GOA2 by endo-alpha-d-(1 --> 4)-polygalacturonase led to the isolation of three pectic subunits, GOA2-I, GOA2-II, and GOA2-III, in addition to oligogalacturonides. GOA2-I was shown to consist of 1,2-linked Rhap and 1,4-linked GalpA in an approximately 1:1 ratio, and NMR-analysis showed that the monomers were linked together in a strictly alternating manner. The galactose units in GOA2-I were found as terminal-, 1,3-, 1,6-, 1,4-, 1,3,4-, and 1,3,6-linked residues, while the arabinofuranosyl existed mainly as terminal- and 1,5-linked units. A rhamnogalacturonan-I type structure was suggested being the predominant part of GOA2-I. According to linkage analysis GOA2-II and GOA2-III contained glycosidic linkages characteristic for rhamnogalacturonan-II type structures. GOA2 was shown by sedimentation velocity in the analytical ultracentrifuge, to have a broad degree of polydispersity with a mode s(20,w) value of approximately 1.9 S, results reinforced by atomic force microscopy measurements. The polydispersity, as manifested by the proportion of material with s(20,w) > 3 S, decreased significantly with enzyme treatment. The abilities of GOA2, GOA2-I, GOA2-II, and GOA2-III to induce the proliferation of B cells, and to exhibit complement fixing activities were tested. In both test systems, GOA2-I showed significantly greater effects compared to its native pectin GOA2. GOA2-I was in addition shown to exhibit a more potent intestinal immune stimulating activity compared to GOA2. The ability of GOA2 to induce secretion of proinflammatory cytokines was examined. Marked upregulations in mRNA for IL-1beta from rat macrophages and IFN-gamma from NK cells were found.

In situ, chemical and macromolecular study of the composition of Arabidopsis thaliana seed coat mucilage

A comprehensive analysis was carried out of the composition of seed coat mucilage from Arabidopsis thaliana using the Columbia-0 accession. Pectinaceous mucilage is released from myxospermous seeds upon imbibition, and in Arabidopsis consists of a water-soluble, outer layer and an adherent, inner layer. Analysis of monosaccharide composition in conjunction with digestion with pectolytic enzymes conclusively demonstrated that the principal pectic domain of both layers was rhamnogalacturonan I, and that in the outer layer this was unbranched. The macromolecular characteristics of the water-soluble mucilage indicated that the rhamnogalacturonan molecules in the outer layer were in a slightly expanded random-coil conformation. The inner, adherent layer remained attached to the seed, even after extraction with acid and alkali, suggesting that its integrity was maintained by covalent bonds. Confocal microscopy and monosaccharide composition analyses showed that the inner layer can be separated into two domains. The internal domain contained cellulose microfibrils, which could form a matrix with RGI and bind it to the seed. In effect, in the mum5-1 mutant where most of the inner and outer mucilage layers were water soluble, cellulose remained attached to the seed coat. Immunolabeling with anti-pectin antibodies indicated the presence of galactan and arabinan in the inner layer, with the latter only present in the non-cellulose-containing external domain. In addition, JIM5 and JIM7 antibodies labeled different domains of the inner layer, suggesting the presence of stretches of homogalacturonan with different levels of methyl esterification.

Homogalacturonan synthesis in Arabidopsis thaliana requires a Golgi-localized protein with a putative methyltransferase domain

Pectins are a family of complex cell-wall polysaccharides, the biosynthesis of which remains poorly understood. We identified dwarf mutants with reduced cell adhesion at a novel locus, QUASIMODO2 (QUA2). qua2-1 showed a 50% reduction in homogalacturonan (HG) content compared with the wild type, without affecting other cell-wall polysaccharides. The remaining HG in qua2-1 showed an unaltered degree of methylesterification. Positional cloning and GFP fusions showed that QUA2, consistent with a role in HG synthesis, encodes a Golgi-localized protein. In contrast to QUA1, another Golgi-localized protein required for HG-synthesis, QUA2 does not show sequence similarity to glycosyltransferases, but instead contains a putative methyltransferase (MT) domain. The Arabidopsis genome encodes 29 QUA2-related proteins. Interestingly, the transcript profiles of QUA1 and QUA2 are correlated and other pairs of QUA1 and QUA2 homologues with correlated transcript profiles can be identified. Together, the results lead to the hypothesis that QUA2 is a pectin MT, and that polymerization and methylation of homogalacturonan are interdependent reactions.

Fast data preprocessing for chromatographic fingerprints of tomato cell wall polysaccharides using chemometric methods

The variability in the chemistry of cell wall polysaccharides in pericarp tissue of red-ripe tomato fruit (Solanum lycopersicon Mill.) was characterized by chemical methods and enzymatic degradations coupled to high performance anion exchange chromatography (HPAEC) and mass spectrometry analysis. Large fruited line, Levovil (LEV) carrying introgressed chromosome fragments from a cherry tomato line Cervil (CER) on chromosomes 4 (LC4), 9 (LC9), or on chromosomes 1, 2, 4 and 9 (LCX) and containing quantitative trait loci (QTLs) for texture traits, was studied. In order to differentiate cell wall polysaccharide modifications in the tomato fruit collection by multivariate analysis, chromatograms were corrected for baseline drift and shift of the component elution time using an approach derived from image analysis and mathematical morphology. The baseline was first corrected by using a "moving window" approach while the peak-matching method developed was based upon location of peaks as local maxima within a window of a definite size. The fast chromatographic data preprocessing proposed was a prerequisite for the different chemometric treatments, such as variance and principal component analysis applied herein to the analysis. Applied to the tomato collection, the combined enzymatic degradations and HPAEC analyses revealed that the firm LCX and CER genotypes showed a higher proportion of glucuronoxylans and pectic arabinan side chains while the mealy LC9 genotype demonstrated the highest content of pectic galactan side chains. QTLs on tomato chromosomes 1, 2, 4 and 9 contain important genes controlling glucuronoxylan and pectic neutral side chains biosynthesis and/or metabolism.

Cellulase and protease preparations can extract pectins from various plant byproducts

The use of protease and cellulase preparations to extract pectins from plant byproducts (chicory, cauliflower) was investigated. Different enzymatic preparations were characterized by their activities toward proteins, cellulose, and pectins. These preparations were then tested regarding pectin extraction, and extraction conditions (nature and concentration of enzyme, incubation time) were optimized. Enzymatic and acidic extractions were compared and also combined in sequential extractions. This study shows that it is possible to extract pectins by using cellulases and proteases. Enzymes can extract pectins with a higher yield ( approximately 35%) than acid (approximately 28%) but enzyme-extracted pectins have a smaller molar mass (300,000 g/mol) than acid-extracted pectins (500,000 g/ mol). Different hypotheses are tested and discussed to explain this mass difference.