Apple Cell Walls Research Articles

Differential effects of pectin-based dietary fibre type and gut microbiota composition on in vitro fermentation outcomes

Interactions between human gut microbiota and dietary fibres (DF) are influenced by the complexity and diversity of both individual microbiota and sources of DF. Based on 480 in vitro fermentations, a full factorial experiment was performed with six faecal inocula representing two enterotypes and three DF sources with nanometer, micrometer, and millimeter length-scales (apple pectin, apple cell walls and apple particles) at two concentrations. Increasing DF size reduced substrate disappearance and fermentation rates but not biomass growth. Concentrated DF enhanced butyrate production and lactate cross-feeding. Enterotype differentiated final microbial compositions but not biomass or fermentation metabolite profiles. Individual donor microbiota differences did not influence DF type or concentration effects but were manifested in the promotion of different functional microbes within each population with the capacity to degrade the DF substrates. Overall, consistent effects (independent of donor microbiota variation) of DF type and concentration on kinetics of substrate degradation, microbial biomass production, gas kinetics and metabolite profiles were found, which can form the basis for informed design of DF for desired rates/sites and consequences of gut fermentation. These results add further evidence to the concept that, despite variations between individuals, the human gut microbiota represents a community with conserved emergent properties.

A determination of the composition and structure of the polysaccharides fractions isolated from apple cell wall based on FT-IR and FT-Raman spectra supported by PCA analysis

Generally in plants, cell wall polysaccharides are the main determinants of tissue properties and contents of an essential part of dietary fiber, prebiotics, or cosmetic ingredients. Therefore, evaluation of the content and structure of polysaccharides is crucial to understanding and controlling their functionality. Vibrational spectroscopy has already proven to be very useful in studying wall-based compounds. Here, it was proposed to use the FT-IR and FT-Raman spectra combined with PCA analysis to discriminate and distinguish pectic and hemicellulosic fractions isolated from apple parenchyma as an example. Reference measurements have been done on commercially available polysaccharides in order to identify relevant fingerprint bands. The similarities of different polysaccharide fractions from apple: water, imidazole, dilute alkali-soluble polysaccharides (WSP, ISP, DASP, respectively), and polysaccharides soluble in three potassium hydroxide concentration (KOHs) to the reference polysaccharides were found. In the case of both types of spectroscopy, the region below 1800 cm−1 was used to differentiate the samples. The results showed that the WSP, ISP, and DASP fractions have band patterns similar to the pectic polysaccharides, but also contain bands characteristic of polysaccharides containing arabinan and galactan. While the KOH fractions showed the greatest similarities to the hemicellulose polysaccharides, especially the glucomannan and xyloglucan. The results showed that FT-IR and FT-Raman spectra supported by PCA can be useful for studying the structure of polysaccharide fractions directly isolated from plant cell wall material.

Cell wall polysaccharides from Annona squamosa: Chemical and functional characterization

Several extraction methods were used to find out what the custard apple cell wall polysaccharides were made of and how they were structured. These included water (WSP), chelator (CSP), sodium carbonate (NSP), potassium hydroxide at 1 mol/L (KSH-1), and potassium hydroxide at 4 mol/L (KSH-4). The five fractions had different structures and make-ups, as shown by FT-IR, molecular weight measurements, sugar composition analysis, and methylation experiments. The results indicated that NSP made up the majority of the fruit's cell wall polysaccharide fraction. As for apparent viscosity, the viscosity and thermal stability of WSP were highest. In terms of apparent viscosity and thermal stability, WSP ranked highest. The stability of NSP and KSH-1 was better. Methylation analysis showed that CSP had galactose and galacturonic acid as the main chains. KSH-4 had a xyloglucan backbone. Compared to the other three fractions, NSP and CSP had the highest antioxidant capacity. Through this study, there is potential for custard apple polysaccharides to be used in the food and biological industries.

Transcriptome analysis reveals key metabolic pathways and gene expression involving in cell wall polysaccharides-disassembling and postharvest fruit softening in custard apple (Annona squamosa L.)

This study aimed to investigate the effect of custard apple cell wall polysaccharides-disassembling on postharvest fruit softening and to explore its key metabolic pathways and gene expression. Custard apple fruit was stored at 15 ± 0.5 °C for 12 days, it was found that the decreased significantly in fruit firmness, contents of Na2CO3-soluble pectin, hemicellulose and cellulose, and the increased significantly in water-soluble pectin and CDTA-soluble pectin. The activities of cell wall-degrading relevant enzymes in fruit were improved significantly during storage, including cellulase, polygalacturonase, pectin methyl esterase, neutral xylanase, β-galactosidase, and β-D-glucosidase. The RNA sequencing results revealed 41,545 nonredundant unigenes and 7571 differentially expressed genes (DEGs) in custard apple fruit samples. Functional annotation and DEGs data revealed cell wall degradation potentially involved in starch and sucrose metabolism, amino sugar and nucleotide sugar metabolism, galactose metabolism, pentose and glucuronate interconversions. Specifically, two EG and six β-Glc genes controlled the cellulose decomposition, and one β-xyl and one GATU genes involved in the degradation of hemicellulose, and two PME, one Pel, and four PG genes were the major regulators of pectin disassembling. These results provide a molecular foundation for explaining fruit softening and extending shelf life of custard apple.

Effect of in vitro gastric digestion conditions on physicochemical properties of raw apple fruit cell wall polysaccharides

The effects of in vitro gastric digestion conditions on the properties of the soluble (SC) and insoluble (IC) components of apple cell walls were investigated. Apple fruits were homogenized and successively treated in natural saliva (3 min, 37 °C) and in simulated gastric fluid (SGF, 2 h, 37 °C). The incubation pH (5.0, 3.0, 1.8) and the ratio of apple mixture to SGF (1:0.05, 1:0.5, 1:1, v/v) were varied. Pectin (GalA 74 wt%, Mw 1800 × 103 g/mol, yield 1.9–2.4%) was a major high-molecular-weight component of SC obtained at pH 1.8, whereas at pH 3.0 and 5.0, proteins (41–55 wt%) and phenolic compounds (2.7–3.1 wt%) were dissolved together with pectins (15–24 wt% GalA, Mw 28-33 × 103 g/mol, yield 0.6–0.8%). Rhamnogalacturonan-I (RG-I) and homogalacturonan (HG) were identified in all pectins. HG was the major component of pectins extracted at pH 1.8; RG-I was the major component of pectins extracted at pH 3.0 and 5.0. The dissolution of cell wall pectins of apple fruits in SGF increased the viscosity of the SC of the apple mixture, decreased the hardness of the apple mixture, increased the water retention and water swelling capacity of the IC, and improved the capacity of high-molecular-weight soluble and insoluble components to retard glucose diffusion. The difference in surface morphology of insoluble components obtained at different values of pH incubation was observed under a SEM.

Modification of apple, beet and kiwifruit cell walls by boiling in acid conditions: Common and specific responses

Cell wall (CW) degradation causes texture loss of plant-based products after processing. However, these losses differ in intensity, which could be due to cell wall structure or plant tissue internal pH conditions. To distinguish these two factors, CWs isolated from apple, beet and kiwifruit were subjected to boiling at pH 2.0, 3.5 and 6.0. Pectin depolymerization was the least pronounced at pH 3.5, while galacturonic acid contents of all CWs decreased at pH 6.0 due to the β-elimination. Pectins were solubilized, and their size decreased with increased pH during CW treatment. At pH 6.0, degrees of methylation decreased mostly in apple and beet CWs while galactose decreased more in kiwifruit CW. At pH 2.0, arabinan was lost in apple and beet CW due to acid hydrolysis. Apple CW was the most susceptible to degradation either at pH 2.0 or 6.0, while beet CW was more degraded at pH 2.0. In contrast, kiwifruit CW was the least susceptible to degradation whichever the pH. Acid hydrolysis and β-elimination appeared to be common mechanisms that cause loss of neutral sugars, often from pectin side chains, and galacturonic acid, respectively, but their effects were of different intensities. This work has a guiding significance for improving texture in the thermally canning process.

Resolving the nanostructure of sodium carbonate extracted pectins (DASP) from apple cell walls with atomic force microscopy and molecular dynamics

The diluted alkali-soluble fraction of the cell wall pectic matrix extracted with sodium carbonate (DASP) from apple fruit (M. domestica cv. Golden Delicious) was subjected to extensive analysis aimed at refining the current view concerning its molecular structure. Pectins were examined by means of atomic force microscopy (AFM) and HPLC chemical analysis. In addition to this, computational chemistry was employed to characterize the structural features of the basic plant cell wall polysaccharides and their possible assemblies. The AFM imaging revealed that DASP molecules deposited on mica structurally resembled rod-like objects, consisting of relatively long linear sections separated by bend points or branches. Locally molecules also formed aggregates, which were visible as an amorphous phase, concentrated around linear sections. Based on chemical analysis combined with molecular dynamics (MD) the linear chains were identified as sections of unbranched homogalacturonan, while the second most abundant polysaccharide present in DASP – arabinose – was considered to constitute the amorphous aggregates. The study showed that despite being present in small amounts, rhamnose is an important factor affecting the formation of the characteristic shape of DASP molecules on mica. The structural characterization of the bend points showed that linear molecules oriented at specific angles are most likely to be formed by two sections of homogalacturonan separated by a single rhamnose unit. AFM images confirmed that this is a common feature of the molecular structure of the DASP fraction, suggesting a possible role in the networking of pectic polysaccharides. Rhamnose interspersions within the homogalacturonan chains lead to the formation of spatial structures, which resemble kinked rods with segments having the ability to change their relative positions. The higher mobility of the linear sections as well as the higher number of segments increases the number of possible interactions with surrounding molecules and thus increases its ability to form gels. Therefore, it is expected that the number of rhamnose units and the length of the linear homogalacturonan sections will be one of the factors that influence the gelling abilities of pectin. Furthermore, it was proposed that branch points are created, similar to bend points, by single interspersions of rhamnose, which connect three homogalacturonan chains or short sections (two or three dimers) of rhamnogalacturonan-I with a homogalacturonan side branch. The third proposed alternative was a complex of two adjacent homogalacturonan chains, one of them having a single rhamnose insertion causing a bend in the structure.

Confirmation by solid-state NMR spectroscopy of a strong complex phenol-dietary fiber with retention of antioxidant activity in vitro

The aim of this study was to prepare a complex between the olive phenolic compounds, hydroxytyrosol (HT), 3,4-dihydroxyphenylglycol (DHPG) and their mixture, with the soluble and insoluble dietary fiber of apple cell wall. A strong interaction between phenols and the apple cell wall occurred during the drying phase and it was confirmed by ultraviolet–visible spectrometry, Fourier transform infrared spectrometry, differential scanning calorimetry, thermogravimetry and especially by solid-state 13C NMR spectroscopy. The antiradical activity by DPPH, ABTS and ORAC assays confirmed that the simple phenolic HT/DHPG maintained in part their antioxidant activity after complexation with the apple cell wall. In addition, the HT/DHPG-soluble and insoluble fractions obtained after simulated gastrointestinal fluids retained this antioxidant activity. These complexes may be protected from absorption during gastrointestinal transit to reach the colon. In the case of the soluble dietary fiber, an enzymatic treatment, in a simulation of hydrolysis by colonic microflora, released oligomers with potential antioxidant activity from this complex. Therefore, the intake of HT/DHPG bound to the fiber of apple cell wall could provide many of the health benefits associated with dietary fiber, and be fermented by gut bacteria to contribute to a healthy antioxidant environment.

Adsorption isotherm studies on the interaction between polyphenols and apple cell walls: Effects of variety, heating and drying

The adsorption capacity of principal phenolic compounds onto cell walls from three apple varieties was investigated. Isothermal adsorption modelled with Langmuir, Freundlich and Redlich-Peterson equations were carried out over a range of concentrations from 0.5 to 30 mM before and after cell walls were subjected to boiling, oven-drying or freeze-drying. The isotherm data were best fitted by the Langmuir model in all cases. Polyphenols selectively adsorbed onto cell walls with maximum binding capacities ranging from 140 to 580 µg/mg cell walls depending on surface charge. Increased pectin in apple cell walls caused a 129%–311% decrease in the adsorption of negatively charged polyphenols, presumably due to electrostatic repulsive forces. Boiling had limited effect on cell wall polysaccharides and polyphenol-cell wall interactions. However, more than twofold reduction in binding capacities of polyphenols was induced after drying by altering the structural (i.e. binding sites) and compositional (i.e. pectin degradation) characteristics of cell walls.

Xyloglucan intake attenuates myocardial injury by inhibiting apoptosis and improving energy metabolism in a rat model of myocardial infarction

The development of coronary heart disease can be divided into preocclusion and postocclusion steps. We previously showed that cell wall polysaccharides consisting of a high content of arabinose and/or xylose, such as apple pectin, protected against myocardial injury by inhibiting postocclusion steps. We hypothesized that xyloglucan, another apple cell wall polysaccharide that consists of a high content of xylose, might also show myocardial protection. To test the hypothesis, rats were supplemented with either tamarind xyloglucan (TXG) (1, 10, and 100 mg/kg per day) or cotton cellulose (CCL) (100mg/kg per day) for 3 days. Then, rats underwent 30 minutes of ischemia followed by 3 hours of reperfusion. Supplementation with TXG at a dosage greater than 10mg/kg per day significantly reduced the infarct size (IS), whereas supplementation with CCL at 100mg/kg per day did not reduce IS. TXG supplementation up-regulated the expression of myoglobin and fatty acid-binding protein, both of which are known to be involved in apoptosis and ATP generation. Indeed, TXG supplementation inhibited apoptosis through decrease in p38 and JNK phosphorylation, increase in Bcl-2/Bax ratio, inhibition in the conversion of procaspase-3 to cleaved caspase-3, and decrease in the generation of DNA nicks. From these results, we demonstrated that xyloglucan in apple can protect against myocardial injury by inhibiting apoptosis and improving energy metabolism. Therefore, apple xyloglucan and pectin contribute to the known beneficial effects of apple in reducing the risk of coronary heart disease by blocking postocclusion steps through apoptosis inhibition. In addition, this study demonstrates the feasibility of developing TXG as a cardioprotectant.

Binding selectivity of dietary polyphenols to different plant cell wall components: Quantification and mechanism

Selected polyphenols exhibited binding selectivity to different cellulose-based composites and apple cell walls. For catechin, cellulose is the dominant binding component, whereas hemicelluloses (xyloglucan and arabinoxylan) apparently did not contribute to polyphenol adsorption in the presence of cellulose. In contrast, ferulic acid and cyanidin-3-glucoside bound to cellulose-based composites and apple cell walls with different affinities, showing that both electrostatic interactions and plant cell wall microstructure were important. Negatively-charged pectin-containing cell walls exhibited the most extensive binding of positively-charged cyanidin-3-glucoside, and bound negatively-charged ferulic acid least effectively. Langmuir binding isotherms predicted the maximum amount of adsorbed polyphenols to be in the range of 30–150% plant cell wall mass. NMR and CLSM analysis support the interactions between polyphenols and plant cell walls and show that although polyphenols are associated with plant cell walls under hydrated conditions, they are not immobilised on polymer surfaces.

Solid-state 13C NMR study of the mobility of polysaccharides in the cell walls of two apple cultivars of different firmness

Solid-state 13C nuclear magnetic resonance (NMR) was used to compare differences in mobility of the cell wall polysaccharides of ‘Scifresh’ and ‘Royal Gala’ apples after 20weeks of storage. The texture of ‘Scifresh’ apples was markedly firmer than that of ‘Royal Gala’ at the end of storage. In a novel approach Two Pulse Phase Modulation (TPPM) decoupling was combined with cross polarisation (CP) and single pulse excitation (SPE) experiments. The resulting high resolution solid-state SPE spectra, unprecedented for apple cell walls, allowed a detailed insight into the physical and chemical properties of very mobile polysaccharides such as the arabinan and galactan side chains of the pectic polysaccharide rhamnogalacturonan I (RG-I). NMR showed that the cellulose rigidity was the same in the two cultivars, while arabinans were more mobile than galactans in both. Unexpectedly, arabinans in ‘Scifresh’ cell walls were more mobile than those in ‘Royal Gala’ which was unforeseen considering the greater firmness of the ‘Scifresh’ cultivar.

Impact of Processing on the Noncovalent Interactions between Procyanidin and Apple Cell Wall

Procyanidins can bind cell wall material in raw product, and it could be supposed that the same mechanism of retention of procyanidins by apple cell walls takes place in cooked products. To evaluate the influence of cell wall composition and disassembly during cooking on the cell walls' capacity to interact with procyanidins, four cell wall materials differing in their protein contents and physical characteristics were prepared: cell wall with proteins, cell wall devoid of protein, and two processed cell walls differing by their drying method. Protein contents varied from 23 to 99 mg/g and surface areas from 1.26 to 3.16 m(2)/g. Apple procyanidins with an average polymerization degree of 8.7 were used. The adsorption of apple procyanidins on solid cell wall material was quantified using the Langmuir isotherm formulation. The protein contents in cell wall material had no effect on procyanidin/cell wall interactions, whereas modification of the cell wall material by boiling, which reduces pectin content, and drying decreased the apparent affinity and increased the apparent saturation levels when constants were expressed relative to cell wall weight. However, boiling and drying increased apparent saturation levels and had no effect on apparent affinity when the same data were expressed per surface units. Isothermal titration calorimetry indicated strong affinity (K(a) = 1.4 × 10(4) M(-1)) between pectins solubilized by boiling and procyanidins. This study higllights the impact of highly methylated pectins and drying, that is, composition and structure of cell wall in the cell wall/procyanidin interactions.

Variability of cell wall polysaccharides composition and hemicellulose enzymatic profile in an apple progeny

The genetic variability of apple cell walls polysaccharides chemical composition and structure was assessed in a progeny of 141 individuals harvested over 2 years. The variability of the hemicelluloses oligosaccharides released by glucanase was analyzed by MALDI-TOF MS. The genetic contribution was distinguished from harvest year as well as from parental crossing patterns and scab resistance selection. Results showed that harvest year had a major impact on cell wall polysaccharide composition and structure. Within each harvest, genetic effect impact more significantly cell wall polysaccharide chemistry than does reciprocal crossing or early scab selection. Uronic acids, glucose, galactose and xylose contents as well as some glucomannan and xyloglucan structures have a high heritability. This first cell wall chemotyping of an apple progeny opens the way for future searches of genetic markers for the chemical variability of cell wall polysaccharides.

Preliminary studies on partial reduction of Colletotrichum acutatum infection by proteinase inhibitors extracted from apple skin

Colletotrichum acutatum, a fungal pathogen that causes soft rot in fruit, produced protease when grown on casein or apple cell wall, as revealed by a clear zone around the well filled with C. acutatum medium in a radial diffusion assay. A protease-inhibiting protein (PI) was also extracted from healthy stored apple, cultivar Cripps Pink, and its activity was tested in vitro and in vivo against a protease produced by C. acutatum. In in vitro trials the inhibition rate determined by radial diffusion assay was over 41% after 24 h, while in inoculated fruit the inhibition ranged from 23.5% to 45% after 5 days at 20 °C. The protease inhibitor extracted from healthy apple skin was a heat-denaturable protein since the halo produced by protein extracted from C. acutatum and added to boiled protein extracted from healthy apple skin tissue was 338.7 mm 2, significantly higher than the halo produced by protein extracted from C. acutatum diluted with fresh protein extracted from healthy tissue (220.7 mm 2). Protein secreted by C. acutatum grown in induced buffer media was tested by polyacrylamide gel electrophoresis. SDS-PAGE of crude enzyme extract revealed the presence of various protein bands that could be ascribed by their molecular mass as putative aspartic proteinase, extracellular alkaline proteinase and serine protease. Genomic analyses are, however, in progress to identify the proteins involved in Colletotrichum patogenicity. More investigations are required to identify the nature of the substance responsible for C. acutatum inhibition in apple and to evaluate the possibility of manipulating the protease inhibitor levels in fruit to reduce soft rot caused by C. acutatum.

Mechanical characteristics of artificial cell walls

Artificial plant cell walls were produced from bacterial cellulose and cell wall constituents. The artificial cell walls were stored at low, medium and high relative humidity, and then subjected to micro-mechanical tests. From chemical composition and microstructure analysis it was found that, among all artificial cell wall materials produced, the most representative analogue of natural apple cell wall was based on bacterial cellulose supplemented with xyloglucan and pectin. Uniaxial tensile tests revealed that the different cell wall materials differed in their mechanical properties; increasing the humidity during storage resulted in a decrease in the value of the secant modulus. The cell wall model material obtained may be used for the simulation of the effect of external factors on the physical and chemical properties of cell walls.

Factors affecting the conversion of apple polyphenols to phenolic acids and fruit matrix to short-chain fatty acids by human faecal microbiota in vitro

Proanthocyanidins (PAs) in apples are condensed tannins comprised mostly of (-)-epicatechin units with some terminal (+)-catechins. PAs, especially those having a long chain-length, are absorbed in the upper intestine only to a small extent and are passed to the colon. In the colon they are subjected to microbial metabolism by colonic microbiota. In the present article, the ability of human microbiota to ferment apple PAs is studied. Freeze-dried fruit preparations (apple, enzymatically digested apple, isolated cell-walls, isolated PAs or ciders) from two varieties, Marie Ménard and Avrolles, containing PAs of different chain lengths, were compared. Fermentation studies were performed in an in vitro colon model using human faecal microbiota as an inoculum. The maximal extent of conversion to known microbial metabolites, was observed at late time point for Marie Ménard cider, having short PAs. In this case, the initial dose also contributed to the extent of conversion. Long-chain PAs were able to inhibit the in vitro microbial metabolism of PAs shown as low maxima at early time points. Presence of isolated PAs also suppressed SCFA formation from carbohydrates as compared with that from apple cell wall or faecal suspension without substrates. The low maximal extents at early time points suggest that there is a competition between the inhibitory effect of the PAs on microbial activity, and the ability to convert PAs by the microbiota.

Role of pectic polysaccharides in structural integrity of apple cell wall material

Texture modulating properties of aqueous dispersions of apple cell wall material differed from those of tomato or kiwifruit, particularly under high shear. It was previously hypothesized that this may be due to the fact that the apple cell wall showed less in vivo solubilization of pectic polysaccharides during ripening compared to tomato or kiwifruit. However, in vitro solubilization of the pectic polysaccharide content of apple CWM by endo-polygalacturonase and/or extraction with 0.05 M sodium carbonate, did not affect the loss in wall integrity shown by tomato or kiwifruit CWMs under shear. In addition, the pectin-depleted residue after Na2CO3 extraction possessed better water retaining and viscosity generating properties than the original cell wall material. Following treatment of apple CWM with cellulase, the viscosity of suspensions decreased, emphasising the role that the cellulose–hemicellulose network plays in the water-retaining capacity of the cell wall. Residue from CWM after cellulase treatment consisted of ∼85% pectic polysaccharides. Surprisingly, the integrity of these “cellulose-free” walls was maintained after shear. It is concluded that differences in structural properties of the CWMs of apple compared to kiwifruit or tomato are not simply related to pectin solubilization but to a fundamental difference in the architecture of the apple cell wall.

Firming of fruit tissues by vacuum-infusion of pectin methylesterase: Visualisation of enzyme action

Apple pieces were vacuum-impregnated with either a pectin methylesterase (PME) and calcium solution or with water prior to pasteurization. Pasteurized apple pieces impregnated with PME and calcium showed a significantly higher firmness. Moreover, solid state 13C NMR spectroscopy of apple cell wall residues revealed an increase of their molecular rigidity. Exogenous PME addition involved a decrease from 82% to 45% of apple pectin degree of methyl-esterification. Microscopic observations of apple slices immunolabelled with antibodies specific for pectins showed that (i) demethyl-esterification was more intense in the cell wall region lining intercellular spaces (demonstrating a key role for these intercellular channels in the enzyme penetration in the tissue during vacuum-infusion) and that (ii) the number of calcium-dimerized deesterified homogalacturonan chains increased. The results corroborate the hypothesis that vacuum-impregnated PME action liberates free carboxyl groups along pectin chains that could interact with calcium, increasing the rigidity of pectins and finally the mechanical rigidity of apple tissue.

Effect of Apple Cell Walls and Their Extracts on the Activity of Dietary Antioxidants

The effect of dietary fiber in the form of apple cell walls and pectin extracts on natural antioxidants was examined. Cell walls (CW), isolated from apples ( Malus domestica Borkh. cv. "Pacific Rose"), were incubated with ascorbic acid (AA) or quercetin in N-2-hydroxyethylpiperazine- N'-2-ethanesulfonic acid (HEPES) buffer (pH 6.5) at 37 degrees C for 2 h. The resulting supernatants were characterized by a ferric reducing antioxidant power (FRAP) assay and cyclic voltammetry (CV). The experiments were repeated with pectin isolated from the apple cell walls and commercial pectins and showed that polysaccharide preparations stabilized AA effectively but offered little protection against quercetin oxidation. The water-soluble components from cell walls appeared to be responsible for the observed effects of cell-wall polysaccharide preparations on antioxidant activity.