Comparative study of the cell wall composition of broccoli, carrot, and tomato: Structural characterization of the extractable pectins and hemicelluloses

Pectin modifications and the role of pectin-degrading enzymes during postharvest softening of Jonagold apples

This study aimed at understanding softening in Jonagold apple (Malus×domestica Borkh.) fruits, by investigating pectin modifications and the evolution of pectin-modifying enzymes during postharvest storage and ripening. Jonagold apples were harvested at commercial maturity and stored at different temperatures and controlled atmosphere conditions for 6 months, followed by exposure to ambient shelf life conditions (20 °C under air) for 2 weeks. The composition of the pectic material was analysed. Furthermore, the firmness and the ethylene production of the apples were assessed. Generally, the main changes in pectin composition associated with the loss of firmness during ripening in Jonagold apples were a loss of side chains neutral sugars, increased water solubility and decreased molar mass. Also, the activities of four important enzymes possibly involved in apple softening, β-galactosidase, α-arabinofuranosidase, polygalacturonase and pectin methylesterase, were measured. Pectin-related enzyme activities highly correlated with ethylene production, but not always with pectin modifications.

Ultrasound effects on the degradation kinetics, structure, and antioxidant activity of sea cucumber fucoidan

The effects of ultrasound on the molecular weight, structure, and antioxidant potential of a fucoidan found in Isostichopus badionotus were investigated. The results showed the molecular weight (Mw) of fucoidan decreased obviously after ultrasound treatment. Higher ultrasonic intensity, lower temperature, and lower fucoidan concentrations led to a more effective sonochemical effect. The kinetic model for fucoidan degradation fitted to 1/M(wt)-1/M(w0) = kt at the tested temperature. The optimized degradation conditions by response surface methodology (RSM) were temperature, 12 °C, and intensity, 508 W/cm². Structural analysis by FTIR and NMR indicated the fucoidan kept the linear tetrasaccharide repeating units as the original polysaccharides after the ultrasound treatment, with only slight destruction of the middle nonsulfated fucose units. Antioxidant activity assay showed the antioxidant activity was slightly improved by the ultrasound treatment. The results suggested that ultrasound treatment is an effective approach to decrease the M(w) of fucoidan with only minor structural destruction.

Effect of high-intensity ultrasound on the physicochemical properties and nanostructure of citrus pectin

BACKGROUND

Modified pectin has been found to have various biological activities. The preparation of modified pectin is generally accomplished by either chemical or enzymatic depolymerisation processes, but both methods have several disadvantages. Ultrasound treatment is simple and requires shorter times and lower temperatures than conventional techniques used for processing plant materials. In recent years the application of ultrasound to modify polysaccharides has received increasing attention. The objective of this study was to use ultrasound to modify citrus pectin.

RESULTS

The average molecular weight of citrus pectin decreased under different ultrasonic conditions. The average molecular weight decreased from 464 to 296 kDa after 30 min of sonication. The degree of methylation of citrus pectin changed slightly and its monosaccharide component remained unchanged when high-intensity ultrasound was applied. The reduced (Gal+Ara)/Rha ratio after ultrasonication suggested degradation in the neutral sugar side chains of citrus pectin. Atomic force microscopy results confirmed the degradation of citrus pectin chains by ultrasound at nanolevel.

CONCLUSION

Ultrasound is an effective way to pretreat or modify pectin. The degradation of citrus pectin is due to the cavitational effects of ultrasound. Thus ultrasound may be useful in establishing environmentally friendly extraction and modification technologies for pectin.

Galacturonosyltransferase 4 silencing alters pectin composition and carbon partitioning in tomato

Pectin is a main component of the plant cell wall and is the most complex family of polysaccharides in nature. Its composition is essential for the normal growth and morphology pattern, as demonstrated by pectin-defective mutant phenotypes. Besides this basic role in plant physiology, in tomato, pectin structure contributes to very important quality traits such as fruit firmness. Sixty-seven different enzymatic activities have been suggested to be required for pectin biosynthesis, but only a few genes have been identified and studied so far. This study characterized the tomato galacturonosyltransferase (GAUT) family and performed a detailed functional study of the GAUT4 gene. The tomato genome harbours all genes orthologous to those described previously in Arabidopsis thaliana, and a transcriptional profile revealed that the GAUT4 gene was expressed at higher levels in developing organs. GAUT4-silenced tomato plants exhibited an increment in vegetative biomass associated with palisade parenchyma enlargement. Silenced fruits showed an altered pectin composition and accumulated less starch along with a reduced amount of pectin, which coincided with an increase in firmness. Moreover, the harvest index was dramatically reduced as a consequence of the reduction in the fruit weight and number. Altogether, these results suggest that, beyond its role in pectin biosynthesis, GAUT4 interferes with carbon metabolism, partitioning, and allocation. Hence, this cell-wall-related gene seems to be key in determining plant growth and fruit production in tomato.

Cell wall composition of tomato fruit changes during development and inhibition of vesicle trafficking is associated with reduced pectin levels and reduced softening

Fruit development entails a multitude of biochemical changes leading up to the mature green stage. During this period the cell wall will undergo complex compositional and structural changes. Inhibition of genes encoding elements of the machinery involved in trafficking to the cell wall presents us with a useful tool to study these changes and their associated phenotypes. An antisense SlRab11a transgene has previously been shown to reduce ripening-associated fruit softening. SlRab11a is highly expressed during fruit development which is associated with a period of pectin influx into the wall. We have analysed the cell wall polysaccharides at different stages of growth and ripening of wild type and antisense SlRab11a transgenic tomato (Solanum lycopersicum cv, Ailsa Craig) fruit. Our results demonstrated intriguing changes in cell wall composition during the development and ripening of wild type Alisa Craig tomato fruit. Analysis of SlRab11a expression by TaqMan PCR showed it to be expressed most strongly during growth of the fruit, suggesting a possible role in cell wall deposition. The SlRab11a antisense fruit had a decreased proportion of pectin in the cell wall compared with the wild type. We suggest a new approach for modification of fruit shelf-life by changing cell wall deposition rather than cell wall hydrolytic enzymes.

Fibres from flax overproducing β-1,3-glucanase show increased accumulation of pectin and phenolics and thus higher antioxidant capacity

BACKGROUND

Recently, in order to improve the resistance of flax plants to pathogen infection, transgenic flax that overproduces β-1,3-glucanase was created. β-1,3-glucanase is a PR protein that hydrolyses the β-glucans, which are a major component of the cell wall in many groups of fungi. For this study, we used fourth-generation field-cultivated plants of the Fusarium -resistant transgenic line B14 to evaluate how overexpression of the β-1,3-glucanase gene influences the quantity, quality and composition of flax fibres, which are the main product obtained from flax straw.

RESULTS

Overproduction of β-1,3-glucanase did not affect the quantity of the fibre obtained from the flax straw and did not significantly alter the essential mechanical characteristics of the retted fibres. However, changes in the contents of the major components of the cell wall (cellulose, hemicellulose, pectin and lignin) were revealed. Overexpression of the β-1,3-glucanase gene resulted in higher cellulose, hemicellulose and pectin contents and a lower lignin content in the fibres. Increases in the uronic acid content in particular fractions (with the exception of the 1 M KOH-soluble fraction of hemicelluloses) and changes in the sugar composition of the cell wall were detected in the fibres of the transgenic flax when compared to the contents for the control plants. The callose content was lower in the fibres of the transgenic flax. Additionally, the analysis of phenolic compound contents in five fractions of the cell wall revealed important changes, which were reflected in the antioxidant potential of these fractions.

CONCLUSION

Overexpression of the β-1,3-glucanase gene has a significant influence on the biochemical composition of flax fibres. The constitutive overproduction of β-1,3-glucanase causes a decrease in the callose content, and the resulting excess glucose serves as a substrate for the production of other polysaccharides. The monosaccharide excess redirects the phenolic compounds to bind with polysaccharides instead of to partake in lignin synthesis. The mechanical properties of the transgenic fibres are strengthened by their improved biochemical composition, and the increased antioxidant potential of the fibres supports the potential use of transgenic flax fibres for biomedical applications.

Ultrasound effects on the degradation kinetics, structure and rheological properties of apple pectin

The effects of ultrasound on the molecular weight of apple pectin were investigated. The structure and rheological properties of the degradation products were also tentatively identified by High Performance Liquid Chromatography-Photodiode Array Detector (HPLC-PAD), Infrared spectroscopy (IR), Nuclear Magnetic Resonance spectroscopy (NMR) and Rheometer. The results indicated that the weight-average molecular weight of apple pectin decreased obviously after ultrasound treatment. The molecular weight of degradation products had a uniform and narrow distribution. Ultrasound intensity and temperature play an important role in the degradation reaction. Degradation kinetics model of apple pectin fitted to 1/M(t) - 1/M(0) = kt from 5 to 45 °C. The degree of methylation of apple pectin reduced according to IR analysis when ultrasound was applied. Ultrasound treatment could not alter the primary structure of apple pectin according to the results determined by HPLC, IR and NMR. Meanwhile, the viscosity of apple pectin was 10(3) times as large as that of ultrasound-treated apple pectin. The ultrasound-treated apple pectin showed predominantly viscous responses (G' < G") over the same frequency range. The results suggested that ultrasound provided a viable alternative method for the modification of pectin.

Use of FT-IR Spectra and PCA to the Bulk Characterization of Cell Wall Residues of Fruits and Vegetables Along a Fraction Process

This study focuses on the analysis of polysaccharide residues from the cell walls of fruits and vegetables: tomato, potato, pumpkin, carrot and celery root. An alcohol-insoluble residue was prepared from plant material by extraction using the hot ethyl alcohol method and then cell wall fractions soluble in trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetate, sodium carbonate and alkaline solution were sequentially extracted. Infrared spectroscopy combined with Fourier transform (FT-IR) was used to evaluate differences among cell wall residues and among species after each step of sequential extraction of pectins and hemicelluloses. Additionally, pectic substances were identified using an Automated Wet Chemistry Analyser. Principal component analysis (PCA) was applied to FT-IR spectra in two regions: 1,800–1,200 cm⁻¹ and 1,200–800 cm⁻¹ in order to distinguish different components of cell wall polysaccharides. This method also allowed us the possibility of highlighting the most important wavenumbers for each type of polysaccharide: 1,740, 1,610 and 1,240 cm⁻¹ denoting pectins or 1,370 and 1,317 cm⁻¹ denoting hemicelluloses and cellulose, respectively.

Effect of extraction time and temperature on the characteristics of loosely bound pectins from Japanese plum

The cell wall composition of Japanese plums (Prunus salicina) at six developmental stages was previously evaluated (Ponce et al., J. Agric. Food Chem. 2010, 58, 2562-2570). This fruit is an interesting source of pectins, polysaccharides of valuable functionality for pharmaceutical and food formulations. In the present work it was investigated how the different conditions for the aqueous extraction of pectins from Japanese plums affect the yield as well as their chemical and rheological characteristics. It has been determined that extraction with water at room temperature for periods longer than 2h did not produce additional increment of yield (12%) but decreased the average molecular weights of the extracted pectins. Pectins with a degree of methylation ≈40% with high viscosity in water and with adequate molecular weights (≈72,000) were obtained. Conversely, utilization of boiling water for extraction increased considerably the yields (33-38%) but the extracted pectins showed significant lower viscosity in water in spite of their higher molecular weights. The poorer thickening ability was associated to the lower proportion of arabinose residues present in the hairy regions of the pectin macromolecules extracted by hot water, which led the polymers to interact more transiently in a 2% w/v water solution.