Compositional changes in 'Bartlett' pear ( Pyrus communis L.) cell wall polysaccharides as affected by sunlight conditions

Antioxidant response and quality of sunburn Beurré D'Anjou pears (Pyrus communis L.)

Sunburn is a physiological fruit disorder induced by exposure to excessive solar radiation. This disorder leads to significant losses in the yield of marketable fruits by negatively affecting quality parameters such as maturity and external color of the fruits. The purpose of this work was to characterize the physiological and biochemical aspects related to oxidative metabolism in Beurré D'Anjou pear fruit with different sunburn levels. Fruits were collected and classified into three sunburn levels at harvest: no sunburn (S0), mild sunburn (S1), and moderate sunburn (S2). On sunburned area, the maturity indices were measured on the fruit flesh, while external color, photosynthetic and photoprotective pigments, total phenols, electrolyte leakage, lipid peroxidation, antioxidant capacity and antioxidant enzymatic activities were determined on fruit peel. The hue angle and saturation of peel color of pears with different sunburn levels showed significant reduction with increasing damage. These changes in peel color were associated with a reduction in chlorophyll content and variations in carotenoid and anthocyanin levels. Due to metabolic changes resulting from defense and adaptive responses to high solar radiation, sunburned tissues showed significantly increased firmness, soluble solids content, and starch degradation, and lower acidity compared to undamaged fruits. We observed also increased antioxidant capacity in the peel of S1 and S2 fruit, related to higher phenolic contents and increased SOD and APX activities. Consistent with previous reports in apple, our study demonstrates that sunburn affects pear fruit quality traits and maturity state by enhancing oxidative metabolism.

The antimicrobial activity of biogenic silver nanoparticles synthesized from extracts of Red and Green European pear cultivars

Green nanotechnology stands amongst the leading giants of innovation for the twenty first century technological advances. More interesting, is the use of natural products as reducing agents. These could be recyclable materials from fruits and vegetables to produce nanoparticles (NPs) with novel properties. In the current study, silver NPs (AgNPs) were synthesized using the water extracts from the peel and flesh of two Pyrus communis L. cultivars, namely, the Forelle (Red) Pears (RPE) and Packham Triumph (Green) Pears (GPE). The AgNPs were characterized by UV-Vis spectrophotometry, Dynamic Light Scattering (DLS), High Resolution Transmission Electron Microscopy (HRTEM) and Fourier Transform Infra-Red Spectroscopy (FTIR). The antibacterial activities of the AgNPs were evaluated using agar well diffusion and microdilution assays. The cytotoxicity of the AgNPs was investigated on a rat macrophage (RAW 264.7) cells using MTT assay. Both the RPE and GPE were capable of synthesizing the AgNPs at high temperatures (70 and 100 °C). The AgNPs exhibited antibacterial activity against the test strains, and also had low toxicity towards the RAW 264.7 cells. Thus, the synthesized AgNPs have a potentially viable use in bio-applications for treatment of bacterial infections.

Structural properties of diluted alkali-soluble pectin from Pyrus communis L. in water and salt solutions

The self-assembly and gelation of low-methoxyl diluted alkali-soluble pectin (LM DASP) from pear fruit (Pyrus communis L. cv. Conference) was studied in water and salt solutions (NaCl and CaCl₂, constant ionic strength) without pH adjustment at 20 °C. The samples at different LM DASP concentrations were characterized using rheological tests, Fourier-transform infrared spectroscopy, dual-angle dynamic light scattering and atomic force microscopy. LM DASP from pear fruit (Pyrus communis L.) showed gelling ability. The indices (aggregation index and shape factor) based on light scattering may be useful for the characterization of structural changes in polysaccharide suspension, particularly for the determination of a gel point. The results obtained may be important for the food, cosmetic and pharmaceutical industries where pectin is used as a texturizer, an encapsulating agent, a carrier of bioactive substances or a gelling agent.

Valorization of Bio-Residues from the Processing of Main Portuguese Fruit Crops: From Discarded Waste to Health Promoting Compounds

Food processing generates a large amount of bio-residues, which have become the focus of different studies aimed at valorizing this low-cost source of bioactive compounds. High fruit consumption is associated with beneficial health effects and, therefore, bio-waste and its constituents arouse therapeutic interest. The present work focuses on the main Portuguese fruit crops and revises (i) the chemical constituents of apple, orange, and pear pomace as potential sources of functional/bioactive compounds; (ii) the bioactive evidence and potential therapeutic use of bio-waste generated in the processing of the main Portuguese fruit crops; and (iii) potential applications in the food, nutraceutical, pharmaceutical, and cosmetics industries. The current evidence of the effect of these bio-residues as antioxidant, anti-inflammatory, and antimicrobial agents is also summarized. Conclusions of the revised data are that these bio-wastes hold great potential to be employed in specific nutritional and pharmaceutical applications.

Cell wall composition of alginate coated and pulsed light treated fresh-cut cantaloupes (Cucumis melo L. Var. Reticulatus Cv. Glamour) during chilled storage

This study was to investigate the effects of optimised alginate coating combined with repetitive pulsed light (RPL) on cell wall composition of fresh-cut cantaloupes during chilled storage. Fresh-cut cantaloupes were coated with alginate (1.86%, w/v) followed by RPL treatment (0.9 J cm^-2 at every 48 h up to 26 days) during storage of 36 days. Cell wall composition of fresh-cut cantaloupes was determined at every 12 days while microscopic analysis was conducted on day 2 and day 36. Alginate was effective in maintaining high pectin fractions of fresh-cut cantaloupes while RPL showed greater contribution in maintaining hemicellulose fraction. However, the combination of alginate and RPL was the most effective treatment to maintain the overall cell wall fractions that contributed to the cell wall integrity of fresh-cut cantaloupes during storage. The alginate + RPL samples also had the greatest cell turgidity and shape with well-defined cell walls at the end of storage.

Photooxidative stress activates a complex multigenic response integrating the phenylpropanoid pathway and ethylene, leading to lignin accumulation in apple (Malus domestica Borkh.) fruit

Photooxidative stress, when combined with elevated temperatures, triggers various defense mechanisms leading to physiological, biochemical, and morphological changes in fruit tissue. Furthermore, during sun damage, apple fruit undergo textural changes characterized by high flesh firmness compared to unexposed fruit. Fuji and Royal Gala apples were suddenly exposed to sunlight on the tree and then sampled for up to 29 days. Cell wall components and lignin biosynthetic pathway analyses were carried out on the fruit tissue. At harvest, Fuji apples with different sun exposure levels, such as exposed to direct sunlight (Exp), shaded (Non-Exp), and with severe sun damage (Sev), were also characterized. In fruit suddenly exposed to sunlight, the expression levels of phenylpropanoid-related genes, phenylalanine ammonia lyase (MdPAL), chalcone synthase (MdCHS), and flavanone-3-hydroxylase (MdF3H), were upregulated in the skin and flesh of Exp and Sev. Exposure had little effect on the lignin-related genes caffeic acid O-methyltransferase 1 (MdCOMT1) and cinnamyl alcohol dehydrogenase (MdCAD) in the skin; however, the expression of these genes was highly induced in the flesh of Exp and Sev in both cultivars. Lignin deposition increased significantly in skin with sun injury (Sev); in flesh, this increase occurred late during the stress treatment. Additionally, the ethylene biosynthesis genes 1-aminocyclopropane-1-carboxylate synthase (MdACS) and 1-aminocyclopropane-1-carboxylate oxidase (MdACO) were highly expressed in the skin and flesh tissues but were more upregulated in Sev than in Exp during the time-course experiment, which paralleled the induction of the phenylpropanoid pathway and lignin accumulation. At harvest, flesh from Sev fruit exhibited higher firmness than that from Non-Exp and Exp fruit, although no differences were observed in the alcohol-insoluble residues (AIR) among groups. The fractionation of cell wall polymers revealed an increase in the uronic acid contents of the water-soluble pectin fraction (WSF) in Exp and Sev tissues compared to Non-Exp tissues, while the other pectin-rich fractions, that is, CDTA-soluble (CSF) and Na2CO3-soluble (NSF), were increased only in Sev. The amount of hemicellulose and cellulose did not differ among fruit conditions. These findings suggest that increases in the flesh firmness of apples can be promoted by photooxidative stress, which is associated with the induction of lignin accumulation in the skin and flesh of stressed fruit, with the involvement of stress phytohormones such as ethylene.

Canopy attachment position influences metabolism and peel constituency of European pear fruit

BACKGROUND

Inconsistent pear fruit ripening resulting from variable harvest maturity within tree canopies can contribute to postharvest losses through senescence and spoilage that would otherwise be effectively managed using crop protectant and storage regimes. Because those inconsistencies are likely based on metabolic differences, non-targeted metabolic profiling peel of 'd'Anjou' pears harvested from the external or internal canopy was used to determine the breadth of difference and link metabolites with canopy position during long-term controlled atmosphere storage.

RESULTS

Differences were widespread, encompassing everything from expected distinctions in flavonol glycoside levels between peel of fruit from external and internal canopy positions to increased aroma volatile production and sucrose hydrolysis with ripening. Some of the most substantial differences were in levels of triterpene and phenolic peel cuticle components among which acyl esters of ursolic acid and fatty acyl esters of p-coumaryl alcohol were higher in the cuticle of fruit from external tree positions, and acyl esters of α-amyrin were elevated in peel of fruit from internal positions. Possibly the most substantial dissimilarities were those that were directly related to fruit quality. Phytosterol conjugates and sesquiterpenes related to elevated superficial scald risk were higher in pears from external positions which were to be potentially rendered unmarketable by superficial scald. Other metabolites associated with fruit aroma and flavor became more prevalent in external fruit peel as ripening progressed and, likewise, with differential soluble solids and ethylene levels, suggesting the final product not only ripens differentially but the final fruit quality following ripening is actually different based on the tree position.

CONCLUSIONS

Given the impact tree position appears to have on the most intrinsic aspects of ripening and quality, every supply chain management strategy would likely lead to diverse storage outcomes among fruit from most orchards, especially those with large canopies. Metabolites consistently associated with peel of fruit from a particular canopy position may provide targets for non-destructive pre-storage sorting used to reduce losses contributed by this inconsistency.

Phytohormone Interaction Modulating Fruit Responses to Photooxidative and Heat Stress on Apple (Malus domestica Borkh.)

Sun-related physiological disorders such as sun damage on apples (Malus domestica Borkh) are caused by cumulative photooxidative and heat stress during their growing season triggering morphological, physiological, and biochemical changes in fruit tissues not only while it is on the tree but also after it has been harvested. The objective of the work was to establish the interaction of auxin (indole-3-acetic acid; IAA), abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) and its precursor ACC (free and conjugated, MACC) during development of sun-injury-related disorders pre- and post-harvest on apples. Peel tissue was extracted from fruit growing under different sun exposures (Non-exposed, NE; Exposed, EX) and with sun injury symptoms (Moderate, Mod). Sampling was carried out every 15 days from 75 days after full bloom (DAFB) until 120 days post-harvest in cold storage (1°C, > 90%RH). Concentrations of IAA, ABA, JA, SA, were determined using UHPLC mass spectrometry, and ET and ACC (free and conjugated MACC) using gas chromatography. IAA was found not to be related directly to sun injury development, but it decreased 60% in sun exposed tissue, and during fruit development. ABA, JA, SA, and ethylene concentrations were significantly higher (P ≤ 0.05) in Mod tissue, but their concentration, except for ethylene, were not affected by sun exposure. ACC and MACC concentrations increased until 105 DAFB in all sun exposure categories. During post-harvest, ethylene climacteric peak was delayed on EX compared to Mod. ABA and SA concentrations remained stable throughout storage in both tissue. JA dramatically increased post-harvest in both EX and Mod tissue, and orchards, confirming its role in low temperature tolerance. The results suggest that ABA, JA, and SA together with ethylene are modulating some of the abiotic stress defense responses on sun-exposed fruit during photooxidative and heat stress on the tree.

Characterization and quantification of fruit phenolic compounds of European and Tunisian pear cultivars

The flesh and peel of 19 pear cultivars (8 Tunisian dessert cultivars, 8 European dessert cultivars and 3 French perry pear cultivars) were studied for their phenolic composition. Phenolic compounds were identified by HPLC/ESI-MS² and individually quantified by HPLC-DAD. Five classes of polyphenols were present: flavan-3-ols, phenolic acids, flavonols, anthocyanins and simple phenolics (hydroquinones). The total phenolic content ranged between 0.1g/kg Fresh Weight (FW) ('Conference' cultivar) and 8.6g/kg FW ('Plant De Blanc' cultivar) in the flesh and between 1.6g/kg FW ('William vert' cultivar) and 40.4g/kg FW ('Arbi Chiheb' cultivar) in the peel. Procyanidins, analyzed after thioacidolysis, were the main phenolic compounds in all pear cultivars either in the pulp or the peel, their constitutive units being essentially (-)-epicatechin. Tunisian dessert pears and French perry pears are richer in procyanidins with very high degree of polymerization (>100) for Tunisian pears. Peel procyanidins were less polymerized (from 4 to 20). Pear peel phenolic profile was more complex especially for Tunisian cultivars, with flavonols and in some cultivars anthocyanins.

Cell Wall Metabolism in Response to Abiotic Stress

This review focuses on the responses of the plant cell wall to several abiotic stresses including drought, flooding, heat, cold, salt, heavy metals, light, and air pollutants. The effects of stress on cell wall metabolism are discussed at the physiological (morphogenic), transcriptomic, proteomic and biochemical levels. The analysis of a large set of data shows that the plant response is highly complex. The overall effects of most abiotic stress are often dependent on the plant species, the genotype, the age of the plant, the timing of the stress application, and the intensity of this stress. This shows the difficulty of identifying a common pattern of stress response in cell wall architecture that could enable adaptation and/or resistance to abiotic stress. However, in most cases, two main mechanisms can be highlighted: (i) an increased level in xyloglucan endotransglucosylase/hydrolase (XTH) and expansin proteins, associated with an increase in the degree of rhamnogalacturonan I branching that maintains cell wall plasticity and (ii) an increased cell wall thickening by reinforcement of the secondary wall with hemicellulose and lignin deposition. Taken together, these results show the need to undertake large-scale analyses, using multidisciplinary approaches, to unravel the consequences of stress on the cell wall. This will help identify the key components that could be targeted to improve biomass production under stress conditions.

A Japanese plum α-l-arabinofuranosidase/β-D-xylosidase gene is developmentally regulated by alternative splicing

A full-length cDNA clone named PsARF/XYL was obtained from Prunus salicina Lindl., and determined to encode a putative α-l-arabinofuranosidase/β-d-xylosidase belonging to glycoside hydrolase (GH, EC 3.2.1.-) family 3. Two related PsARF/XYL cDNAs were amplified, one from a fully-spliced transcript (PsARF/XYLa) and another one from an intron-retained transcript (PsARF/XYLb). The protein deduced from PsARF/XYLb is a truncated peptide at C-terminus that conserves the active-site amino acid sequence. High levels of PsARF/XYLa and PsARF/XYLb transcripts are detectable in several plant tissues. PsARF/XYLb transcripts accumulate progressively during the phase of exponential fruit growth but they become barely noticeable during on-tree ripening, or after a 6-h exposure of preclimacteric full-size plums to ethylene. In contrast, PsARF/XYLa is expressed throughout fruit development, and transcript accumulation parallels the climacteric rise in ethylene production during ripening. PsARF/XYLa expression is strongly induced in preclimacteric full-size plums after a 6-h treatment with physiologically active concentrations of ethylene. These findings suggest that PsARF/XYL gene is post-transcriptionally regulated by alternative splicing during development and that ethylene may be involved in this regulation. The isolation of a partial cDNA clone, PsARF1, is also reported. It encodes a putative cell-wall α-l-arabinofuranosidase, and its transcription is rapidly inhibited by ethylene in mature green plums.

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.