Quality attributes and cell wall properties of strawberries (Fragaria annanassa Duch.) under calcium chloride treatment

Application of Isochoric Impregnation: Effects on Microbial and Physicochemical Parameters and Shelf Life of Strawberries Stored Under Refrigeration

This study evaluates the effectiveness of isochoric impregnation during isochoric cold storage in extending the shelf life of strawberries. Strawberries in two different impregnation solutions-(1) sucrose solution and (2) sucrose solution containing calcium chloride (CaCl2) and ascorbic acid (AA)-were first stored in an isochoric chamber at -2 °C/48 MPa for 1 week, followed by refrigeration at 4 °C for 3 weeks. For comparison, strawberries were also immersed in each solution for 1 week at 4 °C then refrigerated at 4 °C for 3 weeks. Additionally, a control group of fresh strawberries was stored at 4 °C for 4 weeks. The quality of the strawberries was assessed at 1-week intervals throughout the storage period. Isochoric cold storage effectively inhibited microbial growth and reduced the weight loss of the strawberries compared to refrigerated storage. Also, isochoric cold storage resulted in strawberries that retained their color attributes, whereas refrigeration led to a significant change in their color attributes. Isochoric impregnated strawberries in the sucrose solution containing CaCl2 and AA showed better mechanical properties and higher nutrient contents (anthocyanins and ascorbic acid) than those impregnated in the sucrose solution, impregnated in the solutions at 4 °C, and refrigerated with no impregnation (control). The results demonstrated that isochoric cold storage in a solution containing sucrose, CaCl2, and ascorbic acid effectively maintained the quality of the strawberries, as indicated by parameters such as firmness, color retention, and reduced microbial growth. This method extended the strawberries' shelf life by up to 4 weeks.

Impact of postharvest calcium chloride treatments on decay rate and physicochemical quality properties in strawberry fruit

BACKGROUND

Post-harvest losses cause significant product losses in the world, which leads to food waste. Therefore, it is of great importance for people to have access to sufficient amounts of products by increasing the storage period of fruits with applications such as post-harvest calcium chloride (CaCl2). In this study, the effect of calcium chloride (CaCl2) on physical quality parameters and bioactive contents of stored strawberry fruit (Albion cv.) was investigated. Accordingly, strawberries were treated with 2%, 4% and 6% CaCl2 before storage and stored for 15 days (0 ± 0.5 °C and 90 ± 5% RH). Analyses and measurements were conducted every 5 days during the storage period.Weight loss, decay rate, soluble solids content (SSC), acidity, pH, respiration rate, organic acids (malic, citric, ascorbic, fumaric, oxalic, succinic and tartaric) and phenolic compounds (catechin, chlorogenic, ferulic, gallic, o-coumaric, p-coumaric, protocatechuic, quercetin, rutin and syringic) were analyzed as quality parameters during storage.

RESULTS

In the study, in general, the best values were observed in 6% CaCl2-treated fruits in terms of weight loss, SSC, TA, decay and respiration rates, although they varied according to different storage periods. Similarly, in terms of phenolic compounds, organic acids and vitamin C, 6% CaCl2-treated fruits had significantly better prevention of quality losses. In addition, the most common phenolic compound of strawberry fruits was gallic acid, followed by chlorogenic acid and catechin, respectively. On the other hand, the predominant organic acid observed in the fruits was malic acid, followed by citric acid, succinic acid and oxalic acid, respectively.

CONCLUSIONS

In this study, it was observed that CaCl2 applications more effectively prevented weight loss and decay rate by reducing the respiration rate compared to the control group at the end of the storage period (15th day). It was concluded that, particularly, the 6% CaCl2 dose can be used as an important treatment to extend storage life by preserving fruit quality and biochemical changes.

Alleviation of the degradation of cell wall pectin contributes to the maintenance of integrity of papaya (Carica papaya L.) fruit tissue during abnormal chilling injury behavior

Papaya (Carica papaya L.) is highly susceptible to chilling injury (CI), which primarily causes surface pitting, black scald, susceptibility to fungal infection, and the breakdown of tissue. It developed rapidly at 6 °C but was significantly suppressed at 1 °C, which indicated that the papaya tissue was more solid at a lower temperature. This rare phenomenon is considered to be abnormal CI behavior. The maintenance of fruit tissue integrity during abnormal CI behavior may be related to modifications of the cell wall pectin. The modifications of cell wall pectin were studied during storage at 1 and 6 °C. Storage at 1 °C alleviated the progression of CI and inhibited the degradation of pectin components and cell wall structure of papaya fruit. The increase in water-soluble pectin and the solubilization of cyclohexanediamine tetraacetic acid- (CDTA-) and sodium carbonate (Na2CO3)-soluble pectin was limited at 1 °C. Storage at this temperature limited the detachment of linear backbone chains and minimized the degradation of branching and reticular structure in the pectin molecules. Storage at this temperature also delayed the decrease in the size of pectin backbone and helped to prevent the loss of neutral sugars from the pectin side chains. Thus, alleviation of the degradation of cell wall pectin contributes to the structural integrity of the cell wall and thus helps the maintenance of the tissue integrity of papaya at 1 °C.

Foliar spraying of boron prolongs preservation period of strawberry fruits by altering boron form and boron distribution in cell

Boron (B), an essential micronutrient for fruit development, also plays a crucial role in maintaining the shelf life of strawberries (Fragaria ananassa Duch.) by affecting cell wall structure and components. We investigated the distribution pattern of B within cells and cell walls in strawberry fruits under different B levels and revealed the relationship between the B distribution in cell walls and fruit firmness after harvesting. Foliar spraying of 0.1% H3BO3 promoted the growth of strawberry seedlings and improved fruit yield and flesh firmness by 45.7% and 25.6%. During the fruit softening and decay process, the content of bound B and cell wall-B decreased while more B was allocated to the protoplast and apoplast. The changes in B distribution in cells were attributed to cell damage during fruit decay, and B extended the freshness period of the fruits by alleviating the decrease of B distribution in cell walls. After leaving the fruits at room temperature for 10 h, the B content in different cell wall components significantly decreased, while foliar spraying of B alleviated the reduction of B content in covalently bound pectin (CBP), cellulose, and hemicellulose. Meanwhile, B spraying on fruit decreased the activity of cell wall degradation enzymes, including polygalacturonase (PG) and pectin lyase (PL), by 20.2% and 38.1%, while enhancing the demethylation of pectin by increasing pectin methylesterase (PME) activity from 21.6 U/g to 25.7 U/g. Thus, foliar spraying of 0.1% H3BO3 enhances the cross-linking of B with cell wall components and maintains cell wall structure, thereby prolonging the shelf life of strawberry fruits.

Ectopic Expression of MADS-Box Transcription Factor VvAGL12 from Grape Promotes Early Flowering, Plant Growth, and Production by Regulating Cell-Wall Architecture in Arabidopsis

The MADS-box family, a substantial group of plant transcription factors, crucially regulates plant growth and development. Although the functions of AGL12-like subgroups have been elucidated in Arabidopsis, rice, and walnut, their roles in grapes remain unexplored. In this study, we isolated VvAGL12, a member of the grape MADS-box group, and investigated its impact on plant growth and biomass production. VvAGL12 was found to localize in the nucleus and exhibit expression in both vegetative and reproductive organs. We introduced VvAGL12 into Arabidopsis thaliana ecotype Columbia-0 and an agl12 mutant. The resulting phenotypes in the agl12 mutant, complementary line, and overexpressed line underscored VvAGL12's ability to promote early flowering, augment plant growth, and enhance production. This was evident from the improved fresh weight, root length, plant height, and seed production, as well as the reduced flowering time. Subsequent transcriptome analysis revealed significant alterations in the expression of genes associated with cell-wall modification and flowering in the transgenic plants. In summary, the findings highlight VvAGL12's pivotal role in the regulation of flowering timing, overall plant growth, and development. This study offers valuable insights, serving as a reference for understanding the influence of the VvAGL12 gene in other plant species and addressing yield-related challenges.

Hyperspectral imaging for estimating leaf, flower, and fruit macronutrient concentrations and predicting strawberry yields

Managing the nutritional status of strawberry plants is critical for optimizing yield. This study evaluated the potential of hyperspectral imaging (400-1,000 nm) to estimate nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca) concentrations in strawberry leaves, flowers, unripe fruit, and ripe fruit and to predict plant yield. Partial least squares regression (PLSR) models were developed to estimate nutrient concentrations. The determination coefficient of prediction (R2P) and ratio of performance to deviation (RPD) were used to evaluate prediction accuracy, which often proved to be greater for leaves, flowers, and unripe fruit than for ripe fruit. The prediction accuracies for N concentration were R2P = 0.64, 0.60, 0.81, and 0.30, and RPD = 1.64, 1.59, 2.64, and 1.31, for leaves, flowers, unripe fruit, and ripe fruit, respectively. Prediction accuracies for Ca concentrations were R2P = 0.70, 0.62, 0.61, and 0.03, and RPD = 1.77, 1.63, 1.60, and 1.15, for the same respective plant parts. Yield and fruit mass only had significant linear relationships with the Difference Vegetation Index (R2 = 0.256 and 0.266, respectively) among the eleven vegetation indices tested. Hyperspectral imaging showed potential for estimating nutrient status in strawberry crops. This technology will assist growers to make rapid nutrient-management decisions, allowing for optimal yield and quality.

Bacterial cellulose nanofibers used as nanofillers improved the fresh-keeping performance of gelatin-based edible coating for fresh-cut apples

In this study, bacterial cellulose nanofibers (BCNs) (0%, 1%, 2%, and 3%) were used as nanofillers to prepare gelatin-based edible films, and their physical properties and fresh-keeping performance were investigated. The microstructure observation showed that the BCNs were well dispersed in the gelatin-based edible films and the surface roughness of the films increased with the increase of BCNs content. X-ray diffraction and thermogravimetric analysis showed that the crystallinity and thermal stability of the film were significantly increased with the increase of BCNs. Fourier-transform infrared spectroscopy analysis suggested that hydrogen bond interactions occurred between BCNs and gelatin polymers, leading to improved mechanical properties with the increase of BCNs content. Furthermore, the barrier performance was also improved with the increase of BCNs content, where gelatin-based edible films with 2% BCNs showed the best mechanical property. Meanwhile, the gelatin-based film-forming solutions (FFSs) containing different BCNs were coated on the fresh-cut apples and the corresponding fresh-keeping performance was investigated. The results showed that the fresh-keeping parameters of fresh-cut apples coated with FFSs containing BCNs were better as compared with those of pure gelatin FFSs. Moreover, the fresh-keeping parameters were improved with the increase of BCNs, especially the FFSs containing 2% BCNs that showed the best fresh-keeping parameters. Therefore, BCNs, used as nanofillers, are an excellent enhancer to improve the fresh-keeping performance of the gelatin-based edible coating, showing a promising potential application in the food preservation field.

Postharvest Calcium Chloride Treatment Strengthens Cell Wall Structure to Maintain Litchi Fruit Quality

Litchi (Litchi chinensis Sonn.) fruit deterioration occurs rapidly after harvest and is characterized by pericarp browning, pulp softening, and decay. In this study, we found that calcium chloride (CaCl₂) treatment (5 g L^-1 CaCl₂ solution vacuum infiltration for 5 min) affected the cell wall component contents and cell wall-degrading enzyme activities of litchi fruit during storage at room temperature. CaCl₂ treatment significantly increased the contents of Ca²⁺ and cellulose, while it decreased the water-soluble pectin content, and the activities of polygalacturonase, β-galactosidase, and cellulase in the litchi pericarp. Meanwhile, the treatment resulted in significantly increased contents of Ca²⁺, water-soluble pectin, ionic-soluble pectin, covalent-soluble pectin and hemicellulose, and upregulated activities of pectinesterase and β-galactosidase, while significantly decreasing the activities of polygalacturonase and cellulase in litchi pulp. The above results indicate that CaCl₂ treatment strengthened the cell wall structure of litchi fruit. More importantly, the enzymatic browning of the pericarp, softening of the pulp, and disease incidence were delayed. The treatment had a more pronounced effect on the pericarp than on the pulp. We consider CaCl₂ treatment to be a safe and effective treatment for maintaining the postharvest quality of litchi fruit.

Effect of Edible Coating Enriched with Natural Antioxidant Extract and Bergamot Essential Oil on the Shelf Life of Strawberries

In this study, the effects of the application of edible coatings on the shelf life of the strawberry were evaluated, with the aim of extending the fruit's availability and shelf life while preserving its qualitative characteristics. In particular, the application of edible coatings enriched with a natural antioxidant to strawberries was evaluated for their physicochemical, microbial, and structural properties, during a storage period (up to 14 days) at refrigerated temperature. The experimental plan provided the formulation for edible coatings enriched with different concentrations of a natural antioxidant extract obtained from bergamot (Citrus bergamia Risso) pomace (1, 2.5, and 5%), bergamot essential oil (0.1% v/v and 0.2% v/v), and a synthetic antioxidant, butylated hydroxytoluene (BHT, 100 ppm). Moreover, a control test with untreated strawberries was considered. The enriched gum Arabic coatings provided good results related to the preservation of the qualitative parameters of the strawberries. The samples coated with the antioxidant extract (2.5%, sample D) and bergamot essential oil (0.1%, sample F) showed the best maintenance of the qualitative parameters after 14 days, showing lower decay rates (36% D and 27% F), good acceptability by consumers (between 5 and 6), and good retention of ascorbic acid (>30 mg 100 g^-1).

Transcriptomic and metabolomic profiling of strawberry during postharvest cooling and heat storage

Temperature is one of the most important factors regarding fruit postharvest, however its effects in the strawberry fruits quality in postharvest remains to be evaluated. In this study, the effects of cold and heat storage temperature on fruit quality of 'Benihoppe' strawberry were performed. The results showed that different temperatures could affect the metabolism of hormone, anthocyanin, reactive oxygen species (ROS), and transcription level of responsive factors. The synthesis of terpenoids, amino acids, and phenylpropanoids in strawberries were also changed under different temperatures, which finally changed the quality characteristics of the fruit. We found HSF20 (YZ1)-overexpressed fruits were sensitive to cold and heat conditions but CBF/NF-Y (YZ9)-overexpressed fruits promoted coloring under cold treatment. This study clarified the effect of postharvest cooling and heat treatments on quality and transcriptional mechanism of strawberries fruits. Moreover, these results provided an experimental basis for further research on improving the quality of strawberry berries during postharvest periods.

Effects of electrolysed water and levulinic acid combination on microbial safety and polysaccharide nanostructure of organic strawberry

This study aimed to better understand the effects of acidic electrolysed water (AEW, 4 mg/L) and levulinic acid (LA, food grade, 2%) combination on organic strawberry over 7 days. This combined method reduced the population of strawberry's natural microbiota by 1-2 log CFU/g and kept the level of inoculated Escherichia coli O157:H7 and Salmonella below the detection limit (2 log CFU/g) during the whole storage period. Meanwhile, AEW + LA did not affect the physicochemical qualities of strawberries significantly, maintaining most texture and biochemical attributes at an acceptable level (e.g., firmness, colour, soluble solids content and organic acid content). Atomic force microscopy further revealed that the treatment containing LA preserved the sodium carbonate soluble pectin (SSP) nanostructure best by maintaining their length and height, and slowed the breakdown of SSP chains by promoting acid-induced bonding and soluble pectin precipitation. These results demonstrated that low concentration AEW and LA combination is a promising sanitising approach for organic strawberry preservation.

The Effect of Pre- and Postharvest Calcium Gluconate Treatments on Physicochemical Characteristics and Bioactive Compounds of Sweet Cherry during Cold Storage

The effects of pre- and postharvest calcium gluconate (Ca-Glu) treatments on some physicochemical characteristics and bioactive compounds of sweet cherry cv. Sweetheart during cold storage were investigated. For preharvest treatments, the Ca-Glu (1%) solution was applied to the cherry trees two times at 21 and 35 days after full bloom stage. Control trees were sprayed with distilled water at the same days. Sweet cherries, sprayed with and without Ca-Glu, were dipped into cold water (4°C) containing calcium gluconate (1%) for 30 s and only in cold water (4°C) as control, after harvest Following each treatment, cherries were placed in plastic boxes and stored at 1 ± 0.5 °C and 90 ± 5% relative humidity for 3 weeks. The weight losses of cherries increased over time but calcium (Ca) treatments, especially pre-and postharvest combination, limited these increases compared to control groups. The best result for suppressing the respiration rate of cherries was also obtained from combined treatment. Moreover, combined treatment delayed the losses of titratable acidity, fruit firmness, decay rate and sensory quality in sweet cherries during storage comparison with the pre or postharvest application of Ca-Glu alone. The effect of Ca-Clu treatments on stem chlorophyll content and antioxidant activity was not significant. Preharvest and combined treatments retarded the loss of ascorbic acid content of cherries compared to postharvest and control treatments. The total phenolic and anthocyanin content increased regularly throughout storage, regardless of treatment; however, Ca treatments delayed the accumulation of these compounds. As a result, the combined Ca-Glu treatment could be a promising method for maintaining some physicochemical characteristics and bioactive compounds in sweet cherries during cold storage.

Impact of Chitosan, Sucrose, Glucose, and Fructose on the Postharvest Decay, Quality, Enzyme Activity, and Defense-Related Gene Expression of Strawberries

Strawberry is one of the most highly consumed fruits worldwide, but is extremely perishable. This study systematically compared the effects of chitosan, sucrose, glucose, and fructose immersion on the physiology and disease development in harvested strawberries. After storage at 15 °C for 9 days, all sugar treatment groups had significantly higher total soluble solids and total anthocyanin content than those of the control group. All sugar treatment groups inhibited malondialdehyde accumulation. At the end of the storage, chitosan, glucose, and fructose maintained higher superoxide dismutase activity and chitosan maintained higher catalase activity. The chitosan and glucose groups had lowest fruit decay index, followed by sucrose and fructose groups. The fruit firmness and luster were better maintained in the glucose group. Furthermore, genes related to sucrose metabolism (e.g., FaSUS1 and FaSUS2), titratable acidity accumulation (e.g., FaMDH1, FaMDH2, FaCS1, and FaCS2), disease resistance (e.g., FaPGIP1, FaWRKY1, and FaWRKY33) and to anabolic jasmonic acid and abscisic acid pathways (e.g., FaJAZ1, FaJAZ2, FaOPR3, FaNCED1, and FaNCED2) were regulated to varying degrees, suggesting that chitosan and glucose participate in plants’ immune signaling networks and regulate disease resistance in fruit through hormone pathways. The findings provide new insights into the physiological regulation of harvested strawberries.

Development of gum arabic-based nanocomposite films reinforced with cellulose nanocrystals for strawberry preservation

The present study aimed to develop a new bio-nanocomposite film based on gum arabic (GA) reinforced with cellulose nanocrystals (CNC). CNC was successfully fabricated and its microstructure was characterized. Subsequently, the effects of CNC on the rheological, physicochemical and functional properties of GA-based films were systematically evaluated. Results showed that the tensile strength (2.21 MPa) and elongation at break (62.79%) of film incorporated with 4% (w/w) CNC were effectively increased compared with the GA film (1.08 MPa and 42.50%). Additionally, 4% CNC reduced the water vapor and oxygen permeability by 10.61% and 25.30% respectively, while improved the ultraviolet light barrier and thermal stability of film. The well dispersion and filling effect of nanofiller contributed to form a compact and homogeneous film structure. Furthermore, the film containing 4% CNC decreased the weight loss of strawberries by 23.80% compared with the control group, thus delaying the deterioration of strawberry quality during storage.

Effect of temperature fluctuation on colour change and softening of postharvest sweet cherry

The inevitable temperature fluctuation during cold chain transport accelerates the colour change and softening of postharvest sweet cherry, leading to further deterioration of quality and decline of the marketable value of cherries. The influences of temperature fluctuation on the contents of total anthocyanin, phenolic, malondialdehyde, and sodium carbonate-soluble pectin (SSP), as well as the activities of polyphenoloxidase (PPO) and peroxidase (POD) in sweet cherry, were assessed. In addition, the effects of temperature fluctuation on the activities of polygalacturonase (PG), pectin methyl esterase (PME), and beta-galactosidase (β-Gal) activities, and the paPG, paPME, and paPME genes expression were studied. The evolution of SSP nano-morphology was measured by atomic force microscopy. The results showed that the temperature fluctuation promoted anthocyanin synthesis, phenolic metabolism, and malondialdehyde accumulation, which immediately affected the brightness (6.2% lower than that of the cherry stored at 5 °C) of sweet cherry. Temperature fluctuation also led to a significant increase in POD and PPO activities during subsequent isothermal storage, accelerating the colour change (24.8% more than that of the cherry stored at 5 °C), which almost reached the level observed during constant 10 °C storage. In addition, temperature fluctuation not only affected the firmness (13.7% lower than that of the cherry stored at a constant temperature of 5 °C) of fruit immediately, but also, during subsequent isothermal storage, accelerated the deterioration of firmness (19.6% lower than that of the cherry stored at a constant temperature of 5 °C). This could be explained by temperature fluctuation inducing the upregulation of paPG1-3, paPME3, and paPME4 expression, which led to a 3.5 and 1.5-fold increase in PG and PME activity, respectively. This led to degradation of the aggregated SSP to its nanostructural basic units. Furthermore, temperature fluctuation resulted in upregulated expression of paβ-Gal1 and paβ-Gal3 and enhanced β-Gal activity during subsequent isothermal storage. The results provide theoretical guidance for the transportation, storage, and preservation of postharvest sweet cherry.

The inevitable temperature fluctuation induced anthocyanin synthesis, phenolic metabolism, and alkali-soluble pectin degradation, which lead to sweet cherry enzymatic browning and softening.

The Quality Evaluation of Postharvest Strawberries Stored in Nano-Ag Packages at Refrigeration Temperature

Different percentages (0%, 1%, 5%, and 10%) of nano-Ag particles were added to polylactic acid (PLA) to make an active nanocomposite packaging film. Strawberries were packaged by the nanocomposite films and stored at 4 ± 1 °C for 10 days. The freshness of strawberries was assessed by regularly measuring the physicochemical properties of the strawberries in each packaging film. The difference in the freshness of strawberries was evaluated by determining the following parameter changes: weight loss, hardness, soluble solids, titratable acid, color, vitamin C, total phenol, free radical scavenging activity, peroxidase activity, and sensory evaluation. The results revealed that the active nanocomposite packaging film has better preservation effect when compared with pure PLA film. Its preservation effect is mainly reflected in the more effective reduction of vitamin C loss, delaying the decline of total phenols and 1-Diphenyl-2-picrylhydrazyl (DPPH) in strawberries. It also showed better physical properties. The results showed that the PLA nanocomposite packaging film could effectively preserve freshness of strawberries.

Ultrasound enhances calcium absorption of jujube fruit by regulating the cellular calcium distribution and metabolism of cell wall polysaccharides

BACKGROUND

Ultrasound has been applied in fruit pre-washing processes. However, it is not sufficient to protect fruit from pathogenic infection throughout the entire storage period, and sometimes ultrasound causes tissue damage. The goal of this study was to investigate the effects of calcium chloride (CaCl₂ , 10 g L^-1 ) and ultrasound (350 W at 40 kHz), separately and in combination, on jujube fruit quality, antioxidant status, tissue Ca²⁺ content and distribution along with cell wall metabolism at 20 °C for 6 days.

RESULTS

All three treatments significantly maintained fruit firmness and peel color, reduced respiration rate, decay incidence, superoxide anion, hydrogen peroxide and malondialdehyde and preserved higher enzymatic (superoxide dismutase, catalase and peroxidase) and non-enzymatic (ascorbic acid and glutathione) antioxidants compared with the control. Moreover, the combined treatment was more effective in increasing tissue Ca²⁺ content and distribution, inhibiting the generation of water-soluble and CDTA-soluble pectin fractions, delaying the solubilization of Na₂ CO₃ -soluble pectin and having lower activities of cell wall-modifying enzymes (polygalacturonase and pectate lyase) during storage.

CONCLUSION

These results demonstrated that the combination of CaCl₂ and ultrasound has potential commercial application to extend the shelf life of jujube fruit by facilitating Ca²⁺ absorption and stabilizing the cell wall structure. © 2017 Society of Chemical Industry.

Structural changes in cell wall pectins during strawberry fruit development

Strawberry (Fragaria × anannasa Duch.) is one of the most important soft fruit. Rapid loss of firmness occurs during the ripening process, resulting in a short shelf life and high economic losses. To get insight into the role of pectin matrix in the softening process, cell walls from strawberry fruit at two developmental stages, unripe-green and ripe-red, were extracted and sequentially fractionated with different solvents to obtain fractions enriched in a specific component. The yield of cell wall material as well as the per fresh weight contents of the different fractions decreased in ripe fruit. The largest reduction was observed in the pectic fractions extracted with a chelating agent (trans-1,2- diaminocyclohexane-N,N,N'N'-tetraacetic acid, CDTA fraction) and those covalently bound to the wall (extracted with Na₂CO₃). Uronic acid content of these two fractions also decreased significantly during ripening, but the amount of soluble pectins extracted with phenol:acetic acid:water (PAW) and water increased in ripe fruit. Fourier transform infrared spectroscopy of the different fractions showed that the degree of esterification decreased in CDTA pectins but increased in soluble fractions at ripen stage. The chromatographic analysis of pectin fractions by gel filtration revealed that CDTA, water and, mainly PAW polyuronides were depolymerised in ripe fruit. By contrast, the size of Na₂CO₃ pectins was not modified. The nanostructural characteristics of CDTA and Na₂CO₃ pectins were analysed by atomic force microscopy (AFM). Isolated pectic chains present in the CDTA fractions were significantly longer and more branched in samples from green fruit than those from red fruit. No differences in contour length were observed in Na₂CO₃ strands between samples of both stages. However, the percentage of branched chains decreased from 19.7% in unripe samples to 3.4% in ripe fruit. The number of pectin aggregates was higher in green fruit samples of both fractions. These results show that the nanostructural complexity of pectins present in CDTA and Na₂CO₃ fractions diminishes during fruit development, and this correlates with the solubilisation of pectins and the softening of the fruit.

Metabolomic and physico-chemical approach unravel dynamic regulation of calcium in sweet cherry fruit physiology

Calcium (Ca²) nutrition has a significant role in fruit physiology; however, the underlying mechanism is still unclear. In this study, fruit quality in response to CaCl₂, applied via foliar sprays (Ca²) or/and hydro-cooling water (Ca_HC), was characterized in 'Lapins' cherries at harvest, just after cold storage (20 days at 0 °C) as well as after cold storage followed by 2 days at 20 °C, herein defined as shelf-life period. Data indicated that pre- and post-harvest Ca²⁺ applications increased total Ca²⁺ and cell wall bound Ca²⁺, respectively. Treatment with Ca reduced cracking whereas Ca + Ca_HC condition depressed stem browning. Both skin penetration and stem removal were affected by Ca²⁺ feeding. Also, several color- and antioxidant-related parameters were induced by Ca²⁺ treatments. Metabolomic analysis revealed significant alterations in primary metabolites among the Ca²⁺ treatments, including sugars (eg., glucose, fructose), soluble alcohols (eg., arabitol, sorbitol), organic acids (eg.,malate, quinate) and amino acids (eg., glycine, beta-alanine). This work helps to improve our knowledge on the fruit's response to Ca²⁺ nutrition.

Identification of quantitative trait loci controlling high Calcium response in Arabidopsis thaliana

Natural variation for primary root growth response to high Ca stress in Arabidopsis thaliana was studied by screening a series of accessions (ecotypes) under high Calcium (40 mM CaCl₂ ) conditions. The genetic basis of this variation was further investigated by QTL analysis using recombinant inbred lines from Landsberg erecta (Ler)×Cape Verde Islands (Cvi) cross. Four QTLs were identified in chromosome 1, 2 and 5,and named response to high Calcium (RHCA) 1–4. The three QTLs (RHCA1, RHCA2 and RHCA4) were further confirmed by analysis of near isogenic lines harboring Cvi introgression fragments in Ler background. Real-time PCR analysis showed that several genes associated with high Ca response including SMT1 and XHT25 have changed expression pattern between Ler and near isogenic lines. These results were useful for detecting molecular mechanisms of plants for high Ca adaption.

Fruit softening and pectin disassembly: an overview of nanostructural pectin modifications assessed by atomic force microscopy

BACKGROUND

One of the main factors that reduce fruit quality and lead to economically important losses is oversoftening. Textural changes during fruit ripening are mainly due to the dissolution of the middle lamella, the reduction of cell-to-cell adhesion and the weakening of parenchyma cell walls as a result of the action of cell wall modifying enzymes. Pectins, major components of fruit cell walls, are extensively modified during ripening. These changes include solubilization, depolymerization and the loss of neutral side chains. Recent evidence in strawberry and apple, fruits with a soft or crisp texture at ripening, suggests that pectin disassembly is a key factor in textural changes. In both these fruits, softening was reduced as result of antisense downregulation of polygalacturonase genes. Changes in pectic polymer size, composition and structure have traditionally been studied by conventional techniques, most of them relying on bulk analysis of a population of polysaccharides, and studies focusing on modifications at the nanostructural level are scarce. Atomic force microscopy (AFM) allows the study of individual polymers at high magnification and with minimal sample preparation; however, AFM has rarely been employed to analyse pectin disassembly during fruit ripening.

SCOPE

In this review, the main features of the pectin disassembly process during fruit ripening are first discussed, and then the nanostructural characterization of fruit pectins by AFM and its relationship with texture and postharvest fruit shelf life is reviewed. In general, fruit pectins are visualized under AFM as linear chains, a few of which show long branches, and aggregates. Number- and weight-average values obtained from these images are in good agreement with chromatographic analyses. Most AFM studies indicate reductions in the length of individual pectin chains and the frequency of aggregates as the fruits ripen. Pectins extracted with sodium carbonate, supposedly located within the primary cell wall, are the most affected.

Individual and combined effects of CaCl₂ and UV-C on the biosynthesis of resveratrols in grape leaves and berry skins

The individual and combined effects of calcium chloride (CaCl2) and ultraviolet C (UV-C) light on the synthesis of resveratrol in grape leaves and berry skins were investigated. Results showed that all treatments could increase leaf resveratrol contents at least about 5 times, but the combination treatment was the most efficient. Moreover, compared with UV-C treatment, the combination treatment delayed the decline of resveratrol contents. The expression levels of phenylalanine ammonia lyase (PAL), cinnamate-4-hydroxylase (C4H), coumaroyl-CoA ligase (4CL), and stilbene synthase (STS) and 3-O-β-glycosyltransferases, which are related to the synthesis of resveratrol, increased in response to these treatments, paralleling the change in resveratrol content. All treatments also induced the biosynthesis of resveratrol in berry skins at room temperature. The berries of these treatments held at room temperature for 1 day were further stored under low temperature (-1 ± 0.5 °C, RH 95%) for 27 days, and the results showed that all treatments continuously increased berry skin resveratrol content, with the combination treatment being most efficient. During cold storage, resveratrol content remained at high levels and reached a maximum (about 247.7 μg/g FW) at 13 days, then showed a slight decline, though it remained high by the end of storage. Berry firmness and total soluble solids content showed slight changes during cold storage, but there were no differences among the treatments. Thus, the combination treatment of CaCl2 and UV-C could be an efficient method for increasing resveratrol content of table grapes during storage under low temperature. This would be potentially beneficial for producing functional fruits.