Effect of nitric oxide on pericarp browning of harvested longan fruit in relation to phenolic metabolism

The roles of nitric oxide in improving postharvest fruits quality: Crosstalk with phytohormones

Nowadays, improving the quality of postharvest fruits has become a hot research topic. Nitric oxide (NO) is often regarded as a signaling molecule that delays the postharvest senescence of fruits. Moreover, phytohormones affect the postharvest senescence of fruits. This review mainly describes how NO improves the postharvest quality of fruits by delaying postharvest fruit senescence, mitigating fruit cold damage and controlling postharvest diseases. Furthermore, the crosstalk of NO and multiple plant hormones effectively delays the postharvest senescence of fruits, and the major crosstalk mechanisms include (1) mediating phytohormone signaling. (2) inhibiting ETH production. (3) stimulating antioxidant enzyme activity. (4) decreasing membrane lipid peroxidation. (5) maintaining membrane integrity. (6) inhibiting respiration rate. (7) regulating gene expression related to fruit senescence. This review concluded the roles and mechanisms of NO in delaying postharvest fruit senescence. In addition, the crosstalk mechanisms between NO and various phytohormones on the regulation of postharvest fruit quality are also highlighted, which provides new ideas for the subsequent research.

Synergistic improvement of antioxidant and antibacterial properties of carbon quantum complexes with zinc doping and chlorogenic acid for longan preservation

The deterioration of fruit could reduce the shelf life, decreased marketability and substantial economic value. Thus, a safe, simple, economical and environmentally friendly preservation technology for fruit is of great significance. Here, the postharvest preservation technology was investigated with zinc-doped carbon quantum dots and chlorogenic acid (Zn-CQDs/CGA) composite. Zn-CQDs/CGA composite were synthesized, which exhibits superior antioxidant and antibacterial activities. The binding mechanism of the Zn-CQDs/CGA composite was investigated, which revealed that the bindings of two components were mainly driven by hydrogen bonding and van der Waals forces to create a novel composite. The Zn-CQDs/CGA composite was applied to longan preservation and was found to significantly reduce the incidence of mildew spot, browning of fruit endocarp and pulp, as well as the degree of degradation of quality indexes. These results suggest that the Zn-CQDs/CGA composite has the potential for inhibiting browning and preserving the quality of longan during storage.

Utilizing VIS-NIR Technology to Generate a Quality Index (Qi) Model of Barhi Date Fruits at the Khalal Stage Stored in a Controlled Environment

Saudi Arabia is a prominent producer of dates, producing 1.6 million tons annually. There is a need to evaluate the physical properties and quality of fruits non-destructively and then modeled and predict them throughout the storage period. The aim of the current study was to generate a quality index (Qi) and visible-near-infrared spectra (VIS-NIR) models non-destructively to predict properties of Barhi dates including objective and sensory evaluations. A total of 1000 Barhi fruits were sorted into three stages of maturation, ranging from 80 to 100% yellowish. The physical properties (hardness, color, TSS, pH, and sensory evaluations) of Barhi dates were measured and modeled with Qi based on VIS-NIR of fresh Barhi fruits and during storage in ambient (25 °C), cold (1 °C), and CA (1 °C with 5%:5% O2:CO2, 85% RH) conditions for up to 3 months. The prediction of Qi was non-destructively based on VIS-NIR utilizing PLSR and ANN data analysis. The results showed that the shelf-life of stored Barhi fruits were 20, 40, and 120 days corresponding to 25 °C, cold (1 °C), and CA, respectively. It was found that VIS-NIR spectroscopy was helpful in estimating the Qi of Barhi fruits for PLSR and ANN data analysis, respectively, in calibration with an R2 of 0.793 and 0.912 and RMSEC of 0.110 and 0.308 and cross-validation with an R2 of 0.783 and 0.912 and RMSEC of 0.298 and 0.308. The VIS-NIR spectrum has proven to be an effective method for the evaluation of the Qi of Barhi fruits and their physical properties throughout the supply chain in the handling, processing, transportation, storage and retail sectors. It was found that ANN is more suitable than PLSR analysis.

GA3 Treatment Delays the Deterioration of 'Shixia' Longan during the On-Tree Preservation and Room-Temperature Storage and Up-Regulates Antioxidants

Gibberellic acids had been proven to improve the fruit quality and storability by delaying deterioration and maintaining the antioxidant system. In this study, the effect of GA₃ spraying at different concentrations (10, 20, and 50 mg L^-1) on the quality of on-tree preserved 'Shixia' longan was examined. Only 50 mg L^-1 GA₃ significantly delayed the decline of soluble solids (22.0% higher than the control) and resulted in higher total phenolics content (TPC), total flavonoid content (TFC), and phenylalanine ammonia-lyase activity in pulp at the later stages. The widely targeted metabolome analysis showed that the treatment reprogrammed secondary metabolites and up-regulated many tannins, phenolic acids, and lignans during the on-tree preservation. More importantly, the preharvest 50 mg L^-1 GA₃ spraying (at 85 and 95 days after flowering) led to significantly delayed pericarp browning and aril breakdown, as well as lower pericarp relative conductivity and mass loss at the later stages of room-temperature storage. The treatment also resulted in higher antioxidants in pulp (vitamin C, phenolics, and reduced glutathione) and pericarp (vitamin C, flavonoids, and phenolics). Therefore, preharvest 50 mg L^-1 GA₃ spraying is an effective method for maintaining the quality and up-regulating antioxidants of longan fruit during both on-tree preservation and room-temperature storage.

1H NMR-Based Metabolic Profiling to Follow Changes in Pomelo Cultivars during Postharvest Senescence

This study investigated metabolite changes in three pomelo cultivars during postharvest senescence using ¹H NMR-based metabolic profiling. Three pomelo cultivars, 'Hongroumiyou', 'Bairoumiyou' and 'Huangroumiyou', abbreviated as "R", "W" and "Y" according to the color of their juice sacs, were stored at 25 °C for 90 days, and NMR was applied to determine the metabolite changes in juice sacs during storage. Fifteen metabolites were identified, including organic acids, sugars, amino acids, fatty acids, phenols and naringin. Partial least squares discriminant analysis (PLS-DA) was used to screen the significant metabolites according to the variable importance for the projection (VIP) scores in three pomelo cultivars during 90 days of storage. Additionally, eight metabolites, naringin, alanine, asparagine, choline, citric acid, malic acid, phosphocholine and β-D-glucose, were screened to be the crucial biomarkers with VIP > 1. The undesirable flavor of "bitter and sour" during the 60 days of storage was mainly attributed to the naringin, citric acid and sugars. According to the correlation analysis, the citric acid content determined by NMR showed a significantly positive relationship with that analyzed by HPLC. These findings suggested that NMR technology was accurate and efficient for metabolomic analysis of pomelo fruit, and the ¹H NMR-based metabolic profiling can be efficient during quality evaluation and useful for improving the fruit flavor quality during postharvest storage.

Induction of salt tolerance in Brassica rapa by nitric oxide treatment

Salinity is one of the major plant abiotic stresses increasing over time worldwide. The most important biological role of nitric oxide (NO) in plants is related to their development and growth under abiotic conditions. The present experiment was conducted to study the effect of salt stress (0 and 100 mM) and NO (0 and 80 μM) on two different ecotypes of Brassica rapa (L.): PTWG-HL and PTWG-PK. The different growth attributes, biochemical and physiological parameters, and the mineral contents were examined. The results indicated increased hydrogen peroxide (H₂O₂), relative membrane permeability, malondialdehyde (MDA), and Na⁺ content and decreased plant biomass in both ecotypes (PTWG-PK and PTWG-HL) under salt stress. In contrast, NO treatment resulted in increased plant biomass, chlorophyll content, and total soluble proteins and decreased H₂O₂, relative membrane permeability, MDA, total phenolic content, catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and Na⁺. The combined effect of salt stress and NO application increased the chlorophyll a content, total phenolic content, and total soluble proteins, but decreased H₂O₂, relative membrane permeability, MDA, and Na⁺. The response of carotenoids, anthocyanins, and K⁺, Ca²⁺, and Cl^- ions varied in both ecotypes under all treatment conditions. The PTWG-PK ecotype showed maximum overall growth response with the application of NO. Henceforth, it is proposed that the molecular mechanisms associated with NO-induced stress tolerance in plants may be exploited to attain sustainability in agriculture under changing climate scenarios.

A Comprehensive Analysis of Physiologic and Hormone Basis for the Difference in Room-Temperature Storability between ‘Shixia’ and ‘Luosanmu’ Longan Fruits

Although the effects of phytohormones (mainly salicylic acid) on the storability of longan fruit have been reported, the relationship between postharvest hormone variation and signal transduction and storability remains unexplored. The basis of physiology, biochemistry, hormone content and signalling for the storability difference at room-temperature between ‘Shixia’ and ‘Luosanmu’ longan fruit were examined. ‘Luosanmu’ longan exhibited faster pericarp browning, aril breakdown and rotting during storage. ‘Luosanmu’ pericarp exhibited higher malondialdehyde but faster decreased total phenolics, flavonoid, glutathione, vitamin C, catalase activity and gene expression. Higher H2O2 and malondialdehyde but lower glutathione, glutathione-reductase and peroxidase activities, while higher activities and gene expressions of polygalacturonase, β-galactosidase and cellulose, lower covalent-soluble pectin, cellulose and hemicellulose but higher water-soluble pectin were observed in ‘Luosanmu’ aril. Lower abscisic acid and methyl jasmonate but higher expressions of LOX2, JAZ and NPR1 in pericarp, while higher abscisic acid, methyl jasmonate and salicylic acid together with higher expressions of ABF, JAZ, NPR1 and PR-1 in ‘Luosanmu’ aril were observed. In conclusion, the imbalance between the accumulation and scavenging of active oxygen in ‘Luosanmu’ longan might induce faster lipid peroxidation and senescence-related hormone signalling and further the polymerization of phenolics in pericarp and polysaccharide degradation in aril.

NUCLEOCYTOPLASMIC shuttling of ETHYLENE RESPONSE FACTOR 5 mediated by nitric oxide suppresses ethylene biosynthesis in apple fruit

Nitric oxide (NO) is known to modulate the action of several phytohormones. This includes the gaseous hormone ethylene, but the molecular mechanisms underlying the effect of NO on ethylene biosynthesis are unclear. Here, we observed a decrease in endogenous NO abundance during apple (Malus domestica) fruit development and exogenous treatment of apple fruit with a NO donor suppressed ethylene production, suggesting that NO is a ripening suppressor. Expression of the transcription factor MdERF5 was activated by NO donor treatment. NO induced the nucleocytoplasmic shuttling of MdERF5 by modulating its interaction with the protein phosphatase, MdPP2C57. MdPP2C57-induced dephosphorylation of MdERF5 at Ser260 is sufficient to promote nuclear export of MdERF5. As a consequence of this export, MdERF5 proteins in the cytoplasm interacted with and suppressed the activity of MdACO1, an enzyme that converts 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. The NO-activated MdERF5 was observed to increase in abundance in the nucleus and bind to the promoter of the ACC synthase gene MdACS1 and directly suppress its transcription. Together, these results suggest that NO-activated nucleocytoplasmic MdERF5 suppresses the action of ethylene biosynthetic genes, thereby suppressing ethylene biosynthesis and limiting fruit ripening.

Effects of Various Polymeric Films on the Pericarp Microstructure and Storability of Longan (cv. Shixia) Fruit Treated with Propyl Disulfide Essential Oil from the Neem (Azadirachta indica) Plant

Plant extracts represent a rich repository of metabolites with antioxidant and antimicrobial properties. Neem (Azadirachta indica) is a medicinal plant considered the tree of the 21st century. In this study, we investigated the antioxidant and antimicrobial effects of propyl disulfide (PD), a major volatile compound in neem seed, against the pericarp browning (BI), microbial decay incidence (DI), and water loss of longan fruit. Fresh longan cv. Shixia samples were packaged in oriented polypropylene (OPP) and polyethene (PE) packages of different thicknesses (20, 40, and 60 µm). Sterile gauze was fixed inside the packages and 500 uL of PD was placed on them to avoid the direct contact of PD with fruit samples. Packages were sealed immediately to minimize vaporization and stored at 12 ± 1 °C for 18 days. Fruit samples packaged in open net packages served as controls. The results showed that fruit treated with PD in OPP and PE packages significantly prevented losses of water, DI, and BI compared to control treatment. PD also maintained the color, TSS values, TA values, pH values, high peel firmness, high TPC content, and high TFC content, and reduced the activity levels of PPO and POD. Scanning electron microscope (SEM) analysis indicated that the exocarp, mesocarp, and endocarp of longan peel were smooth, uniform, and compact with no free space compared to control, where crakes, a damaged and loose structure, and a lot of fungal mycelia were found. The shortest shelf life of 9 days was observed in control as compared to 18 days in OPP-20 and OPP-40; 15 days in OPP-60, PE-20, and PE-40; and 12 days in PE-60 packaging films. Therefore, PD as a natural antioxidant and antimicrobial agent, in combination with OPP-20 and OPP-40 polymeric films, could successfully be applied commercially to extend the postharvest shelf life of longan.

Essential oil from Lavandula angustifolia elicits expression of three SbWRKY transcription factors and defense-related genes against sorghum damping-off

Sorghum damping-off, caused by Fusarium solani (Mart.) Sacc., is a serious disease which causes economic loss in sorghum production. In this study, antagonistic activity of lavender essential oil (EO) at 0.5, 0.75, 1.0, 1.25, 1.5, and 1.6% against F. solani was studied in vitro. Their effects on regulation of three SbWRKY transcription factors, the response factor JERF3 and eight defense-related genes, which mediate different signaling pathways, in sorghum were investigated. Effects of application under greenhouse conditions were also evaluated. The results showed that lavender EO possesses potent antifungal activity against F. solani. A complete inhibition in the fungal growth was recorded for lavender EO at 1.6%. Gas chromatography-mass spectrometric analysis revealed that EO antifungal activity is most likely attributed to linalyl anthranilate, α-terpineol, eucalyptol, α-Pinene, and limonene. Observations using transmission electron microscopy revealed many abnormalities in the ultrastructures of the fungal mycelium as a response to treating with lavender EO, indicating that multi-mechanisms contributed to their antagonistic behavior. Results obtained from Real-time PCR investigations demonstrated that the genes studied were overexpressed, to varying extents in response to lavender EO. However, SbWRKY1 was the highest differentially expressed gene followed by JERF3, which suggest they play primary role(s) in synchronously organizing the transcription-regulatory-networks enhancing the plant resistance. Under greenhouse conditions, treating of sorghum grains with lavender EO at 1.5% prior to infection significantly reduced disease severity. Moreover, the growth parameters evaluated, the activities of antioxidant enzymes, and total phenolic and flavonoid contents were all enhanced. In contrast, lipid peroxidation was highly reduced. Results obtained from this study support the possibility of using lavender EO for control of sorghum damping-off. However, field evaluation is highly needed prior to any usage recommendation.

Effect of Sodium Alginate in Combination with Zataria multiflora Boiss. on Phenolic Compounds, Antioxidant Activity, and Browning Enzymes of Fresh In-Hull Pistachio (Pistacia vera L.)

The color of fresh pistachio is used as a postharvest quality indicator. The present study was performed to investigate the chemical properties of fresh pistachios coated with different sodium alginate concentrations (1 and 1.5%), various amounts of Shirazi thyme essential oil (0.3 and 0.5%), and their combination during storage (2 ± 1°C and 85 ± 5% RH). Over the storage duration, chemical parameters were measured on days 13, 26, and 39. The results showed that although the application of sodium alginate in combination with thyme essential oil decreased polyphenol oxidase activity in comparison with other treatments, the highest total phenolics and phenylalanine ammonia lyase activity were found in pistachios coated with alginate (1%) + thyme essential oil (0.3% and 0.5%). In general, it was proven that treatments containing 1% alginate + 0.3% essential oil had the ability to maintain the quality of fresh pistachio fruit approximately over 39 days of storage.

Postharvest melatonin treatment inhibited longan (Dimocarpus longan Lour.) pericarp browning by increasing ROS scavenging ability and protecting cytomembrane integrity

Postharvest melatonin treatments have been reported to improve the quality and storability, especially to inhibit browning in many fruits, but the effect had not been systematically investigated on longan fruit. In this study, the effect of 0.4 mM melatonin (MLT) dipping on the quality and pericarp browning of longan fruits stored at low temperature was investigated. The MLT treatment did not influence the TSS content of longan fruits but lead to increased lightness and h° value while decreased a* value of pericarp. More importantly, the treatment significantly delayed the increase in electrolyte leakage and malonaldehyde accumulation, inhibited the activities of polyphenol oxidase and peroxidase, and thus retarded pericarp browning. In addition, the treatment significantly inhibited the production of O2 •- and H2O2 while promoted the accumulation of glutathione, flavonoids, and phenolics at earlier storage stages in longan pericarp. Interestingly, the activities of ascorbate peroxidase (APX) and superoxide dismutase (SOD) were significantly upregulated but activities of catalase were downregulated in the MLT-treated longan pericarp. MLT treatment effectively enhanced APX and SOD activities, increased flavonoid, phenolics, and glutathione content, protected cytomembrane integrity, inhibited the production of O2 •- and H2O2 and browning-related enzymes, and thus delayed the longan pericarp browning.

Chemistry of enzymatic browning in longan fruit as a function of pericarp pH and dehydration and its prevention by essential oil, an alternative approach to SO2 fumigation

Background

Longan fruit is a rich source of bioactive compounds; however, enzymatic browning of pericarp and microbial decay have limited its postharvest life. SO₂ has widely been used to overcome these limitations; however, due to safety and regulatory concerns, alternative means should be identified. In this study, antioxidant and antimicrobial properties of thymol (TH) essential oil were investigated against the enzymatic browning and decay of longan fruit.

Methods

Fruits were coated with TH (4%) for 5 min, sealed in polyethylene (PE) packages and stored at 4 °C for 42 d. Fruits immersed in distilled water (DW) and stored in PE were used as control.

Results

TH extended the postharvest life of longan to 42 d than 28 d in DW. TH residues decreased from 142 to 11.17 mg kg^-1, while no residues were found at day 42. TH significantly (P ≤ 0.05) reduced the respiration rate, inhibited polyphenol oxidase (PPO) and peroxidase (POD) enzyme activities, sustained high phenols/flavonoids and prevented pericarp browning (BI) than DW. TH also effectively (P ≤ 0.05) maintained the color values, firmness of peel and aril, total soluble solids (TSS), titratable acidity (TA), inhibited decay incidence (DI) and resulted in lower ethanol content than DW. BI as a function of pericarp pH was highly correlated; pH and BI (r = 0. 97), with PPO (r = 0.93) and with water loss (r = 0.99). A high coefficient of correlation of BI was found with the pericarp pH, enzymes, phenolic, water loss and decay incidence with ethanol. TH could be the best alternative to SO₂ and other synthetic preservatives.

Inhibitory mechanism of low-oxygen-storage treatment in postharvest internal bluing of radish (Raphanus sativus) roots

Oxidative stress in radish roots causes internal blue discoloration and decreases vegetable quality. Accordingly, the effects of different oxygen concentration treatment on this coloration during storage was investigated; 4-hydroxyglucobrassicin content (a precursor of the blue component); the reactive oxygen species (ROS) superoxide (O₂^-) and hydrogen peroxide (H₂O₂); the antioxidants ascorbic acid (AsA) and glutathione (GSH); and the activities and gene expression levels of the enzymes catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), glutathione peroxidase (GPX), were monitored under normal and low-oxygen conditions. The results indicated that packaging radish roots under 10% O₂ prevents blue discoloration by decreasing the activity and expression of the oxidant enzyme POD, increasing the levels of antioxidant and reducing substances, and upregulating antioxidant enzymes, all of which act to decrease the generation of ROS (O^2- and H₂O₂).

Assessment of the optical properties of peaches with fungal infection using spatially-resolved diffuse reflectance technique and their relationships with tissue structural and biochemical properties

This research measured the optical absorption (µ_a) and reduced scattering (μ_s') properties in peaches during quality deterioration, and determine the relationships of the optical parameters with select structural and biochemical parameters. Spatially resolved reflectance was measured for healthy and fungal infected peaches, followed by physical (the size and tissue color), structural [membrane permeability and SEM], and biochemical (Vc, soluble sugar, titratable acid, chlorophyll, total phenolic content) measurements. Both µ_a and µ_s' were correlated well with the cellulosic structural and biochemical parameters of peaches, and they had the best correlations with those quality parameters at 675 nm. The correlation of μ_s' with membrane permeability was the highest from -0.962-0.743, while μ_a had the best correlation with the chlorophyll content at 675 nm which is an indicator of plant maturation and senescence. These findings would be useful for further development of an effective optical technique for early disease detection of peach fruit.

Effects of acidic electrolyzed water treatment on storability, quality attributes and nutritive properties of longan fruit during storage

The aim of this study was to use acidic electrolyzed water (AEW) to treat longan fruit and evaluate the effects of AEW treatment on storability, quality attributes and nutritive properties of longans during storage. The data indicated that, as compared to the control samples, AEW treatment could effectively reduce the respiration rate and pericarp cell membrane permeability, retard the occurrences of pericarp browning, pulp breakdown and fruit disease, keep a higher rate of commercially acceptable fruit. Additionally, AEW treatment could suppress the decrease of chromaticity values of L*, a* and b* of the fruit surface, keep higher amounts of pericarp carotenoid, chlorophyll, flavonoid and anthocyanin, maintain higher amounts of pulp total soluble solid (TSS), total soluble sugars, sucrose and vitamin C. These results demonstrated that AEW treatment at pH of 2.5, ACC of 80 mg/L could maintain higher quality attributes and nutritive properties, and display better storability of harvested longans.

Effects of different substrates on low-temperature storage of fresh ginseng

BACKGROUND

Fresh ginseng was buried in three types of sand with different moisture contents and three types of soil and then stored at 2 °C to determine the effects of these storage substrates on fresh ginseng.

RESULTS

At a storage time of 200 days, ginseng stored in underforest soil softened the most slowly and had a significantly greater firmness compared to the other samples (P < 0.05). The amount of most ginsenosides changed after storage for most of the substrates. Samples stored in ginseng soil and biological fertilizer had the highest concentration of total saponin and ginseng polysaccharides, respectively. Fresh ginseng stored in medium-water content sand had a significantly lower polyphenol oxidase activity (P < 0.05). A significant difference was observed in the total concentration of nucleosides and nucleobases between the ginseng samples stored with and without substrates (P < 0.05).

CONCLUSION

The data obtained in the present study suggest that the use of storage substrates is an optimal method for extending the shelf life of fresh ginseng without detrimental effects on its components. © 2019 Society of Chemical Industry.

Polyamine Induction in Postharvest Banana Fruits in Response to NO Donor SNP Occurs via l-Arginine Mediated Pathway and Not via Competitive Diversion of S-Adenosyl-l-Methionine

Nitric oxide (NO) is known to antagonize ethylene by various mechanisms; one of such mechanisms is reducing ethylene levels by competitive action on S-adenosyl-L-methionine (SAM)—a common precursor for both ethylene and polyamines (PAs) biosynthesis. In order to investigate whether this mechanism of SAM pool diversion by NO occur towards PAs biosynthesis in banana, we studied the effect of NO on alterations in the levels of PAs, which in turn modulate ethylene levels during ripening. In response to NO donor sodium nitroprusside (SNP) treatment, all three major PAs viz. putrescine, spermidine and spermine were induced in control as well as ethylene pre-treated banana fruits. However, the gene expression studies in two popular banana varieties of diverse genomes, Nanjanagudu rasabale (NR; AAB genome) and Cavendish (CAV; AAA genome) revealed the downregulation of SAM decarboxylase, an intermediate gene involved in ethylene and PA pathway after the fifth day of NO donor SNP treatment, suggesting that ethylene and PA pathways do not compete for SAM. Interestingly, arginine decarboxylase belonging to arginine-mediated route of PA biosynthesis was upregulated several folds in response to the SNP treatment. These observations revealed that NO induces PAs via l-arginine-mediated route and not via diversion of SAM pool.

The effect of desulfurization on the postharvest quality and sulfite metabolism in pulp of sulfitated "Feizixiao" Litchi (Litchi chinensis Sonn.) fruits

The residual sulfite caused by sulfur fumigation (SF) is a hazard to health and influenced the export trade of litchi. Desulfurization (DS) is a valid chemical method to reduce the residual sulfite. However, the effect of DS on fumigated litchi has not been studied at physiological and molecular level. This study was aimed to evaluate the effect of DS (SF plus 3% desulfurizer) on the postharvest quality, sulfite residue, and the sulfite metabolism in sulfitated "Feizixiao" litchi during the 4°C storage. Results indicated that the DS promoted the color recovery of sulfitated litchi and achieved an effect similar to SF on controlling rot and browning. DS recovered the water content and respiration rate of sulfitated litchi pericarp. Thus, DS improves commodity properties of sulfitated litchi. Moreover, DS greatly reduced sulfite residue especially in pulp and ensured the edible safety of sulfitated litchi. The activities of sulfite oxidase, sulfite reductase, serine acetyltransferase, and O-acetylserine(thiol) lyase in pulp increased after SF but fell down after DS while the expressions of their encoding genes decreased after SF but then rallied after DS. These results indicated the key role of these enzymes in sulfite metabolism after SF and DS changed the sulfite metabolism at both enzymatic and transcriptional level. It could be concluded that DS used in this study was an effective method for improving the color recovery and ensuring the edible safety of sulfitated litchi by not only chemical reaction but also both of enzymatic and transcriptional regulation.

Preharvest zinc sulfate spray improves the storability of longan (Dimocarpus longan Lour.) fruits by protecting the cell wall components and antioxidants of pericarp

BACKGROUND

Zinc (Zn) fertilization has been reported to improve the quality and storability of many fruits, but the mechanism had not been systematically studied. In this study, the effect of preharvest 0.2% zinc sulfate (ZnSO₄ ) spray on the storability of longan fruits was investigated.

RESULTS

The preharvest ZnSO₄ spray did not significantly influence the quality but increased the Zn content in longan pericarp by 12.5-fold. More importantly, the treatment significantly reduced the rotting rate, pericarp browning, and aril breakdown of longan fruits stored at room temperature and low temperature. Physiological and biochemical results indicated that the treatment resulted in higher water retention capacity and inhibited the degradation of cellulose, pectin, flavonoid, and phenolics of longan pericarp at the late stages of storage. Consistent with these results, the activity of cellulase, polygalacturonase, polyphenol oxidase, and lipoxygenase was significantly inhibited in the ZnSO₄ -treated longan pericarp at the late stages of storage.

CONCLUSION

Higher Zn content in the ZnSO₄ -treated longan pericarp might help to enhance the resistance against microbial infection, inhibit the hydrolysis of cell wall components, and thus effectively protected the cell wall components, maintained the cellular compartmentation, and prevented the phenolics and flavonoid from degradation by browning-related enzymes. © 2018 Society of Chemical Industry.

The Changes in Metabolisms of Membrane Lipids and Phenolics Induced by Phomopsis longanae Chi Infection in Association with Pericarp Browning and Disease Occurrence of Postharvest Longan Fruit

This study investigated the changes in metabolisms of membrane lipids and phenolics caused by Phomopsis longanae Chi infection in association with pericarp browning and fruit disease occurrence of postharvest longans. Compared with the uninoculated-longans, the longans inoculated by P. longanae exhibited higher cellular membrane permeability; higher PLD, lipase, and LOX activities; and higher levels of saturated fatty acids (SFAs) and phosphatidic acid but lower levels of phosphatidylinositol, phosphatidylcholine, and unsaturated fatty acids (USFAs). Additionally, the longans inoculated by P. longanae showed higher activities of POD and PPO but a lower amount of total phenolics. These findings suggested that infection of P. longanae enhanced activities of PLD-, lipase-, and LOX- stimulated degradations of membrane lipids and USFAs, which destroyed the integrity of the cell membrane structure, resulting in enzymatic browning by contact of phenolics with POD and PPO, and resulting in reduction of resistance to pathogen infection and accordingly accelerated disease occurrence of postharvest longan fruit.

Sodium nitroprusside stimulated production of tropane alkaloids and antioxidant enzymes activity in hairy root culture of Hyoscyamus reticulatus L

Hyoscyamus reticulatus L. is a herbaceous biennial belonging to the solanaceae family. Hyoscyamine and scopolamine as main tropane alkaloids accumulated in henbane are widely used in medicine to treat diseases such as parkinson's or to calm schizoid patients. Hairy roots media manipulation which uses elicitors to activate defense mechanisms is one of the main strategies for inducing secondary metabolism as well as increasing the production of valuable metabolites. Cotyledon-derived hairy root cultures were transformed by Agrobacterium rhizogenes. Sodium nitroprusside (SNP), a nitric oxide donor), was used in various concentrations (0, 50, 100, 200 and 300 μM) and exposure times (24 and 48 h). Treatment with SNP led to a significant reduction in fresh and dry weight of hairy roots, compared to control cultures. ANOVA results showed that elicitation of hairy root cultures with SNP at different concentrations and exposure times significantly affected the activity of as antioxidant enzymes such as catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX). The highest hyoscyamine and scopolamine production (about 1.2-fold and 1.5-fold increases over the control) was observed at 50 and 100 μM SNP at 48 and 24 hours of exposure time, respectively. This is the first report of SNP elicitation effects on the production of tropane alkaloids in hairy root cultures.

Phomopsis longanae Chi-Induced Change in ROS Metabolism and Its Relation to Pericarp Browning and Disease Development of Harvested Longan Fruit

Phomopsis longanae Chi is a major pathogenic fungus that infects harvested longan fruit. This study aimed to investigate the effects of P. longanae on reactive oxygen species (ROS) metabolism and its relation to the pericarp browning and disease development of harvested longan fruit during storage at 28°C and 90% relative humidity. Results showed that compared to the control longans, P. longanae-inoculated longans displayed higher indexes of pericarp browning and fruit disease, higher O2 -. generation rate, higher accumulation of malondialdehyde (MDA), lower contents of glutathione (GSH) and ascorbic acid (AsA), lower 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging ability and reducing power in pericarp. In addition, P. longanae-infected longans exhibited higher activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) in the first 2 days of storage, and lower activities of SOD, CAT, and APX during storage day 2-5 than those in the control longans. These findings indicated that pericarp browning and disease development of P. longanae-infected longan fruit might be the result of the reducing ROS scavenging ability and the increasing O2 -. generation rate, which might lead to the peroxidation of membrane lipid, the loss of compartmentalization in longan pericarp cells, and subsequently cause polyphenol oxidase (PPO) and peroxidase (POD) to contact with phenolic substrates which result in enzymatic browning of longan pericarp, as well as cause the decrease of disease resistance to P. longanae and stimulate disease development of harvested longan fruit.

Effect of exogenous γ-aminobutyric acid treatment on the enzymatic browning of fresh-cut potato during storage

The aim of this study was to evaluate the effect of γ-aminobutyric acid (GABA) treatment on the enzymatic browning of fresh-cut potatoes. The browning index and activities of browning and defense-related enzymes were analyzed after 0, 1, 2, 3, 4, 5, and 6 days of storage at 4 °C. The results showed that the treatment with 20 g/L GABA for 10 min significantly retarded the browning of fresh-cut potatoes. GABA inhibited the browning of fresh-cut potatoes by enhancing the activities of catalase and superoxide dismutase, and decreasing the activities of polyphenol oxidase and reactive oxygen species. The results suggest that GABA plays an important role in reducing the browning of fresh-cut potatoes. Hence, GABA treatment is a promising approach for reducing the browning and maintaining the quality of fresh-cut potatoes.

Effects of a high O2 dynamic-controlled atmosphere technology on the browning of postharvest white mushroom (Agaricus bisporus) in relation to energy metabolism

Browning is one of the main problems in senescence of mushrooms, and it is also one of the most important attributes accounting for the loss of the quality and reduction in market value. In order to study the relationship between the energy metabolism and the browning of white mushroom under high O2 dynamic-controlled atmosphere (HO-DCA), mushrooms were stored in 100% O2 (SCA1), 80% O2 + 20% CO2 (SCA2), 100% O2 for three days and then transferred into the treatment of 80% O2 + 20% CO2 (HO-DCA) at 2 ± 1 ℃ and air as control. In this study, adenosine triphosphate (ATP) content, energy charge level, sensory evaluation, browning of surface and flesh, cell membrane integrity, exogenous ATP, polyphenol oxidase (PPO) and peroxidase (POD) activity and genes encoding PPO of the white mushroom were investigated. These were all closely related to the browning of products. The optimal storage condition of the HO-DCA treatment could delay the browning of pericarp and flesh tissues of the mushrooms, inhibit PPO activity and reduce the relative expression levels of the three genes encoding PPO. Meanwhile, it maintained moderate POD activity, good sensory properties and cell membrane integrity in a certain extent and thus slowed down the senescence of mushrooms. Results indicated that there was a positive correlation between the ATP content and whitening index ( r = 0.901). In addition, HO-DCA maintained a higher ATP level, prolonged the storage time to 28 days and it might be an ideal strategy for preserving the quality of mushroom during storage.

DNP and ATP induced alteration in disease development of Phomopsis longanae Chi-inoculated longan fruit by acting on energy status and reactive oxygen species production-scavenging system

As compared with P. longanae-inoculated longans, DNP treatment for P. longanae-inoculated longans exhibited higher fruit disease index and pericarp browning index, lower ATP amount and energy charge level, lower activities of SOD, CAT and APX, lower amounts of AsA and GSH, lower levels of DPPH radical scavenging activity and reducing power, higher O₂^- generating rate and MDA amount. However, supply of ATP for P. longanae-inoculated longans showed the contrary effects. These results gave convincing evidence that DNP treatment for accelerating pericarp browning and disease development of harvested longans caused by P. longanae was due to decreases of energy production and ROS scavenging capacity, and increases of O₂^- accumulation and membrane lipid peroxidation. Whereas, supply of ATP for retarding pericarp browning and disease development of harvested longans caused by P. longanae was due to increases of energy production and ROS scavenging capacity, and reductions of O₂^- accumulation and membrane lipid peroxidation.

The Effect of the Application of Edible Coatings on or before Ultraviolet Treatment on Postharvested Longan Fruits

This study compared the effect of application of edible coating on or before ultraviolet treatment on postharvest longan fruits. The treated longan fruits were examined for weight loss, respiration rate, surface color changes, enzymatic activities (PPO, POD, and PAL), and total phenolic contents throughout the 7 storage days at ambient temperature. In addition, coat homogeneity was examined and cell structure of longan flesh at the end of storage was observed. The results showed that when UV was applied before coating (i.e., chitosan or carrageenan), it had relatively lower PPO and PAL activities and retained higher TPC in longan pericarp. However, the changes in enzymatic activities did not affect the surface lightness and browning index as they were more influenced by the type of coating, in which combination treatments with carrageenan showed higher surface lightness and lower browning index compared to treatment combinations containing chitosan. However, when UV treatment preceded coating, the combinations of UV plus chitosan coating produced lower PPO and PAL activities and retained better cell structure with less damage than the combinations of UV plus carrageenan coating. UV plus carrageenan coating showed relatively higher weight loss and respiration rate, with cell structure exhibiting bigger intercellular spaces at the end of storage. Therefore, application of UV treatment followed by chitosan coating was found to be the best treatment combination for controlling enzymatic activities and reducing senescence rate of longan fruits.

Impact of Postharvest Nitric Oxide Treatment on Lignin Biosynthesis-Related Genes in Wax Apple (Syzygium samarangense) Fruit

The role of nitric oxide (NO) during storage in wax apple through NO (10 μL/L) fumigate fruit was investigated. Wax apple fruit treated with NO had a significantly lower rate of weight loss, a softening index, and loss of firmness during storage. The transcriptional profile of 10 genes involved in lignin biosynthesis has been analyzed using quantitative real-time polymerase chain reaction (qRT-PCR). The qRT-PCR analysis showed nine genes regulated in the wax apple (p < 0.05) upon NO fumigation, which coincided with the enzyme activity results (NO group lower than control group in peroxidase, phenylalanine ammonia-lyase, and 4-coumarate-CoA ligase), whose total lignin content decreased upon treatment with NO. These results indicate that NO treatment can effectively delay the softening and senescence of wax apple fruit and play an important regulatory role in lignin biosynthesis.

Application of α-aminoisobutyric acid and β-aminoisobutyric acid inhibits pericarp browning of harvested longan fruit

BACKGROUND

Pericarp browning is a critical problem resulting in reduced commercial value and shelf life of longan fruit.

RESULTS

Two non-protein amino acids, α-aminoisobutyric acid (AIB) and β-aminoisobutyric acid (BAIB) at 100 and 1 mM were applied to longan fruit prior to storage for up to 8 days at 25 °C respectively. Contents of the major five phenolics (gallic acid, catechin, corilagin, epicatechin and gallocatechin gallate) were assayed by high-performance liquid chromatography (HPLC). Physiological properties related to pericarp browning of longan fruit were investigated during storage. Respiration rate, membrane permeability, malondialdehyde (MDA) content, and activities of polyphenol oxidase (PPO) and peroxidase (POD) were down-regulated by AIB or BAIB treatments, with significantly lower pericarp browning index and higher proportion of edible fruit than the control. Moreover, exogenous application of AIB and BAIB maintained higher contents of catechin, corilagin, epicatechin and gallocatechin gallate, but lower content of gallic acid compared to the control in the pericarp of longan fruit during storage, which was associated with the oxidation of browning substrate.

CONCLUSIONS

Pericarp browning was inhibited and storage life of longan fruit was extended effectively by AIB and BAIB treatments with AIB treatment being more significant than BAIB. The findings may provide a new strategy for controlling pericarp browning of harvested longan fruit.

Inhibitory effects of α-Na8SiW11CoO40 on tyrosinase and its application in controlling browning of fresh-cut apples

α-Na8SiW11CoO40 was synthesized and characterized. The inhibitory effects of α-Na8SiW11CoO40 on the activity of mushroom tyrosinase and the effects of α-Na8SiW11CoO40 on the browning of fresh-cut apples were studied. The Native-PAGE result showed that α-Na8SiW11CoO40 had a significant inhibitory effect on tyrosinase. Kinetic analyses showed that α-Na8SiW11CoO40 was an irreversible and competitive inhibitor. The inhibitor concentration leading to a 50% reduction in activity (IC50) was estimated to be 0.239 mM. Additionally, the results also showed that α-Na8SiW11CoO40 treatment could significantly decrease the browning process of apple slices and inhibit the polyphenol oxidase (PPO) activity. Moreover, application of α-Na8SiW11CoO40 resulted in higher peroxidase activity and promoted high amounts of phenolic compounds and ascorbic acid. This study may provide a promising method for the use of polyoxometalates to inhibit tyrosinase activity and control the browning of fresh-cut apples.

Role of plant hormones and their interplay in development and ripening of fleshy fruits

Plant hormones have been extensively studied for their roles in the regulation of various aspects of plant development. However, in the last decade important new insights have been made into their action during development and ripening, in both dry and fleshy fruits. Emerging evidence suggests that relative functions of plant hormones are not restricted to a particular stage, and a complex network of more than one plant hormone is involved in controlling various aspects of fruit development. Though some areas are extensively covered, considerable gaps in our knowledge and understanding still exist in the control of hormonal networks and crosstalk between different hormones during fruit expansion, maturation, and various other aspects of ripening. Here, we evaluate the new knowledge on their relative roles during tomato fruit development with a view to understand their mechanism of action in fleshy fruits. For a better understanding, pertinent evidences available on hormonal crosstalk during fruit development in other species are also discussed. We envisage that such detailed knowledge will help design new strategies for effective manipulation of fruit ripening.