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

Tert-Butylhydroquinone retards longan fruit deterioration by regulating membrane lipid and energy metabolisms

Longan fruit deteriorates rapidly after harvest, which limits its storability. This study aimed to investigate the effect of tert-butylhydroquinone (TBHQ) on quality maintenance, membrane lipid metabolism, and energy status of longan fruit during 25 °C storage. Compared with control fruit, TBHQ treatment maintained better marketable fruit rate and suppressed activities of phospholipase D (PLD), lipase, and lipoxygenase (LOX), and downregulated expressions of DlPLD, DlLOX, and Dllipase. TBHQ also increased the ratio of unsaturated fatty acids to saturated fatty acids (U/S) and the index of unsaturated fatty acids (IUFA). In addition, higher levels of ATP, ADP, energy charge, NADP+/ NADPH as well as higher activities of H+-ATPase, Ca2+-ATPase and NADK were also observed in TBHQ-treated fruit. These results suggested that TBHQ may maintain postharvest quality of longan fruit by regulating membrane lipid and energy metabolisms.

Comparative transcriptome and metabolome reveal the role of acidic electrolyzed oxidizing water in improving postharvest disease resistance of longan fruit

Acidic electrolyzed oxidizing water (AEOW) was applied to suppress disease development and maintain good quality of fresh fruit. However, the involvement of AEOW in improving disease resistance of fresh longan remains unknown. Here, transcriptomic and metabolic analyses were performed to compare non-treated and AEOW-treated longan during storage. The transcriptome analysis showed AEOW-induced genes associated with phenylpropanoid and flavonoid biosynthesis. The metabolome analysis found the contents of coumarin, phenolic acid, and tannin maintained higher levels in AEOW-treated longan than non-treated longan. Moreover, the weighted correlation network analysis (WGCNA) was performed to identify hub genes, and a gene-metabolite correlation network associated with AEOW-improved disease resistance in longan was constructed by the co-analysis of transcriptomics and metabolomics. These findings identified a series of important genes and metabolites involving in AEOW-induced disease resistance of longan fruit, expanding our knowledges on fruit disease resistance and quality maintenance at the transcript and metabolic levels.

The metabolism of membrane lipid participates in the occurrence of chilling injury in cold-stored banana fruit

Banana fruit is highly vulnerable to chilling injury (CI) during cold storage, which results in quality deterioration and commodity reduction. The purpose of this study was to investigate the membrane lipid metabolism mechanism underlying low temperature-induced CI in banana fruit. Chilling temperature significantly induced CI symptoms in banana fruit, compared to control temperature (22 °C). Using physiological experiments and transcriptomic analyses, we found that chilling temperature (7 °C) increased CI index, malondialdehyde content, and cell membrane permeability. Additionally, chilling temperature upregulated the genes encoding membrane lipid-degrading enzymes, such as lipoxygenase (LOX), phospholipase D (PLD), phospholipase C (PLC), phospholipase A (PLA), and lipase, but downregulated the genes encoding fatty acid desaturase (FAD). Moreover, chilling temperature raised the activities of LOX, PLD, PLC, PLA, and lipase, inhibited FAD activity, lowered contents of unsaturated fatty acids (USFAs) (γ-linolenic acid and linoleic acid), phosphatidylcholine, and phosphatidylinositol, but retained higher contents of saturated fatty acids (SFAs) (stearic acid and palmitic acid), free fatty acids, phosphatidic acid, lysophosphatidic acid, diacylglycerol, a lower USFAs index, and a lower ratio of USFAs to SFAs. Together, these results revealed that chilling temperature-induced chilling injury of bananas were caused by membrane integrity damage and were associated with the enzymatic and genetic manipulation of membrane lipid metabolism. These activities promoted the degradation of membrane phospholipids and USFAs in fresh bananas during cold storage.

Comprehensive analyses of membrane lipids and phenolics metabolisms reveal the developments of chilling injury and browning in Chinese olives during cold storage

The impacts of chilling injury (CI) temperature (2 °C) and non-CI temperature (8 °C) on the CI development, browning occurrence, and its underlying mechanism in Chinese olives were investigated. The results showed that, 2 °C induced higher levels of CI index, browning degree, chromaticity a* and b* values, but lower values of h°, chlorophyll and carotenoid contents in Chinese olives as compared to 8 °C. Furthermore, 2 °C raised cell membrane permeability, increased the activities of phospholipase D, lipase and lipoxygenase, accelerated the hydrolyses of phosphatidylcholine and phosphatidylinositol to phosphatidic acid, and promoted the conversions of unsaturated fatty acids to saturated fatty acids in Chinese olives. Moreover, 2 °C-stored Chinese olives showed higher activities of peroxidase and polyphenol oxidase, but lower contents of tanin, flavonoid and phenolics. These findings demonstrated that the CI and browning developments in Chinese olives were closely associated with the metabolisms of membrane lipid and phenolics.

Effect of oxyresveratrol on the quality and membrane lipid metabolism of shiitake mushroom (Lentinus edodes) during storage

The effect of oxyresveratrol on postharvest quality and membrane lipid metabolism of shiitake mushroom was investigated. The result exhibited that oxyresveratrol retarded browning, maintained firmness and alleviated occurrence of decay of shiitake mushroom. The oxidation and hydrolysis of membrane phospholipids were suppressed by oxyresveratrol treatment, which was associated with reduced LOX and PLD activities and increased SOD and CAT activities. The membrane lipidomics of shiitake mushroom was determined by LC-MS. 385 lipid species and 13 fatty acids in membrane lipids were identified by multiple reaction monitoring method. Compared with control group, the phospholipic acid and lysophospholipid reduced by 29.24% and 21.29% in oxyresveratrol-treated group, respectively, which alleviated hydrolysis of phospholipid. Meanwhile, oxyresveratrol maintained the unsaturation of fatty acids and alleviated oxidation of phospholipid. These results demonstrated that oxyresveratrol could play a dual role of inhibiting the oxidation and hydrolysis of phospholipids to mitigate cellular damage of shiitake mushroom.

DNP and ATP regulate the breakdown occurrence in the pulp of Phomopsis longanae Chi-infected longan fruit through modulating the metabolism of membrane lipid

This study aimed to illustrate how DNP and ATP affected the pulp breakdown occurrence in P. longanae-infected longan and their relationship with the membrane lipid metabolism. Compared with P. longanae-inoculated samples, the pulp of DNP-treated P. longanae-infected longan exhibited higher cellular membrane permeability, breakdown index, activities of PI-PLC, PLD, PC-PLC, LOX, and lipase, and values of SFAs, PA, and DAG, while lower levels of PI, PC, USFAs, IUFA and U/S. However, the opposite findings were observed in ATP-treated P. longanae-infected longan. The data manifested that DNP-increased the pulp breakdown occurrence in P. longanae-inoculated samples was due to the elevated MLDEs activities that reduced the contents of phospholipids (PI, PC) and USFAs, disrupting the cell membrane structures. Nevertheless, ATP decreased the pulp breakdown occurrence in P. longanae-inoculated samples, which was ascribed to the reduced MLDEs activities that raised phospholipids (PI, PC) and USFAs contents, thus maintaining the cell membrane structures.

Preparation and evaluation of a novel chlorine dioxide preservative based on citric acid grafted carboxymethyl chitosan

Instrument-free chlorine dioxide (ClO₂) preservative for fruit and vegetable has gained great attention due to its convenience and safety. In this study, a series of carboxymethyl chitosan (CMC) with citric acid (CA) substituents were synthesized, characterized, and further used to prepare a novel ClO₂ slow-releasing preservative for longan. UV-Vis and FT-IR spectra revealed that CMC-CA#1-3 were successfully prepared. Further potentiometric titration showed that the mass ratios of CA grafted in CMC-CA#1-3 were 0.18:1, 0.42:1, and 0.42:1, respectively. The composition and concentration of ClO₂ slow-releasing preservative were optimized, and the best formulation was as follows: NaClO₂:CMC-CA#2:Na₂SO₄:starch = 3:2:1:1. The maximum ClO₂ release time of this preservative reached >240 h at 5-25 °C, and the maximum release rate always occurred at 12-36 h. Longan treated with 0.15-1.2 g ClO₂ preservative had significantly (p < 0.05) higher L* and a* values but lower respiration rate and total microbial colony counts than the CK group (0 g ClO₂ preservative). After 17 days of storage, longan treated with 0.3 g ClO₂ preservative had the highest L* value of 47.47 and lowest respiration rate of 34.42 mg·kg^-1·h^-1, showing the best pericarp color and pulp quality. This study provided a safe, effective, and simple solution for longan preservation.

Amelioration of Chilling Injury by Fucoidan in Cold-Stored Cucumber via Membrane Lipid Metabolism Regulation

Cucumber fruit is very sensitive to chilling injury, which rapidly depreciates their commodity value. Herein, the effect of fucoidan treatment on cucumber under cold stress were investigated. Fucoidan treatment of cold-stored cucumber alleviated the occurrence of chilling injury, delayed weight loss, lowered electrolyte leakage and respiration rate, and retarded malondialdehyde accumulation. Different from the control fruit, fucoidan treated fruit showed a high level of fatty acid unsaturated content, fatty acid unsaturation, and unsaturation index and increased ω-FDAS activity, along with upregulated expression levels of CsSAD and CsFAD genes. Fucoidan reduced the phosphatidic acid content and membrane lipid peroxidation, lowered the phospholipase D (PLD) and lipoxygenase (LOX) activity, and downregulated the expression levels of CsPLD and CsLOX genes. Collectively, fucoidan treatment maintained the integrity of cell membrane in cold-stress cucumbers. The results provide a new prospect for the development of fucoidan as a preservative agent in the low-temperature postharvest storage of cucumbers.

Dynamic Change of Carbon and Nitrogen Sources in Colonized Apples by Penicillium expansum

Penicillium expansum is a necrotrophic pathogen, which actively kills host cells and obtains nutrients from dead cells to achieve infection. However, few reports have elucidated the differential levels of carbon and nitrogen sources over increasing distances of the leading edge in fungal colonized fruit tissues during colonization. Our results showed that the highest consumption of sucrose and fructose, as well as the accumulation of glucose, were found in the decayed region of P. expansum-colonized ‘Delicious’ apple fruit compared with the healthy region at the leading edge and the healthy region 6 mm away from the leading edge. As nitrogen sources, the contents of methionine, glutamate, leucine, valine, isoleucine and serine were the lowest in the decayed region compared with the healthy regions during colonization. In addition, the titratable acidity, oxalic acid, citric acid, succinic acid and malic acid showed the highest accumulation in the decayed region compared with the healthy regions. P. expansum colonization induced the accumulation of saturated fatty acids in the decayed region, while the level of unsaturated fatty acids was the lowest. These changes were not observed in the healthy regions. These results indicated that P. expansum kills cells in advance of its colonization in order to obtain the nutrients of the apple tissue from the distal leading tissue of the colonized apple. It is understood that more carbon and nitrogen sources are required for fungal colonization, and a stronger defense response against colonization occurred in the fruit, causing the transit of nutrients from the distal tissue to the infected sites.

Botrytis cinerea mediated cell wall degradation accelerates spike stalk browning in Munage grape

Munage grape (Vitis vinifera L. cv. Munage.) is a unique cultivar in southern Xinjiang, China. Spike stalk browning in this species has becomes more common in recent years, negatively impacting the shelf life, and causing severe economic losses during storage. This study investigated the changes in metabolisms of cell wall by Botrytis cinerea infection in association with spike stalk browning. Morphological and physiological observations showed that preharvest B. cinerea infection accelerates the spike stalk browning during storage in Munage grapes by promoting cell wall degradation. Accordingly, the cell structures in infected spike stalk showed severe collapse, while the cell structures in uninfected spike stalk remained relatively complete. Furthermore, the contents of CDTA-soluble pectin (CSP), Na₂ CO₃ -soluble pectin (NSP), cellulose, and hemicellulose were reduced, while the water-soluble pectin (WSP) content was increased during infection. In addition, the activities of polygalacturonase (PG), pectin methylesterase (PME), beta-galactosidase (β-Gal), and cellulase (Cx) were highly promoted by B. cinerea. Correspondingly, the expression levels of VvPG were markedly upregulated after inoculation and played a major role in cell wall degradation. Additionally, the spike stalk inoculated by B. cinerea showed higher activities of PPO and POD, and content of total phenolics. These results contribute to elucidating the relationship between cell wall degradation induced by B. cinerea during spike stalk browning and provide a basis for future research on improving the ability of the host cell wall to resist degrading enzymes. PRACTICAL APPLICATIONS: Botrytis cinerea is the main fungal pathogen causing the gray mold of grapes. It usually enters the tissue early in crop development, has a long incubation period, and rapidly infects the tissue when the environment is favorable and the host physiology changes. Gray mold has been reported as one of the major postharvest diseases of grapes. However, there are relatively few reports on the pathways through which B. cinerea causes the browning of grape stalks. Controlling browning caused by B. cinerea may require clarification of the physiological and molecular mechanisms by which browning occurs. The elucidation of the role of B. cinerea in causing browning of grape stalks through the cell wall degradation pathway will help to provide scientific basis for further controlling browning, maintaining freshness of stalks, developing biological agents to prevent browning, improving grape quality, and extending storage period.

Phomopsis longanae Chi causing the pulp breakdown of fresh longan fruit through affecting reactive oxygen species metabolism

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P. longanae raised longan pulp O₂^–. generation rate and contents of H₂O₂ and MDA.

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P. longanae reduced ROS scavenging enzymes activities (CAT, SOD, APX) in longan pulp.

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P. longanae lowered the amounts of endogenous antioxidant substances in longan pulp.

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P. longanae decreased longan pulp DPPH radical scavenging ability and reducing power.

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P. longanae stimulated longan pulp breakdown via reducing ROS scavenging capacity.

Phomopsis longanae Chi is a crucial pathogen causing fruit spoilage in postharvest fresh longan. The influence of P. longanae invasion with a suspension containing 1 × 10⁴P. longanae spores per mL on the breakdown occurrence and ROS metabolism in pulp of longan cv. Fuyan during storage at 28 °C was explicated. Compared to control group, more severe development of pulp breakdown (PB), higher PB index, O₂^–. generation rate, H₂O₂ and MDA content, but lower SOD, APX and CAT activities, GSH, AsA, flavonoid and total phenolics amounts, ability of scavenging DPPH radical, and reducing power were displayed in the pulp of P. longanae-infected fruit during days 0–5. In this context, P. longanae induced breakdown of longan pulp by reducing the scavenging ability of ROS and increasing the cumulation of ROS, thereby enhancing the structural collapse and lipid peroxidation of cell membrane, which were responsible for the PB of harvested longans.

ε-Poly-l-Lysine Enhances Fruit Disease Resistance in Postharvest Longans (Dimocarpus longan Lour.) by Modulating Energy Status and ATPase Activity

ε-poly-l-lysine (ε-PL) holds a strong antibacterial property and is widely used for food preservation. However, the application of ε-PL to enhance fruit disease resistance in postharvest longans (Dimocarpus longan Lour.) has not been explored. The objective of this study was to explore the impact of ε-PL treatment on disease occurrence and energy metabolism of longans infected with Phomopsis longanae Chi (P. longanae). It was found that, in comparison with P. longanae-inoculated longans, ε-PL could decrease the fruit disease index and adenosine monophosphate (AMP) content, increase the amounts of adenosine triphosphate (ATP), adenosine diphosphate (ADP), and energy charge, and enhance the activities of adenosine triphosphatase (ATPase) (such as H⁺-, Mg²⁺-, and Ca²⁺-ATPase) in the mitochondria, protoplasm, and vacuole. The results suggest that the higher levels of ATPase activity and energy status played essential roles in disease resistance of postharvest longan fruit. Therefore, the ε-PL treatment can be used as a safe and efficient postharvest method to inhibit the disease occurrence of longan fruit during storage at room temperature.

Study on browning mechanism of fresh-cut eggplant (Solanum melongena L.) based on metabolomics, enzymatic assays and gene expression

Enzymatic browning is one of the crucial problems compromising the flavor and texture of fresh-cut fruit and vegetables. In this study, an untargeted metabolomics approach based on liquid chromatography-mass spectrometry (LC-MS) was used to explore the browning mechanism in fresh-cut eggplant. Metabolomics studies showed that with the increase of fresh-cut time, the contents of 946 metabolites changed dynamically. The metabolites having the same trend share common metabolic pathways. As an important browning substrate, the content of chlorogenic acid increased significantly, suggesting that may be more important to fresh-cut eggplant browning; all 119 common differential metabolites in 5 min/CK and 3 min/CK contrastive groups were mapped onto 31 KEGG pathways including phenylpropanol metabolism, glutathione metabolism pathway, et al. In physiological experiments, results showed that the Phenylpropanoid-Metabolism-Related enzymes (PAL, C4H, 4CL) were changed after fresh-cut treatment, the activities of three enzymes increased first and then decreased, and reached the maximum value at 5 min, indicating the accumulation of phenolic substances. At the same time, ROS were accumulated when plant tissue damaged by cutting, the activities of related antioxidant enzymes (SOD, APX and CAT) changed dynamically after oxidative damage. SOD and APX content increased significantly and reached the maximum value at 10 min after cutting, and then showed a downward trend. However, CAT activity increased sharply and reached the maximum value within 3 min after cutting, then maintained the same activity, and showed a downward trend after 30 min. These data fully demonstrated that the activities of browning related enzymes and gene expression increased with the prolonging of fresh cutting time. We explained the browning mechanism of fresh-cut eggplant by combining metabolomics and physiology, which may lay the foundation for better understanding the mechanism of browning during the fruits and vegetables during processing.

Variations of membrane fatty acids and epicuticular wax metabolism in response to oleocellosis in lemon fruit

Oleocellosis is a physiological disorder causing blemishes on fruit surface. This study investigated the influence of oleocellosis on the membrane fatty acids and wax in lemon fruit rinds at the morphological, physiological, metabolic and molecular levels by using a variety with a high incidence rate of oleocellosis (green lemon). Oleocellosis-damaged rinds showed loose and flaky wax layers with more fissures on the surface, as well as higher contents of C16 and C18 fatty acids and very long chain (VLC) fatty alkanes while lower contents of VLC fatty aldehydes. The main differentially expressed genes, including FabZ, FAD2 and SAD6 involved in the accumulation of C16 and C18 fatty acids and CER1 involved in the transformation of VLC fatty aldehydes to VLC fatty alkanes, were up-regulated by oleocellosis. These results indicate that oleocellosis accelerates the accumulation of membrane free fatty acids and transformation of VLC fatty aldehydes to VLC fatty alkanes.

Influences of 1-methylcyclopropene-containing papers on the metabolisms of membrane lipids in Anxi persimmons during storage

Objectives

The aim of this work was to analyse the effects of 1-methylcyclopropene (1-MCP) treatment on the metabolisms of membrane lipids in postharvest Anxi persimmons during storage.

Materials and methods

Anxi persimmon (Diospyros kaki L. f. cv. Anxi) fruits were treated by paper containing 1-MCP with a concentration of 1.35 μl/l. The cellular membrane permeability was analysed by the electric conductivity meter. The activities of lipoxygenase (LOX), phospholipase (PLD) and lipase were determined by spectrophotometry. The component and relative amounts of membrane fatty acids were determined using gas chromatograph (GC).

Results

The 1-MCP-treated Anxi persimmons manifested a lower electrolyte leakage rate, lower LOX, PLD and lipase activities, higher levels of unsaturated fatty acids (USFAs), higher ratio of USFAs to saturated fatty acids (SFAs) (U/S), higher index of USFAs (IUFA), but lower levels of SFAs.

Conclusions

The degradation and the metabolisms of membrane lipids could be suppressed by 1-MCP treatment, which might be accountable for the delaying softening of postharvest Anxi persimmons during storage.

Hydrogen peroxide reduced ATPase activity and the levels of ATP, ADP, and energy charge and its association with pulp breakdown occurrence of longan fruit during storage

The effects of hydrogen peroxide (H₂O₂) on the contents of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate (AMP), the level of energy charge, and the activity of adenosine triphosphatase (ATPase) in pulp of harvested longan fruit, and its association with longan pulp breakdown occurrence were studied. The results showed that, compared to the control longans, H₂O₂-treated longans exhibited a higher index of pulp breakdown, a higher amount of AMP, but lower levels of ATP, ADP and energy charge. H₂O₂-treated longans also exhibited lower activities of Mg²⁺-ATPase, Ca²⁺-ATPase, and H⁺-ATPase in mitochondrial membrane, vacuolar membrane, and plasma membrane as compared to the control longans. Above findings demonstrated that H₂O₂ caused longan pulp breakdown by depleting energy and lowering the ATPase activity, indicating H₂O₂-induced pulp breakdown in harvested longan fruit was due to energy deficit.

The role of ROS-induced change of respiratory metabolism in pulp breakdown development of longan fruit during storage

Compared to the control longans, hydrogen peroxide (H₂O₂)-treated longans exhibited higher index of pulp breakdown, higher fruit respiration rate, higher activities of pulp phosphohexose isomerase (PGI), succinate dehydrogenase (SDH), cytochrome C oxidase (CCO), ascorbic acid oxidase (AAO) and polyphenol oxidase (PPO), but lower activity of pulp nicotinamide adenine dinucleotide kinase (NADK). H₂O₂-treated longans also exhibited lower total activities of pulp glucose-6-phosphate dehydrogenase (G-6-PDH) and 6-phosphogluconate dehydrogenase (6-PGDH), lower levels of pulp NADP(H), but higher levels of pulp NAD(H). These data indicated that H₂O₂-stimulated longan pulp breakdown was owing to a decreased proportion of pentose phosphate pathway (PPP), the increased proportions of Embden-Meyerhof-Parnas pathway (EMP), tricarboxylic acid (TCA) cycle and cytochrome pathway (CCP) in total respiratory pathways. These findings further revealed that H₂O₂ could enhance respiration rate, and thus accelerate pulp breakdown occurrence and shorten the shelf life of longan fruit.

Changes in Metabolisms of Antioxidant and Cell Wall in Three Pummelo Cultivars during Postharvest Storage

The juice sacs of pummelo fruit is susceptible to softening during storage at 25 °C, which causes quality deterioration and flavor loss during postharvest pummelo storage. This study investigated the changes in metabolisms of antioxidant and cell wall in juice sacs of three pummelo cultivars—Hongroumiyou (HR), Bairoumiyou (BR) and Huangroumiyou (HuR)—during postharvest storage. The results revealed that, with the extension of storage, the juice sacs of three pummelo cultivars exhibited a decrease in total antioxidant capacity (TAC), DPPH and ABTS radical scavenging activity; a decline in total phenols (TP) content and an increase firstly then a decrease in total ascorbic acid (TAA) content; and a decrease in lipoxygenase (LOX) activity and a rise initially, but a decline in activities of ascorbate peroxidase (APX) and glutathione peroxidase (GPX). Additionally, increased water-soluble pectin (WSP), but declined propectin, ionic-soluble pectin (ISP) and chelator-soluble pectin (CSP); as well as an increase from 0 d to 60 d then followed by a decline in activities of pectinesterase (PE), polygalacturonase (PG) and pectate lyase (PL) were observed. These results suggested that the metabolisms of antioxidant and cell wall could result in softening and senescence of pummelo fruit.

Fibroin Delays Chilling Injury of Postharvest Banana Fruit via Enhanced Antioxidant Capability during Cold Storage

storage Banana fruit after harvest is susceptible to chilling injury, which is featured by peel browning during cold, and it easily loses its nutrition and economic values. This study investigated the role of fibroin treatment in delaying peel browning in association with the antioxidant capability of postharvest banana fruit during cold storage. Compared to the control fruit, fibroin-treated fruit contained higher amounts of Pro and Cys during overall storage as well as higher glutathione (GSH) during the middle of storage. Conversely, fibroin-treated fruit exhibited a lower peel browning index and reactive oxygen species (ROS) level during overall storage as well as lower contents of hexadecanoic acid and octadecanoic acid by the end of storage compared to control fruit. In addition, fibroin-treated banana fruit showed higher activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) in relation to upregulation SOD, CAT, and GR as well as peroxiredoxins (MT3 and GRX) during the middle of storage. These results highlighted the role of fibroin treatment in reducing peel browning by enhancing the antioxidant capability of harvested banana fruit during cold storage.