Acidic electrolyzed-oxidizing water treatment mitigated the disease progression in Phomopsis longanae Chi-infected longans by modulating ROS and membrane lipid metabolism

Postharvest harmful pathogenic infestation leads to rapid decay in longan fruit. Compared with P. longanae-infected longans, AEOW alleviated fruit disease severity and diminished the O2-. production rate and MDA content. It also increased APX, CAT, and SOD activities, delayed the decrease in the levels of GSH and AsA, as well as the reducing power and DPPH radical scavenging ability, which resulted in a decline in membrane lipid peroxidation in P. longanae-infected longans. Additionally, AEOW reduced LOX, lipase, PI-PLC, PC-PLC, and PLD activities, maintained higher levels of PC, PI, IUFA, USFAs, and U/S, while reducing levels of PA, DAG, SFAs, and CMP. These effects alleviated membrane lipid degradation and peroxidation in P. longanae-infected longans. Consequently, AEOW effectively maintained membrane integrity via improving antioxidant capacity and suppressing membrane lipid peroxidation. This comprehensive coordination of ROS and membrane lipid metabolisms improved fruit resistance and delayed disease development in longans.

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.

Hydrogen peroxide induced changes in the levels of disease-resistant substances and activities of disease-resistant enzymes in relation to the storability of longan fruit

The influences of hydrogen peroxide (H2O2) on the storability and metabolism of disease-resistant substances in fresh longan were investigated. Compared to the control samples, H2O2-treated longan exhibited a higher index of fruit disease, pericarp browning, and pulp breakdown, a higher rate of fruit weight loss, but lower chromaticity values (L*, a* and b*) in pericarp appearance, and a lower commercially acceptable fruit rate. Additionally, H2O2-treated longan showed a lower lignin content, lower activities of enzymes including phenylalnine ammonia lyase (PAL), cinnamate 4-hydroxylase (C4H), 4-coumaryl coenzyme A ligase (4-CL), cinnamate dehydrogenase (CAD), peroxidase (POD), chitinase (CHI), and β-1,3-glucanase (GLU). These data collectively suggest that H2O2 negatively impacted the storability of fresh longan. This can be attributed to H2O2's role in reducing the levels of disease-resistant substances and suppressing the activities of disease-resistant enzymes, implying that H2O2 reduced the postharvest storability of longan by compromising its disease resistance.

The effect of ε-poly-l-lysine treatment on molecular, physiological and biochemical indicators related to resistance in longan fruit infected by Phomopsis longanae Chi

Postharvest longan fruits are subjected to Phomopsis longanae Chi (P. longanae) infection that lead to fruit quality deterioration. We hypothesized that ε-poly-l-lysine (ε-PL) could enhance fruit disease resistance in longans. Through physiological and transcriptomic analyses, the results showed that, compared to P. longanae-infected longan fruit, ε-PL + P. longanae treatment reduced the disease development of longan fruits. Additionally, ε-PL + P. longanae treatment increased the contents of disease-resistant substances (lignin and H₂O₂) and the activities of disease-resistance enzymes (CHI, PAL, PPO, C4H, CAD, GLU, 4CL, and POD). Furthermore, the expressions of genes relevant to the phenylpropanoid biosynthesis pathway and plant-pathogen interaction pathway (Rboh, FLS2, WRKY29, FRK1, and PR1) were up-regulated by ε-PL + P. longanae treatment. These findings demonstrated that ε-PL treatment inhibited the disease development of postharvest longan fruits were associated with the increased accumulation of disease-resistant related substances, as well as the raised activities and genes expressions of disease-resistance related enzymes.

Saccharomyces cerevisiae-incorporated and sucrose-rich sodium alginate film: An effective antioxidant packaging film for longan preservation

A sodium alginate (SA) film incorporated with Saccharomyces cerevisiae (SE) and sucrose (SU) was fabricated to control the quality and pericarp browning of longan. The SE with satisfactory glutathione production was selected as the antioxidant agent. The scanning electron microscopy (SEM) results revealed that the SU-rich SA film could be used as an effective carrier to protect the cell integrity of SE. The FTIR and mechanical property results indicated that the SA-SE film with the incorporation of SU has good flexibility due to the existence of hydrogen bonds. Notably, the cell viability of the SE was significantly improved with the addition of SU, which positively affects the antioxidant property of the film during the storage period. Finally, the SA-SE-3.0%SU films obviously improved the quality and pericarp browning of longan. The SA-based film incorporated with SU and SE may be established as a novel antioxidant fruit packaging material.

Acidic electrolyzed water treatment retards softening and retains cell wall polysaccharides in pulp of postharvest fresh longans and its possible mechanism

•

AEW delayed pulp softening of longans via suppressing cell wall disassembly.

•

AEW down-regulated expression levels of longan pulp cell wall degrading-related genes.

•

AEW decreased activities of cell wall degrading enzymes in pulp of harvested longans.

•

AEW retained higher levels of longan pulp CWM, CSP, ISP, cellulose, and hemicellulose.

Effects of acidic electrolyzed water (AEW) treatment (pH = 2.5, ACC = 80 mg L⁻¹, 10 min) on pulp firmness, amounts of CWM and CWP, activities and expression of relevant genes of CWDEs in pulp of Fuyan longan during storage at 25 °C were evaluated. Compared to control samples, during storage, AEW-treated fruit retained a higher pulp firmness, prevented WSP formation, reduced the degradation of CSP, cellulose and hemicellulose, and lowered CWDEs activities and their corresponding gene expression. When stored for 5 d, pulp firmness (113.6 g mm⁻¹), CWM (13.9 g kg⁻¹), and CSP (1.4 g kg⁻¹) in AEW-treated fruit displayed the clearly higher contents than those in control samples. These data suggest that AEW treatment can slow down the pulp softening and retain higher pulp CWP levels in postharvest fresh longans, which was because AEW lowered activities of CWDEs and its gene expression levels, and maintained the cell wall structure's integrity.

Impacts of exogenous ROS scavenger ascorbic acid on the storability and quality attributes of fresh longan fruit

The impacts of reactive oxygen species (ROS) scavenger ascorbic acid (AsA) treatment on the storability and quality attributes of 'Fuyan' longan fruit were explored. Compared to control samples, the treatment of 4 g L^-1 AsA solution clearly reduced fruit weight loss, indexes of fruit disease and pericarp browning, retained higher percentage of commercially acceptable fruit, higher values of chromaticity a^∗, chromaticity b^∗ , and chromaticity L^∗ , delayed pigment degradation in longan pericarp, and retarded the decreases of nutritive ingredients in longan pulp. When stored for 6 d, vitamin C (0.08 g kg^-1), sucrose (20.70 g kg^-1), total soluble sugar (56.32 g kg^-1), and total soluble solids (12.4%) in AsA-treated fruit displayed the clearly higher contents than those in control samples. These data suggested that the treatment of exogenous ROS scavenger AsA could effectively enhance the quality attributes and storability of postharvest longan fruit, thereby lengthen their postharvest shelf-life.

Influence of hydrogen peroxide on the ROS metabolism and its relationship to pulp breakdown of fresh longan during storage

•

H₂O₂ down-regulated expression of ROS scavenging-related genes in longan pulp.

•

H₂O₂ reduced activities of ROS scavenging enzymes (SOD, CAT, APX) in longan pulp.

•

H₂O₂ reduced ROS scavenging capacity and raised O₂^–. generation rate in longan pulp.

•

H₂O₂ promoted lipid peroxidation of cell membrane in pulp of harvested longan fruit.

•

H₂O₂-reduced ROS scavenging capacity led to H₂O₂-stimulated pulp breakdown of longans.

The influence of hydrogen peroxide (H₂O₂) on the ROS metabolism and its relationship to pulp breakdown of fresh longan cv. Fuyan during storage was evaluated. Contrasted to control fruit, H₂O₂-treated samples manifested a higher index of pulp breakdown, an enhanced rate of O₂^–. generation, and an increased amount of MDA, but lower APX, CAT and SOD activities, reduced expressions of DlAPX, DlCAT and DlSOD, and lower concentrations of total phenolics, flavonoid, AsA, and GSH as well as lower levels of free radicals scavenging capacity. These data revealed that H₂O₂-induced pulp breakdown of longan was because H₂O₂ reduced ability of removing ROS but increased ROS generation and accumulation, which promoted peroxidation of cell membrane lipid, and subsequently led to damaging cell membrane structure and breakdown occurrence in pulp of postharvest fresh longan.

The role of cell wall polysaccharides disassembly in Lasiodiplodia theobromae-induced disease occurrence and softening of fresh longan fruit

Cell wall polysaccharides in fruits act a pivotal role in their resistance to fungal invasion. Lasiodiplodia theobromae (Pat.) Griff. & Maubl. is a primary pathogenic fungus causing the spoilage of fresh longan fruit. In this study, the influences of L. theobromae inoculation on the disassembly of cell wall polysaccharides in pericarp of fresh longans and its association with L. theobromae-induced disease and softening development were investigated. In contrast to the control, samples with L. theobromae infection showed more severe disease development, lower firmness, lower amounts of cell wall materials, covalent-soluble pectin, ionic-soluble pectin, cellulose and hemicellulose, whereas higher value of water-soluble pectin, higher activities of cell wall polysaccharide-disassembling enzymes (cellulase, β-galactosidase, polygalacturonase and pectinesterase). These findings revealed that cell wall polysaccharides disassembly induced by enzymatic manipulation was an essential pathway for L. theobromae to infect harvested longans, and thus led to the disease occurrence and fruit softening.

Chitosan postharvest treatment suppresses the pulp breakdown development of longan fruit through regulating ROS metabolism

The influences of Kadozan, a novel chitosan formulation, on the pulp breakdown and ROS metabolism in postharvest 'Fuyan' longans were studied. Compared with control longans, the longans treated with 1:500 Kadozan dilution (V_Kadozan: V_{Kadozan + Water}) exhibited the suppressed development of pulp breakdown, higher AsA and GSH amounts, higher activities of ROS-scavenging enzymes like SOD, CAT, APX and POD, higher reducing power, and higher scavenging ability for DPPH radical, but a lower MDA amount, lower levels of ROS including O₂^- and H₂O₂. These findings indicated that the application of 1:500 Kadozan dilution (V_Kadozan: V_{Kadozan + Water}) for harvested longans could enhance the ROS-scavenging capacity to decrease the generation and accumulation of ROS, and a lower level of ROS could slow down the peroxidation progress of membrane lipids, alleviate the damage of longan pulp cellular membrane structure, and ultimately suppress pulp breakdown occurrence of harvested longans.

Sequential extraction and enrichment of pesticide residues in Longan fruit by ultrasonic-assisted aqueous two-phase extraction linked to vortex-assisted dispersive liquid-liquid microextraction prior to high performance liquid chromatography analysis

A simple, green and efficient method for extraction, purification and enrichment of pesticide residues of triazoles and pyrethroids in Longan fruit was developed by ultrasonic-assisted aqueous two-phase extraction (UAATPE) coupled to vortex-assisted dispersive liquid-liquid microextraction (VADLLME). Using an aqueous two-phase system (ATPS) of ethanol/K₂HPO₄ as extraction solvent, the composition of the ATPS, extraction temperature and time were investigated, respectively. Then VADLLME process also was optimized by investigating type and volume of extracting and dispersive solvents, vortex-assisted time and salt addition. The optimum conditions were as follows: the ATPS composition of ethanol concentration 30.0% (w/w) and K₂HPO₄ concentration 25% (w/w), extraction temperature 70 °C and extraction time 15 min for UAATPE; 1-dodecanol 200 μL as extraction solvent, ethanol 1.25 mL as dispersive solvent, vortex-assisted time 1.5 min and addition of NaCl 4% (w/v) for VADLLME. Ethanol as extraction solvent and dispersive solvent could directly connect UAATPE with VADLLME without extra steps. By means of HPLC-DAD detection, nine pesticides had good linearity ranged from 0.0200 to 13.59 μg/mL (R² ≥ 0.9957). LODs and LOQs were in the range of 0.005576-0.01740 μg/mL and 0.01859-0.05010 μg/mL, respectively. UAATPE-VADLLME coupled to HPLC was successfully applied to simultaneous determination of multiple pesticides in Longan fruit, and mean recoveries and RSDs were between 76.95% and 98.63%, 1.2% and 9.8%, respectively. Furthermore, myclobutanil, fenpropathrin and deltamethrin were detected in pericarp and pulp of Longan samples from different districts, respectively.

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.

Effects of chitosan treatment on the storability and quality properties of longan fruit during storage

Effects of various concentrations of Kadozan (chitosan) treatment on storability and quality properties of harvested 'Fuyan' longans were investigated. Compared to the control samples, Kadozan treated-longans displayed lower fruit respiration rate, lower pericarp cell membrane permeability, pericarp browning index, pulp breakdown index, fruit disease index, and weight loss, but higher rate of commercially acceptable fruit, higher levels of pericarp chlorophyll, carotenoid, anthocyanin, flavonoid and total phenolics, higher amounts of pulp total soluble sugar, sucrose, total soluble solids, and vitamin C. These results revealed Kadozan treatment could increase storability and retain better quality of harvested longan fruit. Among different concentrations of Kadozan, the dilution of 1:500 (V_Kadozan: V_{Kadozan + Water}) showed the best results in storability and maintained the best quality of longans during storage. These findings demonstrated that Kadozan could be a facile and eco-friendly postharvest handling approach for increasing storability and lengthening shelf-life of harvested 'Fuyan' longan fruit.

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.

reduced energy status and ATPase activity and its relation to disease development and pericarp browning of harvested longan fruit

This study aimed to investigate the effects of Lasiodiplodia theobromae (Pat.) Griff. & Maubl (L. theobromae) inoculation on the energy status and activity of adenosine triphosphatase (ATPase) during L. theobromae-induced disease development and pericarp browning of harvested 'Fuyan' longan (Dimocarpus longan Lour. cv. Fuyan) fruit. The results showed that, compared to the control longans, L. theobromae-inoculated longans displayed higher indices of fruit disease and pericarp browning, lower pericarp ATP and ADP contents, higher AMP content, lower level of energy charge, as well as lower activities of Ca²⁺-ATPase, Mg²⁺-ATPase and H⁺-ATPase in membranes of plasma, vacuole, and mitochondria. These results indicated that the infection of L. theobromae reduced energy status and ATPase activities, caused ions disorder, damaged the integrity and function of the cell and organelles including vacuole and mitochondria in pericarp of longan fruit, which contributed to L. theobromae-promoted disease development and pericarp browning of harvested longan fruit during storage.