Sucrose, cell wall, and polyamine metabolisms involve in preserving postharvest quality of 'Zaosu' pear fruit by L-glutamate treatment.

'Zaosu' pear fruit is prone to yellowing of the surface and softening of the flesh after harvest. This work was performed to assess the influences of L-glutamate treatment on the quality of 'Zaosu' pears and elucidate the underlying mechanisms involved. Results demonstrated that L-glutamate immersion reduced ethylene release, respiratory intensity, weight loss, brightness (L*), redness (a*), yellowness (b*), and total coloration difference (ΔE); enhanced ascorbic acid, soluble solids, and soluble sugar contents; maintained chlorophyll content and flesh firmness of pears. L-glutamate also restrained the activities of neutral invertase and acid invertase, while enhancing sucrose phosphate synthetase and sucrose synthase activities to facilitate sucrose accumulation. The transcriptions of PbSGR1, PbSGR2, PbCHL, PbPPH, PbRCCR, and PbNYC were suppressed by L-glutamate, resulting in a deceleration of chlorophyll degradation. L-glutamate concurrently suppressed the transcription levels and enzymatic activities of polygalacturonases, pectin methylesterases, cellulase, and ß-glucosidase. It restrained polygalacturonic acid trans-eliminase and pectin methyl-trans-eliminase activities as well as inhibited the transcription levels of PbPL and Pbß-gal. Moreover, the gene transcriptions and enzymatic activities of arginine decarboxylase, ornithine decarboxylase, S-adenosine methionine decarboxylase, glutamate decarboxylase, γ-aminobutyric acid transaminase, glutamine synthetase along with the PbSPDS transcription was promoted by L-glutamate. L-glutamate also resulted in the down-regulation of PbPAO, PbDAO, PbSSADH, PbGDH, and PbGOGAT transcription levels, while enhancing γ-aminobutyric acid, glutamate, and pyruvate acid contents in pears. These findings suggest that L-glutamate immersion can effectively maintain the storage quality of 'Zaosu' pears via modulating key enzyme activities and gene transcriptions involved in sucrose, chlorophyll, cell wall, and polyamine metabolism.

2-hydroxy-3-phenylpropanoic acid suppressed the growth of Alternaria alternata through damaging cell membrane integrity and modulating reactive oxygen species metabolism.

Black spot rot caused by Alternaria alternata is one of the major postharvest disease of apple fruit during logistic. This study evaluated in vitro inhibitory effect of 2-hydroxy-3-phenylpropanoic acid (PLA) at various concentrations on A. alternata and the possible mechanisms involved in its action. Results showed that different concentrations of PLA inhibited conidia germination and mycelial growth of A. alternata in vitro, and 1.0 g L-1 was the lowest effective concentration to suppress A. alternata growth. Moreover, PLA significantly reduced relative conductivity and increased malondialdehyde and soluble protein contents. PLA also increased H2O2 and dehydroascorbic acid contents, but reduced ascorbic acid content. Additionally, PLA treatment inhibited catalase, ascorbate peroxidase, monodehydroascorbate acid reductase, dehydroascorbic acid reductase and glutathione reductase activities, whereas promoted superoxide dismutase activity. All these findings suggest that the possible mechanisms involved in the inhibitory effect of PLA on A. alternata included damaging the cell membrane integrity to cause electrolyte leakage and destroying reactive oxygen species balance.

l-Glutamate maintains the quality of apple fruit by mediating carotenoid, sorbitol and sucrose metabolisms.

BACKGROUND: l-Glutamate is involved in many important chemical reactions in horticultural products and improves postharvest disease resistance. Quality decline of apple fruit caused by senescence and fungus invasion often leads to tremendous losses during logistics. This study was performed to evaluate the variations of quality attributes, carotenoid, sorbitol and sucrose metabolisms in apples (cv. Qiujin) after l-glutamate dipping treatment. RESUITS: l-Glutamate immersion maintained high values of L*, a* and b*, flesh firmness, titratable acidity, as well as the total soluble solids, soluble sugar, reducing sugar and ascorbic acid contents in apples. l-Glutamate also decreased mass loss, respiratory rate and ethylene release, enhanced sucrose synthase-cleavage, acid invertase and neutral invertase activities, whereas reduced sorbitol dehydrogenase, sucrose phosphate synthase, sucrose synthase synthesis and sorbitol oxidase activities in apples. Moreover, l-glutamate inhibited lutein, ß-carotene and lycopene accumulation, and down-regulated phytoene synthase, lycopene ß-cyclase, ζ-carotene desaturase, phytoene desaturase, carotenoid isomerase, ζ-carotene isomerase and carotenoids cleavage dioxygenase gene expressions, but up-regulated 9-cis-epoxycarotenoid dioxygenase gene expression in apples. CONCLUSION: Postharvest l-glutamate dipping treatment can keep apple quality by modulating key enzyme activity and gene expression in sorbitol, sucrose and carotenoid metabolisms. © 2023 Society of Chemical Industry.

Preparation and antibacterial mechanism of cinnamaldehyde/tea polyphenol/polylactic acid coaxial nanofiber films with zinc oxide sol to Shewanella putrefaciens.

In this study, the coaxial nanofiber films were prepared by coaxial electrospinning technique with cinnamaldehyde (CMA) and tea polyphenol (TP) as core material and polylactic acid (PLA) as shell material, and to obtain food packaging materials with great physicochemical and antibacterial properties, zinc oxide (ZnO) sol were added into PLA, and ZnO/CMA/TP-PLA coaxial nanofiber films were prepared. Meanwhile, the microstructure and physicochemical properties were determined, and the antibacterial properties and mechanism were investigated with Shewanella putrefaciens (S. putrefaciens) as target. The results show that the ZnO sol makes the physicochemical properties and antibacterial properties of the coaxial nanofiber films improve. Among them, the 1.0 % ZnO/CMA/TP-PLA coaxial nanofibers have smooth and continuous uniform surfaces, and their encapsulation effect on CMA/TP and antibacterial properties are the optimal. The synergistic action of CMA/TP and ZnO sol cause severe depression and folding of the cell membrane of S. putrefaciens, makes cell membrane permeability increase and of intracellular materials spillage, interference the bacteriophage protein expression, and makes macromolecular protein degraded. In this study, the introduction of oxide sols into polymeric shell materials by in-situ synthesis technique can provide theoretical support and methodological guidance for the application of electrospinning technology in the field of food packaging.

Acibenzolar-S-methyl activates phenylpropanoid pathway to enhance resistance against Alternaria alternata in pear fruit.

BACKGROUND: Alternaria alternata is a causal agent of black spot rot of pear fruit after harvest. Acibenzolar-S-methyl (ASM) has been shown to be a potential elicitor of tolerance in several horticultural products. This work was performed to research the influence of ASM on black spot rot of Docteur Jules Guyot pears and vital enzyme activity and gene expression in the phenylpropanoid pathway. RESULTS: ASM remarkably decreased the lesion diameter of A. alternata-inoculated pears. ASM also increased phenylalanine ammonialyase, cinnamate 4-hydroxylase, cinnamyl alcohol dehydrogenase, peroxidase, polyphenol oxidase activities and gene expression, and enhanced 4-coumarate/coenzyme A ligase activity in pears. Moreover, ASM improved the content of phenylalanine, total phenolic compounds, caffeic acid, flavonoids, anthocyanin and lignin in pears. CONCLUSION: ASM could modulate vital enzyme activity and gene expression in the phenylpropanoid pathway to accelerate metabolite synthesis, thereby enhancing resistance against A. alternata in pears. © 2022 Society of Chemical Industry.

Comprehensive responses of aroma production in 'Benihoppe' strawberry to low oxygen associated with the changes of key gene expressions and energy levels.

BACKGROUND: The influence of low oxygen on the biosynthesis of aroma-related esters and alcohols in strawberries has been well revealed. However, how low-oxygen conditions affect other volatile compounds, such as terpenes and furans, is still to be elucidated. RESULTS: The effects of 2 kPa O2 low oxygen on the biosynthesis of aroma in 'Benihoppe' strawberries were comprehensively investigated in this study. The results showed that, like esters, the accumulations of key terpene alcohols and furans in strawberries were also inhibited by 2 kPa O2 low oxygen during storage and subsequent shelf life, which was associated with the down-regulation of expression of FaNES1 (nerolidol synthase) and FaOMT (O-methyltransferase). However, no anaerobic fermentation occurred in 'Benihoppe' strawberries since no ethanol and acetaldehyde were produced under the 2 kPa O2 condition. As expected, the 2 kPa O2 condition suppressed the respiratory intensity and lowered the energy charge to maintain the quality of strawberries. The negative effects of low-oxygen storage on aroma accumulations and the energy charge of strawberries were more pronounced when transferred to the period of shelf life. CONCLUSION: The 2 kPa O2 condition caused a full-scale loss of aroma in 'Benihoppe' strawberries, including esters and alcohols as well as terpenes and furans, which was mainly reflected in the reduction of aroma emissions rather than the production of off-flavor, probably due to the reduced expressions of related genes and energy charge. © 2022 Society of Chemical Industry.

Acibenzolar-S-methyl activates calcium signalling to mediate lignin synthesis in the exocarp of Docteur Jules Guyot pears.

'Docteur Jules Guyot' pears were immersed in acibenzolar-S-methyl (ASM) and 0.01 mol L-1 ethyl glycol tetra acetic acid (EGTA) to investigate the changes of Ca2+ receptor proteins and phenylpropanoid pathway. Results showed that ASM treatment increased the activities of phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H), 4-coumarate coenzyme A ligase (4CL), polyphenol oxidase (PPO), and cinnamyl alcohol dehydrogenase (CAD) in the exocarp of pears, whereas EGTA pre-treatment inhibited the activities of these enzymes. ASM treatment also enhanced the transcription of PcPAL, PcC4H, Pc4CL, PcC3H, PcCOMT, PcCCoAOMT, PcCCR, PcPOD, PcCDPK1, PcCDPK2, PcCDPK5, PcCDPK11, PcCDPK13, PcCBL1, PcCBL9, PcCIPK14, and PcCML27 in pears. EGTA + ASM treatments inhibited the transcription of PcPAL, PcC4H, Pc4CL, PcC3H, PcCCR, PcF5H, PcCAD, PcCDPK11, PcCDPK26, PcCDPK32, PcCBL1, PcCIPK14, PcCIPK23, and PcCaM in the fruit. All these results indicated that ASM induced the gene expressions of Ca2+ receptor proteins, the key enzyme activities and gene expressions in phenylpropanoid pathway; Ca2+ mediated phenylpropane metabolism in pears after ASM treatment.

Comparative analysis of expression profiles of metacaspase (MC) genes between two apple (Malus domestica) cultivars with distinct ripening behavior.

The purpose of this research was to determine expression profiles of metacaspase (MC) genes during ripening and senescence of two apple cultivars with distinct ripening behavior. "Golden Delicious" and "Fuji" harvested at commercial maturity were used as materials. Our data revealed that flesh firmness, respiration rate, ethylene production, metacaspase (MC) activity, superoxide anion (O2 •- ) production rate, relative electrical conductivity (REC), hydrogen peroxide (H2 O2 ), and malondialdehyde (MDA) contents in "Golden Delicious" were higher than in "Fuji" during ripening. At 35 days, no DNA ladder was observed in both cultivars, and tonoplast disintegration was only observed in "Golden Delicious" by transmission electron microscope (TEM), indicating that programmed cell death (PCD) was initiated earlier in "Golden Delicious" than in "Fuji." A total of 18 MC genes were detected to be expressed in both cultivars. For those genes expressed only in "Golden Delicious," MdMC06, MdMC10, MdMC12, and MdMC21 might play a role in the early stage of ripening, whereas MdMC19 might be associated with the late stage of ripening. MdMC15 was expressed only in "Fuji." The remaining MC genes were differentially expressed in both cultivars during ripening. These results would provide useful information to further underlie the relationships among MC genes, PCD and storability of different apple cultivars. PRACTICAL APPLICATIONS: Apple is one of the most popular fruits in the world. Different apple cultivars vary in their ripening behavior and storability, but the molecular mechanism has not yet been fully elucidated. "Golden Delicious" and "Fuji" are two important apple cultivars worldwide. Our data indicated that PCD was initiated earlier in "Golden delicious" than in "Fuji" during postharvest ripening and senescence. MdMCs showed variable expression patterns in both cultivars during ripening. MdMC15 and MdMC19 might be closely associated with the early stage of PCD. These results would provide useful information to further decode the molecular mechanisms responsible for different storage storability of apple cultivars.

Organic acids metabolism and GABA shunt involved in maintaining quality of Malus domestica by methyl jasmonate treatment.

Apples (cv. Golden Delicious) were used as the materials to investigate methyl jasmonate (MeJA) dipping on quality parameters, organic acids metabolism and GABA shunt during storage at 21 ± 1 °C and 75 ± 5 % relative humidity. Results demonstrated that MeJA treatment reduced mass loss, respiratory intensity and ethylene release, and maintained higher flesh firmness and soluble solid content of apples. MeJA also decreased malic acid content, increased succinic and tartaric acids contents, and inhibited cytoplasmic aconitase (Cyt-ACO), NADP-malate (NADP-ME), phosphoenolpyruvate dehydrogenase (PEPC), mitochondrial citrate synthase (Mit-CS), glutamate dehydrogenase (GAD), and GABA transferase (GABA-T) activities in apples. NADP-isocitrate dehydrogenase (NADP-IDH), mitochondrial cis-aconitase (Mit-ACO), and cytoplasmic NAD-malate dehydrogenase (CytNAD-MDH) activities in apples were also enhanced by MeJA dipping. Moreover, MeJA dipping enhanced MdCytNAD-MDH and MdNADP-IDH expressions, and down-regulated MdGAD, MdGABA-T, MdNADP-ME, MdPEPC, MdCyt-ACO and MdMit-CS expressions in apples. These results suggest that MeJA dipping can maintain storage quality of "Golden Delicious" apples by regulating organic acids metabolism and GABA shunt.

Determining the Effects of Light on the Fruit Peel Quality of Photosensitive and Nonphotosensitive Eggplant.

With the development of facility agriculture, low-light stress is a prominent problem and a popular research topic currently. In this study, transcriptome analysis was used to analyze the genes in the fruit peel of photosensitive and nonphotosensitive eggplant and to explore the mechanism of changes in fruit color, texture, hormone content, aroma, and taste of these two different types of eggplant. We identified 51, 65, 66, and 66 genes involved in synthesizing anthocyanins, texture, hormone content, and aroma and flavor, respectively, in the two different types of eggplant based on the variation in gene expression trends in the fruit peel. These results provide a basis for further analysis of the molecular mechanism underlying the regulatory processes in eggplant fruits under low-light stress.

Immunogenicity and safety of an inactivated SARS-CoV-2 vaccine (Sinopharm BBIBP-CorV) coadministered with quadrivalent split-virion inactivated influenza vaccine and 23-valent pneumococcal polysaccharide vaccine in China: A multicentre, non-inferiority, open-label, randomised, controlled, phase 4 trial.

BACKGROUND: The safety and immunogenicity of the coadministration of an inactivated SARS-CoV-2 vaccine (Sinopharm BBIBP-CorV), quadrivalent split-virion inactivated influenza vaccine (IIV4), and 23-valent pneumococcal polysaccharide vaccine (PPV23) in adults in China is unknown. METHODS: In this open-label, non-inferiority, randomised controlled trial, participants aged ≥ 18 years were recruited from the community. Individuals were eligible if they had no history of SARS-CoV-2 vaccine or any pneumonia vaccine and had not received an influenza vaccine during the 2020-21 influenza season. Eligible participants were randomly assigned (1:1:1), using block randomization stratified, to either: SARS-CoV-2 vaccine and IIV4 followed by SARS-CoV-2 vaccine and PPV23 (SARS-CoV-2 + IIV4/PPV23 group); two doses of SARS-CoV-2 vaccine (SARS-CoV-2 vaccine group); or IIV4 followed by PPV23 (IIV4/PPV23 group). Vaccines were administered 28 days apart, with blood samples taken on day 0 and day 28 before vaccination, and on day 56. RESULTS: Between March 10 and March 15, 2021, 1152 participants were recruited and randomly assigned to three groups (384 per group). 1132 participants were included in the per-protocol population (375 in the SARS-CoV-2 + IIV4/PPV23 group, 380 in the SARS-CoV-2 vaccine group, and 377 in the IIV4/PPV23 group). The seroconversion rate (100 % vs 100 %) and GMT (159.13 vs 173.20; GMT ratio of 0.92 [95 % CI 0.83 to 1.02]) of SARS-CoV-2 neutralising antibodies in the SARS-CoV-2 + IIV4/PPV23 group was not inferior to those in the SARS-CoV-2 vaccine group. The SARS-CoV-2 + IIV4/PPV23 group was not inferior to the IIV4/PPV23 group in terms of seroconversion rates and GMT of influenza virus antibodies for all strains except for the seroconversion rate for the B/Yamagata strain. The SARS-CoV-2 + IIV4/PPV23 group was not inferior to the IIV4/PPV23 group regarding seroconversion rates and GMC of Streptococcus pneumoniae IgG antibodies specific to all serotypes. All vaccines were well tolerated. CONCLUSIONS: The coadministration of the inactivated SARS-CoV-2 vaccine and IIV4/PPV23 is safe with satisfactory immunogenicity. This study is registered with ClinicalTrials.gov, NCT04790851.

Trehalose Regulates Starch, Sorbitol, and Energy Metabolism to Enhance Tolerance to Blue Mold of "Golden Delicious" Apple Fruit.

The efficacy of trehalose on the lesion diameter of apples (cv. Golden Delicious) inoculated with Penicillium expansum was evaluated to screen the optimal concentration. The changes in gene expression and activity of the enzyme in starch, sorbitol, and energy metabolism were also investigated in apples after trehalose treatment. The results revealed that trehalose dipping reduced the lesion diameter of apples inoculated with P. expansum. Trehalose suppressed the activities and gene expressions of ß-amylase, NAD-sorbitol dehydrogenase, and NADP-sorbitol dehydrogenase, whereas it decreased the sorbitol 6-phosphate dehydrogenase gene expression and amylose, amylopectin, total starch, and reducing sugar contents. Additionally, trehalose improved the gene expressions and activities of α-amylase, starch-branching enzymes, total amylase, H+-ATPase, and Ca2+-ATPase, as well as soluble sugar, adenosine triphosphate, and adenosine diphosphate contents and energy charge in apples. These findings imply that trehalose could induce tolerance to the blue mold of apple fruit by regulating starch, sorbitol, and energy metabolism.

Low temperature delays degreening of apple fruit by inhibiting pheophorbide a oxygenase (PAO) pathway and chlorophyll oxidation during ripening.

The effects of low temperature (LT) on chlorophyll (Chl) degradation in peel of apple fruit during ripening were investigated. Apples collected at commercial maturity were stored at 4 ± 0.5°C. Our data indicated that LT treatment reduced respiration rate and ethylene production and slowed down softening of apple fruit during ripening. The LT treatment delayed increase in L*, a*, and b* values and decrease in Chl content compared with controls. The LT treatment reduced hydrogen peroxide (H2 O2 ) and malondialdehyde (MDA) contents and decelerated superoxide anion (O2 ·- ) production rate in chloroplast of peel compared with controls during ripening. The LT treatment differentially reduced activities of pheophytin pheophorbide hydrolase (PPH), Mg-dechelatase (MDcase), chlorophyll-degrading peroxidase (Chl-POX), and Chl oxidase, while enhanced SOD activity in chloroplast of peel during ripening. Expression levels of MdHCARa, MdNYC1, MdNYC3, MdNYE1, MdRCCR2, MdPPH1, MdPAO6, MdPAO8, and MdNOL2 in peel were differentially reduced by LT treatment during ripening. Our results indicated that LT treatment might delay Chl degradation through inhibiting PAO pathway and Chl oxidation during ripening of apple fruit. PRACTICAL APPLICATIONS: The LT is a common practice used to extend storage life of apple fruit. Degreening caused by Chl degradation is an integral part of fruit ripening, and elucidating its mechanism is an important subject for fruit quality maintenance. Our data indicated that LT delayed degreening of apple fruit by inhibiting PAO pathway and Chl oxidation during ripening. These results will provide useful information for clarifying molecular mechanisms of LT in regulation of degreening and also for quality maintenance of apple fruit.

Postharvest melatonin dipping maintains quality of apples by mediating sucrose metabolism.

Senescence is a pivotal factor that causes quality breakdown and economic loss of fruit after harvest. In this study, 'Golden Delicious' apples were used as the materials to investigate the effect of melatonin dipping on quality parameters and sucrose metabolism during room temperature storage. Postharvest melatonin treatment inhibited respiratory intensity and ethylene release, increased flesh firmness, soluble sugar, ascorbic acid, and soluble solid contents, and titratable acid in apples. Furthermore, melatonin treatment inhibited acid invertase and neutral invertase activities, increased sucrose synthase and sucrose phosphate synthase activities, and repressed the activities of sorbitol dehydrogenase, sorbitol oxidase and sucrose synthase cleavage in apple fruit. All these findings suggest that exogenous application of melatonin could maintain quality of 'Golden Delicious' apples by mediating the enzyme activity in sucrose metabolism.

Effects of 1-methylcyclopropene (1-MCP) treatment on ethanol fermentation of Nanguo pear fruit during ripening.

The aim of this study was to analyze the effects of 1-methylcyclopropene (1-MCP) on ethanol fermentation of Nanguo pears during ripening. Pears were exposed to 1 µl/L 1-MCP and stored at 20 ± 2°C. Our data indicated that postharvest application of 1-MCP maintained flesh firmness and reduced ethylene production and respiration rate during storage compared with untreated fruits. 1-MCP treatment delayed the second glucose peak during fruit ripening. The contents of pyruvate and acetyl-CoA were generally reduced by 1-MCP treatment, and at the same time, their peaks were delayed by it during storage compared with controls. The contents of citric acid (CA) and oxaloacetate (OA) were increased by 1-MCP, whereas the contents of acetaldehyde and ethanol were reduced during the whole storage period compared with controls. Activities of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) were reduced by application of 1-MCP during the early stage of storage, and the appearance of their peak activities was also delayed after treatment with 1-MCP. These data showed that postharvest application of 1-MCP could effectively delay the production of the "alcohol taste" of Nanguo pears during ripening. PRACTICAL APPLICATIONS: Nanguo pear is one of the most common cultivars that widely grow in northeast China. It is preferred by many consumers for its unique "alcohol taste", which is mainly produced through ethanol fermentation during ripening. Until now, the mechanisms for regulating ethanol fermentation in ripening Nanguo pears are still unclear. Our data indicated that postharvest application of the ethylene action inhibitor 1-MCP could effectively delay the production of the "alcohol taste" of Nanguo pears during ripening. The data from this study can provide reference data for maintaining the quality of postharvest Nanguo pears.

Acibenzolar-S-methyl activates mitogen-activated protein kinase cascade to mediate chlorophyll and carotenoid metabolisms in the exocarp of Docteur Jules Guyot pears.

BACKGROUND: Acibenzolar-S-methyl (ASM), a well-known plant activator, has been used to protect fruit and vegetable from fungal invasion and maintain quality. However, little is known about the molecular mechanism of ASM in regulating chlorophyll and carotenoid metabolisms. Therefore, Docteur Jules Guyot pears were used as the materials to study the changes of hydrogen peroxide (H2 O2 ) production, mitogen-activated protein kinase (MAPK) cascade, transcription factors, chlorophyll, and carotenoid metabolisms after ASM and PD98059 (a MAPK cascade blocker) treatments. RESULTS: ASM increased NADPH oxidase (NOX) and superoxide dismutase (SOD) activities, and H2 O2 content, promoted PcMAPKKK1, PcMAPKK3, and PcMAPK6 expressions, and down-regulated PcMYC2, PcPIF1, PcPIF3, and PcPIF4 expressions in exocarp of pears. ASM also delayed the decrease of chlorophyll a and b contents, and inhibited the accumulation of ß-carotene, lycopene and lutein, PcNYC1, PcHCAR, PcPPH, PcSGR1/2, PcPAO, PcPSY, PcLCYB, PcCRTZ2, PcCCS1 expressions, and promoted PcLCYE expression. PD98059 + ASM treatments depressed SOD and NOX activities and H2 O2 content, inhibited PcMAPKKK1, PcMAPKK3, PcMAPK6, PcPIF1, and PcPIF3 expressions, and promoted PcMYC2 and PcPIF4 expressions in exocarp of pears. Additionally, PD98059 + ASM accelerated PcNYC1, PcHCAR, PcPPH, PcSGR1/2, PcPAO, PcPSY, PcCYB, PcCRTZ2, and PcCCS1 expressions, thereby reducing chlorophyll a and b contents, and promoting ß-carotene, lycopene and lutein contents. CONCLUSIONS: Postharvest ASM treatment promoted the production of H2 O2 to activate the MAPK cascade, then phosphorylated/dephosphorylated transcription factors expression, and delayed chlorophyll decomposition and carotenoid synthesis in pears. © 2022 Society of Chemical Industry.

Preparation of three-layer flaxseed gum/chitosan/flaxseed gum composite coatings with sustained-release properties and their excellent protective effect on myofibril protein of rainbow trout.

Plant essential oils lose their activity due to unstable chemical properties and volatility, and the coating can improve their stability by encapsulating. The three-layer coatings were prepared by tape casting method with flaxseed gum (FG) and chitosan (CS) as film-forming materials, eugenol (EG) and laurel essential oil (LEO) as preservatives. The composite coatings were characterized, and their physicochemical properties, release properties, antibacterial and antioxidant properties were determined. Meanwhile, the protective effect of the composite coatings on rainbow trout fillets myofibril protein was studied. The mechanical properties of the FG/CS/FG coatings are better than FG coating. The release of EG and LEO from the coatings are followed simple diffusion mechanism. After added essential oils, the antibacterial and antioxidant properties of the composite coatings are significantly enhanced. In the preservation process of the rainbow trout fillets, the composite coatings can reduce the carbonyl content, increase the sulfhydryl content and Ca2+-ATPase activity. The ß-sheet content is 6.09%-15.63% higher than that of control, indicating the coatings are helpful to maintain the order of myofibril protein. The composite coatings slowed down the decrease of antioxidant enzyme activity, thus delay the protein oxidation. Because of long-term antibacterial and antioxidant properties, the composite coatings have potential value in food preservation or food packaging materials.

Exogenous γ-aminobutyric acid maintains fruit quality of apples through regulation of ethylene anabolism and polyamine metabolism.

In this study, 'Golden Delicious' apples were dipped with γ-aminobutyric acid (GABA) solution to investigate the changes of quality parameters, ethylene anabolism, polyamine metabolism and GABA shunt. Results showed that GABA distinctly suppressed respiratory rate, reduced titratable acidity, maintained higher soluble solid content and pericarp firmness of apples. Compared to the control, GABA also repressed the activities and gene expressions of polyamine oxidase (PAO) and diamine oxidase (DAO), enhanced MdMT, MdMS, MdSAMS, MdSAMDC, MdSPDS, MdODC, MdADC, and MdACL5 expressions, and accelerated the accumulation of putrescine, spermidine, and spermine in the exocarp of apples. Moreover, GABA decreased ethylene release, MdACS and MdACO gene expressions in the exocarp. In addition, exogenous GABA activated MdGAD, MdGDH, MdGS expressions and inhibited MdGABA-T and MdSSADH expressions in the GABA shunt, therefore increased endogenous GABA, pyruvic acid and glutamate contents in the exocarp. These findings suggest that exogenous GABA regulates ethylene anabolism, polyamine metabolism and GABA shunt to maintain fruit quality of 'Golden Delicious' apples.

Effects of 1-MCP treatment on sprouting and preservation of ginger rhizomes during storage at room temperature.

The purpose of this study was to explore the effects of 1-MCP on the sprouting and preservation of ginger rhizomes during storage at room temperature. Ginger rhizomes were treated with 1 µL L-1 1-methylcyclopropene (1-MCP) and stored at 23 ± 0.2 °C. Our data showed that application of 1-MCP reduced the rate of sprouting during storage compared with the control rhizome. Respiration rate and the reducing sugar content were also reduced following 1-MCP treatment, while the starch content increased. 1-MCP treatment increased the total phenol content and inhibited polyphenol oxidase (PPO) activity. 1-MCP treatment was also associated with a higher ascorbic acid content but a reduced crude fiber content. The generation of superoxide anion free radicals (O2-), hydrogen peroxide (H2O2) and malondialdehyde (MDA) was lower following 1-MCP treatment, while the activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) were higher compared with the controls. These results suggested that application of 1-MCP could reduce sprouting rates, decrease the accumulation of ROS, and maintain the quality of ginger rhizomes during storage at room temperature. It would be useful to further explore the role and mechanisms of action of ethylene in regulating the sprouting of ginger rhizomes.

Roles of calcium-dependent protein kinases mediated reactive oxygen species homeostasis in inducing resistance of apples by acibenzolar-S-methyl.

This study was carried out to investigate the effect of acibenzolar-S-methyl (ASM) and ethylenebis (oxyethylenenitrilo) tetraacetic acid (EGTA) treatments on calcium-dependent protein kinases (CDPKs) and reactive oxygen species (ROS) metabolism in apples. Postharvest ASM treatment increased H2O2 content, reduced glutathione and ascorbic acid contents, and NADPH oxidase, peroxidase, ascorbate peroxidase, superoxide dismutase and glutathione reductase activities and retarded catalase activity and MdCAT expression in apples. ASM treatment enhanced MdSOD, MdPOD, MdAPX, MdGR, MdCDPK1, MdCDPK4, MdCDPK5, MdCDPK7, and MdCDPK21 expressions in apples. However, EGTA + ASM treatments suppressed H2O2, glutathione and ascorbic acid contents, NADPH oxidase, peroxidase, superoxide dismutase, ascorbate peroxidase and glutathione reductase activities. EGTA + ASM treatments suppressed the selected genes expressions in ROS metabolism and CDPKs, but up-regulated MdCAT expression in apples. These findings suggest that CDPKs play a vital role in regulating ROS metabolism and involve in inducing resistance in apples by ASM.