Multiple 1-MCP treatment more effectively alleviated postharvest nectarine chilling injury than conventional one-time 1-MCP treatment by regulating ROS and energy metabolism

Carvacrol enhances antioxidant activity and slows down cell wall metabolism by maintaining the energy level of 'Guifei' mango

BACKGROUND

Postharvest mango fruit are highly susceptible to rapid ripening, softening and senescence, greatly limiting their distribution. In this study, we evaluated the potential effects of carvacrol (0.06 g L-1) on mango (25 ± 1 °C) and the mechanisms by which it regulates antioxidant activity, energy and cell wall metabolism.

RESULTS

The results showed that carvacrol treatment delayed the 'Guifei' mango color transformation (from green to yellow) and the decrease in firmness, titratable acidity, weight loss and soluble solids content, and suppressed the increase in relative conductivity, malondialdehyde content and reactive oxygen species (H2O2 and O2 ·-) as well as enhancing antioxidant activity. In addition, carvacrol treatment increased ascorbic acid and reduced glutathione levels, ascorbate peroxidase, glutathione reductase, monodehydroascorbate reductase and dehydroascorbate reductase activities in mango. Meanwhile, energy level (adenosine triphosphate, adenosine diphosphate, adenosine monophosphate and energy charge) content and energy metabolizing enzyme activities (H+-ATPase, Ca2+-ATPase, succinate dehydrogenasepears and cytochrome C oxidase) were increased on carvacrol treatment, which resulted in the maintenance of higher energy levels. Finally, the application of carvacrol was effective in maintaining firmness and cell wall components by inhibiting the activities of polygalacturonase, cellulase, pectin methyl esterase and β-galactosidase.

CONCLUSION

The current study demonstrates that carvacrol effectively delays the ripening and softening of mangoes by modulating energy metabolism and cell wall dynamics through the attenuation of oxidative stress. © 2024 Society of Chemical Industry.

24-Epibrassinolide treatment alleviates frost damage of apple flower via regulating proline, ROS, and energy metabolism

Frost damage to apple flowers significantly affects both the quality and yield of apples, potentially leading to substantial economic losses. This study investigates the application of the environmentally friendly plant hormone 24-epibrassinolide (EBR) on apple flowers to assess its effects under frost stress conditions. The findings indicate that exogenous EBR treatment maintained favorable flower morphology, mitigated pistil browning, and reduced ion leakage. Furthermore, EBR enhanced the ICE-CBF-COR signaling pathway and increased proline accumulation by modulating gene expression and enzyme activity involved in proline metabolism, promoting osmotic adjustment ability of cells. Furthermore, EBR treatment retarded the increase of H2O2, O2·-, and malonaldehyde (MDA), and increased the enzymatic activity and gene expression of antioxidant enzymes such as superoxide dismutase (SOD), Catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POD), thereby augmenting the antioxidant capacity of tissues. Additionally, the study found that exogenous EBR reduced AMP content, promoted ATP content and energy charge level, improved succinic dehydrogenase (SDH), cytochrome oxidase (CCO), H+-ATPase, Ca2+-ATPase enzyme activity, and enhanced the energy supply of the cells. Consequently, we hypothesized that EBR treatment could enhance the frost resistance in apple flowers by synergistically ameliorating cold signaling, osmotic adjustment, antioxidant capacity, and energy status.

Deciphering the Effect of Postharvest 1-MCP Treatment Coupled with Low-Temperature Storage on the Physiological Activities and Edible Quality of Melon

Fruits are an important source of a healthy diet due to their essential nutrients for daily intake. Melon is known as a significant fruit crop of the Cucurbitaceae family based on its various dietary benefits, but its shelf life needs to be maintained for long-term usage. 1-Methylcyclopropene (1-MCP) is a cyclopropene-derived synthetic plant growth regulator (PGR) that is used for significantly delaying the ripening process and maintaining the shelf life of climacteric fruits during storage. In this study, freshly harvested melon fruits were fumigated with various concentrations (1.0 µL·L-1, 2.0 µL·L-1, and 3.0 µL·L-1) of 1-MCP treatment for 12 h (h) and stored at low temperature (8 ± 1 °C) for 30 days (d). The obtained results showed that 1-MCP fumigation coupled with low-temperature treatment maintains the postharvest shelf life of melon fruit. It was noticed that the increase in color hue (a* (red/green), b* (blue/yellow), L* (lightness)) was slowed down and the external fresh color was effectively maintained. At the same time, the firmness, soluble solids, titratable acids (TAs), and vitamin C (VC) content seemed to be maintained at a high level; weight loss and cell permeability were reduced; respiratory intensity and ethylene emission were inhibited; and the accumulation of superoxide anions and malondialdehyde (MDA) was also reduced. In addition, an upsurge in the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) was noticed in melon fruits under the combined treatment of 1-MCP and low-temperature storage as compared with the control group (CK, without treatment), indicating that 1-MCP treatment can effectively enhance the antioxidant metabolism of melon fruits during storage. Overall, we can recommend that the 3.0 µL·L-1 concentration of 1-MCP had the best effect on maintaining the internal and external quality of sweet melon fruit during storage.

1-Methylcyclopropene Delays Browning and Maintains Aroma in Fresh-Cut Nectarines

The color and aroma of nectarines experience adverse effects from cutting, resulting in the fast senescence of fruit tissue. Therefore, 1-methylcyclopropene (1-MCP) was used to treat postharvest nectarines before cutting, and its effect on the surface browning and aroma alteration were investigated. The results indicated that 1-MCP restrained the soluble quinone (SQC) accumulation in fresh-cut nectarines by regulating the peroxidase (POD) and polyphenol oxidase (PPO) activities and the metabolism of phenolic compounds. Compared with the control, 1-MCP pre-cutting treatment maintained the ultrastructural integrity of the cell wall in fresh-cut nectarines, which also showed reduced malondialdehyde (MDA) content and reactive oxygen species (ROS) and enhanced the 1,1-Diphenyl-2-Picrylhydrazyl (DPPH) radical scavenging activities. Electronic nose and GC-MS analysis revealed that the aroma profiles presented significant differences in the control and 1-MCP treatment during the storage at 0 °C for 10 days. The browning value of the 1-MCP pre-cutting treatment was 29.95% lower than the control, which prevented the loss of aroma on day 10. The fresh-cut nectarines could still maintain the characteristic flavor, while the flesh maintains its firmness. The 1-MCP pre-cutting treatment improves the sensory and aroma characteristics of fresh-cut fruits, which is beneficial to the preservation of fresh-cut fruits, improves transportation efficiency, and then improves the overall quality and market attractiveness of the fruit.

Gum arabic coating alleviates chilling injury of cold-stored peach by regulating reactive oxygen species, phenolic, and sugar metabolism

In this study, gum arabic (GA) coating was employed to mitigate chilling injury in peach fruit, and it was observed that 10% GA coating exhibited the most favorable effect. GA coating significantly inhibited the decline of AsA content and enhanced antioxidant enzyme activity in peach fruit, thereby enhancing reactive oxygen species (ROS) scavenging rate while reducing its accumulation. Simultaneously, GA coating inhibited the activity of oxidative degradation enzymes for phenolics and enhanced synthase activity, thus maintaining higher levels of total phenolics and flavonoids in fruits. Additionally, compared to the control fruit, GA-coated fruits demonstrated higher concentrations of sucrose and sorbitol, accompanied more robust activity of sucrose synthase and sucrose phosphate synthase, as well as reduced activity of acid invertase and neutral invertase. Our study demonstrates that GA coating can effectively enhance the cold resistance of peach fruit by regulating ROS, phenolics, and sugar metabolism, maintaining high levels of phenolics and sucrose while enhancing antioxidant activity.

Hot water mobilizes the metabolism of energy, soluble sugar, cell wall, and phenolics to cope with chilling injury in postharvest snap beans

BACKGROUND

Snap beans (Phaseoulus vulgaris L.) are very sensitive to low temperature during postharvest storage. Pitting, rusting, and water-soaked patches are typical chilling injury (CI) symptoms of snap beans. The appearance of these symptoms reduces the storage quality of snap beans. The energy, soluble carbohydrates, cell wall, and phenolic metabolisms of refrigerated snap beans and their relationship to CI treated with 35 °C hot water (HW) were investigated.

RESULTS

HW treatment reduced CI index and electrolyte leakage and increased the contents of soluble solids, titratable acidity, and chlorophyll. HW treatment maintained higher activities of proton ATPase, calcium ATPase, and cytochrome c oxidase, which resulted in the accumulation of more adenosine triphosphate, adenosine diphosphate, and energy charge. The accumulation of soluble sugar induced by HW treatment was correlated with the stimulation of sucrose phosphate synthase and sucrose synthase. The prevention effect of HW treatment on the degradation of cell wall components was related to the inhibition of pectin methylesterase and cellulase. HW-induced phenol accumulation is associated with an increase in shikimate dehydrogenase, phenylalanine ammonia lyase, cinnamate-4-hydroxylase, and 4-coumarine-coenzyme A ligase, as well as a decrease in polyphenol oxidase.

CONCLUSION

The alleviating effect of HW on CI is due to its regulation of energy, soluble sugar, cell wall, and phenolic metabolism. Therefore, HW treatment may be an effective means to reduce CI of snap beans. © 2024 Society of Chemical Industry.

Composite Coating of Oleaster Gum Containing Cuminal Keeps Postharvest Quality of Cherry Tomatoes by Reducing Respiration and Potentiating Antioxidant System

Exploring the green and affordable protection of perishable cherry tomato fruits during storage, herein, the protective efficacy, and its underpinning mechanisms, of a coating of oleaster gum, alone or incorporated with cuminal, on cherry tomatoes stored at ambient temperature was investigated. The composite coating of oleaster gum with 0.1% cuminal reduced the decay, respiration rate, weight loss, and softening of the fruits and decelerated the decreases in their total soluble solid, titratable acidity, and soluble protein levels, and therefore maintained their marketability. Furthermore, it reduced the accumulation of O2·- and H2O2 in the fruits and mitigated cell membrane lipid oxidation and permeabilization, thereby retarding their senescence. Instrumentally, it elevated the activities of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase and the levels of ascorbic acid and glutathione. This potentiation of the fruits' antioxidant system makes this composite coating a promising approach to keeping the postharvest quality of perishable fruits.

Polysaccharide-Based Edible Biopolymer-Based Coatings for Fruit Preservation: A Review

Over the last decades, a significant rise in fruit consumption has been noticed as they contain numerous nutritional components, which has led to the rise in fruit production globally. However, fruits are highly liable to spoilage in nature and remain vulnerable to losses during the storage and preservation stages. Therefore, it is crucial to enhance the storage life and safeness of fruits for the consumers. To keep up the grade and prolong storage duration, various techniques are employed in the food sector. Among these, biopolymer coatings have gained widespread acceptance due to their improved characteristics and ideal substitution for synthetic polymer coatings. As there is concern regarding the safety of the consumers and sustainability, edible coatings have become a selective substitution for nurturing fruit quality and preventing decay. The application of polysaccharide-based edible coatings offers a versatile solution to prevent the passage of moisture, gases, and pathogens, which are considered major threats to fruit deterioration. Different polysaccharide substances such as chitin, pectin, carrageenan, cellulose, starch, etc., are extensively used for preparing edible coatings for a wide array of fruits. The implementation of coatings provides better preservation of the fruits such as mango, strawberry, pineapple, apple, etc. Furthermore, the inclusion of functional ingredients, including polyphenols, natural antioxidants, antimicrobials, and bio-nanomaterials, into the edible coating solution matrix adds to the nutritional, functional, and sensory attributes of the fruits. The blending of essential oil and active agents in polysaccharide-based coatings prevents the growth of food-borne pathogens and enhances the storage life of the pineapple, also improving the preservation of strawberries and mangoes. This paper aims to provide collective data regarding the utilization of polysaccharide-based edible coatings concerning their characteristics and advancements for fruit preservation.

Recent advances in postharvest technologies for reducing chilling injury symptoms of fruits and vegetables: A review

Low temperature storage is widely used in the storage and transportation of postharvest fruits and vegetables. However, the negative effects of chilling injury (CI) on certain fruits and vegetables cannot be ignored. Therefore, efficient CI prevention technologies were used for reducing CI. This paper expounds the mechanisms of CI, common symptoms of CI and its impacts on the quality of fruits and vegetables, and summarizes the application of CI prevention technology. CI control methods are mainly classified into physical treatments (hot shock, near-freezing storage, high relative humidity storage, light-proof storage, and electromagnetic field), chemical treatments (melatonin, 1-methylcyclopropene, astragalus polysaccharides, γ-aminobutyric acid, 24-epibrassinolide, methyl jasmonate, trisodium phosphate, glycine betaine, and salicylic acid, etc.), coating treatments (sodium alginate, chitosan, carboxymethyl cellulose and aloe vera gel, etc.) and their combined treatments. These treatments have enhanced antioxidant activity, enzyme activity, membrane system integrity, and energy levels, thereby reducing the CI of fruits and vegetables.

Crucial roles of sorbitol metabolism and energy status in the chilling tolerance of yellow peach

In this study, we compared sorbitol metabolism, energy metabolism, and CI development in yellow peach fruit at 1 °C (less susceptible to CI) and 8 °C (more susceptible to CI) storage to elucidate potential connections between them. The results indicated that storage at 1 °C effectively maintained the textural quality of yellow peach fruit and delayed the onset of CI by 12 days compared to 8 °C. This positive effect might be attributable to 1 °C storage maintaining higher sorbitol content throughout the storage duration, thus sustaining the higher adenosine triphosphate (ATP) level and energy charge. The regulation of sorbitol accumulation by 1 °C storage was closely linked to the metabolic activity of sorbitol, which stimulated sorbitol synthesis by enhancing sorbitol-6-phosphate dehydrogenase (S6PDH) activity after 12 days while suppressing sorbitol degradation via decreased sorbitol oxidase (SOX) and NAD+-sorbitol dehydrogenase (NAD+-SDH) activities before 24 days. In addition, the notable up-regulation in the NAD+-SDH activity in the late storage period promoted the conversion of sorbitol to fructose and glucose under 1 °C storage, thereby providing ample energy substrate for ATP generation. Moreover, sorbitol acts as a vital signaling molecule, and substantially up-regulated expressions of sorbitol transporters genes (PpeSOT3, PpeSOT5, and PpeSOT7) were observed in fruit stored at 1 °C, which might promote sorbitol transport and improve cold tolerance in peach fruit. Taken together, these findings suggested that 1 °C storage delayed CI by enhancing sorbitol metabolism and transporter activity, promoting sorbitol accumulation, and finally elevating the energy status in yellow peach fruit.

Exogenous melatonin activates the antioxidant system and maintains postharvest organoleptic quality in Hami melon (Cucumis. melo var. inodorus Jacq.)

Hami melon is prone to postharvest perishing. Melatonin is a signaling molecule involved in a variety of physiological processes in fruit, and it improves fruit quality. We hypothesized that melatonin treatment would improve the storage quality of Hami melon by altering its respiration and reactive oxygen species (Graphical abstract). Our results indicated that optimal melatonin treatment (0.5 mmol L-1) effectively slowed the softening, weight loss, and respiratory rate of the Hami melon fruit. Furthermore, melatonin markedly improved the antioxidant capacity of the fruit and protected it from oxidative damage by decreasing its contents of superoxide anions, hydrogen peroxide, and malondialdehyde. Melatonin significantly enhanced the activities of superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase. The total phenol, total flavonoids, and ascorbic acid contents were maintained by melatonin treatment. This treatment also repressed the activities of lipase, lipoxygenase, and phospholipase D, which are related to lipid metabolism. Thus, exogenous melatonin can maintain postharvest organoleptic quality of Hami melon fruit by increasing its antioxidant activity and inhibiting reactive oxygen species production.

Synergistic Effects of 1-MCP Fumigation and ε-Poly-L-Lysine Treatments on Delaying Softening and Enhancing Disease Resistance of Flat Peach Fruit

Flat peach, a predominant fruit consumed in China, is highly susceptible to softening and perishable. The impact of 1-methylcycloproene (1-MCP) fumigation combined with ε-poly-L-lysine (ε-PL) on softening and postharvest reactive oxygen species (ROS) and phenylpropanoid pathway metabolisms in peaches and its relationship to disease resistance were investigated. Findings revealed that a combination of 1 µL L-1 1-MCP and 300 mg L-1 ε-PL effectively suppressed the activity of cell-wall-degrading enzymes and the disassembly of cell wall structure, thus maintaining higher firmness and lower decay incidence. Compared to the control group, the synergistic approach bolstered enzymatic responses linked to disease resistance and ROS-scavenge system, consistently preserving total phenolics, flavonoids, ascorbic acid, and glutathione levels. Concurrently, the accumulation of hydrogen peroxide and malondialdehyde was significantly diminished post-treatment. These results show that there is good synergistic effect between 1-MCP and ε-PL, which could effectively maintain the quality of flat peach fruit by modulating cell wall metabolism and enhancing the resistance.

Effects of Exogenous Application of Glycine Betaine Treatment on 'Huangguoggan' Fruit during Postharvest Storage

Loss of quality in citrus fruit is a common occurrence during postharvest storage due to oxidative stress and energy consumption. In recent years, glycine betaine (GB) has been widely applied to postharvest horticulture fruit. This study aimed to investigate the effect of GB treatment (10 mM and 20 mM) on the quality and antioxidant activity of 'Huangguogan' fruit during postharvest storage at room temperature. Our results indicated that both 10 mM and 20 mM treatments effectively reduced weight and firmness losses and maintained total soluble solid (TSS), titratable acidity (TA), and ascorbic acid contents. Additionally, GB treatment significantly increased the activity of antioxidant enzymes, maintained higher levels of total phenols and total flavonoids, and led to slower accumulation of H2O2. A transcriptome analysis conducted at 28 days after treatment (DAT)identified 391 differentially expressed genes (DEGs) between 20 mM GB (GB-2) and the control (CK) group. These DEGs were enriched in various pathways, particularly related to oxygen oxidoreductase, peroxidase activity, and flavonoid biosynthesis. Overall, the application of GB proved beneficial in enhancing the storability and extending the shelf life of 'Huangguogan' fruit.

Fabrication of BODIPY/polyvinyl alcohol/alkaline lignin antibacterial composite films for food packing

Foodborne pathogens seriously endanger people's health and cause significant economic losses. Therefore, it is of great significance to design potent packaging materials with the function of alleviating food spoiling and extending shelf life. Here, three BODIPY derivatives (named as N-BDPI, B-BDPI and P-BDPI) were synthesized by substituting the 8-position of BODIPY with naphthalene, biphenyl and pyridine groups, respectively, and their photophysical properties as well as antibacterial capacities were characterized. The results demonstrated that N-BDPI had the best singlet oxygen generation ability and could completely kill S. aureus under light irradiation with the minimum inhibitory concentration of only 50 nmol/L. In addition, 1.0% BDPI@PVA/AL composite film was fabricated by doping N-BDPI into polyvinyl alcohol (PVA) and alkaline lignin (AL) exhibited high antibacterial activity on Gram-positive bacteria. The coating of strawberries with 1.0% BDPI@PVA/AL film not only effectively inhibited the mildew of strawberries, but also extended their shelf life.

Glycine betaine inhibits postharvest softening and quality decline of winter jujube fruit by regulating energy and antioxidant metabolism

Winter jujube fruit easily softens after harvest. To investigate the effects of glycine betaine (N,N,N-trimethylglycine; GB) treatment on the quality of postharvest jujubes, fresh winter jujubes (Zizyphus jujuba Mill. cv. Dongzao) were immersed in 20 mmol·L^-1 GB for 20 min. The results showed that GB application can effectively maintain cell wall component content by restraining gene expression and enzyme activities, including PG, CX, PME and β-Glu. Meanwhile, the activities of antioxidant enzymes (APX, CAT, SOD, POD) and the contents of nonenzymatic antioxidants (MDA, H₂O₂, ASA, GSH) were enhanced in treated jujubes, thereby reducing the content of ROS. In addition, energy metabolism enzyme activities (H⁺-ATPase, Ca²⁺-ATPase, SDH and CCO) and gene expression were also significantly increased, thus maintaining higher energy levels (ATP, ADP, AMP and EC). In summary, GB enhances ATP biosynthesis by increasing energy metabolism. It offers essential energy for the antioxidant metabolism, thus retarding the softening of postharvest jujubes.

The Effects of Combined 1-Methylcyclopropene and Melatonin Treatment on the Quality Characteristics and Active Oxygen Metabolism of Mango Fruit during Storage

In this study, mango fruit (Tainong No. 1) was treated with either 0.1 mg/L 1-methylcyclopropene (1-MCP) alone or with a combination of 0.1 mg/L 1-MCP and 0.2 mM melatonin (MT). The mango fruit was then stored for 10 days at 25 °C and 85-90% relative humidity. Quality characteristics and the active oxygen metabolism of postharvest mangoes were evaluated every 2 days. Compared to untreated mango fruit, those with the treatments of 1-MCP alone or 1-MCP + MT had a better appearance and higher levels of soluble sugar, ascorbic acid, and titratable acidity. Moreover, these treatments prevented the loss of fruit firmness, successfully delayed the escalation of a* and b* values, and reduced malondialdehyde content and superoxide anion generation rate. After 10 days of storage, mango fruit treated by 1-MCP alone or 1-MCP + MT exhibited increased activities of antioxidant enzymes such as ascorbate peroxidase, catalase, superoxide dismutase, and other peroxidases; nevertheless, the two treatment protocols maintained higher mango total phenolic content only at the later stage of storage. These findings suggest that mango fruit treated with 1-MCP alone or with 1-MCP + MT improves the quality characteristics and antioxidant activities. Moreover, compared to 1-MCP treatment alone, 1-MCP + MT-treated mangoes exhibited higher quality and a stronger regulation of active metabolism during storage.

Advances in gas fumigation technologies for postharvest fruit preservation

This work summarizes the application of gas fumigation technology in postharvest fruit quality management and related biochemical mechanisms in recent years. Gas fumigants mainly include SO2, ClO2, ozone, NO, CO, 1-MCP, essential oils, H2S and ethanol. This work indicated that gas fumigation preservatives can effectively improve postharvest fruit quality, which is mainly manifested in delaying senescence, inhibiting browning, controlling disease and alleviating chilling injury. Gas preservatives are mainly involved in postharvest fruit quality control in the roles of antifungal agent, anti-browning agent, redox agent, ethylene inhibitors, elicitor and pesticide remover. Different gas preservatives have different roles, but most of them have multiple roles at the same time in postharvest fruit quality management. In addition, the role of some gas preservatives with direct antifungal activity in the control of postharvest fruit diseases can also activate defense systems to improve fruit resistance. It should be noted that some gas fumigation treatments with slow-release effects have been developed recently, which may allow gas fumigation gases to perform better. Moreover, some gas fumigants can cause irrational side effects on the fruit and some combined treatments need to be found to counteract such side effects.

1-Methylcyclopropene and UV-C Treatment Effect on Storage Quality and Antioxidant Activity of ‘Xiaobai’ Apricot Fruit

The ‘Xiaobai’ apricot fruit is rich in nutrients and is harvested in summer, but the high temperature limits its storage period. To promote commercial quality and extend shelf life, we investigated the effectiveness of Ultraviolet C (UV-C) combined with 1-methylcyclopropene (1-MCP) treatment on ‘Xiaobai’ apricot fruit stored at 4 ± 0.5 °C for 35 days. The results revealed that the combination treatment of 1-MCP and UV-C performed better than either UV-C or 1-MCP alone in fruit quality preservation. The combination treatment could delay the increase in weight loss, ethylene production, and respiration rate; retain the level of soluble solid content, firmness, titratable acid, and ascorbic acid content; promote the total phenolics and flavonoids accumulation; improve antioxidant enzyme activity and relative gene expression, and DPPH scavenging ability; and reduce MDA, H2O2, O2.− production. The combined treatment improved the quality of apricot fruit by delaying ripening and increasing antioxidant capacity. Therefore, combining UV-C and 1-MCP treatment may be an effective way to improve the post-harvest quality and extend the storage period of the ‘Xiaobai’ apricot fruit, which may provide insights into the preservation of ‘Xiaobai’ apricot fruit.

A comprehensive review of intelligent packaging for fruits and vegetables: Target responders, classification, applications, and future challenges

Post-harvest fruits and vegetables are extremely susceptible to dramatic and accelerated quality deterioration deriving from their metabolism and adverse environmental influences. Given their vigorous physiological metabolism, monitoring means are lacking due to the extent that unnecessary waste and damage are caused. Numerous intelligent packaging studies have been hitherto carried out to investigate their potential for fruit and vegetable quality monitoring. This state-of-the-art overview begins with recent advances in target metabolites for intelligent packaging of fruits and vegetables. Subsequently, the mechanisms of action between metabolites and packaging materials are presented. In particular, the exact categorization and function of intelligent packaging of fruits and vegetables, are all extensively and comprehensively described. In addition, for the sake of further research in this field, the obstacles that impede the scaling up and commercialization of intelligent packaging for fruits and vegetables are also explored, to present valuable references.

Knockdown of Sly-miR164a Enhanced Plant Salt Tolerance and Improved Preharvest and Postharvest Fruit Nutrition of Tomato

Salinity stress is a serious limitation to tomato growth and development. The aim of this study was to investigate the effects of Sly-miR164a on tomato growth and fruit nutritional quality under salt stress. The results showed that the root length, fresh weight, plant height, stem diameter and ABA content of miR164a#STTM (knockdown of Sly-miR164a) lines were higher than those of WT and miR164a#OE (overexpression of Sly-miR164a) lines under salt stress. Compared with WT, miR164a#STTM tomato lines exhibited lower ROS accumulation under salt stress. In addition, the fruits of miR164a#STTM tomato lines had higher soluble solids, lycopene, ascorbic acid (ASA) and carotenoid content compared with WT. The study indicated that tomato plants were more sensitive to salt when Sly-miR164a was overexpressed, while knockdown of Sly-miR164a enhanced plant salt tolerance and improved fruit nutritional value.

Exogenous Application of Melatonin to Green Horn Pepper Fruit Reduces Chilling Injury during Postharvest Cold Storage by Regulating Enzymatic Activities in the Antioxidant System

Chilling injury (CI) caused by exposure to low temperatures is a serious problem in the postharvest cold storage of pepper fruit. Melatonin (MT) has been reported to minimize CI in several plants. To evaluate the effectiveness of MT to minimize CI in green horn pepper and the possible mechanism involved, freshly picked green horn peppers were treated with MT solution at 100 μmol L−1 or water and then stored at 4 °C for 25 d. Results showed that MT treatment reduced CI in green horn pepper fruit, as evidenced by lower CI rate and CI index. MT treatment maintained lower postharvest metabolism rate and higher fruit quality of green horn peppers, as shown by reduced weight loss and respiratory rate, maintened fruit firmness and higher contents of chlorophyll, total phenols, flavonoids, total soluble solids and ATP. Additionally, the contents of hydrogen peroxide, superoxide radical, and malondialdehyde were kept low in the MT-treated fruit, and the activities of the enzymes peroxidase, superoxide dismutase, and catalase were significantly elevated. Similarly, the ascorbate–glutathione cycle was enhanced by elevating the activities of ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase, to increase the regeneration of ascorbic acid and glutathione. Our results show that MT treatment protected green horn pepper fruit from CI and maintained high fruit quality during cold storage by triggering the antioxidant system

A Synergistic Effect Based on the Combination of Melatonin with 1-Methylcyclopropene as a New Strategy to Increase Chilling Tolerance and General Quality in Zucchini Fruit

Zucchini fruit are highly sensitive to low temperatures leading to significant peel depressions, increasing weight loss and making them impossible to be commercialized. In this study the effect on the reduction of chilling injury (CI) assaying different postharvest treatments to cv. Cronos was evaluated. We have compared the application of substances such as 1-methylcyclopropene (1-MCP) with the application of a natural origin compound as melatonin (MT), both with demonstrated activity against CI in different vegetal products. The effects of MT (1 mM) by dipping treatment of 1 h and 1-MCP (2400 ppb) have been evaluated on zucchini fruit during 15 days of storage at 4 °C plus 2 days at 20 °C. Treatments applied independently improved some fruit quality parameters in comparison with control fruit but were not able to manage CI even though they mitigated the impact on several parameters. However, when these two separated strategies were combined, zucchini cold tolerance increased with a synergic trend. This synergic effect affected in general all parameters but specially CI, being also the only lot in which zucchini fruit were most effectively preserved. This is the first evidence in which a clear positive effect on zucchini chilling tolerance has been obtained combining these two different strategies. In this sense, the combined effect of 1-MCP and MT could be a suitable tool to reach high quality standards and increasing shelf life under suboptimal temperatures.

Advances in chilling injury of postharvest fruit and vegetable: Extracellular ATP aspects

Due to the global use of cold chain, the development of postharvest technology to reduce chilling injury (CI) in postharvest fruits and vegetables during storage and transport is needed urgently. Considerable evidence shows that maintaining intracellular adenosine triphosphate (iATP) in harvested fruits and vegetables is beneficial to inhibiting CI occurrence. Extracellular ATP (eATP) is a damage-associated signal molecule and plays an important role in CI of postharvest fruits and vegetables through its receptor and subsequent signal transduction under low-temperature stress. The development of new aptasensors for the simultaneous determination of eATP level allows for better understanding of the roles of eATP in a myriad of responses mediated by low-temperature stress in relation to the chilling tolerance of postharvest fruits and vegetables. The multiple biological functions of eATP and its receptors in postharvest fruits and vegetables were attributed to interactions with reactive oxygen species (ROS) and nitric oxide (NO) in coordination with phytohormones and other signaling molecules via downstream physiological activities. The complicated interconnection among eATP in relation to its receptors, eATP/iATP homeostasis, ROS, NO, and heat shock proteins triggered by eATP recognition has been emphasized. This paper reviews recent advances in the beneficial effects of energy handling, outlines the production and homeostasis of eATP, discusses the possible mechanism of eATP and its receptors in chilling tolerance, and provides future research directions for CI in postharvest fruits and vegetables during low-temperature storage.

Physiological and Transcriptome Analyses of CaCl2 Treatment to Alleviate Chilling Injury in Pineapple

The post-harvest ripening of pineapples can be effectively postponed by refrigerated storage. Nevertheless, internal browning (IB) frequently appears in pineapples after refrigerated storage during the course of the shelf life at room temperature, which is known as chilling injury (CI). In this study, the chilling injury of pineapple fruit was induced by a low temperature (6 °C) and transferred to normal-temperature storage; the best concentration of 50 μmol/L of CaCl₂ was selected by the IB appearance and electrical conductivity. Fruit quality, reactive oxygen species (ROS), antioxidants, and transcription factors were investigated. The physiological data results indicated that pineapples treated with 50 μmol/L of CaCl₂ maintained fruit quality, decreased reactive oxygen species (ROS), and enhanced the antioxidant activity of fruits, alleviating internal browning (IB) symptoms in pineapple fruit. The expressions of related genes were also consistent with the physiological changes by the transcriptome data analysis. In addition, we focused on some related metabolic pathways, including phenylpropanoid biosynthesis, MAPK pathway, plant hormone, plant-pathogen interaction, tricarboxylic acid cycle (TAC), and fatty acid biosynthesis. We performed integrative analyses of transcriptome data combined with a series of physiology and experimental analyses on the internal browning of pineapples, which will be of great significance to extending the shelf life of pineapples through molecular biology in the future.

Abnormal chilling injury of postharvest papaya is associated with the antioxidant response

Generally, the lower the temperature and/or the longer the duration of low temperature, the more serious chilling injury (CI) symptom appears in fruit. However, our previous study showed that the higher storage temperature (6°C) resulted in a more serious CI in papaya fruit compared to that stored at 1°C, which could be viewed as an abnormal CI behavior. This study investigated the antioxidant responses that existed in abnormal CI behavior of papaya fruit. Compared to 6°C, antioxidant enzyme activities of papaya fruit which was stored at 1°C were maintained at a higher level while the circulatory metabolism of the ascorbate-glutathione cycle (AsA-GSH) was more vigorous in papaya fruit, as indicated by higher superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and monodehydroascorbate reductase (MDHAR) activities and higher AsA and GSH levels, which could reduce the superoxide anion (·O₂ ^- ) production rate and the hydrogen peroxide (H₂ O₂ ) content. Suppressed reactive oxygen species (ROS) generation in papaya fruit at 1°C resulted in reduced membrane permeability and malondialdehyde (MDA) accumulation when compared to that at 6°C, thus the development of CI was restricted during storage at 1°C. This study deepened the understanding of differential antioxidant responses during cold storage at 1°C and 6°C in papaya fruit and provided a theoretical basis for further study on the mechanism of the abnormal CI behavior in papaya fruit. PRACTICAL APPLICATIONS: Low-temperature storage is one of the most effective methods to preserve fruit and vegetable products. While, inappropriate low temperature could induce CI, and the damage caused by CI is often more serious than estimated. Therefore, it is necessary to study the physiological and biochemical characteristics of different postharvest fruits and vegetables to prolong storage period, improve storage quality and reduce the loss of products. This study analyzed the antioxidant reaction in abnormal CI behavior of papaya, which could contribute to the further study on the mechanism of CI in papaya fruit and provide theoretical basis for the development of preservation technology of papaya fruit.

Coupling of myo-inositol with salinity regulates ethylene-induced microalgal lipid hyperproduction in molasses wastewater

With the goal of cost-effective and high-efficient microalgae-based biodiesel production, this study evaluated the feasibility of the joint strategy concerning myo-inositol (MI) and salinity stress on lipid productivity of Monoraphidium sp. QLY-1 in molasses wastewater (MW). The maximal lipid productivity (147.79 mg L^-1 d^-1) was obtained under combined 0.5 g L^-1 MI and 10 g L^-1 NaCl treatment, which was 1.40-fold higher than the control. Meanwhile, the nutrients removal from MW was markedly increased under MI-NaCl treatment. Moreover, exogenous MI upregulated key lipogenic genes' expressions, activated autophagic activity and ethylene (ET) signaling, and ultimately alleviated the salinity-induced damage via reactive oxygen species (ROS) signaling. Further pharmacologic experiment confirmed the indispensable role of ET in the lipogenesis progress under the combined treatment. These data demonstrated the combined salinity stress and MI treatment to be capable for lipid hyperproduction and wastewater nutrients removal, which contributes to practically integrating the microalgae cultivation with wastewater treatment.

Trehalose Alleviated Salt Stress in Tomato by Regulating ROS Metabolism, Photosynthesis, Osmolyte Synthesis, and Trehalose Metabolic Pathways

Trehalose plays a critical role in plant response to salinity but the involved regulatory mechanisms remain obscure. Here, this study explored the mechanism of exogenous trehalose-induced salt tolerance in tomato plants by the hydroponic test method. Our results indicated that 10 mM trehalose displayed remarkable plant biomass by improving growth physiology, which were supported by the results of chlorophyll fluorescence and rapid light-response curve. In the salinity environment, trehalose + NaCl treatment could greatly inhibit the decrease of malondialdehyde level, and it increases the contents of other osmotic substances, carbohydrates, K+, and K+/Na+ ratio. Meanwhile, trehalose still had similar effects after recovery from salt stress. Furthermore, trehalose pretreatment promoted trehalose metabolism; significantly increased the enzymatic activity of the trehalose metabolic pathway, including trehalose-6-phosphate synthase (TPS), trehalose-6-phosphate phosphatase (TPP), and trehalase (TRE); and upregulated the expression of SlTPS1, SlTPS5, SlTPS7, SlTPPJ, SlTPPH, and SlTRE under saline conditions. However, the transcriptional levels of SlTPS1, SlTPS5, and SlTPS7 genes and the activity of TPS enzyme were reversed after recovery. In addition, we found that hydrogen peroxide (H2O2) and superoxide anion (O2 -) were accumulated in tomato leaves because of salt stress, but these parameters were all recovered by foliar-applied trehalose, and its visualization degree was correspondingly reduced. Antioxidant enzyme activities (SOD, POD, and CAT) and related gene expression (SlCu/Zn-SOD, SlFe-SOD, SlMn-SOD, SlPOD, and SlCAT) in salt-stressed tomato leaves were also elevated by trehalose to counteract salt stress. Collectively, exogenous trehalose appeared to be the effective treatment in counteracting the negative effects of salt stress.

Mitigating effects of chitosan coating on postharvest senescence and energy depletion of harvested pummelo fruit response to granulation stress

The effect of chitosan coating exposure on juice sac granulation and energy metabolism in harvested pummelo fruit was investigated. Pummelo fruits were exposed to 1.5% chitosan coating, and then stored at 20 ± 2 °C for about 150 days. Postharvest chitosan coating treatment apparently alleviated the development of juice sac granulation as well as the increases in weight loss, pulp firmness, cell membrane permeability and cellulose content. The levels of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and energy charge (EC) in the chitosan-coated fruit showed significantly higher levels than those of the respective controls. Meanwhile, the enzymses actively engaged in energy metabolism such as H⁺-ATPase, Ca²⁺-ATPase, Mg²⁺-ATPase, cytochrome C oxidase (CCO), succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) were markedly maintained by chitosan coating. Besides, notably high contents of acetyl-CoA, cis-aconitate, succinate, fumarate and oxaloacetate were observed in the chitosan-coated fruit. The results highlighted that chitosan coating could delay postharvest senescence of pummelo fruit by reducing the rate of energy depletion while maintaining higher levels of key metabolites taking part in tricarboxylic acid (TCA) cycle at room temperature storage.

Determination of 1-methylcyclopropene residues in vegetables and fruits based on iodine derivatives

An innovative method was established for the determination of 1-methylcyclopropene (1-MCP) in vegetables and fruits. Due to its small molecular weight and low boiling point, it was difficult to obtain quantitative analysis for 1-MCP, especially at the residual level. In this work, based on its iodine derivatives, 1-MCP was derived to 1,2-diiodo-1-methylcyclopropane, which was much easier for trace and accurate chromatographic analysis. During the method validation, the method validation results were satisfactory in terms of linearity (4 ~ 400 µg/L, and R² ≥ 0.959), matrix effect (-89% ~ -13%), accuracy (80 ~ 100%), sensitivity (limits of quantification, 5 μg/kg) and precision (relative standard deviations ≤ 19%), which was in accordance with the Chinese guidelines for the testing of pesticide residues in crops. Finally, the proposed analytical method was used to monitor the 1-MCP residue levels in commercially available samples, and all the values were below 5 µg/kg, which satisfied the EU or Japan MRLs of 1-MCP.

Metabolomic and Transcriptomic Profiling Provide Novel Insights into Fruit Ripening and Ripening Disorder Caused by 1-MCP Treatments in Papaya

Treatment with 1-methylcyclopropylene (1-MCP) is an effective technique to preserve fruits, but inappropriate treatment with 1-MCP causes a ripening disorder (rubbery texture) in papaya fruit. In this study, a combined metabolomic and transcriptomic analysis was conducted to reveal the possible mechanism of the ripening disorder caused by unsuitable 1-MCP in papaya. A total of 203 differential accumulated metabolites (DAMs) were identified in the metabolome analysis. Only 24 DAMs were identified in the control (CK) vs. the 1-MCP 2 h group, and they were primarily flavonoids. Ninety and 89 DAMs were identified in the CK vs. 1-MCP 16 h and 1-MCP 2 h vs. 1-MCP 16 h groups, respectively, indicating that long-term 1-MCP treatment severely altered the metabolites during fruit ripening. 1-MCP 16 h treatment severely reduced the number of metabolites, which primarily consisted of flavonoids, lipids, phenolic acids, alkaloids, and organic acids. An integrated analysis of RNA-Seq and metabolomics showed that various energy metabolites for the tricarboxylic acid cycle were reduced by long-term treatment with 1-MCP, and the glycolic acid cycle was the most significantly affected, as well as the phenylpropane pathway. These results provide valuable information for fruit quality control and new insight into the ripening disorder caused by unsuitable treatment with 1-MCP in papaya.