1-MCP regulates ethylene biosynthesis and fruit softening during ripening of ‘Tegan Blue’ plum

To investigate the effects of postharvest application of 1-MCP on ethylene production and fruit softening, activities of ethylene biosynthesis and fruit softening enzymes were measured during postharvest ripening of plum (Prunus salicina Lindl. cv. Tegan Blue) fruit after being exposed to 1-MCP (0, 0.5, 1.0 or 2.0 μL L⁻¹) at 20 ± 1 °C for 24 h. Following the treatments, fruit were allowed to ripen at ambient temperature (20 ± 1 °C), and ethylene production in fruit, activities of ACS and ACO, ACC content and fruit softening enzymes (PE, EGase, exo-PG and endo-PG) in fruit skin and pulp were recorded at different intervals. Postharvest application of 1-MCP significantly delayed and suppressed the climacteric ethylene production with reduction in the activities of ethylene biosynthesis enzymes (ACS, ACO) and ACC content, and fruit softening enzymes (PE, EGase, exo-PG and endo-PG) in the skin as well as in pulp tissues. The reduction was more pronounced with increased concentrations of 1-MCP. 1-MCP treated fruit showed different rates of fruit softening and activities of ethylene biosynthesis enzymes in the skin and pulp tissues which warrant further investigation on regulation of gene expression related to these enzymes with the inhibitory effect of 1-MCP.     

Mode of action of nitric oxide in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of ‘Kensington Pride’ mango

The mode of action of nitric oxide (NO) in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of mango fruit was investigated. Hard mature green mango (Mangifera indica L. cv. ‘Kensington Pride’) fruit were fumigated with 20 μL L⁻¹ NO for 2 h at 21 °C and allowed to ripen at 21 ± 1 °C for 10 d, or stored at 13 ± 1 °C for 21 d. During ripening and cool storage, ethylene production and respiration rate from whole fruit were determined daily. The 1-aminocyclopropane-1-carboxylic acid (ACC) content, activities of ACC synthase (ACS), ACC oxidase (ACO), and fruit softening enzymes such as pectin esterase (PE), endo-1,4-β-d-glucanase (EGase), exo- and endo-polygalacturonase (exo-PG, endo-PG) as well as firmness and rheological properties of pulp were determined at two- and seven-day intervals during ripening and cool storage, respectively. NO fumigation inhibited ethylene biosynthesis and respiration rate, and maintained higher pulp firmness, springiness, cohesiveness, chewiness, adhesiveness, and stiffness. NO-fumigated fruit during cool storage and ripening had lower ACC contents through inhibiting the activities of both ACS and ACO in the fruit pulp. NO-fumigated fruit showed decreased activities of exo-PG, endo-PG, EGase, but maintained higher PE activity in pulp tissues during ripening and cool storage. In conclusion, NO fumigation inhibited ethylene biosynthesis through inhibition of ACS and ACO activities leading to reduced ACC content in the fruit pulp which consequently, reduced the activities of fruit softening enzymes during ripening and cool storage.     

Role of putrescine in regulating fruit softening and antioxidative enzyme systems in ‘Samar Bahisht Chaunsa’ mango

The role of putrescine (PUT) in regulating fruit softening, antioxidative enzymes and biochemical changes in fruit quality was investigated during ripening and cold storage of mango (Mangifera indica cv. Samar Bahisht Chaunsa). Fruit were treated with various PUT concentrations (0.0, 0.1, 1.0 and 2.0 mM) and were allowed to ripen at 32 ± 2 °C for 7 days, or stored at 11 ± 1 °C for up to 28 days. Respiration rate and ethylene production were measured daily during ripening and cold storage. Cell wall degrading enzymes such as exo-polygalacturonase (exo-PG), endo-polygalacturonase (endo-PG), pectin esterase (PE), endo-1,4-β-d-glucanase (EGase), antioxidative enzymes including superoxide dismutase (SOD), peroxidase (POX), and catalase (CAT), fruit firmness as well as biochemical fruit quality characteristics were estimated during ripening and cold storage at 2 and 7 day intervals, respectively. PUT treatments reduced respiration rate, ethylene production and maintained higher fruit firmness during ripening as well as cold storage. PUT-treated fruit exhibited significantly suppressed activities of cell wall enzymes (exo-, endo-PG and EGase), but retained higher PE activity during ripening and cold storage. Total phenolic and antioxidant contents were significantly higher in PUT-treated fruit during ripening as well in the cold storage period than in the controls. Activities of antioxidative enzymes (CAT, POX and SOD) were also significantly higher in PUT-treated fruit during ripening as well as cold storage. SSC and SSC:TA were lower in PUT-treated fruit, while TA and ascorbic acid content showed the reverse trend. In conclusion, pre-storage 2.0 mM PUT treatment inhibited ethylene production and suppressed the activities of cell wall enzymes, while resulting in higher activities of antioxidative enzymes and maintaining better fruit quality during ripening and cold storage.     

Regulation of stony hard peach softening with ACC treatment

Controlling the rate of fruit softening in melting-flesh peaches is a primary goal of the fruit industry. Stony hard (SH) peach varieties lack the ability to synthesize 1-aminocyclopropane-1-carboxylic acid (ACC), the precursor of ethylene, which is required for fruit maturation. SH peaches thus have crisp flesh that remains firm during ripening. In this study, we developed a simple technique to stimulate fruit softening by a single spray application of ACC at a concentration of 10–20 mM, which was sufficient to allow ethylene synthesis and fruit softening. Higher concentrations of ACC increased ethylene production, and made the fruit softer. Ethylene synthesis was limited to the first 2–3 d after ACC treatment, after which fruit ceased softening and retained its remaining firmness. These results indicate that a single application of ACC solution can be used to regulate the process of fruit softening in SH peaches.     

Physiology and quality response of harvested banana fruit to cold shock

Experiments were conducted to examine softening and quality responses of harvested banana fruit to cold shock treatment intended to extend shelf-life. Fruit were immersed in ice-water for 1 h, then treated with or without 100 μL L^?1 ethylene for 24 h at 24 °C, and finally stored at 20 °C. Fruit firmness, chlorophyll content, ethylene production, respiration rates, contents of pectin, starch and sugar, and the activities of the cell wall modifying enzymes polygalacturonase (PG), pectin methylesterase (PME) and CMCase (cellulase, endo-1,4-β-glucanase) were analyzed. Total amylase activity was also measured. Immersion in ice-water for 1 h effectively inhibited ripening-associated processes, including peel de-greening and pulp softening during storage or ripening. The delay in ripening was also manifest in reduced ethylene production and respiration rates. The inhibition of softening by cold shock treatment was related to decreased PG and PME activities, that is, retardation of pectin solubilization/degradation. Reduced activities of CMCase and total amylase and conversion of starch to sugar by ice-water immersion also contributed to the delay in softening of harvested banana fruit.     

Ethanol vapor treatment maintains postharvest storage quality and inhibits internal ethylene biosynthesis during storage of oriental sweet melons

In order to evaluate the effect of ethanol vapor treatments (0.5 mL/kg and 3 mL/kg) on postharvest storage at 23 °C, quality of oriental sweet melons, and to clarify the mechanism of the inhibition of senescence, we investigated physiological and quality changes induced by ethanol vapor, decay incidence, internal ethylene concentration (IEC) and ethylene-related enzymes activities as well as gene expression. Both ethanol vapor treatments, irrespective of concentration, significantly (P < 0.5) delayed skin color changes, retarded softening and suppressed fruit decay in ethanol vapor-treated fruit. Between the two treatments, 0.5 mL/kg of ethanol vapor maintained better quality in storage than that of 3 mL/kg. Compared with the control, both ethanol vapor treatments resulted in different profiles and composition of aromatic volatile compounds of fruit during storage, and a significant increase of ethyl esters, including ethyl acetate, ethyl butanoate, ethyl hexanoate, ethyl 2-methylbutanoate, 3-(methylthio) propionate and 2-phenethyl acetate, and five new ethyl esters were also detected. Both treatments increased alcohol acyl-transferase (AAT) activity levels, which peaked earlier than in the control, but there were no significant differences in activities of alcohol dehydrogenase (ADH). Both treatments significantly (P < 0.5) suppressed internal ethylene concentrations (IEC) during storage at 23 °C, which was evident from reducing 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) and ACC oxidase (ACO) activities, and inhibiting ACC biosynthesis, and the effect of the 0.5 mL/kg treatment was better than that of 3 mL/kg. Real-time quantitative PCR (Q-PCR) analysis showed that the expression patterns of CM-ACO1, CM-ACO2, CM-ACS1 and CM-ACS2 were consistent with ethylene production during storage. These results suggest that postharvest ethanol vapor treatments markedly delayed the senescence of harvested oriental sweet melons, maintained better quality in storage and improved levels of volatile aroma compounds, especially the ethyl esters, through suppressing the expression of particular members of ethylene-forming enzyme gene families as well as ethylene biosynthesis, and the effect is dose dependent.     

Antioxidant systems of ripening avocado (Persea americana Mill.) fruit following treatment at the preclimacteric stage with aqueous 1-methylcyclopropene

Preclimacteric avocado (Persea americana Mill. cv. Booth 7) fruit were treated with aqueous 1-methylcyclopropene (1-MCP) at 0.93 and 9.3 mmol m⁻³ and then stored at 20 °C to investigate the effect of 1-MCP on antioxidant systems of mesocarp tissue during ripening. Exposure to 1-MCP concentrations significantly delayed softening and peak ethylene production. 1-MCP significantly delayed accumulation of total soluble phenolics, flavonoids, and total antioxidant capacity although levels eventually reached control fruit maxima. The influence of 1-MCP was more pronounced at the higher concentration. Activities of peroxidase [POD (EC 1.11.1.7)], superoxide dismutase [SOD (EC 1.15.1.1)], catalase [CAT (1.11.1.6)] and l-ascorbate peroxidase [APX (EC 1.11.1.11)] increased during early ripening of control fruit followed by slight (CAT) or significant (POD, APX) declines with further ripening. Increases in activities of all enzymes were delayed in proportion to 1-MCP concentration, and maximum activities attained during ripening were largely unaffected by 1-MCP. Postclimacteric declines in POD and APX were not observed at the higher 1-MCP concentration, possibly reflecting incomplete ripening. The results indicate that changes in antioxidant parameters of avocado fruit are not markedly influenced by 1-MCP but are delayed or altered in proportion to the general suppression of ripening as indicated by ethylene production and fruit softening trends. Together with previously published reports, the data also indicate that the effects of ethylene-action suppression on antioxidant parameters during ripening vary considerably among different fruits. Relationships between antioxidant systems, ethylene and ripening are discussed.     

Effects of preharvest nitric oxide treatment on ethylene biosynthesis and soluble sugars metabolism in ‘Golden Delicious’ apples

In order to examine the influence of preharvest nitric oxide (NO) treatment on ethylene biosynthesis and soluble sugar metabolism in ‘Golden Delicious’ apples, apple trees were sprayed with 50 μM sodium nitroprusside (SNP) (a donor of NO) 14 days before harvest. The results indicated that preharvest SNP treatment can increase the NO content and the NOS activity in apple fruit, therefore, delay the accumulation of ethylene due to its inhibition on the activities of 1-aminocyclopropane-1-carboxylate synthase (ACS) and 1-aminocyclopropane-1-carboxylate oxydase (ACO). Fructose is the main sugar in ‘Golden Delicious’ apple. The synthesis of sucrose was stimulated and the decomposition of sucrose was inhibited by this treatment, thus causing the accumulation of sucrose. We can draw a conclusion that pre-harvest SNP (50 μM) treatment can increase the NO content of fruit during storage, while higher NO content can further regulate fruit ripening through its effect on ethylene and sugar metabolism in ‘Golden Delicious’ apple fruit during storage at 18 °C.     

Treatment with 1-MCP and the role of ethylene in aroma development of mountain papaya fruit

Mountain or highland papaya (Vasconcellea pubescens) is a climacteric fruit which develops a strong and characteristic aroma during ripening. The dynamics of aroma volatile production during ripening of whole papaya fruit were analysed by headspace-SPME. The main compounds produced by the fruit were esters (aliphatic and branched) and alcohols: the most abundant esters were ethyl acetate, ethyl butanoate, methyl butanoate and butyl acetate, comprising 88% of the volatiles in fully ripe fruit; butanol was the most abundant alcohol. Among the volatiles produced, ethyl butanoate, ethyl acetate, ethyl hexanoate and ethyl 2-methylbutanoate were found to be the most potent odour compounds. During ripening of mountain papaya fruit there was an increase in the total content of both esters and alcohols. In order to clarify the role of ethylene in aroma formation, mature fruit were treated with 0.3 μL L⁻¹ of 1-MCP (16 h at 20 °C) or with 2 g L⁻¹ Ethrel, and then allowed to ripen at 20 °C. The treatment of the fruit with 1-MCP inhibited the rise in ethylene production in the fruit, while Ethrel advanced the development of the climacteric phase. Most esters identified in mountain papaya were dependent on ethylene, showing an increase in production during ripening and in response to Ethrel treatment, and a strong reduction in response to 1-MCP treatment. The data presented provide evidence that most esters produced by mountain papaya are derived from fatty acids and amino acid metabolic pathways, both of them being affected by ethylene.     

Combined treatment of aminoethoxyvinylglycine (AVG) and 1-methylcyclopropene (1-MCP) reduces melting-flesh peach fruit softening

The effects of postharvest application of aminoethoxyvinylglycine (AVG) and 1-methylcyclopropene (1-MCP) on ethylene production and fruit quality, and thus on transportation and shelf-life, were evaluated in melting-flesh peaches. AVG (150 mg L⁻¹) significantly reduced ethylene production, and the effect was enhanced in combination with 1-MCP (1 μL L⁻¹). However, fruit treated with AVG alone softened to untreated control levels 2 d after harvest (DAH). Treatment with 1-MCP significantly reduced the rate of softening until 2 DAH, but the fruit rapidly softened thereafter, and reached untreated control levels by 4 DAH. A combination of AVG and 1-MCP significantly reduced fruit tissue softening throughout ripening. The effect of each chemical on flesh firmness indicated that 1-MCP affected fruit response in the early stages of ripening up to 4 DAH, and AVG significantly reduced softening in the latter stages from 4 to 9 DAH. Peaches treated with AVG and 1-MCP retained their ground color during ripening, but the effect of each chemical on color is unclear. The present study indicates that combined treatment with AVG and 1-MCP significantly delays the ripening of melting-flesh peaches.     

Effect of ethylene concentration on quality parameters of fresh tomatoes stored using a carbon-heat hybrid ethylene scrubber

Tomato fruit were stored in cold rooms at 8 °C containing an adsorbent–catalyst device including activated carbon–1% Pd either alone or with a heater (175 °C) programmed to heat at 3 h pulse intervals. Cold rooms without the adsorbent–catalyst system were used as controls. The use of the device led to very low concentrations of both ethylene and CO₂ inside the cold rooms when compared with activated carbon–1% Pd alone or control rooms. In addition, the parameters related to ripening such as respiration rate, ethylene production, 1-aminocylcopropane-1-carboxylic acid (ACC, free and conjugated), colour changes, softening, decrease in total acidity (mainly citric and ascorbic acids) and lycopene were significantly higher in stored tomato fruit in control rooms than in those stored in cold rooms with both adsorbent–catalyst systems. The magnitude of the delay in these parameters was always significantly greater with the use of the device with respect to activated carbon–1% Pd alone. Thus, this device could be considered as a new tool to eliminate the ethylene surrounding fruit and vegetables in storage areas, avoiding the detrimental effects of ethylene action and leading to maintenance of their postharvest quality. Other additional advantages are the auto-regeneration process, when heat pulses were applied to the adsorbent–catalyst system, and the fact that it is an environmentally friendly technology.     

Effects of chlorine dioxide treatment on respiration rate and ethylene synthesis of postharvest tomato fruit

Tomato fruit at the mature green stage were treated with ClO₂ gas in a sealed container for 12 h, and then stored at 23 °C with 85% relative humidity (RH) for 23 d. Respiration rate, respiration-related enzymes including phosphohexose isomerase (PHI), succinate dehydrogenase (SDH), and glucose-6-phosphate dehydrogenase (G-6-PDH) and 6-phosphogluconate dehydrogenase (6-PGDH), ethylene production, and the expression of LeAOX1a, LeCOX1, LeACS2, LeACS4 and LeACO1 genes were measured. The results showed that application of ClO₂ gas was effective in reducing total respiration, cytochrome pathway respiration and the expression of LeCOX1, but no significant reduction in the activities of respiration-related enzymes was observed during storage. Fruit treated with ClO₂ resulted in lower ethylene production. Furthermore, the expression of ethylene biosynthesis related genes, including LeACS2, LeACS4 and LeACO1 was reduced by the ClO₂ treatment. These results indicate that ClO₂ treatment might delay the ripening of tomato fruit, possibly by a mechanism involving suppression of respiration rate and ethylene biosynthesis.     

Residual effects of low oxygen storage of mature green fruit on ripening processes and ester biosynthesis during ripening in bananas

Mature green banana (Musa sapientum L. cv. Cavendish) fruit were stored in 0.5%, 2%, or 21% O₂ for 7 days at 20 °C before ripening was initiated by ethylene. Residual effects of low O₂ storage in mature green fruit on ripening and ester biosynthesis in fruit were investigated during ripening for up to 6 d at 20 °C. Concentrations of ethanol in mature green fruit did not change during storage in both 21% and 2% O₂ atmospheres, but increased in fruit stored in 0.5% O₂. The activities of alcohol dehydrogenase (ADH) in 2% and 21% O₂ atmospheres remained very low throughout the storage period, but significantly increased with 0.5% O₂. After transferring fruit to regular air and trigging ripening with ethylene, yellowing of peel, fruit softening and hydrolysis of starch in fruit stored in low O₂ atmospheres were slower than in the control. Fruit stored in low O₂ also showed a delayed onset of the climacteric peak. The activities of ADH were lower in the low O₂ stored fruit than in the control fruit. Productions of ethyl acetate, isoamyl acetate, and isobutyl acetate were remarkably suppressed by low O₂ storage. Alcohol acetyltransferase activity increased gradually with storage time in all treatments, being significantly lower in fruit with low O₂ pretreatments. The results indicate that low O₂ plus room temperature storage can extend storage life of bananas with the sacrifice of a low production of ester volatiles.     

Profiling shifts in protein complement in tomato fruit induced by atmospheric ozone-enrichment and/or wound-inoculation with Botrytis cinerea

To unravel the mechanism by which low level atmospheric ozone-enrichment (0.05 μmol mol⁻¹) increases the shelf-life of tomato fruit (Lycopersicon esculentum Mill.) by suppressing the growth of pathogens (Botrytis cinerea), protein yield and composition were examined during and following exposure to the gas at 13 °C/95% RH. Ozone-enrichment caused marked changes in protein yield and composition in control tomato fruit and suppressed shifts in the proteome induced by wounding/fungal attack. Wound/fungal-inoculation with B. cinerea resulted in a 7% increase in protein yield, and the down-regulation of at least 32 proteins. A number of proteins affected under ozone and wound/fungal-inoculation treatments are involved in the control of cellular oxidative status. Proteins that may be enhanced under oxidative stress were induced during ozone exposure (e.g. thioredoxin peroxidase-TPX), but suppressed following transfer to ‘clean air’ (e.g. ascorbate peroxidase-APX1). Constitutively-expressed proteins tended to increase reversibly under ozone-treatment, however proteins involved in ripening such as an enzyme related to ethylene biosynthesis (1-aminocyclopropane-1-carboxylate oxidase-ACO) were markedly reduced in ozone-treated tomato fruit but increased in wound-inoculated fruit. Levels of proteins involved in carbohydrate metabolism, pentose phosphate pathway, terpenoid and flavonoid biosynthesis differentiated among the treatments. The presented dataset makes a central contribution to a comprehensive analysis of the manner in which tomato fruit react to ozone-enrichment and/or pathogen infection during storage/transit.