Chilling injury in mango fruit peel: Cultivar differences are related to the activity of phenylalanine ammonia lyase

In mango (Mangifera indica) cv. Nam Dok Mai fruit, stored at 4 °C, peel browning occurred within 9 d, while no browning was found in cv. Choke Anan fruit stored at 4 °C for 30 d. During 6 d of shelf life at 27-28 °C, following various periods of low temperature storage, the peel browning in cv. Nam Dok Mai (if not yet maximal) became worse, whereas little browning was observed in cv. Choke Anan fruit. The pulp of the fruit of both cultivars did not show browning during the 4 °C storage, but the pulp of cv. Nam Dok Mai exhibited some browning during shelf life if the fruit had been stored at 4 °C for more than 18 d. Peel and pulp color were not correlated with total free phenolics. A high correlation coefficient was observed between peel browning and PAL activity in the peel, while a very low correlation was found with peel catechol oxidase activity. The browning in the pulp was not correlated with the measured enzyme activities. The data therefore show a relation between PAL activity in the peel and low temperature-induced peel browning.     

1-MCP extends the storage and shelf life of mangosteen (Garcinia mangostana L.) fruit

Mangosteen (Garcinia mangostana L.) fruit were harvested when the peel (pericarp) was light greenish yellow with scattered pinkish spots. Fruit were exposed to 1 μL L⁻¹ 1-methylcyclopropene (1-MCP) for 6 h at 25 °C and were then stored at 25 °C (control) or 15 °C. The 1-MCP treatment only temporarily delayed softening of the fruit flesh, during storage. Storage life, defined as the time until the pericarp was dark purple, was much longer in fruit stored at 15 °C than in fruit stored at 25 °C. It was also longer in 1-MCP treated fruit (storage life at 15 °C: control 18 d, 1-MCP-treated fruit 27 d). The 1-MCP treatment also increased the length of shelf life, defined as the time until the pericarp turned blackish purple or showed calyx wilting, at 25 °C. 1-MCP treatment reduced ethylene production. It also reduced pericarp levels of 1-aminocyclopropane-1-carboxylic acid (ACC), and the pericarp activities of ACC synthase (ACS) and ACC oxidase (ACO). In the fruit flesh, in contrast, 1-MCP did not affect ACC levels and ACS activity, but the treatment reduced ACO activity. Taken together, both the storage life and the shelf life of the fruit were extended by the 1-MCP treatment. A decrease in ACO activity largely accounted for the effects of the 1-MCP on ethylene production in the pericarp.     

Fruit maturity affects the response of apples to heat stress

Quality changes of apple fruit at different maturity stages in response to heat stress were investigated. ‘Jonagold’ and ‘Cortland’ apples at immature (pre-climacteric), commercial harvest maturity (CHM) and post climacteric maturity (PCM, CHM plus 4 weeks) were harvested and held at 46 °C for 0, 4, 8, or 12 h. Following treatments, fruits were stored in air at 0 °C and evaluated after 0, 1, 2, or 3 months. Quality indices including peel and flesh browning, firmness, titratable acidity, soluble solids, chlorophyll fluorescence (CF), and ethanol production were measured. Results indicated that different cultivars and maturities affected the fruit's resistance to heat stress. ‘Jonagold’ was more resistant to heat stress than ‘Cortland’. Fruit at PCM were most sensitive to heat stress, followed by fruits at CHM and immature stages. When ‘Jonagold’ apples at immature and CHM stages were held at 46 °C for 12 h and then stored for 3 months, flesh browning ratings were negligible compared with 1.4 or 2.9, respectively in ‘Cortland’. Flesh browning rating increased to 1.4 or 4.5 in PCM ‘Jonagold’ held at 46 °C for 8 or 12 h and then stored for 3 months while it was 4.9 or 5.0, respectively, in ‘Cortland’. Heat treatment-induced flesh injury was associated with a decrease in CF. After fruit were exposure to 46 °C for 12 h and then stored for 3 months, Fv/Fm was reduced by 13%, 30%, and 55% in ‘Jonagold’ at immature maturity, CHM and PCM, respectively, while it was reduced by 51%, 58% and 75%, respectively, in ‘Cortland’. Heat stress also caused a decrease in fruit titratable acidity, but had no effect on soluble solids contents. The 8 or 12 h heat treatment resulted in an increase in ethanol production, which was greatest in PCM apples.     

Maturity assessment at harvest and prediction of softening in a late maturing nectarine cultivar after cold storage

The absorption coefficient μ_a measured at 670 nm in fruit pulp at harvest by time-resolved reflectance spectroscopy (TRS) has been shown to be a good maturity index for early nectarine cultivars. By including individual fruit maturity as a biological shift factor (BSF) into a kinetic model for softening it is possible to select fruit with different shelf-life potential. The BSF approach combined with TRS measurement and kinetic modeling of firmness was applied to a late maturing nectarine cultivar (‘Morsiani 90’), ripened at 20 °C after harvest or after storage at 0 °C and 4 °C, the latter conditions inducing chilling injury. At harvest the absorption coefficient μ_a had low values and low variability, indicating advanced maturity, while firmness was similar to that of early cultivars. The softening model took into account these differences, showing parameters similar to those of the early cultivars with the exception of the softening rate which was 2-6 times lower, indicating a slower softening in ‘Morsiani 90’ fruit. Decay of μ_a at 20 °C was also slower. Softening continued during storage at 4 °C, but not at 0 °C. After storage at 0 °C softening was resumed similarly to non-stored fruit, but with much variability. Fruit stored at 4 °C, which showed chilling injury, had a softening rate at 20 °C significantly higher than that of 0 °C fruit. It is suggested that the same changes in cell wall metabolism which induce the appearance of chilling injury also affect firmness and increase softening rate.     

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.     

Anaerobic metabolism during short and long term storage of kiwifruit

Kiwifruit were stored in 0.25% O₂ (ULO), 1% O₂ (LO) and 2% O₂ + 5% CO₂ (CA) and the controls were kept in air. The fruit were held at 0 °C for 34 and 94 d of storage and, after these times, were transferred to 20 °C in air for 14 d of shelf life. During the short term storage (34 d), a significant increase in anaerobic metabolites, above all ethanol, was observed in ULO, LO, and CA fruit (166, 131, 120 μL/L). After the shift to shelf life, a large and unexpected increase in PDC (pyruvate decarboxylase), ADH (alcohol dehydrogenase in the direction of ethanol oxidation), LDH (lactate dehydrogenase), and GPT (glutamate-pyruvate transaminase) was observed, resulting in ethanol depletion (ULO) or no further increase, and an increase in acetaldehyde which, in turn, could have hastened fruit ripening. Even the control fruit showed an increase in ethanol during storage and an increase in enzyme activity during shelf life, especially in ADH, but to a lesser extent without an increase in acetaldehyde. During the long term storage, anaerobic metabolites (ethanol and acetaldehyde) still increased and GPT activity rose significantly in the ULO and CA samples. A burst of enzyme activity was also observed during the second shelf life in the CA and LO samples, but not in the control, while in ULO fruit the activity rose continuously. GPT activity showed the highest peaks in CA and ULO fruit. An ethylene burst was observed in ULO and CA fruit during the second shelf life (about 25 μL/kg-h) but not during the first shelf life. The potential role of these enzymes in kiwifruit stress response during storage and shelf life is discussed.     

Control of lemon green mold by a sequential oxidative treatment and sodium bicarbonate

A sequential oxidative treatment (SOT), using sodium hypochlorite (NaClO) and hydrogen peroxide (H₂O₂) in the presence of a cupric salt inhibited in vitro growth and germination of Penicillium digitatum conidia, causal agent of citrus green mold. Here, modifications of this SOT were evaluated in vivo to control this disease in inoculated lemons. The treatment that consisted of two sequential 2-min baths: one with 200 mg L⁻¹ NaClO followed by a second with 600 mmol L⁻¹ H₂O₂ in the presence of 6 mmol L⁻¹ CuSO₄, resulted in 50% of disease control. When this treatment was combined with a third 2-min bath containing 30 g L⁻¹ NaHCO₃ at 37 °C (SOT-NaHCO₃) and applied at 24 h post-inoculation, green mold incidence was reduced to ∼5%. In non-inoculated lemons stored at 5 °C for 45 d, this treatment did not modify the appearance or weight compared to untreated lemons. Furthermore, phenolic content and the oxygen consumption rate in flavedo and albedo tissues were not affected by the SOT-NaHCO₃. The malondialdehyde content in flavedo tissues increased immediately after treatment, but decreased to levels similar to control fruit 2 d later. The SOT-NaHCO₃ combines compounds that are safe to the environment and human health, thus it represent a potential alternative to synthetic fungicides for the integrated control of postharvest diseases.     

Importance of storage temperatures in maintaining flavor and quality of mandarins

Mandarins suffer from short ‘flavor-life’ compared with other citrus species. The recommended minimum safe temperature for mandarin storage is 5-8 °C. However, because of continuing reductions in permitted chemical residues and increasing concern regarding decay development, mandarins are often shipped at much lower temperatures of 3-4 °C. In the last few years we noticed wide differences in responsiveness of mandarin varieties to chilling, and that the earliest indication of damage was a decrease in flavor acceptability. In the present study, we evaluated changes in flavor and quality of chilling-tolerant ‘Or’ and chilling-sensitive ‘Odem’ mandarins after 4 weeks of storage at 2, 5, or 8 °C followed by 3 days at 20 °C. Low storage temperatures resulted in loss of orange peel color in fruit of both varieties, which became paler and yellowish. The flavor of ‘Or’ mandarins was not affected by different storage temperatures, whereas ‘Odem’ showed severe flavor loss at low storage temperatures. GC-MS analysis of aroma volatiles revealed that changes of storage temperatures had no major effects on aroma volatile contents in ‘Or’ mandarins. However, in ‘Odem’ mandarins, storage at 2 °C caused accumulation of 13 volatiles, mainly terpenes and their derivates, whereas storage at 8 °C resulted in decreases of six volatiles, comprising five terpenes and one terpene derivative. Overall, we conclude that storage temperature is a fundamental factor affecting color and flavor of mandarins, and therefore it is crucial to define the optimal minimum safe temperature for each mandarin variety. Furthermore, massive accumulation of terpenes is most likely the cause for the decrease in flavor acceptability of ‘Odem’ mandarins after storage at low chilling temperatures.     

Low temperature induced changes in activity and protein levels of the enzymes associated to conversion of starch to sucrose in banana fruit

Storage at low temperature is the most frequently used method to extend the shelf life of banana fruit, and is fundamental for extended storage and transport over long distances. However, storage and transport conditions must be carefully controlled because of the high susceptibility of many commercial cultivars to chilling injury. The physiological behavior of bananas at low temperatures has been studied to identify possible mechanisms of resistance to chilling injury. The aim of this work was to evaluate differences in the starch-to-sucrose metabolism of a less tolerant and susceptible (Musa acuminata, AAA cv. Nanicão) and a more tolerant (M. acuminata × Musa balbusiana, AAB, cv. Prata) banana cultivar to chilling injury. Fruits of these cultivars were stored in chambers at 13 °C for 15 d, at which point they were transferred to 19 °C, where they were left until complete ripening. The low temperature induced significant changes in the metabolism of starch and sucrose in comparison to fruit ripened only at 19 °C. The sucrose accumulation was slightly higher in cv. Prata, and different patterns of starch degradation, sucrose synthesis, activity and protein levels of the α- and β-amylases, starch phosphorylase, sucrose synthase and sucrose phosphate synthase were detected between the cultivars. Our results suggest that starch-to-sucrose metabolism is likely part of the mechanism for cold acclimation in banana fruit, and the cultivar-dependent differences contribute to their ability to tolerate cold temperatures.     

Chilling-injury of harvested tomato (Solanum lycopersicum L.) cv. Micro-Tom fruit is reduced by temperature pre-treatments

Heat-shocks were used to reduce the development of chilling injury symptoms during ripening of tomato fruit (Solanum lycopersicum L. cv. Micro-Tom). Mature green tomatoes were immersed in 30-50 °C water for 3-9 min before being chilled at 2.5 °C for 0, 0.5, 1, 2, 3, or 14 days, and then held at 20 °C for an additional 7-14 days. The affect of both heat-shock and chilling treatments were independent of fruit weight. Measured at 20 °C after 14 days of chilling, fruit exposed to 40 °C for 7 min exhibited reduced chilling injury symptoms, as measured by their advanced ripening score and decreased rate of ion leakage into an isotonic 0.2 M mannitol solution. Reduced rates of leakage from the symplastic compartment probably contributed to the 2-fold decrease in the amount of ions in the apoplastic space, when compared to the control. A subsequent paper will report the results of metabolic profiling of Micro-Tom tomato fruit subjected to treatments that significantly decreased their development of chilling injury symptoms.     

Ethylene biosynthesis in apricot: Identification of a ripening-related 1-aminocyclopropane-1-carboxylic acid synthase (ACS) gene

Apricots are climacteric fruits with a high susceptibility to flesh softening and loss of flavor during postharvest storage, and most of the ripening processes are regulated by ethylene, which also has an effect on its own biosynthesis. To understand this process in apricot, inhibition of ethylene biosynthesis and perception was performed for studying key genes involved in the ethylene biosynthetic pathway. Apricots, cv. “Patterson”, were harvested with yellow-green ground color and immediately treated with either the ethylene perception inhibitor 1-methyl cyclopropene (1-MCP) at 10 μL L⁻¹ or the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG) at 1 g L⁻¹. After treatment, quality and physiological attributes such as firmness, color, total soluble solids, acidity, fruit weight, ethylene production and respiration rates were evaluated every 2 d until they ripened at 20 °C. Gene expression analysis was performed by quantitative polymerase chain reaction (qPCR). Both ethylene inhibitors were effective in reducing ethylene production, respiration rate and fruit softening. Three 1-aminocyclopropane-1-carboxylic-acid synthase (ACS) genes were characterized, but only the expression of ACS2 was highly reduced by ethylene inhibition, suggesting a key role in ethylene synthesis at ripening. Contrarily, ACS1 and ACS3 showed a higher expression under ethylene inhibition suggesting that the corresponding genes are individually regulated in a specific mode as observed in other climacteric fruits. Finally, changes in 1-aminocyclopropane-1-carboxylic-acid oxidase genes did not show a consistent pattern of ethylene modulation.     

The effect of metabolic stress disinfection and disinfestation (MSDD) on ‘Hass’ avocado fruit physiology and mortality of longtailed mealybug (Pseudococcus longispinus)

Metabolic stress disinfection and disinfestation (MSDD) is a potential quarantine treatment in which a combination of cycles of rapid decompression and compression are followed by exposure to ethanol vapour under decompression. The response of ‘Hass’ avocado (Persea americana Mill., cv. Hass) to MSDD treatment for control of longtailed mealybug (Pseudococcus longispinus) was investigated. The best treatment for the most resistant life stage (2nd/3rd instars) was 90-min MSDD treatment with 371 mg L⁻¹ ethanol. Early and late season ‘Hass’ avocados were subjected to MSDD treatments (with 371 mg L⁻¹ ethanol), or in air (control). Following the treatments, early season fruit were ripened at 20 °C and 25 °C. Half of the late season fruit were ripened at either 20 °C or 25 °C, and the remainder were stored at 5.5 °C for 6 weeks, then ripened at 20 °C. There were no significant difference in quality and rot incidence between non-treated controls and MSDD-treated fruit. The main disorders found were stem-end and body rots, vascular browning and flesh greying for the stored fruit. There were also no significant differences in fruit respiration rate or ethylene production. Thus, MSDD was shown to be a potentially ‘soft’ disinfestation treatment for surface pests of avocado.     

The combination of curing with either chitosan or Bacillus subtilis CPA-8 to control brown rot infections caused by Monilinia fructicola

Recently, it has been reported that brown rot in peaches and nectarines can be effectively controlled by exposing fruit to 50 °C for 2 h and 95-99% relative humidity (RH). This treatment was effective at reducing infections that had become established in the field. However, it did not provide protection for further Monilinia fructicola infections, indicating that fruit was susceptible to subsequent infections after the treatment process and before cool storage. Chitosan and Bacillus subtilis (strain CPA-8) were evaluated for their ability to prevent M. fructicola infections and for their ability to complement the heat treatment. Two chitosan concentrations (0.5% or 1%) were applied at three temperatures (20, 40 or 50 °C) for 1 min to wounded and unwounded fruit that were artificially inoculated with M. fructicola. One percent chitosan applied at 20 °C had a preventive effect against further M. fructicola infections on heat-treated fruit that had been previously inoculated: brown rot incidence was reduced to 10%, in comparison with the control (73%). However, chitosan applied to wounded fruit had a poor preventive effect. The antagonist, B. subtilis CPA-8, had a preventive effect in controlling M. fructicola infections: the incidence of brown rot was reduced to less than 15% for both varieties evaluated (‘Baby Gold 9’ and ‘Andros’ peaches), in comparison with the control fruit (higher than 98%). In contrast, when fruit were stored at 0 °C, this preventive effect was not detected. These findings indicate that heat-treated fruit can be protected from subsequent fruit infection after heat treatment by use of chitosan or B. subtillis CPA-8, thereby providing packinghouses with an effective biologically based, combined approach to the management of postharvest brown rot.     

Ethanol vapor and saprophytic yeast treatments reduce decay and maintain quality of intact and fresh-cut sweet cherries

The objective of this study was to evaluate the use of an ethanol vapor release pad and a saprophytic yeast Cryptococcus infirmo-miniatum (CIM) to reduce decay and maintain postharvest quality of intact or fresh-cut sweet cherries (Prunus avium) cv. Lapins and Bing. Intact or fresh-cut fruit were packed in perforated clamshells (capacity 454 g) and stored at 1, 10 or 20 °C for up to 21, 14 and 8 d, respectively. For ethanol treatment, a pad made with silica gel powder containing 10 g ethanol and covered with perforated film, which allows ethanol vapor to diffuse gradually, was attached to the upper lid of the clamshells. Ethanol treatment caused accumulation of ethanol in the packaging headspace, about 10 μL L⁻¹ with little change within 14 d at 1 °C, 23 μL L⁻¹ at d 1 and decreased to 15 μL L⁻¹ at d 10 at 10 °C, and 26 μL L⁻¹ at d 1 and decreased to 13 μL L⁻¹ at d 3 at 20 °C. Ethanol content in fruit was less than 9 mg kg⁻¹ in all the control fruit, and increased to 16, 34 and 43 mg kg⁻¹ in ethanol-treated fruit at 1, 10 and 20 °C, respectively. Nonetheless, a sensory taste panel did not perceive any flavor difference from the ethanol treatment. The ethanol treatment retarded softening, darkening, and acid decrease in fruit as well as discoloration of the stems, and extended shelf-life of intact cherries. Ethanol reduced brown rot (Monilinia fructicola) in fresh-cut cherries stored at 20 °C, but not at 1 and 10 °C. A pre-packaging dip in CIM completely controlled brown rot in inoculated fresh-cut cherries stored at 1 °C, and in naturally infected cherries at 20 °C.     

Possible mechanisms of warming effects for amelioration of superficial scald development on ‘Fuji’ apples

Warming of fruit during storage has been shown to decrease scald development, but the mechanisms involved in this effect are poorly understood. The effects of a single warming of 5 days at 20 °C after 2, 4, 6 and 8 weeks storage at 0 °C on development of superficial scald of ‘Fuji’ apples in relation to ethylene, a-farnesene and conjugated trienol (CTol) concentrations have been studied. Malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) concentrations, catalase (CAT) and peroxidase (POX) activities, total phenolic contents and total antioxidant activity were measured in order to assess the effects of the treatments on membrane damage and oxidant and antioxidant activity. Warming after 4 weeks storage reduced scald to the lowest level among all treatments. Warming greatly stimulated internal ethylene concentrations (IECs) and in turn, increased α-farnesene and CTol accumulation. Scald resistance, indicated by CAT and POX activities, total phenolic contents and total antioxidant activity, was higher in fruit in early than in late storage. The warming treatment after 4 weeks of storage resulted in higher concentrations of CTols and H₂O₂, as well as MDA, compared with the control fruit when kept at 20 °C after 6 and 12 weeks of storage, but lower than after 20 and 28 weeks. These results suggest that warming could inhibit scald development by modifying CTol accumulation as well as by affecting generation of accompanying active oxygen species (AOS), and reducing oxidative damage. These changes may cause a shift from a scald-sensitive metabolism to a resistant stage during storage.     

Cold pre-treatment is effective for 1-MCP efficacy in ‘Tsugaru’ apple fruit

1-Methylcyclopropene (1-MCP) treatment maintains apple fruit quality during storage, but its efficacy is dependent on a number of conditions. ‘Tsugaru’ apples are a major early season cultivar in Japan, but because ‘Tsugaru’ fruit produce abundant ethylene, they have a short shelf-life, and efficacy of 1-MCP is not as high with ‘Tsugaru’ as with other cultivars. To improve 1-MCP efficacy, ‘Tsugaru’ fruit were pre-cooled at −1 °C or −3 °C for 24 h before 1-MCP treatment. Ethylene production decreased with the cold treatment, resulting in better storage after 1-MCP treatment. Although ethylene production was low at the end of 24 h of the cold pre-treatment, expression of ACS1, the ethylene receptor genes ERS1, ETR1(a), ETR1b, ETR2 and ETR5, and the cell wall degradation-related gene PG1 all increased with a 24 h cold treatment. It is assumed that these elevated gene expression levels were not caused by ethylene, but more directly by cold stimulus. Thus, a short period of cold stimulus suppresses ethylene production, but induces expression of some genes. 1-MCP treatment was more effective with some initial fruit chilling.     

A preliminary study on the effect of metabolic stress disinfection and disinfestation (MSDD) on ripening physiology and quality of kiwifruit and apple

Metabolic stress disinfection and disinfestation (MSDD) is a relatively new quarantine treatment in which fruit are exposed to rapid decompression and compression cycles and high CO₂ atmosphere, followed by exposure to ethanol vapour under decompression. This study evaluated the ripening response of ‘Hayward’ kiwifruit (Actinidia deliciosa) and ‘Pink Lady’ apple (Malus x domestica) to MSDD treatment, which can control longtailed mealybug (Pseudococcus longispinus). Following the treatments, fruit were held at 20 °C for 7 d for shelf-life assessment, while the remainder were refrigerated at 0.5 °C for 16 weeks. Respiration rate, volatile (ethylene, ethanol and acetaldehyde) production rates, firmness and disorders were measured at regular time intervals. MSDD treatments did not affect the metabolic activities and quality of ‘Pink Lady’ apples. However, firmness was reduced by 4.9 N in non-refrigerated MSDD treated fruit. MSDD treatments did not control superficial scald disorder in refrigerated ‘Pink Lady’ apples. For ‘Hayward’ kiwifruit, treatments increased the respiration rate and ethylene production of short-term refrigerated fruit, promoted endogenous production of ethanol and acetaldehyde in both short-term and long-term refrigerated fruit. MSDD treatments also increased the incidence of rots in refrigerated ‘Hayward’ kiwifruit. MSDD treatments accelerated the softening of short-term refrigerated kiwifruit, but retarded the softening of ‘Hayward’ kiwifruit during the 16 weeks of refrigerated storage. MSDD could potentially be used as a quarantine treatment of apples. Further studies are required on the sensory effect of MSDD treatment.     

Metabolite content of harvested Micro-Tom tomato (Solanum lycopersicum L.) fruit is altered by chilling and protective heat-shock treatments as shown by GC-MS metabolic profiling

The primary aim of this study was to identify metabolites associated with chilling tolerance that was engendered by a heat-shock treatment of tomato fruit pericarp (Solanum lycopersicum L. cv. Micro-Tom). Harvested mature-green fruit were immersed in 20 or 40 °C water for 7 min (‘Heat-Shock’) and then stored at 2.5 °C for 0 or 14 d (‘Chilled’). A reduction in chilling injury symptoms (i.e., slow or abnormal ripening, increased ion leakage, and increased respiration following chilling) was used to select this heat-shock treatment as optimal. Using GC-MS (Gas Chromatography-Mass Spectrometry) metabolite profiling, 363 analytes were detected in fruit pericarp of which 65 are identified metabolites. Principal Component Analysis of these data led to distinct groups among the samples based on their treatments; ‘Chilled’ and ‘Chilled + Heat-Shocked’ fruit were markedly different from each other, while the ‘Non-Chilled Control’ and ‘Heat-Shocked’ fruit were similar and grouped closer to the ‘Chilled + Heat-Shocked’ fruit. These results indicate that the heat treatment provided protection from chilling in part by altering levels of fruit metabolites. The levels of arabinose, fructose-6-phosphate, valine and shikimic acid appear to be associated with this heat-shock induced chilling tolerance since their levels were altered in the ‘Chilled’ samples (p < 0.05), relative to the control and the heat-shocked protected fruit. We also describe the metabolites we identified that could be further studied as being indicative of incipient chilling injury in mature-green tomato fruit.