Prediction ability of firmness decay models of nectarines based on the biological shift factor measured by time-resolved reflectance spectroscopy

The maturity of nectarines at harvest can be assessed by measuring the absorption coefficient at 670 nm (μ_a) with the non-destructive technique of time-resolved reflectance spectroscopy (TRS). A kinetic model links μ_a, converted into the biological shift factor (BSF), to firmness decrease during ripening; in this way the firmness decay model includes the variations in maturity at harvest, thereby allowing prediction of shelf-life for individual fruit. In order to study how this methodology could be practically used at the time of harvest, when μ_a can be measured non-destructively on all fruit, while the destructive measurement of firmness can only be done on a small sample, various firmness decay models were developed using either data at harvest or within 1–2 d after harvest from previous experimental research with nectarines carried out over a 5-year period. These models were then tested for prediction and classification ability by comparing the predicted firmness and class of usability to the actual ones measured during ripening and their performance compared to that of models based on data during the whole shelf-life. Our results suggest that the methodology might be used as a management tool in the nectarine supply chain. Independently from the actual softening rate, the classification at harvest based on μ_a is able to segregate fruit of different quality and maturity according to their softening behaviour during shelf-life. Among the various models, those estimated using data at harvest and after 24 h of shelf-life had better performance than those based only on data at harvest. In the 2002 and 2005 seasons, this model showed a classification ability very close to that of models based on data during the whole shelf-life. However, its performance in the 2004 season was not so good, because it could not take into account the influence of cold storage periods prior to shelf-life. All the steps necessary to apply this methodology are detailed.     

A model for the softening of nectarines based on sorting fruit at harvest by time-resolved reflectance spectroscopy

Time-resolved reflectance spectroscopy (TRS), allows for the complete optical characterization (in terms of the absorption and scattering coefficients) of diffusive media such as fruit, in the spectral range 600–1100 nm, probing a volume to a depth of about 2 cm. The hypothesis was made that the absorption coefficient at 670 nm (μ_a), near the chlorophyll peak, could be an index of fruit maturity at harvest. The aim of this research was to model nectarine softening for fruit of different maturity at harvest, as assessed by μ_a. Nectarine fruit of two sizes (A and B) were picked in 2002, 2003 (cv ‘Spring Bright’) and 2004 (cv ‘Ambra’), measured by TRS at harvest on two opposite sides and ranked by decreasing μ_a averaged per fruit (increasing maturity). Fruit were stored at 0 °C for 3, 10 and 6 days, then at 20 °C for 79, 120 and 117 h in 2002, 2003 and 2004, respectively. Firmness was measured by pressure test (8 mm tip) during shelf life, on two sides of each fruit, and then averaged. Softening at 20 °C followed a logistic model as a function of μ_a at harvest and of time at 20 °C (adjusted R² = 0.85 in ‘Spring Bright’ and 0.75 in ‘Ambra’). The effects of fruit size and cold storage were negligible. The absorption coefficient μ_a explained 13–34% of the variation of firmness. Fruit with different μ_a at harvest softened with the same sigmoidal pattern in time, which was shifted earlier in low μ_a fruit, and later in high μ_a fruit. μ_a accounted for the time shift in softening of individual fruit within the same batch. The value of μ_a can be regarded as an index of the biological age of fruit. By using this model, it is possible to predict individual fruit softening rates at 20 °C.     

Active label-based packaging to extend the shelf-life of “Calanda” peach fruit: Changes in fruit quality and enzymatic activity

Nectarine fruit after cold storage soften normally, but become dry instead of juicy and can develop flesh browning, bleeding and a gel-like or glassy formation of the flesh near the pit. An experiment was conducted to see if time-resolved reflectance spectroscopy could distinguish these internal disorders non-destructively. The optical parameters of absorption coefficient (μ_a) and reduced scattering coefficient (μ′_s) were measured at 670 nm and 780 nm, on nectarine (Prunus persica cv. Morsiani 90) fruit held at 20 °C after harvest or after 30 d of storage at 0 °C or 4 °C. Each day for 5 d 30 fruit were examined both non-destructively and destructively. Other measurements were firmness with a penetrometer, peel colour on the blush and non-blush side, expressible juice, weight loss, and visual rating of internal browning, bleeding, and gel. The fruit had been sorted at harvest according to the value of μ_a670 so that each batch had a similar spread of fruit maturity. More mature fruit (lower μ_a670 values) developed internal browning and bleeding with more severe symptoms compared to less mature ones (higher μ_a670 values). It was found that μ_a780 could distinguish healthy fruits from the chilling injured ones. Canonical discriminant analysis indicated that fruit without cold storage had low μ_a780, less water loss, low firmness, but high μ_a670 and high expressible juice compared with cool stored fruit. Fruit cool stored at 4 °C had high μ_a780 and less expressible juice, lower water loss and lower firmness compared with fruit cool stored at 0 °C. It was concluded that time resolved reflectance spectroscopy could detect internal woolliness and internal browning in nectarines after storage.     

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.     

Effect of prolonged cold storage on the sensory quality of peach and nectarine

To maintain peach and nectarine quality after harvest, low temperature storage is used. Low temperatures induce physiological disorders in peach, but the effect of cold storage on the sensory quality of the fruit before it is damaged by chilling injury syndrome remains unclear. To evaluate the cold storage effect on the sensory quality two peach cultivars (’Royal Glory’ and ‘Elegant Lady’) and two nectarines (’Ruby Diamond’ and ‘Venus’) were harvested at a standardized firmness level and subjected to quality evaluations and sensory analysis at harvest and after storage at 0 °C for 35 d. For both time points, a supplementary ripening followed such that homogeneous flesh firmness and suitability for consumption was achieved.The fruit segregation through the Durofel firmness (DF), evaluated using a non-destructively method (Durofel device), allowed the formation of a uniform group of fruit in terms of flesh firmness (FF), showing scores between 45.1 and 55.9 N. The average FF in fruit ripened immediately after harvest was 22.9 N and 25.6 N in fruit ripened after cold storage for 35 d.The “acceptability” of fruit is highly correlated with “aroma”, “sweetness”, “juiciness”, “texture” and “flavor”. Only the “acid taste” parameter had no significant correlation with “acceptability” or with the other parameters evaluated.It is possible to conclude that the sensory quality and acceptability of peach and nectarine are characteristic of each cultivar and change, depending on the time elapsed after harvest. In general, it was confirmed that nectarine cultivars have a more consistent quality than peach cultivars.     

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.     

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.     

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.     

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.     

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.     

Molecular analysis of softening and ethylene synthesis and signaling pathways in a non-softening apple cultivar, ‘Honeycrisp’ and a rapidly softening cultivar, ‘McIntosh’

A feature of ‘Honeycrisp’ apples [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] is that they maintain flesh firmness over extended storage. The objective of this study was to elucidate molecular mechanisms that are responsible for slow softening of ‘Honeycrisp’ as compared with a rapidly softening cultivar, ‘McIntosh’. Fruit from both cultivars were picked during the normal harvest period and stored at 20 °C for 10 d. Internal ethylene concentrations (IECs) in ‘Honeycrisp’ fruit were lower than in ‘McIntosh’, but at climacteric levels of ethylene ‘Honeycrisp’ fruit maintained their firmness over this period, while ‘McIntosh’ softened rapidly. Concentrations of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) were higher in ‘Honeycrisp’ than in ‘McIntosh’ apples. qRT-PCR analysis was carried out for genes involved in ethylene biosynthesis, perception and signaling [ACC synthase (MdACS); ACC oxidase (MdACO); ethylene receptors (MdETR and MdERS); constitutive triple response (MdCTR); ethylene response factor (MdERF)], as well as those involved in cell wall metabolism [polygalacturonase (MdPG); xyloglucan endotransglucosylase (MdXTH); expansin (MdEXP); β-galactosidase (Md β-GS); arabinofuranosidase (MdAFase); pectate lyase (MdPL)]. At comparable IECs, the expression of genes involved in ethylene synthesis, ethylene perception and signal transduction was generally much higher in ‘Honeycrisp’ than in ‘McIntosh’ fruit. However, the expression of MdAFase and MdEXP3 was generally lower in ‘Honeycrisp’ than in ‘McIntosh’, while that of MdPG and MdPL was extremely low in ‘Honeycrisp’. Expression of MdPG1 was very low, even though IECs were at climacteric levels. Absence of fruit softening in ‘Honeycrisp’ is probably associated with restricted cell wall enzyme activity. The lower maximum IECs found in ‘Honeycrisp’ compared with ‘McIntosh’ do not appear to be related to expression of genes involved in ethylene biosynthesis.     

Impact of harvesting time and fruit firmness on the tolerance to fungal storage diseases in an apple germplasm collection

Blue mold and bitter rot, caused by Penicillium expansum and Colletotrichum gloeosporioides, respectively, are two of the most devastating diseases during and after storage of apple. The present project was conducted to evaluate the level of tolerance to these diseases in apple germplasm, and investigate possible associations with other fruit characteristics such as harvest date, firmness at harvest, softening (loss of firmness during storage) and sun-exposure. Apples were harvested at a maturation stage suitable for storage, inoculated with spore suspensions of P. expansum (127 cultivars) or C. gloeosporioides (70 cultivars), and stored for 6 or 12 weeks for early- and late-maturing cultivars, respectively. Fruit firmness was measured after harvest and after storage, and the difference was used as a measure of fruit softening. Average lesion diameter varied significantly among both early- and late-maturing cultivars. The amount of damage caused by the two diseases was significantly correlated across cultivars. Regression analyses indicated that lesion diameter was positively affected by fruit softening and negatively affected by harvest date and firmness at harvest. Impact of the independent variables was quantified with partial least squares discriminant analysis; approximately 40% of the genetic variation could be explained by these variables with harvest date being the most important. The effect of sun-exposure was analyzed on six bi-colored cultivars but the results were not conclusive. Cultivars that showed relatively small symptoms in spite of being early-maturing and/or only medium firm, may have other traits that are beneficial for storage and could therefore be especially useful in breeding programs.     

Methods to analyze physico-chemical changes during mango ripening: A multivariate approach

Canonical discriminant analysis (CDA) was used to identify the best method to discriminate between maturity and ripening stages, assessed in terms of dry matter content, firmness, color (peel and flesh), total soluble solids content attributes, before and during ‘Keitt’ mango ripening at 20 °C. Dry matter content was determined by hot-air oven and microwave oven methods. Fruit firmness was determined non-destructively by hand squeezing, with a durometer, using acoustic resonance and low-mass elastic impact methods (AWETA), as well as destructively by the penetrometer. Peel and flesh color were expressed as L*, a*, b*, h⁰ and C* values. Total soluble solids content was analyzed from filtered juice from whole fruit tissue and from unfiltered juice squeezed out by hand. Canonical discriminant analysis indicated that the durometer and the penetrometer were better methods to assess firmness than hand firmness, acoustic resonance or impact methods. The best color attributes to follow changes during early stage of ‘Keitt’ mango ripening were a* and b* values of the flesh, whereas b* value of the peel was considered better during later stages of ripening. Results of total soluble solids content in filtered juice from whole fruit tissue were less variable compared to unfiltered juice squeezed out by hand. Dry matter content was better assessed by drying the sample in a microwave oven than in a hot-air oven. A combined CDA including the best methods to assess each ripening attribute, as well as titratable acidity, showed that the best tools to assess changes in fruit during ripening were the penetrometer, followed by flesh a* value and total soluble solids content (from filtered juice from whole fruit).     

Effect of harvest maturity and cold storage on correlations between fruit properties during ripening of apricot (Prunus armeniaca)

Apricots (Prunus armeniaca) were held in air storage at 0 °C and ripened at 20 °C, or ripened at 20 °C straight after harvest, and changes in fruit quality quantified using postharvest and sensory evaluations. Maturity at harvest significantly affected flesh firmness and other quality factors. Mealiness and gel formation only developed in fruit that had been stored at low (0 °C) temperatures. Mealiness did not develop until firmness dropped below approximately 20 N, whereas gel formation began to develop when firmness was as high as 35 N. Development of mealiness and loss of juiciness were correlated; however, slight mealiness was perceived when fruit were still considered juicy. Specific cultivar-related differences were evident in the changes in firmness and development of gel formation during and after cold storage. Fruit were less liked by the sensory panel when firmness dropped below 20 N, as juiciness decreased and mealiness and gel formation increased. Cell wall studies showed changes in yields of water-soluble and CDTA (trans-1,2-cyclohexanediamine tetraacetic acid)-soluble pectin. In fruit ripened after cold storage, mealiness and gel formation was accompanied by an increase in water-soluble pectin and an increase in CDTA-soluble pectin, whereas in apricots ripened straight after harvest, water-soluble pectin increased but CDTA-soluble pectin slightly decreased. All fruit, regardless of maturity or having chilling disorders or not, fitted the same correlation between firmness and uronic acid content of water-soluble pectin, but no pattern was evident for CDTA-soluble pectin. We concluded that the increasing solubilisation of pectin was a major feature of fruit softening in apricot, whereas the differences in CDTA-soluble pectin may reflect differences in strength of cell adhesion.     

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.     

Influence of Md-ACS1 allelotype and harvest season within an apple germplasm collection on fruit softening during cold air storage

Previous studies have demonstrated a relationship between Md-ACS1 allelotype and apple fruit softening at ambient temperatures. The present study was undertaken to further examine the influence of this allelotype (-1/1, -1/2 or -2/2) and its interaction with harvest season (early or late) on changes in internal ethylene concentrations (IEC) and fruit softening during cold air storage. This was carried out by describing natural differences found among old apple cultivars/species and modern commercial cultivars. For late maturing cultivars, Md-ACS1-1/1 was firmer at harvest than Md-ACS1-2/2 with the heterozygote intermediate. However harvest firmness showed no differences among for the early season Md-ACS1 allelotypes. The Md-ACS1-2/2 allelotype had a slower rate of postharvest IEC increase and flesh softening compared with Md-ACS1-1/1 and -1/2 allelotypes, and late maturing cultivars had a slower rate of fruit softening than early maturing cultivars, which was independent of postharvest IEC. All three late season allelotypes and early season Md-ACS1-2/2 were firmer after storage than early season Md-ACS1-1/1 and -1/2 allelotypes, reflecting differences in both harvest firmness and softening rates. While cultivar variation in final firmness could be explained partially through Md-ACS1-mediated postharvest ethylene increases and subsequent softening, much more variation was accounted for by their differences in harvest firmness. These results are discussed in relation to strategies for breeding cultivars with superior flesh textures that are maintained during storage.     

Calcium salts and heat treatment for quality retention of fresh-cut ‘Galia’ melon

‘Galia’ melon is one of the most common cv produced in Spain destined for fresh consumption and/or for the fresh-cut processing industry. Nevertheless, fresh-cut melon is very susceptible to softening during storage, even under chilling and modified atmosphere packaging. This softening process is related to Ca levels in fruit tissue. After preparing trapezoidal shaped sections of ‘Galia’ melons, the pieces were dipped for 1 min a 60 °C in Ca chloride, citrate, lactate, ascorbate, tartrate, silicate, propionate or acetate using a Ca concentration equivalent to 0.4% (0.15 g g⁻¹) pure Ca chloride, combined with 50 mg L⁻¹ H₂O₂ for controlling microbial growth. Dipping in sterile distilled water (without Ca salt) at 60 °C for 1 min was used as a control treatment. Firmness, pectin methylesterase and polygalacturonase activity, Ca content, microbial growth, respiration rate, and sensory evaluation, were evaluated throughout 10 days of storage at 5 °C under a passive modified atmosphere reaching 4.5 kPa O₂ and 14.7 kPa CO₂. At the end of shelf life, Ca ascorbate, chloride and lactate provided melon pieces with a lower respiration rate, increased tissue total Ca content, and maintained a good firmness. In addition, those Ca salts reduced microbial growth. Sensory parameters, such as flavor perception, were kept above the upper limits for marketability. A considerable loss of flavor was found in all treatments except with Ca chlorine, lactate and ascorbate, the only treatments found acceptable from the consumer point of view.     

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.