Combined effects of sodium chlorite dip treatment and chitosan coatings on the quality of fresh-cut d’Anjou pears

This study evaluated the effects of sodium chlorite (SC) alone and its sequential treatment with edible coatings on browning inhibition and quality maintenance of fresh-cut d’Anjou pears. Edible coatings were prepared from chitosan (CH) and its water-soluble derivative carboxymethyl chitosan (CMCH), separately. Pear wedges were immersed in SC solution, followed by coating with CH or CMCH solutions. The samples were packed in unsealed bags and stored at 4 °C for subsequent color, firmness, and weight loss measurement. The effects of the SC and coating treatments on polyphenol oxidase (PPO) inhibition and microbial inactivation were also evaluated. Results indicated that SC exhibited significant (P < 0.05) inhibition of browning and PPO activity. The SC treatment was also strongly effective in inactivating Escherichia coli O157:H7 on pear slices. Coating SC-treated pear slices with CH adversely affected the quality of pear slices by accelerating the discoloration of cut surfaces and increasing the PPO activity. On the contrary, coating SC-treated samples with CMCH significantly prevented the browning reaction and inhibited PPO activity. In addition, SC and CH/CMCH coatings maintained tissue firmness and did not affect weight loss. Our study may provide a scientific basis for the use of SC + CMCH treatment as an alternative preservation treatment for fresh-cut fruits and vegetables.     

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.     

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.     

Effects of UV-C treatment on inactivation of Escherichia coli O157:H7, microbial loads, and quality of button mushrooms

This study investigated the effects of ultraviolet-C (UV-C) light applied to both sides of mushrooms on microbial loads and product quality during storage for 21 d at 4 °C. Microflora populations, color, antioxidant activity, total phenolics, and ascorbic acid were measured at 1, 7, 14 and 21 d of storage. Additionally, the inactivation of Escherichia coli O157:H7 by UV-C was determined. Results showed that UV-C doses of 0.45-3.15 kJ m⁻² resulted in 0.67-1.13 log CFU g⁻¹ reduction of E. coli O157:H7 inoculated on mushroom cap surfaces. UV-C radiation also reduced total aerobic plate counts by 0.63-0.89 log CFU g⁻¹ on the surface of mushrooms. Although mushrooms treated with UV-C had more severe browning with increasing dosage after initial treatment, the control mushrooms also browned as indicted by lower L* and higher a* values after 21 d of storage at 4 °C. In addition, the UV-C treatments apparently inhibited lesion development on the mushroom surface. During the first 7 d, irradiated mushrooms had lower antioxidant activity, total phenolics, and ascorbic acid content compared to non-radiated samples. However, irradiated mushrooms reached similar amounts of these nutrients as the control after 14 d of storage at 4 °C. In summary, UV-C radiation could potentially be used for sanitizing fresh button mushrooms and extending shelf-life.     

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.     

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.     

Hot water treatments reduce leaf yellowing and extend vase life of Asiatic hybrid lilies

The vase life of Asiatic lilies can be limited by leaf yellowing, which can be caused by exposure to low light or temperature during winter growth or in storage. We examined the use of postharvest hot water treatments (HWTs) as a means of reducing leaf senescence in stored (4 °C for 2 weeks) and non-stored Asiatic hybrid lily ‘Elite’ (Lilium sp.). A range of HWTs (45-55 °C for 2.5 or 5 min) was applied to leaves on cut lily stems (but not flowers). Higher temperatures and the longer duration resulted in heat damage, but treatments of 50 °C for 5 min and 52.5 °C for 2.5 min were found to be optimal for minimising leaf yellowing with trace levels of heat damage for both non-stored and stored stems. The onset of yellowing was delayed by 3-4 d, and the occurrence of an unacceptable level of yellowing eliminated for up to 12 d (compared with <6 d for control stems). The physiological effects of these optimal HWTs were examined in terms of water uptake, chlorophyll fluorescence and chlorophyll degradation. Water uptake for optimal HWTs during shelf life was reduced by more than 50% of the control stems. Chlorophyll fluorescence of leaves on control stems showed a reduction in yield (F_v/F_o) over time, which was more marked in lower than upper leaves (thus correlating with yellowing, which was more severe in the lower leaves). Although both optimal HWTs resulted in an initial reduction in yield, there was a recovery over time resulting in a yield that, by 12 d, was as high or significantly higher than control leaves (particularly for the lower leaves). All treatments showed a reduction in chlorophyll content (total, chlorophyll a and chlorophyll b), but control leaves had significantly lower levels after 7 d. HWTs show potential as a non-chemical, simple means of delaying leaf yellowing of Asiatic lilies and thus increasing vase life.     

Effect of atmospheric modification, 1-MCP and chemicals on quality of fresh-cut banana

Fresh-cut banana slices have a short shelf-life due to fast browning and softening after processing. The effects of atmospheric modification, exposure to 1-MCP, and chemical dips on the quality of fresh-cut bananas were determined. Low levels of O₂ (2 and 4 kPa) and high levels of CO₂ (5 and 10 kPa), alone or in combination, did not prevent browning and softening of fresh-cut banana slices. Softening and respiration rates were decreased in response to 1-MCP treatment (1 μL L⁻¹ for 6 h at 14 °C) of fresh-cut banana slices (after processing), but their ethylene production and browning rates were not influenced. A 2-min dip in a mixture of 1% (w/v) CaCl₂ + 1% (w/v) ascorbic acid + 0.5% (w/v) cysteine effectively prevented browning and softening of the slices for 6 days at 5 °C. Dips in less than 0.5% cysteine promoted pinking of fresh-cut banana slices, while concentrations between 0.5 and 1.0% cysteine delayed browning and softening and extended the post-cutting life to 7 days at 5 °C.     

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.     

Biocontrol of Botrytis cinerea in table grapes by non-pathogenic indigenous Saccharomyces cerevisiae yeasts isolated from viticultural environments in Argentina

Botrytis cinerea, the causal agent of gray mold, is an important disease of grapes. Yeasts are members of the epiphytic microbial community on surfaces of fruits and vegetables and because some yeasts inhibit fungi they are used as biocontrol agents. The major objective of the present work was to isolate yeasts from grapes, vineyard soil, and grape must and select them for their ability to prevent gray mold onset after harvest. Yeasts that were found effective against the fungus were also assayed for their possible pathogenicity in humans. Two antagonism experiments were performed to study the effect of yeasts on B. cinerea, an in vitro study with Czapeck Yeast Extract Agar and an in vivo study with grape berries at 2 °C and 25 °C; both experiments were conducted at different yeast concentrations (10⁵, 10⁶ and 10⁷ cfu/mL). Antagonists were subsequently assayed for their ability to colonize and grow in fruit wounds. The biocontrol yeasts were also examined for their possible pathogenicity in humans: phospholipase and proteolytic activity, growth at 37 °C and 42 °C, pseudohyphal formation and invasive growth. A total of 225 yeasts belonging to 41 species were isolated from must and grape berries and 65 of them, representing 15 species, exhibited in vitro inhibition of B. cinerea at 25 °C. These 65 biocontrol yeasts were subsequently assayed in vivo and 16 of them (15 Saccharomyces cerevisiae and 1 Schizosaccharomyces pombe) showed antagonistic properties against B. cinerea at 25 °C. Only one isolate (S. cerevisiae BSc68) was able to inhibit mycelial growth of B. cinerea on grape berries at both 2 °C and 25 °C. The biomass of this strain in grape wounds increased 221.5-fold at 25 °C after 3 d and 325.5-fold at 2 °C after 10 d of incubation. An increase in the concentration of certain yeasts significantly enhanced their antagonistic activity. All yeast isolates determined as biocontrol agents under in vivo conditions were isolated from fermenting musts. Twelve biocontrol agents (S. cerevisiae) revealed one or more phenotypical characteristics associated with pathogenicity in humans but none of them showed all characteristics together. The fact that there exist few reports on S. cerevisiae and none on Sch. pombe as biocontrol agents against B. cinerea makes our results even more relevant.     

没食子酸丙酯对新高梨软化和褐变的影响

通过对没用食子酸丙酯处理的新高梨冷藏期间果胶、多聚半乳糖醛酸酶(PG)活性、总酚和多酚氧化酶(PPO)活性变化规律的分析,研究了没食子酸丙酯处理对新高梨果实软化与褐变的影响。结果表明,没食子酸丙酯减缓了新高梨的可溶性果胶含量的上升,抑制了PG酶活;没食子酸丙酯能减缓新高梨总酚含量的下降,抑制PPO活性;在贮藏过程中,PG酶的最大酶活出现时间总是要比PPO的要早。可以推断,在整个采后贮藏过程中,先是果实的软化衰老导致细胞组织的崩溃,进而产生大量氧自由基,使底物、氧和PPO充分的接触,进而加剧了果实的褐变。     

The frost tolerance of Miscanthus at the juvenile stage: Differences between clones are influenced by leaf-stage and acclimation

Miscanthus, a perennial, C₄ grass, has numerous advantages for biomass production, notably its high yield per hectare and low input requirements. However, establishment of this crop may be affected in Europe by frost damage when stem emergence occurs early in the year. The principal aim of this study was to quantify the impact of frost on young miscanthus shoots at different leaf-stages, and to characterise inter-species variations in frost tolerance. Four clones belonging to two species were tested at three leaf stages in a climate-controlled chamber simulating acclimation conditions and frost treatments. Frost tolerance was scored using a 0-6 visual assessment scale and analysed with nonparametric tests.We were thus able to show that more developed plants (6 or 7-leaf stage) were less frost tolerant than those at the 3 or 5-leaf stage. Plants at the 6 or 7-leaf stage also displayed differences in tolerance between clones. The leaf-stage of the plant is linked to apex height, and this appeared to play a role in frost tolerance. M. sinensis displayed variable frost tolerance (tolerance score of between 3.6 and 4.9), although the three clones observed were always more frost tolerant than M. x giganteus (with a score of 3). Moreover, the differences in frost tolerance were negatively correlated (r = −0.94) with the mean leaf surface area of clones at the time of frost exposure. Finally, we observed that acclimation at 12 °C under strong light intensity (600 μmol m⁻² s⁻¹) enabled an increase in the tolerance of young shoots in all the clones tested.     

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.     

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.     

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.     

Structural and physiological changes associated with the skin spot disorder in apple

Skin spot is an important physiological disorder of ‘Elstar’ apples (Malus × domestica Borkh.) that occurs after fruit have been removed from controlled atmosphere storage. Skin spots are irregular patches of small, round, brown blemishes. Cross-sections reveal a browning of protoplasts (coagulated) and of cell walls that extends into the hypodermis. Skin spots are always associated with linear, gaping and non-gaping microcracks in the cuticle. Staining of apple skin with calcofluor white usually results in white fluorescence of cell walls but, within a skin spot, the white fluorescence is weak or absent. Cell walls within, and in the immediate vicinity of skin spots stain with phloroglucin/HCl indicating the presence of lignin. The area of skin affected by skin spots was positively and linearly correlated with the area of the non-blush fruit surface infiltrated by acridine orange. In general, skin spots were limited to the non-blush fruit surface and occurred more frequently near the stem-end than the calyx region of the fruit. Skin spot areas were correlated with a 2.5-fold increase in water vapour permeability compared with unaffected areas (23.8 ± 4.0 m s⁻¹ with skin spots, 9.6 ± 2.1 × 10⁻⁵ m s⁻¹ without skin spots). Strips of the fruit skin from regions with skin spots had an increased maximum force and modulus of elasticity. Dipping fruit in ascorbic acid (0.1 or 0.3 mM for 10 min) before storage decreased the area affected by skin spots. There was no effect of dipping in ethanol/water (70%, v/v, 15 min) or in solutions of captan (1.5 g L⁻¹, 10 min) or trifloxystrobin (0.1 g L⁻¹, 10 min). In contrast, prestorage treatment with 1-methylcyclopropene (630 nL L⁻¹ for 24 h) or poststorage incubation in H₂O₂ (10% for 2, 6, 10 and 16 h) increased skin spots. Our data are consistent with a typical cell response to an oxidative burst that seems to be focussed on particular regions of the ‘Elstar’ fruit surface by concentrations of cuticular microcracks, and that is possibly caused by reoxygenation injury upon removal from CA storage.     

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.     

UV-C irradiation induces defence responses and improves vase-life of cut gerbera flowers

UV-C (λ = 254 nm) irradiation was effective in reducing Botrytis cinerea floret specking (i.e., lesion development) and maintaining a better postharvest quality of cut gerbera flowers. A range of UV-C doses (0.5-10.0 kJ m⁻²) was tested on ‘Ice cream’ and ‘Ecco’ gerbera flowers to activate germicidal and inducible defence mechanisms. Irradiation of B. cinerea cultures with 0.5, 1.0, 2.5 and 5.0 kJ m⁻² UV-C resulted in up to a 10-fold reduction of conidial germination percentages and significant (P < 0.05) delay of mycelium growth, compared to the non-irradiated control cultures. Moreover, lesion diameters on gerbera florets inoculated with UV-C irradiated B. cinerea cultures were reduced by up to 70%, suggesting that UV-C had a negative effect on the pathogenic strength of the fungi. Lesion diameters on florets of UV-C irradiated gerberas were reduced by up to 55% giving evidence that defence responses in the host tissue were induced. Concentration of total phenolics seemed to be unaffected by 0.5 kJ m⁻² UV-C treatment in both cultivars, but polyphenol oxidase (PPO) activity increased and remained higher compared to the non-irradiated control flowers throughout the 48 h storage period at 20 °C. The increase of PPO suggests that this enzyme might play an important role in host defence mechanisms that suppressed B. cinerea floret specking. Gerbera flowers irradiated with 1.0 or 10.0 kJ m⁻² UV-C showed improvement in vase-life by 1.8 and 2.4 d, decrease in stem break percentages by 43 and 29% and delay in stem break incidence by 3.3 and 1.3 d, respectively.     

Hydrogen ion concentration affects quality retention and modifies the effect of calcium additives on fresh-cut ‘Rocha’ pear

‘Rocha’ pear (Pyrus communis L.) was used as a model system to assess the effect of pH of dipping solutions on quality retention of fresh-cut fruit and its interaction with calcium additives. Pear slices were dipped for 60 s in a buffer solution at pH 3.0, 5.0 or 7.0 and stored at 4.5 °C for 13 days. In other experiments, pear slices were dipped for 60 s in buffer solutions containing 250 mM of calcium ascorbate, lactate, chloride, and propionate, at pH 3.0 or 7.0, and stored at 4.5 °C for 6 days. Browning and softening were more intense in slices dipped in a solution at pH 3.0 than at pH 5.0 or 7.0, but microbial growth was lower in slices treated at pH 3.0. The effect of calcium additives depended on the anion and significant interactions between the effects of calcium salt and pH were observed. Calcium ascorbate was very effective in preserving color and reducing microbial growth irrespective of pH, but enhanced pectin solubilization and tissue softening at pH 3.0. Slices treated with 250 mM calcium propionate or calcium lactate were softer and had higher electrolyte efflux when treated at pH 3.0 than at pH 7.0. Calcium lactate enhanced browning and reduced microbial growth at pH 3.0 but did not affect color or microbial counts at pH 7.0. All calcium treatments enhanced electrolyte leakage. pH of the dipping solution can affect, per se, the quality of fresh-cut fruit. The choice of calcium additives to prevent undesirable changes on visual and sensory quality of cut produce should involve pH ranges that provide the expected benefits.