Superficial Scald Of Apples Research Articles

Apple metabolism under oxidative stress affects plant cell wall structure and mechanical properties

Several studies have shown beneficial effects of short exposure to oxidative stress on stored fruit, such as better preservation, increased firmness, preservation of polyphenolic compounds, and reduced risk of postharvest disorders such as bitter pit and superficial scald in apples. In this study the effect of short-term oxidative stress conditions on the physiology of apple fruit was investigated. Apple fruit of three cultivars were exposed to hypoxic storage conditions of various lengths to induce anaerobiosis. The response of apple fruit to short-term oxidative stress was evaluated by means of cell wall immunolabeling and atomic force microscopy. In addition, the antioxidant capacity and antioxidative activity of apple peels was assessed. Through various techniques, it was shown that short-term oxidative stress conditions promote specific enzymatic activity that induces changes in the cell wall of apple fruit cells. Exposure to short-term stress resulted in the remodeling of cell wall pectic polysaccharides, observed as an increase in the size and complexity of extracted oxalate pectin. Structural changes in the cell wall were followed by an increase in Young’s modulus (compressive stiffness of a solid material, expressed as the relationship between stress and axial strain) of the cell wall material. The data presented in this paper show in a novel way how storage under short-term oxidative stress modifies the cell wall of apple fruit at the molecular level.

Scald-Cold: Joint Austrian-Italian consortium in the Euregio project for the comprehensive dissection of the superficial scald in apples

After harvest, apples are stored at low temperature to slow down the ripening physiological processes. This strategy can, however, also promote the development of superficial scald, a chilling injury-related disorder showing brown-discoloured areas on the fruit skin, totally compromising its marketability. To examine thoroughly the underlying physiological mechanisms and genetic control of superficial scald, the “Scald-Cold” project, a three-year Interegional Project Network, was granted by the European Region Tyrol, South Tyrol and Trentino (EGTC). The project is centred on a comprehensive approach, integrating into a joint effort different scientific disciplines, ranging from genetics and transcriptomics to NIR spectroscopy and hyperspectral imaging, together with the employment of distinct postharvest storage technologies distinguished by a specific regime of low oxygen. The core of this project aims to disclose novel regulatory processes of this disorder, providing new series of tools important for both the scientific and technical communities interested in apple breeding and postharvest. The “Scald-Cold” project will identify new molecular markers suitable for the selection of new apple varieties genetically resistant to superficial scald, while developing tools for an early detection of this phenomenon.

Systems-Based Approaches to Unravel Networks and Individual Elements Involved in Apple Superficial Scald.

Superficial scald is a major physiological disorder in apple fruit that is induced by cold storage and is mainly expressed as brown necrotic patches on peel tissue. However, a global view of the gene-protein-metabolite interactome underlying scald prevention/sensitivity is currently missing. Herein, we have found for the first time that cold storage in an atmosphere enriched with ozone (O3) induced scald symptoms in ‘Granny Smith’ apple fruits during subsequent ripening at room temperature. In contrast, treatment with the ethylene perception inhibitor 1-methylcyclopropene (1-MCP) reversed this O3-induced scald effect. Amino acids, including branched-chain amino acids, were the most strongly induced metabolites in peel tissue of 1-MCP treated fruits. Proteins involved in oxidative stress and protein trafficking were differentially accumulated prior to and during scald development. Genes involved in photosynthesis, flavonoid biosynthesis and ethylene signaling displayed significant alterations in response to 1-MCP and O3. Analysis of regulatory module networks identified putative transcription factors (TFs) that could be involved in scald. Subsequently, a transcriptional network of the genes-proteins-metabolites and the connected TFs was constructed. This approach enabled identification of several genes coregulated by TFs, notably encoding glutathione S-transferase (GST) protein(s) with distinct signatures following 1-MCP and O3 treatments. Overall, this study is an important contribution to future functional studies and breeding programs for this fruit, aiding to the development of improved apple cultivars to superficial scald.

Extending ‘Granny Smith’ apple superficial scald control following long-term ultra-low oxygen controlled atmosphere storage

Superficial scald is an apple postharvest peel browning disorder that contributes to annual losses of susceptible cultivars, principally where crop protectants that control the disorder are restricted. Controlled atmosphere (CA) storage reduces or eliminates superficial scald while apples remain in storage, especially when pO2 is maintained below 1 kPa. However, symptoms often develop during the post-storage cold chain, which can last beyond a month. Diphenylamine (DPA) or 1-methylcyclopropene (1-MCP) treatment can be used to control scald, but application is required within the first weeks of cold air storage following harvest. After this period, treatments are no longer effective due to irreversible physiological changes, hereby referred to as “scald induction”. As a recent report indicates, apple flesh softening can be reduced by 1-MCP treatment following ultra-low oxygen CA (ULO-CA) storage (pO2 ≤ 1.0 kPa). Here, we sought to determine if ULO-CA would also preserve the capacity to control scald with post-CA treatments. To determine this, ‘Granny Smith’ apples were treated with hot water and 1-MCP at harvest or following long-term (>3 months) in-house and commercial ULO-CA for two consecutive years. Different CA storage environments (2.0 kPa and 1.0 kPa O2) and delays in ULO-CA establishment were used in combinations with delayed DPA and 1-MCP treatments to reveal the scald induction timeline and how different storage practices may impact the effectiveness of post-CA scald control measures. Taken together, results indicate that scald induction is effectively delayed during ULO-CA storage and resumes upon return to air storage. 1-MCP and hot water treatments applied after four months of ULO-CA storage were equally effective at controlling scald during subsequent air storage as treatments applied at harvest. However, the efficacy of post-storage treatments relied on the rapid establishment and maintenance of ULO conditions and immediate treatment upon removal from ULO-CA storage. Scald induction resulted from cumulative oxygen exposure occurring prior to, during (pO2) and following CA storage. Conjugated trienol and acylated steryl glycoside levels at the end of ULO-CA storage reflected how much scald induction had occurred and, likewise, the efficacy of post-storage scald mitigation treatments.

1-Methylcyclopropene and extreme ULO inhibit superficial scald in a different way highlighting the physiological basis of this disorder in pear

Despite years of research on the biochemical basis of superficial scald in apples, relatively little is known about the specific regulatory processes involved in pears. To gain further knowledge on these processes, different storage scenarios, controlled atmosphere (CA), 1-methylcyclopropene treatment (1-MCP) and storage under very low O2 concentration (xULO) were used in the scald susceptible ‘Blanquilla’ pears. Ethylene production, α-farnesene (AF), conjugated trienols (CTols) content and changes in ethanol levels were evaluated during storage and further related to superficial scald development and changes in fruit quality upon removal.While 1-MCP completely inhibited ethylene production and fruit softening, only a partial and transient inhibition of these parameters was found for xULO-treated fruit. Both 1-MCP and xULO treatments completely controlled scald disorder, yet in different ways. The reduction in disorder incidence in 1-MCP treated fruit was the result of ethylene inhibition and reduced levels of α-farnesene and CTols. In contrast, xULO treatment only partially inhibited ethylene production and the levels of α-farnesene metabolites but led to increased ethanol levels that were directly related to the scald incidence inhibition. Collectively, these results highlight that superficial scald in pear is not strictly related to ethylene and α-farnesene metabolism and that other compounds, such as the weak antioxidant ethanol, play a determining role in ‘Blanquilla’ pear.

The effects of superficial scald control methods having different effect mechanisms on the scald formation and α-farnesene content in apple cv. ‘Granny Smith’

The principal aim of this study was to investigate the effects of superficial scald control methods having different effect mechanisms on scald formation and α-farnesene content in Granny Smith apples. It was also aimed to evaluate possible alternatives to diphenylamine (DPA) that has been banned in many countries. By this aim, lovastatin and DPA with combined treatments such as heat+oil and ethanol vapour+heat were used. The experiment was conducted with ‘Granny Smith’ cultivar, very sensitive to superficial scald, grown in Isparta (Turkey). After treatments, apples were stored in normal atmosphere (air) at 0°C and 90±5% RH for 6 months. In the apples taken from storage in monthly intervals, α-farnesene content and scald intensity were determined. It was found that all treatments decreased both α-farnesene content and superficial scald formation compared to control group. However, poor correlation between α-farnesene content and scald formation during the storage was found. α-Farnesene contents of lovastatin treated apples were lower than those of DPA during the storage. The methods having different mechanism for control of apple superficial scald should be investigated elaborately.

The Incidence of Superficial Scald in “Wujiuxiang” Pears (Pyrus Pyrifolia Cv. Wujiuxiang) during and after Controlled Atmosphere Storage

AbstractThis work is aimed to assess the effect of the low temperature controlled atmosphere (CA) storage on reducing the incidence of fruit superficial scald in “Wujiuxiang” pears (Pyrus pyrifolia cv. Wujiuxiang). We set up four low temperature CA storage conditions with pCO2 0.03 kPa, 1 kPa, 3 kPa, 5 kPa, respectively, under pO2 3 kPa, and a control under normal air conditions with pCO2 0.03 kPa, pO2 21 kPa. During the low temperature storage and its subsequent period on‐shelf, the incidence of superficial scald as well as the changes in fruit quality and biochemistry such as phenols, relative electrical conductivity, malondialdehyde, polyphenol oxidase and peroxidase activity were monitored and analyzed. Our results showed that low O2 is the most important factor contributing to the reduced incidence of superficial scald during the low temperature CA storage. However, pCO2 less than 3 kPa had no influence on the incidence of superficial scald but higher pCO2 over 3 kPa caused CO2 injury to the stored fruit. In conclusion, low pO2 and pCO2 less than 3 kPa under low temperature is likely the best CA conditions for reducing the incidence of superficial scald in “Wujiuxiang” pears.Practical ApplicationsSuperficial scald, a fruit postharvest physiological disorder has caused a significant loss in the production of “Wujiuxiang” pear, a popular cultivar in China. It is reported that CA storage can reduce efficiently the incidence of superficial scald in apples during storage. This work shows that this is also the case for “Wujiuxiang” pear during and after storage. A low temperature CA storage condition with low pO2 3 kPa while pCO2 lower than 3 kPa is then proposed for application in the storage of this pear.

Use of the index of absorbance difference (IAD) as a tool for tailoring post-harvest 1-MCP application to control apple superficial scald

The aim of this study was to better define postharvest strategies to preserve apple fruit quality during storage with particular attention on superficial scald control as the result of the interaction between 1-methylcyclopropene (1-MCP) treatment and fruit ripening stage. Ripening was no-destructively defined by the “index of absorbance difference” (IAD) measured with a DA-Meter, a portable device based on visible/Near Infra-Red (vis/NIR) spectroscopy. Superficial scald incidence and total content of α-farnesene and conjugated triols (CTols), were assessed at two month intervals, among 6 months of cold storage (1°C) for three consecutive seasons in two apple cultivars, ‘Granny Smith’ and ‘Cripps Pink’. Results demonstrated the reliability of the IAD, not just to assess fruit maturity, but also to predict scald incidence in both apple cultivars as a function of maturity and postharvest control strategy. Consequently, differential post-harvest treatments can be applied to single appropriate apple batches increasing storability and shelf-life, while reducing spoilage.

Untargeted metabolomics investigation of volatile compounds involved in the development of apple superficial scald by PTR-ToF–MS

The superficial scald is an important physiological disorder affecting apple fruit during postharvest storage. To date, the accumulation, and further oxidation, of α-farnesene was considered as the most probable cause for the development of this physiopathy. In order to perform a more broad investigation, a PTR-ToF–MS (proton transfer reaction—time of flight—mass spectrometry) was employed to monitor the volatile organic compounds (VOCs) production along with the progression of this disorder in fruit of “Granny Smith”, an apple variety known to be highly susceptible to scald. The untargeted metabolite investigation was performed on both skin and pulp, as well as comparing control versus treated tissues with 1-methylcyclopropene (1-MCP), an ethylene competitor widely used to prevent the development of this phenomenon. The rapid and non-destructive analysis of the VOC array carried out by PTR-ToF–MS identified three specific groups of metabolites in the skin, among which the 6-methyl-5-hepten-2-one (MHO) resulted significantly associated with the development of the superficial scald in apple. The results proposed in this work suggest the use of this novel equipment for an on-line monitoring of the VOCs released by the apple during the postharvest storage, as well as to use MHO as a possible biochemical marker for an early detection of the superficial scald symptoms.

IDENTIFICATION OF DIFFERENTIALLY EXPRESSED GENES POTENTIALLY ASSOCIATED WITH APPLE (MALUS ×DOMESTICA) SUPERFICIAL SCALD DEVELOPMENT

Apple superficial scald is a recurring postharvest physiological disorder with significant economic impact. Elucidating the molecular mechanisms of apple scald development is essential for prediction and prevention. In this study, differentially expressed genes were identified using suppressive subtraction hybridization (SSH) for two types of apple peel samples, i.e., between healthy tissues and tissues with initial scald symptoms. The most apparent up-regulated genes in tissue showing initial scald symptoms were those encoding proteins functioning in oxidative metabolism, including lipoxygenase, oxidoreductase, and polyphenol oxidase. This result is consistent with the hypothesis that development of apple scald is associated with an imbalance in oxidative metabolism. Several pathogenesis-related (PR) proteins encoding genes were also up-regulated, including apple allergens mal d 1/PR protein 10, apple allergens mal d 3/PR protein 14, PR protein 5 and PR-protein 8 in the tissues with initial scald symptoms. Other up-regulated genes included those encoding transporter proteins such as acyl carrier protein, peptide transporter and putative ABC transporter. Also induced were several proteins related to stress responses including heat shock protein, osmotin-like protein and early-response to dehydration protein. Up to 30% of the identified genes were annotated as “unknown function” and or “hypothetical proteins”.

Genomic organization and sequence polymorphism of a farnesyl diphosphate synthase gene in apples (Malus domestica Borkh.)

Primer pairs were designed to amplify the genomic DNA sequence of the farnesyl diphosphate synthase (FPPS) gene by PCR. The PCR products were sequenced, spliced and compared to the cDNA sequence in the GenBank (accession No. AY083165). The genomic sequence and intron-exon organization of FPPS1 gene in the apple cultivar ‘Fuji’ were thus obtained. The FPPS1 genomic sequence has been registered in the GenBank (accession No. HM545312). It has 11 introns and 12 exons. The sizes of 11 introns were 559 bp, 108 bp, 144 bp, 114 bp, 84 bp, 690 bp, 373 bp, 168 bp, 87 bp, 91 bp and 97bp, and their phases were 0, 1, 0, 0, 0, 2, 0, 0, 0, 0 and 0, respectively. The sizes of 12 exons were 111 bp, 25 bp, 116 bp, 87 bp, 117bp, 89 bp, 52 bp, 96 bp, 45 bp, 90 bp, 72 bp and > 12 bp, respectively. Gene sequence comparison results of five apple cultivars indicated that the development of apple superficial scald was not influenced by the mutations in the exon sequence of FPPS1 gene. A 6-bp repeat unit deletion mutation and many SNP mutations in the introns, mainly in the introns of one allele, were identified in the apple scald-resistant cultivar ‘Golden Delicious’. This is the first report on the genomic organization and coding region polymorphism of FPPS gene in apples and other fruit trees.

Metabolomic Change Precedes Apple Superficial Scald Symptoms

Untargeted metabolic profiling was employed to characterize metabolomic changes associated with 'Granny Smith' apple superficial scald development following 1-MCP or DPA treatment. Partial least-squares discriminant analyses were used to link metabolites with scald, postharvest treatments, and storage duration. Models revealed metabolomic differentiation between untreated controls and fruit treated with DPA or 1-MCP within 1 week following storage initiation. Metabolic divergence between controls and DPA-treated fruit after 4 weeks of storage preceded scald symptom development by 2 months. alpha-Farnesene oxidation products with known associations to scald, including conjugated trienols, 6-methyl-5-hepten-2-one, and 6-methyl-5-hepten-2-ol, were associated with presymptomatic as well as scalded control fruit. Likewise, a large group of putative triterpenoids with mass spectral features similar to those of ursolic acid and beta-sitosterol were associated with control fruit and scald. Results demonstrate that extensive metabolomic changes associated with scald precede actual symptom development.

Superficial Scald and Bitter Pit Development in Cold-Stored Transgenic Apples Suppressed for Ethylene Biosynthesis

The plant hormone ethylene regulates climacteric fruit ripening and plays a major role in the development of superficial scald in apple fruits during cold storage. The effect of cold storage at 0 degrees C on development of superficial scald and bitter pit (BP) in transgenic Greensleeves (GS) apples suppressed for ethylene biosynthesis was investigated. Four apple lines were used: untransformed GS; line 68G, suppressed for 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO); and lines 103Yand 130Y, suppressed for ACC synthase (ACS). Fruits from the transformed lines 68G, 103Y, and 130Y produced very little ethylene during 3 months of cold storage at 0 degrees C and after subsequent transfer to 20 degrees C, whereas untransformed fruits produced significant ethylene during cold storage, which increased dramatically at 20 degrees C. Respiration, expressed as CO(2) production, was similar in all four apple lines. After 2 months at 0 degrees C, all apple lines showed some BP symptoms, but lines 68G and 103Y were more affected than untransformed GS or line 130Y. Both transformed and untransformed apples produced alpha-farnesene, but concentrations were lower in yellow fruit than in green fruit in all lines but 68G. Line 68G produced the most alpha-farnesene after 2 months at 0 degrees C, including both (E,E) alpha-farnesene and (Z,E) alpha-farnesene. Concentrations of (E,E) alpha-farnesene were 100 times greater than those of (Z,E) alpha-farnesene in all lines. After 4 months at 0 degrees C plus 1 week at 20 degrees C, untransformed GS apples exhibited the most superficial scald, whereas fruits from lines 68G and 103Y were less affected and line 130Y had no scald. Superficial scald severity was higher in green fruit than in yellow fruit in all affected lines. These lines also exhibited significant production of 6-methyl-5-hepten-2-one (MHO), a major oxidation product of (E,E) alpha-farnesene. Line 130Y neither exhibited superficial scald nor produced MHO. It is shown here that even transgenic apples suppressed for ethylene biosynthesis genes can produce alpha-farnesene, which in turn can oxidize to free radicals and MHO, leading to scald development.

RESPONSE OF 1‐METHYLCYCLOPROPENE TREATED “GRANNY SMITH” APPLE FRUIT TO AIR AND CONTROLLED ATMOSPHERE STORAGE CONDITIONS

ABSTRACT In the study, the efficacy of 1‐Methylcyclopropene (1‐MCP) on the quality of apples cv. “Granny Smith” was examined. Fruits were stored for 120 and 180 days at 0 ± 0.5C and 90 ± 5% relative humidity (RH) under normal (NA) and controlled atmosphere (CA), and samples taken at 120 and 180 days of storage were kept at 20 ± 2C and 60 ± 5% RH for 7 days. Weight loss was higher in fruits stored under NA. The lowest respiration rates were in CA while the highest rates were found in NA‐stored fruits without pretreated. 1‐MCP + CA reduced the internal ethylene concentration from 10.63 µL/L to 0.60 µL. The incidence and severity of superficial scald was 68.10 and 77.00% in fruits stored in NA. 1‐MCP consistently suppressed the expression of superficial scald. 1‐MCP maintained the quality fruit kept in CA and NA environments to a higher degree than nontreated apples over a 180‐day storage period. The results indicated that cv. “Granny Smith” could be stored successfully under 1‐MCP + CA conditions and that 1‐MCP + NA may be a viable alternative to CA for optimal eating quality.PRACTICAL APPLICATIONS1‐Methylcyclopropene (1‐MCP) is an effective inhibitor of ethylene action and it binds irreversibly to ethylene receptors. 1‐MCP delays the onset of the climacteric ripening of fruits. Recently research has been conducted on the effects of 1‐MCP on postharvest behavior of fruits and vegetables with the objective of reducing physiological disorders and quality losses to prolong their commercial life. The use of 1‐MCP is easy. It is important that the fruit treated with 1‐MCP reach a good sensory quality at the commercial level. Superficial scald of apples is a physiological disorder, which following long‐term storage has the potential to destroy the market value and utility of millions of tons of fresh apples annually. The present work evaluated a prestorage conditioning treatment to protect against this physiological disorder. Results will allow the long storage of apple cv. “Granny Smith,” benefiting growers, exporters, shippers and distributors of this horticultural product.

New data on the effect of solar radiation and α-farnesene on development of apple superficial scald during storage

The previously unknown selective effect of solar radiation on the development of apple superficial scald is established. Superficial scald doesn’t occur on the sun-exposed side of certain green fruits after storing for 2 to 4 months, and in certain colored fruits it is possibly the consequence of a delay in penetration of solar radiation of the blue-green spectrum by anthocyans.

Preharvest 1-Methylcyclopropene Delays Fruit Maturity and Reduces Softening and Superficial Scald of Apples During Long-term Storage

Three experiments were undertaken to evaluate the effects of different preharvest 1-methylcyclopropene (1-MCP) spray treatments on apple (Malus × domestica Borkh.) fruit maturity at harvest and quality after long-term storage in a regular atmosphere or controlled atmosphere (CA). Trees were sprayed within 7 days of the anticipated harvest date (H) and fruit for long-term storage were sampled at either H in the case of ‘Law Rome’ or at harvest dates that were delayed by up to 21 days (H + 21) in the case of ‘Golden Delicious’ and ‘Law Rome’. Preharvest 1-MCP sprays within 7 days of H reduced fruit drop, internal ethylene concentration, and starch index and reduced firmness loss during long-term storage of fruit at delayed harvest dates but had only minor effects on fruit maturity at H. Preharvest 1-MCP sprays reduced the incidence of superficial scald on ‘Law Rome’ apples more effectively than either diphenylamine or CA storage. Application of 1-MCP within 7 days of H may be used to delay harvest date, thereby allowing continued fruit growth without a concomitant advance in fruit maturity and to reduce firmness loss and superficial scald during long-term storage both for normal and delayed harvests.

Diphenylamine Inhibits Respiration of Green Bell Peppers

The mechanism by which diphenylamine (DPA) controls superficial scald in apples and reduces chilling injury in green bell peppers [Capsicum annuum L. var. annuum (Grossum Group)] has been assumed to be related to its antioxidant activity. In the present study, DPA inhibited the respiratory activity of green bell pepper fruit as well as oxygen uptake by the mitochondria isolated from them. When the alternative oxidase was inhibited with n-propyl gallate or disulfiram during state 4 respiration, DPA did not further inhibit O2 uptake. Treating green bell peppers with DPA before storage did not alter the induction and abundance of the alternative oxidase protein in mitochondria which was maximally induced in peppers stored at 4 °C. Whether added before or after the uncoupler, 2,4-dinitrophenol, DPA negated the enhanced O2 uptake associated with uncoupling of electron transfer in isolated mitochondria. These observations indicate that DPA inhibits the flow of electrons through the cytochrome path, probably somewhere in the cytochrome bc1 complex. Although the secondary amine function of DPA makes it a powerful antioxidant, the effectiveness of DPA in reducing chilling injury in green bell peppers and superficial scald in apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] also may be due, in part, to its inhibition of respiration.

1-METHYLCYCLOPROPENE (SMARTFRESH TM) AS AN ALTERNATIVE TO MODIFIED ATMOSPHERE AND CONTROLLED ATMOSPHERE STORAGE OF APPLES AND PEARS

1-Methylcyclopropene (1-MCP), also known as SmartFresh™ (0.14%), blocks ethylene action in harvested fruit. 1-MCP’s mode of action is via a preferential attachment to the ethylene receptor, thereby blocking the effects of both endogenous and exogenous ethylene. This study determined the potential of 1-MCP as an alternative to modified atmosphere (MA) and controlled atmosphere (CA) storage of apples and pears. Three concentrations of 1-MCP were applied for 12 hours at 20°C to ‘Granny Smith’ and ‘Pink Lady’ apples, and ‘Bon Chretien’ and ‘Packham’s Triumph’ pears, harvested at the start and at the end of commercial maturity. Apples and pears were examined after 2, 4 and 6 months, or 6 weeks of storage at –0.5°C respectively, followed by a shelf-life period of 7 days at 15°C. 1-MCP-treated apples were firmer and less ripe than control fruit after storage and had higher levels of titratable malic acid and soluble solids. Untreated fruit developed superficial scald that was exacerbated with increased storage duration. By contrast, 1-MCP resulted in scald-free fruit for the full 6 months of cold storage and during the 7-day shelf-life period. Treated pears showed no maturity differences at the start of shelf-life, but ripening was markedly held back during the shelf-life duration. However, 1-MCP-treated pears remained green after storage and ripened normally after 3 weeks at 15°C. 1-MCP-treated fruit invariably had a firmer, crisper texture compared to untreated fruit. The significance of these findings is the potential use of 1-MCP as an alternative to MA and CA storage of apples and pears, and as a replacement for the use of DPA (diphenylamine) for the control of superficial scald in apples.

Control of apple superficial scald and ripening—a comparison between 1-methylcyclopropene and diphenylamine postharvest treatments, initial low oxygen stress and ultra low oxygen storage

‘Granny Smith’ apple (Malus domestica Borkh.) fruit were treated with 1 μl l−1 1-methylcyclopropene (1-MCP) at room temperature for 12 h. Quality of fruit stored 4 and 6 months in air, under different controlled atmospheres (CA) at low oxygen concentration (1.5, 1.0 and 0.7 kPa O2), with initial low oxygen stress (ILOS) at 0.4 kPa O2 for 2 weeks, and with or without postharvest application of the antioxidant diphenylamine (DPA) were compared. Superficial scald was controlled after long-term storage under 0.7 kPa O2 or with ILOS followed by 1.0 kPa O2, but not solely under 1.0 kPa O2. 1-MCP eliminated the incidence of superficial scald under all long-term air and CA storage conditions. Core flush incidence was not affected by ILOS, but decreased at lower O2 concentrations, and was reduced by 1-MCP or DPA. A disorder, resembling external CO2 injuries, was observed on about 2.5% of fruits of all maturity stages treated with 1-MCP and subsequently stored in CA. Fruit treated with 1-MCP maintained greater firmness and acidity, even after 14 days at 20 °C, than untreated fruit stored under low oxygen. Total soluble solids concentrations were not influenced by 1-MCP. Degreening was effectively inhibited by 0.7 kPa O2 or ILOS immediately after storage, but only by 1-MCP during the subsequent ripening period.

Diphenylamine reduces chilling injury of green bell pepper fruit

Diphenylamine (DPA), an antioxidant widely used to control superficial scald in apples stored at low temperatures, reduced the chilling-induced pitting of green bell pepper (Capsicum annuum L.) fruit in a concentration-dependent manner up to 12 mM. Treatment was effective whether applied as a 2-min dip or injected into the seed cavity prior to storing peppers at 1° C for 6 or 8 days followed by storage at 20° C for an additional 2 days. Ethanol (5%), the solvent used to dissolve the diphenylamine, also reduced chilling injury of green bell peppers, but to a lesser extent than DPA. Changes in all of the chlorophyll fluorescence parameters were observed within 24 h following the exposure of green bell peppers to low temperatures, whereas visible manifestation of chilling injury was not observed until after the peppers had been exposed to several days of low temperatures. Diphenylamine reduced the chilling-induced decline in maximal chlorophyll fluorescence and increased the time taken for maximal chlorophyll fluorescence to occur and the size of the electron acceptor pool. If chilling injury results from oxidative stress induced by low storage temperatures, it is unlikely that chloroplasts were the site of production of active oxygen species in these green bell peppers since they were stored in the dark. The rapidity of chlorophyll fluorescence responses to low temperatures makes chlorophyll fluorescence analysis useful to distinguish between chilling-sensitive and chilling-resistant plant tissues, but does not measure the extent of chilling injury.