Research Updates from the 9^th International Controlled Atmosphere Research Conference

The following summaries are a few of the notable oral and poster contributions related to controlled atmosphere storage of apples that were recently presented at the 9^th International CA Research Conference in East Lansing, Michigan.

Inhibition of ethylene action alters apple and pear fruit responses to CA environments with elevated CO₂, O₂ and/or temperature – David Rudell, Jim Mattheis, and John Fellman, USDA and

Washington State University

Several cultivars of apple (‘Delicious’, ‘Gala’, ‘Golden Delicious’) and pear (‘Bartlett’, ‘d’Anjou’) were used to evaluate how inhibition of ethylene action by 1-MCP impacts fruit response to CA conditions and temperature during storage. In some studies fruit were harvested on multiple dates to incorporate maturity at harvest as another variable. In all studies, fruit were exposed to 1-MCP on the day of harvest for 14-16 hours, then transferred to CA chambers and held for 24 hours prior to establishment of CA conditions. Studies were conducted using CA systems in which atmospheres were established and maintained using flow-through or static environments. Fruit were removed from CA chambers at either 2 (‘Bartlett’, ‘Gala’) or 3 (‘d’Anjou’, ‘Delicious’, ‘Golden Delicious’) month intervals and then rated for external color, disorders and decay incidence. After a 7-day period during which fruit were held at 20ºC, external (color, disorders, decay) and internal quality were evaluated. For the cultivars evaluated, impacts of higher O₂ and CO₂ CA conditions observed were dependent in part on maturity at harvest and storage duration. Exposure to 1-MCP slowed ripening in CA with up to 5% O₂, however, the impact of 1-MCP decreased with increased O₂ concentration and storage duration. Exposure to 1-MCP also slowed ripening at temperatures up to 5ºC. Control of superficial scald on ‘Delicious’ and ‘d’Anjou’ was not compromised by increased O₂ set points. Accelerated ripening (softening, degreening) of 1-MCP treated ‘d’Anjou’ pears stored in 3 or 5% O₂ was observed after 6 and 9 months plus 7 days at 20ºC, but only after 9 months did fruit soften to less than 5.8 lb. Peel degreening increased with CA O₂ concentration but occurred at a slower rate in 1-MCP treated fruit. Development of peel CO₂ injury on ‘Golden Delicious’ apples was enhanced by 1-MCP treatment.

Absorption of 1-MCP by non-target materials during storage – Fernando Vallejo and

Randolph Beaudry, Michigan State University

We tested the sorptive capacity of a number of non-target materials found in apple storage rooms on their capacity to remove 1-MCP from the storage and thereby compete with the fruit for the active compound. Further, we evaluated the impact of temperature and moisture. Non-target materials included bin construction materials (high density polyethylene (HDPE), polypropylene (PP), weathered oak, non-weathered oak, plywood, and cardboard) and wall construction materials (polyurethane foam and cellulose-based fire retardant). Each piece had an external surface area of 76.9 cm². We placed our ‘non-target’ materials in 1-L mason jars and added 1-MCP gas to the headspace at an initial concentration of approximately 30 ppm. Gas concentrations were measured after 2, 4, 6, 8, 10 and 24 hours. The concentration of 1-MCP in empty jars was stable for the 24-hour holding period. Little to no sorption was detected in jars containing dry samples of HDPE, PP, cardboard, polyurethane foam, or fire retardant. Inclusion of plywood, non-weathered oak and weathered oak lead to a loss of 10, 55, and 75% of the 1-MCP after 24 hours. Using dampened materials, no sorption resulted from the inclusion of HDPE, PP, polyurethane foam, or the fire retardant. However, the rate of sorption was not impacted by temperature, and increasing the surface area by approximately 100% only marginally increased the rate of sorption. When dampened oak bin material was included with apple fruit in a proportion similar to that found in fruit storage, 80% depletion occurred in 5 hours compared to approximately 24 hour for fruit alone. The data suggest that in situations where 1-MCP levels can be compromised by wooden and cardboard bin and bin liner materials, but not by plastic bin materials or typical wall construction materials.

Lenticel breakdown of apples following storage and packing – Eugene Kupferman, Eric Curry and Chris Sater, Washington State University

International competition among apple producers has elevated apple appearance to the point that any blemish or marking is unacceptable. Lenticel breakdown (LB) has become more common in recent years on certain varieties including ‘Gala’, ‘Fuji’ and possibly ‘Pink Lady’ apples. LB develops after the fruit has been stored (CA or air), washed and waxed. LB does not develop as significant marking on fruit until after all processes have been completed and all economic inputs have been made. LB appears as either dark black spots surrounding some lenticels or as brown larger circles centered around lenticels. Not all lenticels are affected and the flesh of the fruit is not impacted. Certain orchards have fruit that develops LB more than fruits from other orchards. Evidence will be presented to show that LB develops on lenticels that are cracked, dehydrated and lacking in natural wax. A test has been developed to determine the susceptibility of fruit from specific orchards. Packing procedures have been evaluated extensively in which fruit and water temperatures, soap and detergents, and waxes have been tested. Strategies will be presented on how commercial packers can minimize economic loss from this disorder.

Commercial application of 1-MCP affects storability and disorders of ‘Empire’ apples – Jennifer

DeEll, Jennifer Ayres, and Dennis Murr, Ontario

The objective of this study was to determine the effects of commercial 1-MCP treatment on the incidence of disorders and storability of ‘Empire’ apples. ‘Empire’ fruit were commercially harvested from 21 orchards in southwest Ontario and delivered to two storage operations during the 2003 season. Samples were collected from each orchard and half of the fruit from each sample was placed in the appropriate CA room for 1-MCP treatment (SmartFresh^TM, 0.7-0.8 ppm, 24 hours at 1.1-1.4^oC), while the other half was placed at a similar temperature during the treatment period and then returned to the matching CA room for storage. ‘Empire’ apples treated with 1-MCP had significantly less internal ethylene and were firmer than non-treated fruit after 14 days at 22^oC following treatment. These effects were also observed after CA storage, although there was no significant effect on fruit firmness at storage A where apples had also maintained good firmness (> 15 lb-force) without 1-MCP treatment. Internal browning developed after 9 months in ‘Empire’ apples at storage A and treatment with 1-MCP did not significantly affect the incidence. External CO₂ injury was observed on some ‘Empire’ fruit at storage B and the incidence was higher in apples treated with 1-MCP. It is important to note that no CO₂ injury was observed at storage A, where all apples were drenched with DPA prior to storage.

Interactive effects of 1-MCP, methyl jasmonate and CA storage on quality of ‘

Fuji’ apple fruit – Luiz Argent, Jim Mattheis, et al., USDA, Washington State

The present study evaluated how postharvest treatment with 1-MCP and methyl jasmonate (MJ) affects responses of ‘Fuji’ apple fruit to CA storage conditions. ‘Fuji’ apples were harvested 1 week after optimum maturity for long-term storage from a commercial orchard in north central Washington (seasons one and two) and from four commercial orchards in Santa Catarina, Brazil (season three). Fruit were cooled to 0.5ºC within 24 h of harvest and then stored in air or controlled atmosphere (CA). Fruit from season one were stored in CA with 2% O₂ + 0.05% CO₂; 0.25% O₂ + 0.05% CO₂ or 2% O₂ + 3% CO₂ for 6 months. Fruit from seasons two and three were sorted in CA with 1.5% O₂ + 0.05% CO₂ or 1.5% O₂ + 3% CO₂ for 8 months as a rapid CA (established within 72 h of harvest) or a delayed CA (established after 2, 3, 4 or 6 weeks or harvest). In addition, CO₂ levels in low CO₂ –CA (1.5% O₂ + 0.05% CO₂) were increased to 3% after 1, 2 or 3 months of harvest. Fruit were treated with 1 mM MJ or 1 ppm 1-MCP at harvest. Both CA conditions and 1-MCP treatment reduced ethylene production, improved maintenance of firmness and titratable acidity and reduced incidence of scald and core flush during long-term storage compared with untreated fruit stored in air. 1-MCP treatment was as or more effective as low CO₂-CA storage for reducing ethylene production and preservation of firmness and acidity in ‘Fuji’ apples depending on season and/or storage period. ‘Fuji’ apples stored in 3% CO₂ developed internal browning (CO₂-injury) while fruit stored in 0.25% O₂, 0.05% CO₂ or air did not, regardless of 1-MCP treatment. There were no significant impacts of 1-MCP treatment enhanced incidence and severity of CO₂ injury in rapid CA-stored fruit from Washington, while 1-MCP treatment enhanced incidence and severity of CO₂ injury in rapid CA-stored fruit from Brazil. MJ treatment reduced severity of CO₂-injury. Delaying CA (1.5% O₂ + 3% CO₂) or CO₂ (3%) accumulation during CA reduced the incidence of CO₂-injury. However, CA– and CO₂-delay procedures were less effective on prevention of CO₂-injury for fruit treated with 1-MCP compared with untreated fruit regardless of orchard and region. Results indicate that 1-MCP treatment increased CO₂ injury sensitivity in the earlier period of storage when ‘Fuji’ apples are more susceptible to CO₂-injury.

1-MCP affects physiological disorders in ‘Granny Smith’ apples depending on maturation stage – Gabriela Calvo and Candan Ana Paula, Argentina

‘Granny Smith’ apples are very susceptible to various physiological disorders, with superficial scald being the most important. Application of 1-MCP to ‘Granny Smith’ may extend storage life by reducing scald, loss of firmness and acidity. However, other skin disorders may be enhanced by 1-MCP. The effect of 1-MCP on the incidence of disorder development, ripening during storage, and subsequent shelf-life was investigated in ‘Granny Smith’ apples from different maturity stages (38, 42 and 52% starch degradation). Fruit were exposed to 0 (control) or 0.6 ppm 1-MCP at 1ºC during 24 hours. After 120, 180, 210 and 240 days in regular air at 0.5ºC, fruit were evaluated upon removal from storage and after 7 and 14 days at 20ºC. Application of 1-MCP effectively delayed the ripening rate of the fruit harvested at different times, as indicated by better retention of green peel color, firmness and titratable acidity. 1-MCP treatment significantly reduced superficial scald. Treated fruit developed scald after 240 days of cold storage, while controls developed scald after 120 days. Core flush incidence was also reduced by 1-MCP treatment, even in the fruit from the later harvest, which was the most affected by this disorder. In every evaluation, there was fruit affected by physiological disorders related to calcium deficit, such as bitter pit and lenticel blotch pit. In early-harvested fruit, 1-MCP treated fruit developed less bitter pit and more lenticel blotch pit, but the incidence of both disorders was higher in 1-MCP treated fruit than in control. No significant differences between treatments were detected in second and third harvest dates. We concluded that the effect of 1-MCP on different physiological disorders differs with fruit maturity stage. Disorders related to deficit of calcium where enhanced in 1-MCP treated fruit from early harvest, and as the length of storage increased.

Efficacy of fungicides applied by thermofogging and standard commercial drenching against postharvest diseases on apple and pear fruit – Peter Sanderson et al., Pace International LLC, Washington State and Chile

Fungicides were applied using a XEDA Electrofog machine to ‘Red Delicious’ apple and ‘d’Anjou’ pear fruit in Washington State and ‘Fuji’ apple fruit in Chile. Formulations of imazalil, thiabendazole (TBZ), fludioxonil, and pyrimethanil were applied to bins of ‘Red Delicious’ apple and ‘d’Anjou’ pear fruits immediately after harvest. Decay incidence in both Penicillium expansum inoculated and uninoculated fruit was assessed following 6 mo CA storage. Bins of Fuji apples were either fogged with fludioxonil, pyrimethanil, or TBZ, or drenched with TBZ plus DPA from a commercial drencher. Fruit were stored at 10ºC for 8 week and decay incidence in fruit inoculated with Botrytis cinerea was assessed. Decay in non-inoculated fruit was assessed after an additional 4 weeks of storage. In all trials, pyrimethanil was significantly more effective at controlling disease in inoculated fruit than all other fungicides. Pyrimethanil controlled 73% of blue mold infections in ‘Red Delicious’ apples compared to untreated fruit vs. 8‑19% control from other fungicides. In pear it controlled 60% of blue mold infections compared to untreated fruit, whereas other fungicides only controlled 1-8% of infections. Gray mold was the predominate disease occurring in non-inoculated fruit. All treatments with exception of imazalil significantly reduced gray mold incidence in both apple and pear fruits. In the second trial, pyrimethanil was again the most effective fungicide for controlling gray mold in inoculated fruit (91.2% control vs. 0% control from fludioxonil, and 29% and 23% control from TBZ fogging and drenching, respectively). In unwounded fruit, however, both pyrimethanil and fludioxonil gave similar levels of disease control (65.9% control and 58.9% control, respectively). Disease incidence in non-inoculated fruit was not affected by fogged TBZ and was 50% greater in TBZ drenched fruit than in untreated fruit. Pyrimethanil appears to be the most promising candidate fungicide for commercial development for fogging applications.

Future of modified atmosphere research – Adel Kader, University of California

It is not possible to discuss the future of modified atmosphere (MA) research without considering the broader aspects of research aimed at maintaining quality of fresh horticultural perishables between harvest and consumption. Providing better flavoured fruits and vegetables is likely to increase their consumption, which would be good for the producers and marketers (making more money or at least staying in business) as well as for the consumers (increased consumption of healthy foods). To achieve this goal, we and all those involved in producing and marketing fruits and vegetables need to: (1) replace poor flavour cultivars with good flavour cultivars from among those that already exist and/or by selecting new cultivars with superior flavour and good texture; (2) identify optimal cultural practices that maximize flavour quality, such as optimizing crop load and avoiding excess nitrogen and water; (3) encourage producers to harvest fruits at partially-ripe to fully-ripe stages and vegetables at their optimal maturity stages by developing handling methods that protect these commodities from physical damage; (4) identify optimal postharvest handling conditions (time, temperature, relative humidity, atmospheric composition) that maintain flavour quality of fruits and vegetables and their value-added products. Postharvest-life should be determined on the basis of flavour rather than appearance. The end of the flavour-life results from losses in sugars, acids, and aroma volatiles (especially esters) and/or development of off-flavours (due to fermentative metabolism or odour transfer from fungi or other sources); (5) develop ready-to-eat, value-added products with good flavour; (6) optimize maturity/ripeness stage at the time of processing and select processing methods to retain good flavour of the processed products. Future MA research can be part of research on strategies number 4, 5, and 6 listed above. Continued improvements in polymeric films and other packaging materials will facilitate expanded use of MA packaging to extend post harvest-life of fresh-cut fruits and vegetables and permit their distribution via vending machines. More cost-effective methods for establishing and maintaining MAs will facilitate their use during storage at shipping points, transportation, and storage at destination points. Maintaining the MA chain is the second most important factor after the cold chain in keeping quality and safety of fresh produce between harvest and consumption. Further evaluations are needed of: (1) the synergistic effects of MA and the ethylene-action-inhibitor, 1-MCP, on delaying ripening of partially-ripe climacteric fruits and senescence of vegetables; (2) MA as a component of post harvest integrated pest management (decay of insect control); (3) MA in relation to food safety considerations; and (4) the biological basis of MA effects on fresh horticultural perishables.