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FINAL REPORT DURATION: 99-00

WTFRC Project # Organizational Project # 58-1275-9-076

Project Title: Vapor and nonchemical treatments for decay control and flavor retention in apples.

PI: Robert Saftner, Plant Physiologist, Beltsvile, MD

Organization: USDA, ARS, BA, Produce Quality and Safety Lab (PQSL), Beltsville, MD 20705.

Cooperators: Drs. William Conway and Britta Leverentz, PQSL, Beltsville, MD; Dr. Wojciech

Janisiewicz, Appalachian Fruit Research Station, USDA, ARS,

Kearneysville, WV,

Objectives:

1) Evaluate the efficacy of prestorage air heat, and chemical vapor treatments, alone and in various

combinations, to control postharvest decay while maintaining fruit quality especially flavorassociated

volatile levels.

The principle anticipated benefit of this research is to better understand the relative effectiveness of a

prestorage heat treatment and prestorage vapor treatments of methyl jasmonate (MJ), 1-

methylcyclopropene (1-MCP), and poststorage vapor treatment of allylisothiocyanate (AITC) to

control decay development caused by major postharvest pathogens of apple, i.e., P. expansum, B.

cinerea, and/or C. acutatum and to reduce the dependence of the apple industry upon postharvest use

of synthetic fungicides. High oxygen treatment during cold storage was evaluated as a possible

means of increasing volatile levels.

Significant findings:

• Prestorage 1-MCP treatment reduced decay development caused by P. expansum, B. cinerea,

and C. acutatum between 18 % and 38 % but had no effect on the incidence of pathogeninduced

decay. 1-MCP treatment never increased decay development in apple.

• A high (100 Pa for 3 hours) vapor dose of AITC was phytosanitary eliminating lesion

incidence caused by P. expansum but was also phytotoxic to the fruit unless they were wax

coated prior to the chemical treatment.

• While prestorage heat treatment were phytosanitary at the time of treatment, they provided

little residual protection against the incidence of lesions and decay development caused by P.

expansum, B. cinerea, and C. acutatum.

• Prestorage MJ vapor treatment reduced the natural incidence of decay during storage by

about 50 % but had little to no effect on decay development caused by wound inoculating

fruit with P. expansum, B. cinerea, or C. acutatum.

• Prestorage treatment with 1-MCP followed by a heat treatment led to superficial fruit injury

in one year of testing.

Methods:

This study was conducted over a three year period, during one year of which the WTFRC

funded my proposal to purchase a gas generator. The gas generator was used to generate precise

concentrations of MJ and AITC for testing their antimicrobial properties in apples. Sets of

preclimacteric ‘Golden Delicious’ apples were treated with 0.1 Pa 1-MCP for 18 hours at 20 °C, 38

°C for 4 days, 0.2 or 2 Pa MJ for 24 hours at 20 °C, or left untreated before placing in air storage at 0

°C. Some sets of fruit also were treated with 1-MCP followed by the heat treatment. In addition,

some sets of untreated fruit were stored at 0 °C in a controlled atmosphere of 1.5 kPa O2 and 2.5 kPa

CO2. Other sets of untreated fruit were stored in 100 % O2 for 12 days at 0 °C at the beginning of the

cold storage period, then transferred to air storage at 0 °C. After various cold storage periods, fruit

were warmed to 20 °C, and subsets were either quality evaluated or wound inoculated with 105

spores/mL aliquots of P. expansum, B. cinerea, or C. acutatum. Following one week at 20 °C, lesion

incidence and decay development were measured along with quality-related characteristics of

respiration and ethylene production rates, volatile levels, and Magness-Taylor firmness. Other

untreated sets of fruit were warmed to 20 °C, wound inoculated with P. expansum and treated 2 hours

later with 0, 10, 30, and 100 Pa AITC for 0.25, 1, 2, or 3 hours. Lesion incidence and decay

development were measured 7 to 9 days after treatment with the chemical.

Results and Discussion:

Regarding the antimicrobial treatments, both the heat treatment and the AITC treatment (100

Pa for 3 hours) were phytosanitary, eliminating lesion development caused by wound-inoculated P.

expansum, B. cinerea, or C. acutatum. The heat treatment, however, provided little (~10 %) residual

protection against these pathogens and would require a large input of energy to heat and cool large

quantities of fruit. The heat treatment delayed ripening as indicated by decreased respiration and

ethylene production rates and good maintenance of firmness. While quality-associated volatile

production was initially inhibited, volatile levels recovered to near control levels following storage

for 5 months at 0 °C and 1 week at 20 °C. One other benefit of the heat treatment was a noticeably

increased peel yellowing even when the fruit had received a 1-MCP treatment prior to the heat

treatment. Regarding AITC, it is inexpensive, a natural product, and can be easily reapplied as

needed to control decay pathogens, but the chemical also was phytotoxic to the fruit at doses that are

phytosanitary. To avoid fruit injury, the fruit had to be wax coated before poststorage treatment to

protect against AITC adsorption by the cortical tissue. When AITC was limited to the pathogeninoculated

wound sites, AITC had no effect on fruit quality as indicated by respiration and ethylene

production rates, volatile levels, and flesh firmness being similar to that of untreated fruit.

The prestorage MJ and 1-MCP treatments had no effect on the incidence of lesions caused by

wound inoculating with P. expansum, B. cinerea, or C. acutatum. The 1-MCP treatment provided

residual protection against decay development by these pathogens, i.e., lesion size was decreased

between 18 % and 38 % following storage for 2.5 or 5 months at 0 °C and 1 week at 20 °C. At the

dose used, 1-MCP prevented the climacteric increase in respiration and ethylene production rates, and

maintained flesh firmness at near harvest levels following storage for 5 months at 0 C and 1 week at

20 °C. However, quality-associated volatile levels were inhibited by more than 90 % compared to

that in untreated fruit and peel degreening was noticeably inhibited following storage. What impact

these inhibitory effects of 1-MCP would have on consumer acceptance of ‘Golden Delicious’ apples

is unknown. 1-MCP inhibited ripening more effectively than CA storage. Caution is advised when

combining stress treatments to control ripening and decay development. In one of three years of

testing, treatment with 1-MCP followed immediately by heat treatment led to peel browning during

storage in many of the duel-treated fruit while none of the fruit that were treated with 1-MCP or heat

alone were injured. In the year that injury from the 1-MCP and heat treatments was observed, no

time had been left between the 1-MCP treatment and the heat treatment for 1-MCP outgassing to

occur from the fruit. In the two years that injury was not observed, an 8-hour period had been left

between the two treatments for 1-MCP to outgas. Whether including the outgassing period between

treatments protected the fruit from injury or was the result of physiological variations of the fruit from

different growing seasons is not known. Applying the heat treatment before the 1-MCP treatment has

not been done to our knowledge, but should be evaluated as an alternative strategy to potentially

obtain the beneficial effects of both treatments on quality maintenance and decay control while

lessening the risk of fruit injury. However, until the cause of the fruit injury associated with the duel

treatment is understood, combining these two stressful treatments commercially should be avoided in

‘Golden Delicious’ apples.

Methyl jasmonate treatments of preclimacteric apples at 0.2 or 2 Pa for 24 hours at 20 °C was

not phytosanitary and provided little to no residual protection against wound-inoculated decay

development caused by P. expansum, B. cinerea, or C. acutatum. However, in one year of testing

when natural decay development was higher than normal, MJ vapor treatments reduced the incidence

of lesions by about 50 % during 5 months of storage at 0 °C. These results would suggest that MJ

vapor is not an effective antimicrobial treatment in apples. Methyl jasmonate vapors increased peel

yellowing without affecting flesh firmness, but not as effectively as the heat treatment which

additionally maintained flesh firmness.

The 12-day high oxygen treatment at the beginning of storage at 0 °C did not increase

quality-associated volatile levels in fruit following storage at 0 and 20 °C. The potential

phytosanitary benefits of treating apples with high oxygen during cold storage were not investigated

in this study.

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