Washington Tree Fruit Research Commission

Research Reports

1-MCP: Effects on Flavor and Methods to Compensate or Enhance Apple Flavor Quality (2003)

FINAL PROJECT REPORT
WTFRC Project #PH-01-137
YEAR 0/0
Organization Project #
Title:1-MCP: Effects on Flavor and Methods to Compensate or Enhance Apple Flavor Quality
PI:A. Nathan Reed
Organization:Dept. of Horticulture Penn State University Fruit Research & Extension Center 290 University Drive Biglerville, PA 17307 717.677.6116x2 anr2@psu.edu
 PDF version of report

Co-PIs

James Mattheis                         Ruth Hollender 
USDA-ARS                             Food Science Borland Lab
1104 N. Western Ave.               Penn State University
Wenatchee, WA 98801              University Park, PA  16802

Objectives

  1. Identify flavor component profiles of Gala and Red Delicious at harvest and following storage in regular atmosphere (RA) and controlled atmosphere (CA).
  2. Characterize the effect of an ethylene blocker, 1-MCP, volatile profiles of Gala and Red Delicious during RA and CA storage.
  3. Investigate changes in Gala and Red Delicious volatile profiles in warm temperature storage following periods of cold storage.
  4. Determine the persistence of exogenously applied flavor compounds in Red Delicious and Gala.
  5. Determine if sensory panels can detect differences between exogenous flavor treated and control fruit.

     

Significant findings

  1. Volatiles applied exogenously to Red Delicious resulted in elevated levels in fruit following treatment that persisted for more than three weeks.
  2. The exposure of apples to exogenous volatile esters stimulated increases in other naturally occurring esters and one alcohol volatile but not alpha-farnesene.
  3. The persistence of the applied volatiles was not significantly reduced under commercial packing line procedures.

     

Methods

An individual grower lot of Red Delicious that had been stored in CA for six months was obtained from a commercial CA storage operator and divided randomly into four treatments each with four replications.  The four treatments are described in Table 1.

Experimental procedure included selection of approximately 550 g of fruit (three fruit) per replication. These fruit were weighed and then placed in a 2.44 liter glass tube equipped with teflon seals.  The apples were placed in a temperature-controlled environment (3 oC)and a stream (100 ml/min) of ultra clean air flushed the apples for 20 minutes.  Air from the glass tube containing the apples then passed thru a 250 ml dilution flask.  Volatiles were collected on a solid phase microextraction (SPME) fiber placed directly in the air stream within the dilution flask.  The four replicates of each treatment were measured for volatile composition the day prior to volatile exposure. 

To expose the fruit to ester volatiles weighed samples of individual esters were placed in separate glass petri dishes (Table 2).  The volatiles along with the apples were placed in 0.20 m3 chambers and sealed for 7 days at 0.5oC.  After seven days the atmosphere in each chamber was approximately 2% carbon dioxide and 19% oxygen.  Once the chambers were opened the Petri dishes were weighed to determine total amount of evaporated volatile exposure. 

One day after the apples were removed from volatile ester treatment, the apples were assessed for volatile content by the SPME method described above.  Three days after volatile treatment the fruit were taken to a commercial packinghouse and put into the packing process.  The Red Delicious fruit were numbered with a Sharpie prior to placing them into the dump tank to maintain their identity.  At the time of packing line treatment the line was running Golden Delicious to allow the easy identification of treated fruit.  To investigate packing line effects only half of the volatile treated fruit and half of the control fruit were actually run over the packing line.  The dump tank was unheated but did contain chlorine for sanitation purposes.  Decco Fruit and Vegetable Kleen 241 was used as a soap.  FMC Freshkote 241 HC was the type of wax applied.  The drying tunnel was 29 feet long and the temperature was 90 – 100oF.  Fruit took approximately three minutes to traverse the drying tunnel.  The brushes in the drying tunnel were run at 35-40 rpms.

The day after running on the packing line, Day 14, and for the following three weeks, Days 21, 28 and 35, the apples were analyzed for volatiles by the SPME technique described above.  (Refer to treatment and analysis timeline in Table 3.)

The volatiles collected with the SPME method were analyzed and identified by gas chromatography/mass spectrometry using a 30-meter DB wax capillary column.  Initial oven temperature was 35oC followed by a ramp of 10oC /min to a final temp of 200oC for 10 minutes.  Scans were taken on all masses between 30 – 220 amu.  Between SPME analyses the apples were kept at 0.5oC.

Results and discussion

During the week of exposure in cold storage (0.5oC), the volatile esters evaporated at rates of 99.6, 98.2, and 97.2% for Butyl Acetate, Ethyl-2-methyl butyrate and Hexyl Acetate, respectively.

The esters added showed a significant increase compared to the control fruit following exposure (Fig 1).  Following removal from treatment the rate of their production declined over the next three weeks while being stored in cold temperature. Three weeks following ester treatment the ester levels were still 2-3 times those observed in control fruit.  The concentration of other esters commonly found in Red Delicious also increased significantly to levels of 4 to more than 100X higher than the controls (Table 4). 

Following exposure to the packing line no significant differences in ester production rates as determined by SPME between volatile treated fruit and controls were observed (Fig. 2). 

These results suggest that common practices used on apple packing lines do not affect the overall rate of decline in volatile ester production following volatile enhancement.  An ester enhancement treatment could therefore be applied during the later stages of storage within a sealed cold room.  This treatment effect should not be diminished by the packing process.

Summary Conclusions


  • Gala and Red Delicious volatile profiles are suppressed following CA storage and/or 1-MCP treatment.
  • Volatile production of Gala and Red Delicious following cold storage in RA and CA is enhanced by storing fruit at warm temperatures.
  • In general volatiles applied exogenously to both Gala and Red Delicious were taken up at rates associated with treatment levels and the vapor pressure of the individual chemical.
  • There were no significant differences observed between control and 1-MCP treated fruit with respect to ester uptake.
  • The persistence of volatile uptake is dependent on individual volatile and can be influenced by fruit growing location (block).
  • Weekly sensory analyses of differences between exogenously treated and control fruit were significant in both Gala and Red Delicious for up to six and seven weeks, respectively, following treatment.
  • No significant difference in flavor preference was found between control and ester treated fruit.
  • Volatiles applied exogenously to Red Delicious resulted in elevated levels in fruit following treatment and stimulated increases in other naturally occurring esters and one alcohol volatile but not alpha-farnesene.
  • The persistence of the applied ester volatiles was not significantly reduced under commercial packing line procedures.

Table 1.  Treatments of Red Delicious for flavor volatile ester treatment.
Treatment
Volatile Esters Added
Run on packing line
1
No
No
2
Yes
No
3
No
Yes
4
Yes
Yes

Table 2.  Addition of volatile esters to Red Delicious
Volatile                                    g / 0.20 m3
Butyl acetate                             2.163
Ethyl-2-methyl butyrate  1.352
Hexyl acetate                            0.907


Table 3.  Timeline for ester volatile treatment and analysis of Red Delicious.

Day
Event
0
Initial SPME analysis
3-9
Volatile ester exposure (0.5oF, exposed and controls)
10
Air out following treatment (0.5oF)
11
Post treatment SPME analysis
13
Half of control and volatile exposed apples run on packing line
14
All fruit SPME analysis (1 day post packing line)
21
All fruit SPME analysis (8 days post packing line)
28
All fruit SPME analysis (15 days post packing line)
35
All fruit SPME analysis (22 days post packing line)

Table 4.  Production of volatiles in Red Delicious following 7-day exposure to Butyl acetate, Hexyl acetate and Ethyl-2-methyl butyrate.







Figure 1.  Volatile ester production profile of Butyl Acetate, Hexyl Acetate and Ethyl-2-Methyl Butyl Acetate before and following 1-week volatile exposure.




Figure 2. Volatile ester production profile of Butyl Acetate and Hexyl Acetate prior to and following exposure to commercial packing line treatment.

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