Washington Tree Fruit Research Commission

Research Reports

Use of bioregulators to enhance 'Delicious' fruit quality and maintain fruit condition (2002)

FINAL PROJECT REPORT
WTFRC Project #PH-01-124
YEAR 0/0
Organization Project #16281
Title:Use of bioregulators to enhance 'Delicious' fruit quality and maintain fruit condition
PI:Stephen R Drake
Organization:USDA, ARS, TFRL, Wenatchee, WA
 PDF version of report

Co-PIs

D.C. Elfving, Horticulturist

Washington State University, Wenatchee, WA

Collaborators

M. A. Drake, Food Scientist (Sensory)  
North Carolina State Univ., Raleigh, NC

T.A. Eisele, Food Chemist (Sensory)
Tree Top, Inc. Selah, WA

Objectives

Develop and test uses of bioregulators to enhance 'Delicious' fruit quality and consumer acceptance without loss of long-term storage potential.

 

 

Methods

A.  Two ‘Delicious’ strains:  ('Oregon Spur' and 'Scarletspur') and one strain of 'Gala'
B.  Bioregulator applications:  (AVG alone, and ethephon treatment of previously AVG-treated fruit)
C.  Applications:  (AVG (ReTain): 4 weeks before anticipated commercial harvest; ethephon: One and two weeks before anticipated commercial harvest)
D.  Three harvest dates:  (Commercial harvest, 2 weeks later and 4 weeks later)
E.  Two types of storage:  (Regular and Controlled Atmosphere)
F.  Evaluations:  (at harvest, 90, 150 and 210 days)
1.  Texture (flesh firmness)
2.  Color (external and internal)
3.  Sugars
4.  Acids
5.  Chemical (flesh chlorophyll content, ethylene evolution)
6.  Sensory (organoleptic):  Taste-panel evaluations will be conducted on both fresh apples and processed product (juice).  Tests on fresh apples will be carried out at harvest on different harvest dates as well as following storage.
7.  Physiological disorders (bitter-pit, scald, watercore etc.)

In recent years, concerns have been raised about the potential for negative effects on the fruit quality of ‘Delicious’ apples treated with ethephon to advance maturity and facilitate harvest scheduling.  How long before the achievement of physiological maturity can ethephon be applied with the assurance that the fruit will be capable of developing acceptable eating quality?  What is the relationship between the timing of the ethephon application and the degree of loss, if any, of storage life and quality?  These important questions merit further evaluation of the effects of ethephon on ‘Delicious’ apples.  Recent results in this project have shown that ethephon can stimulate very rapid and subtle changes in fruit quality that are both detectable and preferred by humans but not clearly detectable by traditional laboratory methods.

The bioregulator aminoethoxyvinylglycine (AVG, ReTain®) is now registered for the control of preharvest drop, delay of watercore development and management of harvest maturity in ‘Delicious’ and other apple cultivars.  This material inhibits the natural biosynthesis of ethylene in the fruit, thereby controlling the onset of the climacteric process that results in fruit ripening.  Its use is designed to permit fruit to remain on the tree beyond the point when normal physiological maturity is achieved and without the onset of the climacteric.  This approach permits the extension of harvest scheduling while reducing the risk of fruit drop and fruit-quality loss during and following storage.  The mode of action of AVG is the opposite of ethephon.

Ethephon can be used to temporarily stimulate desirable fruit-quality changes that can be detected by consumers while relying on AVG to prevent the initiation of the climacteric and its inevitable long-term negative consequence, loss of fruit quality.  If AVG-based control of ripening can be maintained in the presence of a single temporary burst of exogenously applied ethephon, it may be possible to improve the consumer acceptance of ‘Delicious’ apples with little or no compromise of storability and shipping behavior.

Significant findings

Ethephon (Ethrel®, Aventis CropScience) produced very rapid changes (over as little as 7 days after application) in ‘Scarletspur Delicious’ fruit quality that were clearly detectable by a human taste panel but were accompanied by only a few small changes in the traditional, laboratory-instrument-based fruit quality measurements of soluble solids content and starch level but no changes in flesh firmness, titratable acidity or sugar/acid ratio.  The changes in fruit quality that were clearly detectable by people were also produced by half the normal concentration of applied ethephon (150 vs. 300 ppm). 

At harvest, use of ethephon had no influence on the firmness or peel color of 'Scarletspur, or Oregonspur Delicious' apples at harvest (Table 1).  Ethephon advanced starch loss, increased soluble solids and the number of drops, and reduced green flesh color.  After RA and CA storage, preharvest ethephon reduced firmness, but also reduced the amount of scald present, enhanced red peel color and reduced green flesh color

Ethephon treatment of apples stimulates the onset of physiological changes known as the “climacteric”, or ripening process.  Once started, this process cannot be completely stopped, even by cold temperatures and controlled-atmosphere conditions.  When ethephon is not used preharvest, the natural initiation of ethylene production in the fruit tissue is the stimulus that starts the irreversible ripening process.

AVG (aminoethoxyvinylglycine, ReTain®, Valent BioSciences) inhibits the natural production of ethylene within the fruit, thereby delaying the start of ripening by inhibiting production of the triggering hormone in fruit tissue.  At harvest, use of AVG enhanced firmness and red peel color, reduced starch loss and watercore development (Table 2).  In both RA and CA storage, apples treated with AVG maintained greater firmness and displayed a deeper red peel color.

AVG delays fruit maturity and the onset of the climacteric, thereby delaying degradative changes in traditional indices of fruit quality (flesh firmness, soluble solids, titratable acidity, starch level).  Preharvest treatment of ‘Delicious’ apples with AVG permits a significant delay in harvest with little or no loss in condition and confers the ability of fruit to retain greater flesh firmness following air or long-term CA storage. This delay in harvest can be associated with improved consumer acceptance.  Organoleptic (taste-panel) evaluations of ‘Delicious’ apple juice has indicated that both the use of Ethephon and harvest delay improves acceptance (Table 3).

In 2001, ReTain (125 ppm) + ethephon (150 or 300 ppm) enhanced sensory quality of both juice and whole apples (Tables 4 and 5).  Apple juice from apples with ReTain alone were similar in sensory preference and like at the first harvest. But, at the third harvest, juice from the control fruit was rated superior in sensory quality (Table 3).  Sensory quality of apple juice with a combination of ReTain + ethephon was preferred and rated superior to juice from control fruit (Table 3).  Use of ReTain + ethephon (300 ppm 2 wks) prior to harvest did not influence sensory quality.

Sensory quality of whole apples (ReTain + ethephon, 300 ppm, 2 wks) was best in overall quality, flavor and texture when compared to control fruit, or fruit with other combinations of ReTain + ethephon @ 150 ppm, or 300 ppm (Table 4).  There was a significant harvest effect and scores were increased from harvest III compared to harvest I.  There was not a harvest x treatment interaction, thus data are pooled across harvest.

Soluble solids, at harvest (2001) of fruit treated with ReTain + ethephon, regardless of the amount of ethephon or time of application, was significantly higher than the soluble solids of the control fruit or fruit with ReTain alone (Table 6).  When individual carbohydrates were considered (Table 6), the amount of sucrose and glucose was highest in ReTain + ethephon treated fruit compared to control fruit or fruit with ReTain alone.

A combination of ReTain + ethephon not only enhanced fruit quality, but also helped to maintain fruit condition during both RA and CA storage.  Ethylene production during both RA and CA storage was significantly less by fruit treated with either ReTain, or ReTain + ethephon when compared to control fruit (Table 7)  This reduced production of ethylene gives a strong indication that apples treated with ReTain or ReTain + ethephon are loosing condition at a slower rate than control fruit.  This enhanced fruit condition for fruit treated with either ReTain or ReTain + ethephon was also evident when firmness was considered (Table 8).  At harvest III, little or no difference in firmness was evident, for treated fruit compared to control fruit.  After RA and CA storage, firmness was much superior in fruit treated with ReTain or ReTain + ethephon compared to control fruit.  In all instances fruit treated with either ReTain or ReTain + ethephon meet or exceeded minimum firmness requirements even after 210 days in CA storage.  It should be remembered that this firmness difference between fruit treated with ReTain or ReTain + ethephon compared to control fruit was harvested 2 weeks after normal commercial harvest (harvest III).

Tables

Table 1.  Influence of Ethephon on 'Scarletspur Delicious' fruit quality, at harvest

 

 

Attribute

 

Harvest

 

Control

 

150 ppm, 1 wk

 

150 ppm, 2 wk

 

300 ppm, 1 wk

 

300 ppm, 2 wk

 

 

Starch (1-6)

 

I

 

2.2cz

 

2.4b

 

2.7a

 

2.4b

 

2.7a

 

 

 

II

 

3.6b

 

4.2a

 

4.2a

 

4.3a

 

4.0a

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Firmness (N)

 

I

 

72.5a

 

72.5a

 

69.8a

 

71.2a

 

70.7a

 

 

 

II

 

65.8a

 

63.2a

 

61.8a

 

62.3a

 

62.7a

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SSC (%)

 

I

 

11.5b

 

12.0ab

 

12.3a

 

12.1ab

 

12.7a

 

 

 

II

 

12.6

 

12.9a

 

13.1a

 

13.1a

 

13.4a

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Peel Color (hue)

 

I

 

14.1a

 

14.0a

 

14.1a

 

14.4a

 

14.0a

 

 

 

II

 

13.0a

 

14.3a

 

14.0a

 

14.4a

 

14.5a
zMeans in a row not followed by a common letter are significantly different (P=0.05).

 


Table 2.  Influence of ReTain on 'Scarletspur  Delicious' fruit quality at harvest and after storage

 

 

 

 

 

 

 

   @ Harvest

 

Storage (RA)

 

Storage (CA)

 

Attribute

 

Harvest

 

Control

 

ReTainz

 

Control

 

ReTain

 

Control

 

ReTain

 

 

Firmness (lbs)

 

I

 

16.5bz

 

17.3a

 

13.0b

 

15.3a

 

15.3b

 

16.0a

 

 

 

II

 

13.9b

 

15.1a

 

10.1b

 

11.7a

 

13.9b

 

14.9a

 

 

Peel Color (hue)

 

I

 

14.0a

 

13.2b

 

14.8a

 

14.1b

 

13.7a

 

12.7b

 

 

 

II

 

13.6a

 

12.9b

 

14.2a

 

13.2b

 

14.7a

 

15.2a

 

 

Starch (1-6)

 

I

 

1.4a

 

1.5a

 

 

 

 

 

 

 

 

 

 

 

II

 

3.0a

 

2.4b

 

 

 

 

 

 

 

 

 

Water Core (%)

 

I

 

0.0a

 

0.0a

 

 

 

 

 

 

 

 

 

 

 

II

 

80.0a

 

18.0b

 

 

 

 

 

 

 

 

zApplied @ 125ppm, 4 weeks before first harvest.
yPairs of means, in a row, not followed by a common letter are significantly different (P=0.05).


Table 3.  Sensory evaluation of 'Scarletspur Delicious' apple juice, at two harvest treated with ethephon, 1 and 2 weeks before anticipated harvest.

 

 

 

 

Harvest I (Sept., 18)

 

Harvest III (Oct., 13)

 

 

 

Preference

 

Intensity

 

Like

 

Preference

 

Intensity

 

Like

 

CK

 

4z

 

3.9by

 

6.0b

 

6

 

4.2b

 

7.4a

 

150 ppm, 2 wk

 

21

 

5.2a

 

7.3a

 

19

 

5.2a

 

7.8a

 

CK

 

2

 

3.8b

 

5.8b

 

6

 

4.0b

 

6.8b

 

300 ppm, 2 wk

 

23

 

5.3a

 

7.4a

 

19

 

5.0a

 

8.0a

 

CK

 

6

 

4.0b

 

6.2b

 

10

 

4.5a

 

7.3a

 

150 ppm, 1 wk

 

19

 

5.2a

 

7.5a

 

15

 

4.6a

 

6.8a

 

CK

 

4

 

3.9b

 

6.2b

 

13

 

4.8a

 

7.5a

 

300 ppm, 1 wk

 

21

 

5.1a

 

7.5a

 

12

 

4.6a

 

7.0a
zNumber of panelists choosing the option (N=25)
yMean of pairs in a column not followed by a common letter are significantly different (P=0.05).

 

 


 

Table 4.  Sensory quality of 'Scarletspur Delicious' apples juice as influenced by bioregulators (ReTain + Ethephon).

 

 

 

 

          Harvest I

 

 

 

     Harvest III

 

Bioregulator

 

         Preference

 

            Like

 

 

 

      Preference

 

         Like

 

CK

 

10az

 

6.16a

 

 

 

17a

 

7.48a

 

ReTain 125 ppm, 4 wks

 

15a

 

6.52a

 

 

 

8b

 

6.64b

 

 

CK

 

7b

 

6.40a

 

 

 

7b

 

6.84a

 

ReTain + Ethephon 150 ppm, 2 wks.

 

18a

 

7.08a

 

 

 

18a

 

7.36a

 

 

CK

 

3b

 

5.88b

 

 

 

4b

 

6.60b

 

ReTain + Ethephon 300, 2 wks.

 

22a

 

7.40a

 

 

 

21a

 

7.40a

 

 

CK

 

6b

 

6.08b

 

 

 

7b

 

6.28b

 

ReTain + Ethephon 150 ppm, 1 wk.

 

19a

 

7.36a

 

 

 

18a

 

7.32a

 

 

CK

 

10a

 

7.04a

 

 

 

15a

 

7.24a

 

ReTain + Ethephon 300 ppm, 1 wk.

 

15a

 

7.04a

 

 

 

10a

 

6.48a
zPairs of means, in a column, not followed by a common letter are significantly different (P=0.005).
(N=25).

 

 

 

 


Table 5.  Sensory quality of whole 'Delicious' apples as influenced by bioregulators (ReTain + Ethephon)

 

 

 

 

 

 

 

 

 

 

    Preferencey

 

 

 

    Overallz

 

       Flavorz

 

     Texturez

 

     Frequency

 

        Percent

 

CK

 

6.4c

 

6.2c

 

6.7ab

 

41

 

17

 

ReTain 125 ppm, 4 wks.

 

6.0d

 

5.8d

 

6.5b

 

23

 

9

 

ReTain + Ethephon 150 ppm, 2 wks.

 

6.5abc

 

6.5abc

 

6.9a

 

48

 

20

 

ReTain + Ethephon 300 ppm, 2 wks.

 

6.7a

 

6.7a

 

7.0a

 

55

 

25

 

ReTain + Ethephon 150 ppm, 1 wk.

 

6.5bc

 

6.4b

 

6.9a

 

30

 

12

 

ReTain + Ethephon 300 ppm, 1 wk.

 

6.6ab

 

6.5ab

 

6.9a

 

41

 

17
(N=240)
zThere was a significant harvest effect.  Hedonic scores were increased for harvest II compared to harvest I.  There was not a harvest x treatment interaction, thus data are pooled across harvest.
yThere was not a significant effect on harvest for overall preference so preference data were pooled across harvest.

 

Table 6.  Influence of ReTain + Ethephon on 'Delicious' fruit carbohydrates @ harvest

 

 

 

 

SSC (%)

 

Sucrose

 

Glucose

 

Fructose

 

Sorbitol

 

Ck

 

10.8bc

 

2.1ab

 

1.5c

 

5.8a

 

0.25cd

 

ReTain, 125 ppm

 

10.5c

 

1.9b

 

1.5c

 

5.7a

 

0.24cd

 

ReTain + Ethephon 150 ppm, 2 wk

 

11.3ab

 

2.3a

 

1.7abc

 

5.9a

 

0.30ab

 

ReTain + Ethephon 300 ppm, 2 wk

 

11.9a

 

2.4a

 

1.9a

 

6.0a

 

0.32a

 

ReTain + Ethephon 150 ppm, 1 wk

 

11.3abc

 

2.3a

 

1.6bc

 

5.9a

 

0.27bc

 

ReTain + Ethephon 150 ppm, 1 wk

 

11.8a

 

2.3a

 

1.8ab

 

6.0a

 

0.32a
Means in a column not followed by a common letter are significantly different (P=0.05).

 

Table 7.  Influence of ReTain + Ethephon on fruit ethylene production (ppm),  @ harvest, after regular, and controlled atmosphere storage, harvest III.
 

 

 

 

@ harvest

 

60 days RA

 

120 days CA

 

 

 

'Scarlet'

 

  'Oregon'

 

   'Scarlet'

 

  'Oregon'

 

    'Scarlet'

 

'Oregon'

 

Ck

 

>1.0

 

>1.0

 

28.04

 

46.21

 

19.55

 

15.53

 

ReTain, 125 ppm

 

0.0

 

<1.0

 

2.89

 

<1.0

 

10.08

 

1.32

 

ReTain + Ethephon 150 ppm, 2 wk

 

<1.0

 

<1.0

 

3.53

 

1.58

 

3.15

 

4.99

 

ReTain + Ethephon 300 ppm, 2 wk

 

<1.0

 

<1.0

 

6.80

 

7.58

 

7.36

 

3.13

 

ReTain + Ethephon 150 ppm, 1 wk

 

<1.0

 

<1.0

 

3.70

 

4.85

 

6.83

 

<1.0c

 

ReTain + Ethephon 150 ppm, 1 wk

 

<1.0

 

<1.0

 

11.48

 

15.90

 

9.00

 

3.22

 

Table 8.  Influence of ReTain + Ethephon on fruit firmness,  @ harvest, after regular, and controlled atmosphere storage, harvest III.

 

 

 

 

@ harvest

 

60 days RA

 

210 days CA

 

 

 

'Scarlet'

 

  'Oregon'

 

   'Scarlet'

 

  'Oregon'

 

    'Scarlet'

 

'Oregon'

 

Ck

 

15.7

 

15.6

 

13.7b

 

13.6b

 

12.0b

 

10.8c

 

ReTain, 125 ppm

 

15.9

 

15.6

 

14.5a

 

14.5a

 

13.6a

 

13.1a

 

ReTain + Ethephon 150 ppm, 2 wk

 

16.5

 

15.7

 

14.2a

 

14.7a

 

12.5ab

 

12.3b

 

ReTain + Ethephon 300 ppm, 2 wk

 

15.9

 

15.5

 

14.1a

 

14.3a

 

12.0b

 

12.6b

 

ReTain + Ethephon 150 ppm, 1 wk

 

16.1

 

15.6

 

14.6a

 

15.1a

 

12.5ab

 

12.9a

 

ReTain + Ethephon 150 ppm, 1 wk

 

16.3

 

15.7

 

14.2a

 

15.1a

 

11.8b

 

12.5ab
Means in a column not followed by a common letter are significantly different (P=0.05)

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