Washington Tree Fruit Research Commission

Research Reports

Consumer perception of MCP-treated apples (2003)

FINAL PROJECT REPORT
WTFRC Project #PH-02-252
YEAR 0/0
Organization Project #14C-4164-2708
Title:Consumer perception of MCP-treated apples
PI:Eugene Kupferman
Organization:WSU Tree Fruit Research and Extension Center 1100 N. Western Avenue; Wenatchee, WA 98801; 509-663-8181 ext. 239; kupfer@wsu.edu
 PDF version of report

Co-PIs

Anna Marin, Oregon State University, Food Innovation Center

 

Objectives

Determine consumer acceptance of MCP-treated Gala apples stored until April in either RA or CA storage.

 

 

Significant findings

Difference testing:
·         Consumers could tell a difference between both MCP CA fruit vs. Control CA fruit and MCP RA fruit vs. Control CA fruit. These findings were statistically significant with 99% confidence.
Preference testing:
·         There was no statistically significant difference in preference for any of the fruit tested; similar numbers of consumers indicated preference for the MCP CA or MCP RA treated fruit (50%) as the Control fruit (40%), with 10% of the consumers indicating no preference.
·         Consumer liking of the fruit was evaluated using a 10 cm line scale where 0=dislike extremely and 10=like extremely. The average overall liking score from all consumers for the MCP CA fruit was 6.88 vs. a score of 7.01 for the Control fruit. The MCA-RA fruit had an average overall liking score of 6.85 vs. a score of 6.92 for the Control fruit. Comparison of scores indicates that they were not significantly different and confirms that there was no overall preference based on treatment. The high average liking scores indicate that all fruit was well liked.
·         For all three treatments, more than 60% of the consumers tested answered that they would probably or definitely buy the apples they were testing, again confirming that the fruit was well liked.
·         When evaluating reasons for preference, apple flavor had the most responses for why consumers preferred a specific treatment. Juiciness was the second most frequently given reason for preference, followed by texture. In both MCP CA and MCP RA treated apples sweetness was a more frequently given reason for preference than for the Control fruit. Sourness was more frequently given as a reason for preference for the Control fruit than for the MCP CA and MCP RA treated fruit.

·        Texture was more frequently given as a reason for not preferring the MCP CA and MCP RA treated apples than for the Control fruit.

Materials and methods

Apple treatment:
Thirty-five packed boxes of Washington Extra Fancy size100 Gala apples were purchased from Stemilt Growers in Wenatchee, Washington, on September 4, 2002, the day after packing. Apples were treated normally through the packing process and had not been treated with 1‑Methylcyclopropene (MCP SmartFreshÔ) prior to packing.

On September 5, 20 boxes were taken to McDougall and Sons’ Baker Flat cold storage facility where they were treated with MCP for 24 hours. The other 15 boxes were placed in the WSU-TFREC postharvest cold room at 32ºF. 
To determine apple quality at time of treatment (prior to storage) on September 9, 25 MCP-treated apples and a similar number of untreated fruits were evaluated for quality. Analysis included both nondestructive firmness with Sinclair Internal Quality‑Firmness Tester (SIQ‑FT) and the Aweta Acoustic Firmness Sensor (AFS) and destructive firmness with the Fruit Texture Analyzer (FTA). Skin color and internal ethylene were also determined. Starch was evaluated on 10 apples from each treatment.
On September 10, 10 boxes of apples treated with MCP and 14 boxes of Control (untreated) fruit were returned to Stemilt for controlled atmosphere (CA) storage. Room atmosphere was 2.0% CO2 and 2.0% O2 with a 32oF temperature. The other 10 boxes of MCP-treated apples were stored in the WSU-TFREC postharvest lab cold room at 32ºF. A box liner was placed in each box before storage to reduce fruit shrivel.
Apples were removed from CA storage on March 6, 2002, and brought to the WSU-TFREC cold room. A 100-apple sample from each treatment was measured for firmness with the SIQ device on March 19, 2003. It was determined that firmness ranges were sufficient to allow us to pair apples with the same SIQ values from the different treatments. This was done to reduce the effect on consumer acceptability by the expected increased firmness levels of the MCP-treated fruit.
All apples were then tested using the SIQ on March 26, 2003, and sorted into categories comprised of equivalent IQ units (between 28 and 35). A 20-apple sample from each treatment [MCP-treated CA fruit, MCP-treated RA fruit and CA-stored fruit (Control)] was sent to Dr. Jim Mattheis’ lab for a profile analysis of volatiles.
After sorting, apple boxes were placed singly on pallets on the floor of the cold room with lids opened to provide adequate cooling overnight before transport. On March 27, apples were transported to Portland, Oregon, and were placed in the OSU Food Innovation Center cold room.
On March 28, boxes of Control fruit were matched with boxes of RA and CA stored MCP-treated fruit that had the same SIQ value. Matched boxes were taken to the Portland Saturday Market for sensory evaluation by consumers.
Immediately prior to being served to consumers, the firmness of each apple was tested using a penetrometer (FTA) on one cheek. Slices of fruit from five apples from each box of fruit were pooled for a soluble solid and acidity measurement.

Consumer test experimental design:
Sensory difference and preference tests were conducted with consumers at the Portland Saturday Market in downtown Portland over a two-day period. Consumers qualified to participate in the test if they ate apples more than once a month. All consumers were first given a difference test of either the MCP CA treated fruit vs. the Control fruit or the MCP RA fruit vs. the Control fruit. If they were correct in being able to distinguish between the two fruit treatments, they were given a preference test with pieces of the same fruit just evaluated in the difference test. Over 600 consumers were tested over the two-day period. Consumer data was collected on tablet and laptop computers using ballots presented in Compusense 4.5.2 data collection software.

Difference tests (first test):
Consumers were given a tray with an apple sample labeled as a reference and two samples of coded fruit, one of which was the same as the reference and the other being the other treatment. Consumers were asked to indicate which sample was the same as the reference. Presentation of fruit was balanced so that half of the consumers got the MCP fruit labeled as the reference fruit and the other half got Control fruit as a reference. Consumers who could tell a difference proceeded to the second test for preference.

Preference tests (second test):
·         Overall liking: Consumers who were correct in the difference test were given a second tray with coded samples of MCP and Control fruit (slices from the same fruit served for the difference test) and asked to rate how much they liked each on a 10 cm line scale. The line scale was anchored on the left with “dislike extremely,” in the center (at 5 cm) with “neither like nor dislike,” and on the right with “like extremely.” Liking scores were based on distance on the line.
·         Purchase intent: After rating liking, consumers rated how likely they would be to buy this apple as an eating quality apple. Ratings were based on the following 5-point scale:
1-      Would definitely not buy
2-      Would probably not buy
3-      might not buy/might buy
4-      Would probably buy
5-   Would definitely buy
·         Preference: Consumers were then asked to indicate which of the two samples they preferred or if they had no preference.
·         Reasons for liking preferred sample: Consumers who had a preference were asked to indicate as many reasons as applied for their preference. The available reasons for preference were texture, juiciness, apple flavor, sweetness, and sourness/tartness.
·         Reasons for disliking sample not preferred: After giving reasons for preference, consumers were asked to indicate as many reasons as applied for disliking the sample they did not prefer. The reasons available for disliking were the same as for liking.
·         Apple eating frequency. After completing the apple taste evaluation and ratings, consumers were asked to indicate which varieties of apples they chose to eat most frequently and how frequently they ate Gala apples.

Results and discussion

Apple treatment:

a)   The pre-storage tests showed that quality was well balanced between the MCP and Control fruit and that ethylene biosynthesis had been suppressed by MCP (Table 1).

Table 1.  Quality attributes prior to storage of Gala apples used in this study.

Treatment
Firm (lbf)
SIQ
(IQ)
Acoustical
(FI)
Starch
0-10

Ethylene
Color
background
Color
red
MCP
17.3
25
25
5.1
0.89
3.3
2.0
Control
18.0
26
25
4.6
17.44
3.3
2.3

b)      Following storage, firmness levels of MCP-treated fruit, as measured by penetrometer, were higher than those of Control fruit but not different in MCP-treated fruit from RA or CA (Table 2). Soluble solids and acidity were highest in the Control fruit.

Table 2.  Quality attributes after storage of Gala apples used in this study.

Treatment
Firmness (mean)
Soluble solids (%)
Acidity (%)
MCP RA
14.6 a
11.7
0.2969
MCP CA
14.5 a
12.3
0.3358
Control
14.1 b
13.3
0.3320

c)      Firmness at time of serving as measured by Sinclair Internal Quality‑Firmness Tester (SIQ‑FT in IQ units) related to firmness as measured destructively with the penetrometer (Table 3). The penetrometer utilized in this study was the Fruit Texture Analyzer (FTA in lbf). Fruit with the highest IQ value (35 IQ) was of intermediate firmness, but we have noted that the SIQ values are the most variable when the IQ is highest and least variable when fruit has lower IQ values.

Table 3.  Comparison of Sinclair Internal Quality (IQ value) and Fruit Textural
Analyzer (FTA) penetrometer values for Gala apples served to consumers.
Sinclair Internal Quality
(IQ units)
Number of apples served to consumers
Firmness (FTA) (lbf)
35
18
15.0 bc
34
68
15.9 a
33
20
15.5 ab
32
260
15.0 bc
31
238
14.6 cd
30
323
14.0 de
29
316
13.7 e
28
39
13.7 e
Letters indicate mean separation by Tukey’s, P=0.05
d)      Analysis of the volatiles associated with each treatment showed that Control fruit had more total esters, alcohols, aldehydes and ketones than those treated with MCP stored in either CA or RA (Table 4). These values confirm previous results, that volatile production is altered by treatment with MCP and storage type. It is important to consider that volatile production is one of several factors impacting fruit quality, therefore a simple relationship between volatile production and preference is not always present.
Table 4.  Volatiles associated with each treatment.
Treatment
Days out of storage
Total esters
Alcohols
Aldehydes
Ketones
Control
1
146.87
21.11
0.93
9.40
MCP CA
1
19.90
9.13
1.02
6.72
MCP RA
1
48.13
23.72
1.07
1.58
Control
7
190.51
21.17
2.33
4.12
MCP CA
7
50.10
7.89
0.58
2.19
MCP RA
7
38.10
9.93
0.88
1.29


Consumer difference testing results:
The difference test results show that consumers could tell a difference between MCP CA fruit and Control fruit and between MCP RA fruit and Control fruit. Table 5 gives the number of consumers giving correct and incorrect responses for each difference test.
Table 5.  Difference test results for two tests: MCP CA vs. Control and MCP RA vs. Control. For each test, the number of correct responses indicates results are statistically significant (P = 0.01).
TEST A

TEST B
MCP CA
MPC CA
Control

MCP RA
Control
MCP RA
Ref sample
Code 184
Code 629

Ref sample
Code 762
Code 435
137 total consumers
83 correct responses
54 incorrect responses

90 total consumers
23 incorrect responses
67 correct responses

Consumer preference test results:
A.  Overall liking and preference:
Results of comparing consumers’ ratings for overall liking for MCP CA fruit vs. Control fruit and MCP RA fruit vs. Control fruit are given in Table 6. The average overall liking scores indicate that the apples were well liked. Panelists were asked directly to indicate which sample they preferred. Results show that there was no significant preference for MCP-treated fruit vs. Control fruit: similar numbers of consumers preferred each kind of fruit.
Table 6.  Comparison of average overall liking scores and preference for treatment and control fruit for two tests: MCP CA vs. Control and MCP RA vs. Control fruit.

                                                        TEST A                                                     TEST B

MCP CA
Control
No Pref

MCP RA
Control
No Pref
Mean overall liking
scores 1
6.88a
7.01a

6.85a
6.92a

# of consumers
preferring
104
86
12

93
73
20
% of consumers
preferring2
51.5%
42.5%
6.0%

50.0%
39.2%
10.8%
1Mean scores with the same letters are NOT significantly different.

2Chi squared statistics:
TEST A: 1.7 ns TEST B: 2.4 ns

B.  Intent to purchase:
Consumers’ responses to purchase intent for the different apples tested are summarized in Table 7. Over 60% of the consumers said they would probably or definitely buy either the MCP-treated or Control fruit. The percentages of consumers who were definitely willing to buy and probably willing to buy were combined, as were those in the “probably” and “definitely not willing to buy” categories.

Table 7.  Consumers’ willingness to buy level for MCP-treated and Control fruit. Values are for % of consumers in the purchase intent category for each treatment.

MCP CA
Control
MCP RA
Control
Would definitely/probably not buy
18.8%
16.8%
16.7%
16.7%
Might buy/might not buy
18.3%
18.8%
22.0%
21.0%
Would probably/definitely buy
62.9%
64.4%
61.3%
62.4%

C.  Reasons for liking and disliking:
  • Consumers’ reasons for liking the apple they preferred are illustrated in Figure 1. The figure compares the number of responses (%) given for each apple and for each of the following five reasons: texture, juiciness, apple flavor, sweetness, and sourness/tartness. The top three reasons for liking the Control fruit were apple flavor, texture and juiciness. The top three reasons for liking both the MCP CA and MCP RA apples were apple flavor, sweetness and juiciness. Sweetness was a reason more frequently used for liking the MCP-treated fruit than for the Control. Texture was cited more frequently as the reason consumers liked the Control fruit better than MCP CA treatment. Sourness/tartness was the reason given more often for liking for the Control better than either MCP treatment.
  • Consumers’ reasons for disliking the apple they did not prefer are illustrated in Figure 2. The figure compares the number of responses (%) given for each apple and for each of the following five reasons: texture, juiciness, apple flavor, sweetness, and sourness/tartness. The reason most frequently given for disliking the MCP CA or RA fruit was texture and then apple flavor. Reasons for disliking the Control fruit were different for the two tests: apple flavor and sourness/tartness for the MCP CA vs. Control test and apple flavor and juiciness for the MCP RA vs. Control test.

Figure 1.  Reasons for liking most frequently given for Control and MCP RA and MCP CA fruit. Values are percentage of responses given for that reason within that test.


Figure 2.  Reasons for disliking most frequently used for Control and MCP RA and MCP CA fruit. Values are percent of responses given for that reason within that test.


D.  Consumer apple eating habits:
The 640 consumers in these tests indicated that they most often chose Fuji and Gala, then Red and Golden Delicious, because of their fresh eating quality.

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