Strategies to modulate 1-MCP effects in `Packham`s Triumph

Transcription

ARTICLES
RIA / Vol. 41 N.º 1
Strategies to modulate 1-MCP effects
in ‘Packham’s Triumph’ pears:
simultaneous application with ethylene
or CO2 and temperature treatments
CALVO, G.1; CANDAN, A. P.1
ABSTRACT
Two trials were conducted in order to evaluate the effectiveness of several approaches to restore ripening
ability of ‘Packham’s Triumph’ pears treated with 1-methylcyclopropene (1-MCP). Results showed that a simultaneous application of 0.3 μL L-1 1-MCP with 0.15 or 0.3 μL L-1 ethylene or with 5% CO2 allowed the fruit to ripen
after 160d of storage. Among these treatments, 0.3 μL L-1 1-MCP with 0.15 μL L-1 ethylene absolutely controlled
superficial scald even after 210d of storage. When 0.6 μL L-1 1-MCP were applied, the simultaneous application
with 0.6 μL L-1 ethylene or with 5% CO2 allowed the softening of the fruit only after 230d, and also maintaining a
very low incidence of superficial scald. The efficacy of temperature treatments depended on the time that fruit
were warmed. A warming of 2 or 3 weeks was needed to restore ripening in fruit treated with 0.6 μL L-1 1-MCP
and stored for 230 or 160d, respectively and 2 weeks was also effective in fruits treated with LSD 1-MCP and
stored for 210d. However, these temperature treatments developed the highest incidence of superficial scald.
In conclusion, the competition for the binding sites by ethylene or CO2 are the most promissory strategies since
they modulate 1-MCP effects maintaining low incidence of superficial scald in ‘Packhams Triumph’ pears.
Keywords: cold storage – ripening - superficial scald.
INTRODUCTION
Some european pears (Pyrus communis) cultivars, such
as ‘Packham’s Triumph’, are highly susceptible to superficial scald, and postharvest treatments with diphenylamine
and ethoxyquin are commercially used to prevent this very
important physiological storage disorder. However, many
countries have banned the use of such antioxidants, which
mandates development of alternative methods to control
scald (Calvo and Kupferman, 2012).
The application of 1-methylcyclopropene (1-MCP) immediately after harvest greatly reduces superficial scald development and its effectiveness was associated to the reduction
of ethylene synthesis, α-farnesenes and conjugated trienols
(Chen and Spotts, 2005). In pears, 1-MCP treatment also
allows delaying softening and loss of green colour (Mitcham
et al., 2001; Calvo, 2004; Ekman et al., 2004).
Pears are extremely sensitive to 1-MCP exposure, compared to apples and the residual effects of the current commercial applicable dose (0.3 μL L-1) are not easily dissipated during a reasonable marketing period (Blankeship and
Dole, 2003) and the concentration that provides an effective
control of superficial scald can inhibit the normal fruit ripening during the marketing period (Chen and Spotts, 2005).
Thus, it is still a challenge to reach a balance between storage benefits and eventual ripening of the fruit for marketing (Mitcham et al., 2001; Villalobos-Acuña et al., 2011). In
pears, the recovery of ethylene sensitivity mainly depends
Area Poscosecha, EEA Alto Valle, Instituto Nacional de Tecnología Agropecuaria (INTA). CC782, CP(8332), Gral. Roca, Río Negro,
Argentina. E-mail: calvo.gabriela@inta.gob.ar; candan.ana@inta.gob.ar
1
Received June 17th 2014 // Accepted March 6th 2015 // Published online April 29th 2015
Strategies to modulate 1-MCP effects in ‘Packham’s Triumph’ pears: simultaneous application with ethylene or CO2 (...)
April 2015, Argentina
on 1-MCP concentration applied, storage length and fruit
ripening stage at the time of treatment (Calvo, 2004).
In order to re-start the ripening process of 1-MCP treated pears, several strategies have been investigated. The
application of exogenous ethylene after cold storage does
not reverse inhibition caused by 1-MCP in pears (Mitcham
et al., 2001; Calvo, 2004). However, the simultaneous application of 1-MCP with ethylene in ratios from 1:0.5 to 1:2
could facilitate subsequent restoration of ripening, probably
by competition of both compounds for the ethylene binding
sites (Manriquez and Defilippi, 2011; Cucci and Regiroli,
2011; Chiriboga et al., 2011). In this sense, a simultaneous
application of 1-MCP and CO2 could also be effective, since
CO2 can reduce the ethylene action due to a competition
at the ethylene receptor site (Burg and Burg, 1967; Gorny
and Kader, 1997) or to secondary effects such as pH changes (Sisler and Wood, 1988). However, this approach had
not been analyzed until the present work. Finally, Bai et al.
(2007) and Chiriboga et al. (2010) reported that warming
the fruits at 10 to 20°C during or after the storage may restore the softening ability of several pear cultivars treated
with 1-MCP, being the effect attributed to the stimulation of
the synthesis of new receptors (Jiang et al., 1999).
The current research was conducted to evaluate the efficacy of different strategies to modulate 1-MCP effects in
‘Packham’s Triumph’ in order to allow the ripening of the
fruit and reducing the occurrence of superficial scald.
1-MCP treatments
Fruit were treated with 0.3 or 0.6 µL L-1 1-MCP in a sealed
chamber by adding warm water on SmartFreshTM powder.
During treatment, fans inside the chambers ensured a fast
and homogeneous gas distribution. Fruit were treated for
24 h during cooling and the chamber was then opened and
thoroughly aerated.
CH4 and CO2 treatments
For simultaneous applications with ethylene, the volume
of an enriched gaseous mixture (5% CH4 in air) needed to
obtain 0.6, 0.3 and 0.15 μL L-1 ethylene in a sealed chamber was taken with a syringe and then injected immediately
after beginning the release of 1-MCP treatment. To obtain
5% CO2 v/v in a sealed chamber, an enriched gaseous mixture (99% CO2 in air) was injected directly from a gas tube
equipped with a flow-meter.
Temperature treatments
Post-storage temperature treatments were carried out prior
each evaluation date, by warming the fruit in a 17 ºC room
during 1, 2 or 3 weeks (according with each treatment) after
which they were returned to cold storage for another 1 week.
Analysis of ethylene production
MATERIAL AND METHODS
Plant material and treatments
In a first trail ‘Packham’s Triumph’ pears from a commercial orchard were harvested at preclimacteric stage on February 10, 2009 (firmness: 64.1 N, soluble solids: 11.3%,
titratable acidity: 2.68 g L-1, colour 117.3 hº, starch degradation: 45.0%). Fruits were treated with 0 μL L-1 (Control),
LSD 1-MCP, 0.6 μL L-1 1-MCP. To modulate 1-MCP effects,
the strategies evaluated were: simultaneous application of
0.3 μL L-1 1-MCP + 0.3 μL L-1 ethylene (0.3+0.3ET), LSD
1-MCP + 0.6 μL L-1 ethylene (0.6+0.6ET), 0.6 μL L-1 1-MCP
+ 5% v/v CO2 (0.6+CO2) and temperature treatments during 2 weeks for 0.3 μL L-1 1-MCP treated fruit (0.3+2W)
or during 2 and 3 weeks for 0.6 μL L-1 1-MCP treated fruit
(0.6+2W and 0.6+3W, respectively). Fruit were packaged in
cardboard pear boxes with plastic liners (LDPE, 25 µm) and
stored at -0.5 ºC for 160 and 230 days.
In a second trial, ‘Packham’s Triumph’ from the same orchard were harvested at preclimacteric stage on February
23, 2010 (firmness: 60.8 N, soluble solids: 11.2%, titratable
acidity: 2.28 g L-1, hº: 116.9, starch degradation: 39.7%).
Fruit were treated with 0 μL L-1 (Control) or 0.3 μL L-1 1-MCP
and the strategies assayed were: simultaneous application
of 0.3 μL L-1 1-MCP + 0.15 μL L-1 ethylene (0.3+0.15ET),
0.3 μL L-1 1-MCP + 5% v/v CO2 (0.3+CO2) and temperature
treatments during 1, 2 or 3 weeks (0.3+1W, 0.3+2W and
0.3+3W, respectively). Fruit were packaged in cardboard
pear boxes with plastic liners (LDPE, 25 µm) and stored at
-0.5 ºC for 150 and 210 days.
The ethylene production (nl g-1 h-1) was measured on 3 replicates of 1 fruit each during the shelf life at 20 °C following
each storage period. Fruit were placed into a 1.5 L sealed
jar for 30 min. A sample of 1 mL from the headspace gas
was evaluated by gas chromatography (GC-14A, Shimadzu, Japan) utilizing an alumina column and a FID detector.
Maturity index assessment
Maturity indexes were evaluated on 3 replicates of 20
fruit each, immediately after storage time and after 7 and
14 d of ripening at 20 °C. Firmness (N) was measured on
two sides of each fruit using an electronic penetrometer
(FTA14, Güss, South Africa) fitted with an 8 mm probe. Soluble solids (%) were measured with a digital refractometer
(PAL1, Atago, Japan) on the juice from fruit of each replication. Titratable acidity (g L-1) was measured by titration
of 10 ml of the juice with NaOH 0.1 N to pH 8.2 end point.
Epidermis color was measured on two opposite sides of
each fruit with a colorimeter (CR400, Minolta, Japan) and
expressed as hue angle (hº), where: hº <102 indicated that
fruit were essentially yellow (Ekman et al., 2004).
Superficial scald assessment
The percentage of fruit showing superficial scald was
measured visually on 3 replicates of twenty fruit each one,
immediately after each storage time and after 7 and 14 d of
ripening at 20 °C.
CALVO, GABRIELA1; CANDAN, ANA PAULA1
ARTICLES
Statistical analysis
inhibited ethylene production until the end of the experimental period, and no differences were observed among
concentrations (Figure 1 and 2).
Data were analyzed by ANOVA and subjected to mean separation by DGC test (0.05) using the software INFOSTAT/
Professional Version 2006p.1. In ethylene production figures,
LSD values according to Fisher test (0.05) are presented.
RESULTS
Ethylene production after storage
Ethylene production (nl/g/h)
80
60
40
LSD=15,5
20
0
0
2
4
6
8
10
12
60
40
LSD=17,3
20
0
150
100
LSD=53,6
50
0
0
2
4
6
8
10
12
14
Time at 20ºC (days)
0.3
Control
0.6+0.6ET
0.6
0.6+CO2
0.6+2W
2
4
6
8
10
12
14
8
10
12
14
B
250
80
0
A
200
14
B
100
250
A
100
In both trials, the ethylene production of control fruit was
detected immediately after removal from cold storage and
reached the climacteric peak after 5 days (160 and 150 d
of storage) and after 2 days of shelf life at 20 ºC (230 and
210 d of storage). Treatments with 0.3 and 0.6 μL L-1 1-MCP
Simultaneous pre-storage application of 1-MCP and
ethylene allowed the ethylene production to resume during ripening, depending on the applied concentrations and
the storage length. In trial 1, 0.3+0.3ET fruit exhibited similar behavior than controls after the two storage periods,
showing that simultaneous application at this concentration
completely restores the fruit ability of producing ethylene. In
contrast, 0.6+0.6ET treatment produced a partial restoration (Figure 1). In trial 2, fruit treated with 0.3+0.15ET increased ethylene production in comparison with those treated with 0.3 μL L-1 1-MCP, but did not reach the climacteric
peak (Figure 2).
200
LSD=36,1
150
100
50
0
0
2
4
6
Time at 20ºC (days)
0.3+0.3ET
0.3+2W
0.6+3W
Figure 1. Ethylene production of during shelf life at 20 ºC after 160
(A) and 230 d (B) of storage ‘Packham’s Triumph’ pears in treated
with different strategies to modulate 1-MCP (Trial 1). LSD according to Fisher test (0.05).
Control
0.3+0.15ET
0.3
0.3+CO2
0.3+1W
0.3+3W
0.3+2W
Figure 2. Ethylene production during shelf life at 20 ºC after 150 d
(A) and 210 d (B) of storage of ‘Packham´s Triumph’ pears treated
with different strategies to modulate 1-MCP (Trial 2). LSD according to Fisher test (0.05).
The effectiveness of simultaneous application of 1-MCP
and CO2 was dependent on the concentration of 1-MCP
applied and the length of storage. In the first trial, 5% CO2
partially restored ethylene production of 0.6 μL L-1 1-MCP
treated fruit only after 230 d of storage (Figure 1). However,
in the second trial when 0.3 μL L-1 1-MCP was applied, the
treatment with 5% CO2 allowed a higher recovery of ethylene production, mainly after 210 d of cold storage (Figure 2).
The efficacy of temperature treatments depended on the
time of exposure at 17 ºC and the storage length. In trial 1,
the efficacy of a 3-week period (0.6+3W) to increase ethylene production was higher than a 2–week period (0.6+2W
and 0.3+2W) (Figure 1). Similarly in trial 2, fruit stored for
up 150 d required 3 weeks at 17 °C to recover the ability
of produce ethylene, while only 1 or 2 weeks were enough
when the fruit was stored longer (Figure 2).
Fruit ripening after cold storage
For pears, optimum fruit firmness to reach the desired
texture and juiciness for consumption is 18-27 N (Bai et
al., 2007; Kappel et al., 1995). According to results presented here, in both trials, control fruit softened beyond the recommended values for consumption after the 7 d at 20 ºC
160 day-storage
Days at 20 ºC
0
7
Firmness
Color
Firmness
Color
(N)
(hº)
(N)
(hº)
Control
58.9 b
108.8 b
35.8 c
99.6 c
0.3 μL L-1
63.1 b
112.0 a
57.9 a
109.4 a
0.3+0.3ET
59.1 b
108.0 b
45.4 b
106.8 b
0.3+2W
64.7 a
109.9 b
59.6 a
101.9 c
0.6 μL L-1
62.2 b
113.1 a
49.3 b
110.3 a
0.6+0.6ET
58.7 b
110.8 b
63.0 a
109.3 a
0.6+CO2
61.2 b
109.6 b
60.7 a
110.5 a
0.6+2W
66.3 a
111.9 a
51.2 b
100.6 c
0.6+3W
58.8 b
106.4 c
45.0 b
95.5 d
p Value
0.0144
0.0002
<0.0001
<0.0001
Control
10.8 e
106.7 c
17.7 c
92.5 c
0.3 μL L-1
60.9 a
113.0 a
56.6 a
109.8 a
0.3+0.3ET
12.2 e
103.1 d
20.5 c
100.7 b
0.3+2W
50.4 c
106.9 c
30.0 b
98.7 b
0.6 μL L-1
63.2 a
112.6 a
64.0 a
109.8 a
0.6+0.6ET
47.6 c
109.5 b
21.9 c
102.0 b
0.6+CO2
57.3 b
111.0 b
35.9 b
106.7 a
0.6+2W
52.6 c
107.2 c
26.1 b
98.6 b
Treatment
0.6+3W
36.0 d
99.2 e
15.3 c
P Value
<0.0001
<0.0001
<0.0001
<0.0001
Control
7.3 d
95.4 d
15.2 b
86.7 c
63.7 a
109.3 a
58.4 a
102.8 a
5.0 d
94.4 d
15.6 b
95.4 b
0.3 μL L-1
0.3+0.3ET
14
230 day-storage
92.7 c
0.3+2W
32.4 c
97.4 c
16.5 b
91.6 c
0.6 μL L-1
71.6 a
110.8 a
57.8 a
102.5 a
0.6+0.6ET
27.1 c
99.9 c
9.6 b
96.2 b
0.6+CO2
46.1 b
104.9 b
12.6 b
94.3 b
0.6+2W
23.7 c
96.9 c
13.7 b
89.5 c
0.6+3W
13.1 d
93.1 d
8.3 b
85.4 d
p Value
<0.0001
<0.0001
<0.0001
<0.0001
Table 1. Firmness and epidermis colour of ‘Packham´s Triumph’ pears treated with different strategies to modulate 1-MCP effect (Trial 1).
Evaluations were done after a 160 and 230 d of storage at -0.5 ºC and after 0, 7 and 14 d shelf life at 20 ºC. Mean separation DGC (0.05).
ARTICLES
150 day-storage
Days at 20 ºC
0
Firmness
Color
Firmness
Color
(N)
(hº)
(N)
(hº)
Control
47.6 b
110.3 b
45.5 b
108.1 c
0.3 μL L-1
54.4 a
115.6 a
51.7 a
113.9 a
0.3+0.15ET
50.9 b
115.0 a
50.7 a
113.9 a
108.2 c
Treatment
0.3+CO2
51.4 b
112.0 b
46.7 b
0.3+1W
55.2 a
112.0 b
51.3 a
110.6 b
0.3+2W
58.0 a
111.1 b
44.4 b
102.4 d
0.3+3W
49.5 b
106.0 c
22.0 c
93.9 e
p Value
0.0220
0.0001
<0.0001
<0.0001
Control
7
14
210 day-storage
8.0 d
102.9 b
7.6 c
102.5 b
0.3 μL L-1
58.8 a
114.6 a
50.6 a
112.7 a
0.3+0.15ET
42.5 b
112.8 a
37.0 b
110.5 a
105.6 b
8.3 c
104.0 b
0.3+CO2
13.3 d
0.3+1W
59.7 a
111.2 a
29.5 b
102.5 b
0.3+2W
54.3 a
107.5 b
11.0 c
97.2 c
0.3+3W
28.1 c
97.4 c
8.0 c
97.5 c
p Value
<0.0001
<0.0001
<0.0001
<0.0001
Control
3.3 c
94.8 b
0.3 μL L-1
51.5 a
107.9 a
0.3+0.15ET
15.8 c
99.1 b
5.5 c
93.5 b
0.3+1W
39.7 a
101.3 b
0.3+2W
23.6 b
96.5 b
0.3+CO2
0.3+3W
12.3 c
94.3 b
p Value
<0.0001
0.0002
Table 2. Firmness and epidermis colour of ‘Packham´s Triumph’ pears treated with different strategies to modulate 1-MCP effect (Trial 2).
Evaluations were done after a 150 and 210 d of storage at -0.5 ºC and after 0, 7 and 14 d shelf life at 20 ºC. Mean separation DGC (0.05).
subsequent to both storage periods. In contrast, fruit treated with 0.3 and 0.6 μL L-1 never reached eating quality, as
they maintained firmness values over 50 N, even after 14
d of shelf life (Tables 1 and 2). All the strategies evaluated
were effective to modulate, the effect of 1-MCP treatment
on firmness, and the effect was greater as the length of cold
storage increases (Tables 1 and 2).
As observed for ethylene production, the efficacy of simultaneous application with ethylene depended on the concentration of 1-MCP used. In the first trial, 0.3+0.3ET treatment
allowed a complete recovery after both storage periods,
and the fruit reached similar firmness values as controls,
but the fruit treated with the 0.6+0.6ET required 14 or 7 d to
reach eating quality after 160 or 230 d of storage, respectively (Table 1). In the second trial, fruit from 0.3+0.15ET
softened at a lower rate than controls and reached firmness
lower than 18 N after 150 d of storage followed by 14 d of
shelf life (Table 2). The recovery of fruit softening caused by
CO2 was complete when it was simultaneously applied to
fruit treated with 0.3 μL L-1 1-MCP (Table 2), but partial when
the concentration was 0.6 μL L-1, requiring a longer storage
period (230 d) to reach an appropriate firmness after 14 d
of shelf life (Table 1).
The effect of temperature treatments on restoring fruit ripening ability was greater when the period at 17 ºC and the cold
storage time were longer. In the first trial we observed that 3
weeks at 17 ºC was effective to modulate 1-MCP effects after
160 d of storage while 2 weeks at 17 ºC were enough when
storage extended up to 230 d irrespective of the applied
dose (Table 1). In the second trial, 3 weeks at 17 ºC was the
only effective temperature treatment allowing correct softening within 7 d of shelf life after 150 d storage, while 2 weeks
at 17 ºC was enough after 210 d of storage (Table 2).
Superficial scald
In the first trail, superficial scald incidence in control fruit
was 27% and 100%, after 160 and 230 d of storage + 7
d of shelf life respectively. In the second trial, control fruit
showed 0% and 56% of affected fruit after 150 and 210 d
of storage followed by 7 d of shelf life (Figure 3), denoting
less susceptibility to scald in fruit of this season. Application
of 0.3 μL L-1 and 0.6 μL L-1 1-MCP reduced the incidence of
the disorder, with a maximum of 8% of affected fruit, after
230 d of storage + 7 d of shelf life in Trial 1 and a complete
inhibition in Trail 2.
The treatments applied to restore fruit ripening maintained a low incidence of scald (Figure 3) when the fruit were
stored for up 150 or 160 d. When storage period was extended for up 230 or 210 d, scald incidence increased and
some of the treatments that proved to be effective in modulating the effects of 1-MCP on firmness showed high incidence of scald. The simultaneous application with ethylene
or CO2 reduced superficial scald respect to controls, with
0.6+0.6ET, 0.6+5%CO2 and 0.3+0.15ET the most effective
Superficial Scald (%)
100
a
A
80
b
60
40
c
a
20
b b
b b b b b
b
0
Control
0.3
0.6+CO2
Superficial Scald (%)
100
d
d d
160 + 7 d
c
c
d
230 + 7 d
0.6
0.3+0.3ET
0.3+2W
0.6+2W
0.6+0.6ET
0.6+3W
a a
B
80
b
60
40
c
20
0
a
b b b b b b
d d
150 + 7 d
Control
d
210 + 7 d
0.3
0.3+1W
0.3+0.15ET
0.3+2W
0.3+CO2
0.3+3W
Figure 3. Superficial scald incidence in ‘Packham´s Triumph’ pears
treated with different strategies to modulate 1-MCP. Data correspond to the percentage of fruit from total population showing scald
symptoms. Evaluations were done following 7 d of shelf life at 20
ºC, after 160 and 230 d of storage in Trial 1 (A) and after 150 and
210 d of storage in Trial 2 (B). Mean separation DGC (0.05).
treatments in Trial 1 and Trial 2, respectively. In general,
temperature treatments were less effective in controlling
superficial scald and the percentage of affected fruit increased with the length of exposure at 17 ºC. Moreover, these
treatments increased the incidence of this disorder compared to control fruit in 2010 (Figure 3).
DISCUSSION
Delaying pear ripening and senescence to extend fruit
storage without the appearance of physiological disorders
is the most important benefit of 1-MCP application (Villalobos-Acuña et al., 2011). However, the use of 1-MCP in
European pears is potentially problematic because the residual effect is not easily dissipated during a reasonable marketing period following cold storage (Ekman et al., 2004;
Chen and Spotts, 2005).
The results of this study show that 1-MCP treatment is
very effective in reducing ethylene production and in delaying ripening in ‘Packham´s Triumph’ pears, as already been
reported in many pear cultivars (Calvo, 2004; Ekman et al.,
2004; Calvo and Sozzi, 2004; Chen and Spotts, 2005). As
was expected, 1-MCP treatment inhibited the normal ripening of the fruit maintaining firmness values above 50 N even
after 14 d of shelf life. Since 1-MCP competes with ethylene
for binding sites, its effectiveness depends on the applied
concentration until receptor saturation (Ekman et al., 2004).
However, no differences between 0.3 and 0.6 mL L-1 1-MCP
were observed in this study, which suggests that 0.3 µL
L-1 may be sufficient to block all the receptors and reduce
ethylene production in ‘Packham´s Triumph’ pears.
The development of superficial scald is the main limitation
in ‘Packhams Triumph’ stored in regular air and the standard
practice for scald control is a postharvest treatment with
ethoxyquin or diphenylamine. However, regulations governing the use of chemicals to control diseases and disorders
of apples and pears in storage are becoming increasingly
stringent, especially in European Union (EU) countries, and
it is essential to develop alternative methods to control this
disorder (Calvo and Kupferman, 2012). Regarding the use
of 1-MCP, it is a good alternative to current chemicals for
control storage scald in apples. However it application to
pears provides control of storage scald as well as the reduction in senescent scald, but ripening may be inhibited
after storage (Calvo and Kupferman, 2012).
Results presented here support that 1-MCP decreased
the incidence of superficial scald but prevented the normal
ripening of the fruits during the entire experimental period
in both trials, which demonstrates the need to adapt this
technology for commercial use. Competitive strategies of
applying 1-MCP with ethylene showed to be effective to
restore the ability of pear to ripen after long cold storage,
though the treatment effectiveness depends strongly on the
concentrations used. Ethylene application overcome the inhibitory effect of 0.3 mL L-1 of 1-MCP after 160d of storage
and it was also effective to restore ripening in fruit treated
with 0.6 mL L-1, after 230 d of storage. It suggests that a si-
ARTICLES
multaneous application of 1-MCP and ethylene (1:1 or 1:0.5
rate) will be effective according with the 1-MCP applied
dose and the storage length. When 0.3 mL L-1 ethylene
was applied to fruit treated with 0.3 mL L-1 1-MCP, ripening
restoration was complete but when the concentration was
0.15 mL L-1 ethylene, the restoration was partial and fruit
showed a ripening rate intermediate between control and
1-MCP treated fruit. Among these treatments, 0.6+0.6ET
and 0.3+0.15 are the most interesting treatments, since
0.3+0.3ET showed higher incidence of superficial scald.
The simultaneous application of 0.6 mL L-1 1-MCP and LSD
ethylene (1:0.5 rates) was the most promising treatment
in ‘Conference’ pears (Chiriboga et al., 2011). Additionally,
1-MCP treatment applied in combination with ethylene (1:1
rates) showed an effect in ripening of ‘Packham’s Triumph’ pears, being this response intermediate compared to
1-MCP applied immediately after harvest and the control
fruit without treatment (Manriquez and Defilippi, 2011).
The simultaneous application of 1-MCP with 5% CO2
was also effective to restart ripening. As was observed with
ethylene application, the CO2 effect was dependent on the
concentration of 1-MCP applied and restored ripening completely in 0.3 μL L-1 1-MCP treated fruit but only partially in
0.6 μL L-1 1-MCP treated fruit. According to our knowledge,
this would be the first study that demonstrates the efficacy
of simultaneous application of CO2 and 1-MCP to reverse
1-MCP ripening inhibition in pears after a sufficient length of
storage. The mechanism by which CO2 counteracts the inhibitor effect of 1-MCP allowing further fruit ripening has to
be elucidated. Burg and Burg (1967) and Gorny and Kader
(1997) proposed that inhibition of ethylene biosynthesis by
CO2 is mediated through the receptor site. Then, the effect
of the simultaneous application could be explained through
the competition between CO2 and 1-MCP for ethylene receptors. On the other hand, it was also demonstrated that
the inhibition by CO2 could influence ethylene production
rather than ethylene perception (De Wild et al., 1999)
mainly through secondary effects such as pH changes (Sisler and Wood, 1988). It is also important to use an appropriate CO2 concentration, since Chavez-Franco and Kader
(1993) reported that in pear, ethylene production was stimulated by 1% CO2 and inhibited by 5-20% CO2. Previous
studies showed that inhibition of ethylene synthesis or action reduces α-farnasene production and consequently inhibits superficial scald (Chen and Spotts, 2005). In this study,
treatments that proved to be more effective in restoring fruit
ripening in fruit treated with 1-MCP were those with a higher incidence of scald, while those that allowed a partial
restoration, such as 0.6+1-MCP+5%CO2 and 0.3+0.15ET,
maintained a lower scald incidence.
Another promising strategy to restore ripening in pears
treated with 1-MCP is to expose the fruit to temperatures
in the range of 15-20 ºC for variable durations. Temperature exposure could favor the release of 1-MCP from the
receptors or the synthesis of new ethylene receptors, or an
interaction of both factors (Villalobos-Acuña et al., 2011).
Temperature treatments were effective in restoring ripening of 1-MCP treated ‘Blanquilla’ and ‘Bartlett’ pears, but
not in Conference and Beurré D’Anjou cultivars (Bai et al.,
2007; Chiriboga et al., 2010). Results obtained in this study indicate that this strategy is effective also in restoring
the ripening ability of ‘Packham’s Triumph’ pears, being the
0.3+1W the most interesting treatment, allowing softening
after 230 d plus shelf life and even controlling superficial
scald. In contrast, fruit treated with 0.3+2W and 0.3+3W recovered the ability to ripen but developed more superficial
scald than control fruit.
In ‘Bartlett’ pears, the most suitable combinations to restore the fruit ripening capability in 0.3 μL L-1 1-MCP treated
fruit were 10 d at 20 ºC or 20 d at 10 ºC after 2 months of
storage, and 10 d at 15 ºC after 4 months of storage 17.
Similarly, 5 to 15 d at 15 ºC was enough to recover fruit
ripening ability in ‘Blanquilla’ pears after 4 months of cold
storage (Chiriboga et al., 2007). Besides the duration of
temperature exposure, the cultivar and storage length, the
temperature treatments are atmosphere dependent, since
the fruit stored in controlled atmosphere required a longer
storage than in regular air to restart the ripening process
(Bai et al., 2007).
The main advantage of temperature treatments lies on
that they can be performed according to marketing needs,
and not prior to storage, as is the case of other strategies
involving simultaneous applications. In contrast, temperature treatments imply logistical problems, particularly if
fruit are already packaged in bags. In terms of logistic, the
simultaneous application of ethylene or CO2 could be an
easy method to modulate 1-MCP effects in pears. However,
one of the main disadvantages of this strategy is that the simultaneous application should be decided before knowing
how long the fruit will be stored.
Collectively, these results show the importance of considering the 1-MCP applied dose and the length of storage to decide the best strategy to modulate 1-MCP effect
and allowed to conclude that the competitive inhibition of
1-MCP by ethylene or CO2 are the most promissory strategies since they modulate 1-MCP effects maintaining low
incidence of superficial scald in ‘Packhams Triumph’ pears.
ACKNOWLEDGEMENTS
The authors would like to acknowledge financial support
from INTA (PNFRU-53911) and AgroFresh®.
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Strategies to modulate 1-MCP effects in `Packham`s Triumph

Transcription

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