imahori 2013 postharvest biology and technology

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Postharvest Biology and Technology 77 (2013) 1927

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Postharvest Biology and Technology

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Residual effects oflow oxygen storage ofmature green fruit on ripeningprocesses and ester biosynthesis during ripening in bananas

Yoshihiro Imahoria,, Kohei Yamamotoa, Hiroshi Tanaka a,Jinhe Bai b

a Laboratoryof PostharvestPhysiology, Graduate School of Life and Environmental Sciences, OsakaPrefecture University, 1-1 Gakuen-cho, Nakaku, Sakai,Osaka 599-8531, Japanb USDA-ARS Horticultural Research Laboratory, 2001 South Rock Road, Ft.Pierce, FL 34945, USA

a r t i c l e i n f o

Article history:

Received 4 August 2012Accepted 12 November 2012

Keywords:

Banana

Low-oxygen atmosphere

Alcohol acetyltransferase

Alcohol dehydrogenase

Ester

Volatile

a b s t r a c t

Mature green banana (Musa sapientum L. cv. Cavendish) fruit were stored in 0.5%, 2%, or 21% O2for 7 days

at 20 C before ripening was initiated by ethylene. Residual effects of low O2 storage in mature green

fruit on ripening and ester biosynthesis in fruit were investigated during ripening for up to 6 d at 20 C.

Concentrations of ethanol in mature green fruit did not change during storage in both 21% and 2% O2atmospheres, but increased in fruit stored in 0.5% O2 . The activities of alcohol dehydrogenase (ADH) in

2% and 21% O2atmospheres remained very low throughout the storage period, but significantly increased

with 0.5% O2. After transferring fruit to regular air and trigging ripening with ethylene, yellowing ofpeel,

fruit softening and hydrolysis of starch in fruit stored in low O2 atmospheres were slower than in the

control. Fruit stored in low O2also showed a delayed onset ofthe climacteric peak. The activities ofADH

were lower in the low O2 stored fruit than in the control fruit. Productions of ethyl acetate, isoamyl

acetate, and isobutyl acetate were remarkably suppressed by low O2 storage. Alcohol acetyltransferase

activity increased gradually with storage time in all treatments, being significantly lower in fruit with

low O2pretreatments. The results indicate that low O2plus room temperature storage can extend storage

life ofbananas with the sacrifice ofa low production ofester volatiles.

2012 Elsevier B.V. All rights reserved.

1. Introduction

Bananas are among the most important fruit in world trade.

As a climacteric fruit, bananas are commercially picked from the

tree at the mature green stage, and then shipped to distant mar-

kets, usually by air or sea. Ripening treatment by ethylene gassing

is usually applied by distributors or retailers directly before retail

display. To protect mature green fruit from ripening during stor-

age and transportation, a common practice is to pre-cool fruit to

13 C and maintain the low temperature during the entire storage

period. However, refrigerationis costly, and an alternative low-cost

methodthat delays ripening would be useful, particularly for small

operators and in developing countries (Wills et al., 1990).

Application of controlled atmospheres (CA) and modified atmo-spheres (MA) can extend the storage life of mature green bananas

(Yahia, 1998). The beneficial effects of CA storage include extending

shelf-life and maintaining quality by decreasing metabolism and

suppressing postharvest decay (Imahori et al., 2004). Palomer et al.

(2005) reported thatCA storage slows respiration, peel de-greening

and changes in sugars, and minimizes the susceptibility of bananas

to crownrot. In a lowoxygen pretreatment, the exposure of mature

Corresponding author. Tel.: +81 72 254 9418; fax: +81 72 254 9418.

E-mail address: [email protected](Y. Imahori).

green banana fruit to low O2 for 2 days was effective in delaying

ripening during storage and after ethylene treatment (Wills et al.,

1982, 1990; Pesis et al., 2001). Most commodities require a mini-

mum o f 1 % O2in CAor MA storage to avoid anaerobic metabolism.

At O2-stress atmospheres,acetaldehydewhichis producedthrough

pyruvate decarboxylation by pyruvate decarboxylase (PDC) is con-

verted to ethanol by alcohol dehydrogenase (ADH) using NADH,

hence, ethanol is usually the major end-product (Imahori et al.,

2004). Accumulated ethanol in fruit drives the biosynthesis of

estersto ethyl esters, thus decreasesproduction of typical fruit aro-

mas,such as butyl acetate,isobutylacetateand isoamyl acetate, and

causes off-flavors (Bai et al., 1990).

Aroma, besides other properties such as texture and appear-

ance, plays an important role in thequality assessment of fruit.Thisparameter influencesconsumeracceptability of food (Jayanty et al.,

2002). Although more than 250 volatile components have been

identified in banana (Jayanty et al., 2002), the banana fruity top

notes are from volatile esters, such as isoamyl acetate and isobutyl

acetate (Macku and Jennings, 1987; Bai et al., 1990; Wendakoon

et al., 2006). The volatiles are formed by esterification of alco-

hols and carboxyl groups catalyzed by alcohol acetyltransferase

(AAT), using alcohol and acetyl CoA as substrates (Lara et al.,

2003). It has been reported that activity of AAT increases with

advanced maturity of fruit but can be inhibited by low O2 con-

centrations during storage of fruit, such as CA storage, decreasing

0925-5214/$ seefrontmatter 2012 Elsevier B.V. All rightsreserved.

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20 Y. Imahori et al. / Postharvest Biology andTechnology 77 (2013) 1927

production of acetate esters (Fellman et al., 1993; Chervin et al.,

2000). The negative impacts of CA storage, ultra-low-oxygen

storage in particular, on volatile emission and biosynthesis is

well documented, especially for apples and pears (Lara et al.,

2003). The increased ethanol levels and/or ADH activity in

fruit stored under a hypoxic atmosphere may be retained dur-

ing subsequent ripening in air, and in some cases may lead

to off-flavors (Lara et al., 2003). Thompson (1998) reported

that exposure of bananas to less than 1% O2

for an unspeci-

fied period causes low O2 injury in the form of a dull yellow

or brown peel discoloration, failure to ripen and off aromas.

Differences in aroma compounds were found between air-

stored and nitrogen-stored post-ripening bananas (Klieber et al.,

2002).

The objective of our research was to determine the toler-

ance of mature green bananas to low oxygen concentrations for

short periods at 20 C, and to examine the effects of low oxy-

gen pretreatments on the biosynthesis of ester in banana fruit

during subsequent ripening at 20C, with the general purpose of

assessing the influence of such storage conditions on fruit quality

during commercial shelf life of the fruit.

2. Materials and methods

2.1. Plant materials and treatments

Hands of mature green banana (Musa sapientum L. cv.

Cavendish) fruit were obtained from a local wholesale market in

Sakai, Japan. They were harvested at a commercial plantation in

the Philippines and shipped at 13C following commercial routes

to the laboratory within5 days of harvest. The fruit were sorted for

absence of visual defects and uniformity of weight and size. Fruit

(fingers) separated from the banana hands were submerged into

20 C water for 5 min, and then dried by paper towel. Six out of 114

fruit were randomly taken for day 0 sample analysis (two fruit per

replicate three replicates), and the rest were divided into three

groups for three gas treatments, 0.5, 2, and 21% O2. For each treat-ment, 36 fruit were evenly divided and placed in three 7-L glass

jars to represent three replicates. Fruit in the jars were stored in

the dark at 20 C and exposed to a given gas combination with a

flow-through system at a flow rate of 250 mLmin1. The gas mix-

tures with different O2levels were obtained by mixing humidified

pure O2 a nd pure N2 . After 7 days, all gas sources for the flow-

through system were replaced by 10L L1 ethylene in air for 24h

to trigger ripening. Finally, fruit were ripened in ethylene-free air

for an additional 7 days at 20 C. A subsample (two out of twelve

fruit per replicate) was taken at days 1, 4 and 7 during storage, and

days 1, 4 and 7 during post-storage ripening.

Oxygen concentration in the flow-through system was moni-

toredusing a gas chromatograph (GC)(Yanaco model G80,Yanaco),

equipped with a thermal conductivity detector (TCD) and a stain-less steel column (3mm1.0m) containing molecular sieve 5A.

The flow rate of the carrier helium gas was 40 mL min1. The

oven was set at 60 C and the injector was kept at 125 C. Eth-

ylene concentration was checked using a GC (GC-8A, Shimadzu)

equipped with a flame ionization detector (FID) and a glass col-

umn (3mm0.5m) containing 80/100 mesh activated alumina.

The flow rate of the carrier N2gas was 40mLmin1. The oven was

set at 40 C and the injector was kept at 140 C.

Ethanol content was measured during storage of mature green

fruit at day 0, 1, 4 and 7, and surface color, respiration rate,

rate of ethylene production, firmness, eating quality, content of

ethanol, isoamyl acetate, isobutyl acetate and ethyl acetate, and

alcohol acetyltransferase (AAT) activity were measured during

post-storage ripening at days 1, 4 and 7. Alcohol dehydrogenase

(ADH) was measured throughout storage and post-storage ripen-

ing.Every treatmentat eachsamplingday included three replicates

and two fruit per replicate.

For non-destructive measurements of attributes, surface color,

respirationrate, rate of ethylene production, two fruit per replicate

labeled for thelast sampling day(post-storage day7) were used on

all experimental days.

For destructive measurements, two fruit per replicate at each

sampling day were peeled, sliced to 0.5mm thick discs, quartered,

and then mixed. Measurements were taken from the fresh tissue

or snap frozen in liquid nitrogen and storage at80 C for up to 30

days.

2.2. Measurement of ethanol content

Ethanol levels were determined according to the method of

Sugiura and Tomana (1983). Frozen tissue (5g) was homoge-

nized with a chilled pestle and mortar in 10mLcold acetone. The

homogenate was quickly transferred to a cold screw-capped glass

bottle and stored at 20 C. The homogenate was filtered through

Advantec No. 2 filter paper. One microliter of the filtrate was

injectedintoGC(Hitachimodel163,Hitachi)equippedwithFIDand

a stainless column (3mm1.0m) containing 50/80 mesh Porapak

Q. The flow rate of the nitrogen carrier gas was 40mLmin1. Theoven temperature was 140 C. The ethanol concentrations in the

sample were calculated from the comparison of peak areas with

those of standards. Amounts of ethanol were expressed asg per

100 gram fresh weight of flesh.

2.3. Volatile compounds analysis

Frozen pulp tissue (5g) was homogenized in a chilled mortar

and pestle with 20mLof 50mM potassium phosphate buffer (pH

7.0). The homogenate was transferred intoa conicalflask andclosed

with a silicon cap. After incubating the sample at 30C for 60min,

1 mLof headspace gas was taken with a glass syringe and injected

into a GC (GC-8A, Shimadzu) equipped with FID and polyethylene

glycol 9000 column (3mm1.0m). The flow rate of the nitrogencarrier gas was 27mLmin1. The oven temperature was 90 C. The

volatile compounds of banana were qualified and quantified by

comparing the retention time and peak size (area) of the authentic

standards.

2.4. Extraction and assay of enzymes

Extraction and assay of ADH were conducted by following the

method ofKe et al. (1994) with some modifications. Briefly, frozen

pulp tissue (5g) was homogenized in a chilled mortar and pestle

with 20mLof 100 mMMES buffer (pH6.5) containing 2 mM dithio-

threitol and 1% (w/v) polyvinylpyrolidone (PVP). The homogenate

was filtered through two layers of Miracloth (Calbiochem) and the

filtrate was centrifuged at 13,000gfor 20min at4 C. Quantifica-tion of enzyme activitywas performed by monitoring the oxidation

of NADH at 340n m at 30 C using a spectrophotometer (Model V-

530, Jasco). Enzyme activities were expressed as moles of substrate

used per minute per gram of protein.

AAT was extracted by following Wendakoon et al. (2006) with

some modifications. Briefly, frozen pulp tissue (5g) was homog-

enized in a chilled mortar and pestle with 20 mL of 100 mM

potassium phosphate buffer (pH 8.0) containing 5 mM dithiothre-

itol and 1% (w/v) PVP. The homogenate was filtered through two

layers of Miracloth (Calbiochem) and the filtrate was centrifuged

at 13,000gfor 20min at 4 C. AAT activity was assayed according

to the method described by Lara et al. (2003) with slight modifi-

cations. The reaction mixture contained 0.1M phosphate (pH 8.0),

5 mM MgCl2, 0.25mM acetyl-CoA, 5 mM isobutyl alcohol, 10mM


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Y. Imahori et al. / Postharvest Biology andTechnology 77 (2013) 1927 21

5,5-dithiobis (nitrobenzoic acid) (DTNB) and an appropriate

amount of the enzyme extract. Quantification of enzyme activ-

ity was performed by monitoring the increase in absorbance at

412nm at 30C, using a spectrophotometer (Model V-530, Jasco).

One activity unit (U) was defined as the increase of absorbance

per minute, and the results were expressed as U per gram of

protein.

Protein in the extracts was determined by the method of

Bradford (1976) with bovine serum albumin as the standard.

2.5. Measurement of soluble solids content (SSC)

The pulp tissue (5g) was homogenized in a mortar and pestle

and fluid was taken after filtering through two layers of Miracloth

(Calbiochem) and the SSC reading was taken with a digital refrac-

tometer (PR-101, Atago, Tokyo, Japan) calibrated against water.

2.6. Measurement of surface color, firmness and eating quality

Fruit color was determined visually and by using a color dif-

ference meter (ND-1001 DP, Nippon Denshoku, Tokyo, Japan), that

expresses the color as HunterL*, a*, b* values. HunterL*, a*, b* val-ues were taken on six different surface portions of each fruit and

the average from two fruit per replicate were used for calculations.

L*b*/a*, a yellowingindexwas calculated to present de-greeningor

yellowing of fruit surface, the higher index value, the more devel-

oped yellow color (Kanellis et al., 1989). The visual appearance

was assessed as described by Pesis et al. (2005). Briefly, the peel

color was expressed as an index on an eight-grade scale: 1 = green;

3= breaker; 5= yellow, green tip; 7= yellow, flecked with brown;

8 = over-ripe.

Firmness evaluation was carried out using a manual fruit firm-

ness tester (FT 327, EFFEGI) fitted with an 8 mm diameter tip. The

measurement was taken from opposite sides in middle of intact

fruit, complete with peel.

Eatingquality was tested infruit after 6 days at20 C after treat-

ment. A taste panel of five experts used a scale of 15, where 1

indicates extremely low quality and 5, extremely good quality.

2.7. Measurement of respiration rate and ethylene production

Rates of respiration and ethylene production were determined

after various storage times. Twofruitwere sealedinside a 1 L jarfor

1 h at 20 C. Respiration rate was obtained by measuring CO2con-

centration. Yanaco model G80 GC was used to qualify and quantify

CO2 concentration. The GC was equipped with a TCD and a stain-

less steel column (3mm1.0m) containing 80/100 mesh Porapak

Q. The flow rate of the carrier helium gas was 40mLmin1. The

oven was set at 60 C and the injector was kept at 125 C. Ethyl-

ene concentrations were measured using a GC (GC-8A, Shimadzu)equipped with FID and a glass column (3mm0.5m) containing

80/100mesh activated alumina. The flow rate of the carrier N2gas

was 40mLmin1. The oven was set at 40 C and the injector was

kept at 140 C.

2.8. Statistical analysis

Data for the analytical determinations were subjected to anal-

ysis of variance (ANOVA) using Statcel 2 (OMS, Saitama, Japan).

Sources of variation were time of storage, low O2 level and dura-

tion of treatments. Mean separations were performed using HSD

in Tukeys test to examine if differences between treatments and

storage time were significant at P=0.05.

0

5

10

15

20

0 1 2 3 4 5 6 7 8

Ethanol(g100g-1FW)

Days in storage at 20C

21%O

2%O

0.5%O

A

2

2

2

0

5

10

15

20

25

0 1 2 3 4 5 6 7 8ADH(molNADHm

in-1mg-1protein)

Days in storage at 20C

21%O

2%O

0.5%O

B

2

2

2

Fig. 1. Changes in ethanol content (A) and alcohol dehydrogenase activity (B) in

maturegreen bananafruits storedin 21%O2() , 2% O2()and0.5% O2() at 20 C.

Data represent means S.E. from three replicate samples.

3. Results

3.1. Effect of low oxygen treatments on ethanol contents and ADH

activity of mature green banana fruit

The concentrations of ethanol in mature green fruit did not

change duringstorage in2% or21% O2at20C. In contrast,the con-

centration in the0.5% O2treatmentat 20C increased 40% after one

day and even more there onwards (Fig. 1A). Accordingly, the activ-

ity of ADH in mature green fruit stored in 2% and 21% O2 at 20C

remained low throughout the entire storage period at 20C, but

in those fruit exposed to 0.5% O2at 20C, the activity significantly

increased 14 times by day 4 and 18 times by day 7, respectively

(Fig. 1B).

3.2. Changes in external appearance, surface color, firmness, SSC,

eating quality, respiration rate and ethylene production during

post-storage ripening

Until ripening was triggering, all fruit remained green with

an L*b*/a* value of 22, regardless of O2 concentration in stor-

age at 20 C. There was no visible injury or decay on any fruit.

However, weak off-flavors were detected in fruit stored in 0.5%

O2 at 20C. During post-storage ripening at 20C, control fruit

degreenedrapidlyas shown in increases ofL*b*/a* values from22

at the beginning of ripening to 7 after 4 days (Fig. 2A). In contrast,

degreening of the fruit stored in 0.5 or 2% O2 at 20

C was slower,


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-25

-20

-15

-10

-5

0

5

10

15

1 4 7

SufaceL*b*/a

*

value

Days at 20C after treatment

a a a

a

b

c

a

abb

0

1

2

3

4

5

6

7

8

1 4 7

Ripning

index


a

a

a

b b

a

b

b

a

0

20

40

60

80

100

120

1 4 7

Firmness(N)


b

a

a

a

b

a

c

b

a

0

5

10

15

20

25

30

1 4 7

SSC(%)


a a a

a

bb

a

b b

A B

C D

Fig. 2. Surface L*b*/a* value (A), ripening index (B), firmness (C) and soluble solids content in pulp (D) of bananas during post-storage ripening at 20 C. Fruits were stored

with 21% O2 (white bars), 2% O2 (shaded bars) or 0.5% O2 (black bars) for 7 days at 20C before triggering off ripening. Data represent means S.E. from three replicate

samples. Values labeled with the same letterare notdifferent at the5% level.

especially for the fruit stored in 0.5% O2at 20C (Fig. 2A). It took 7

days for those fruit stored in low O2turn to yellow (Fig. 2A).

The ripening index reflected the changes in L*b*/a* values and

revealed that the fruit stored in0.5 or 2%O2at20C ripened slowly

(Fig.2B). Thepretreatment with lowoxygen hada significant effecton banana appearance and was efficient in delaying ripening.

During post-storage ripening at 20C, control fruit softened

rapidly as shown in the decreases of values from 80N at the begin-

ning of ripening to 45 N after 4 days (Fig. 2C). In contrast, the

decreases of the fruit stored in 0.5 or 2% O2 at 20C were less,

especially for the fruit stored in 0.5% O2at 20C (Fig. 2C).

SSC in the fresh pulp was very low before ripening was ini-

tiated (Fig. 3). However, four days after initiation of ripening at

20 C, SSC rapidly increased from about 5 to over 20%. SSC continu-

ally increased slowly afterwards (Fig. 2D). Low O2storage at 20C

slowed the increase by a small margin (Fig. 2D).

After initiation of ripening with ethylene and transfer to air at

20 C, scores for flavor, sweetness and softness of the control fruit

were higher than in the low O2

stored fruit at 20C (Table 1).

The respiration rate of the control fruit was higher than for the

low O2stored fruit at 20C until they reached the climacteric peak

on day 3 of post-storage ripening at 20C (Fig. 3A). Fruit stored in

lowO2at20C hadlowerrespirationrates andreached the climac-

teric peak one daylater, with lower peak valuesin comparison withthe control fruit (Fig. 3A). The respiration rate then declined, to a

Table 1

Eating quality determined using a scale of 15 for each parameter in banana fruit

during post-storage ripening.

Parameters Daysat 20C after treatment

Day 4 Day 7

21%O2 2%O2 0.5%O2 21%O2 2%O2 0.5%O2

Flavor 3.2a 1.8b 1.6b 4.6a 3.8a 4.0a

Sweetness 3.4a 2.2b 1.6b 4.6a 4.4a 3.6b

Softness 4.0a 2.6b 1.4c 4.8a 3.8a 3.6a

Valueslabeled with thesame letterare notdifferent at the5% level.


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0

50

100

150

200

0 1 2 3 4 5 6 7 8

CO2(mg

kg-1hr-1)

Days at 20 C after treatment

21%O

2%O

0.5%O

2

2

2

0

1

2

3

4

0 1 2 3 4 5 6 7 8

C2H4(L

kg-1

hr-1)

Days at 20 C after treatment

21%O

2%O

0.5%O

2

2

2

A

B

Fig. 3. Changes in respiration rate (A) and ethylene production (B) in banana fruit

during post-storage ripening. Fruits were stored in 21% O2 (), 2% O2 (), or 0.5%

O2() for 7 daysat20 C priorto triggering offripening by ethylene.Datarepresent

meansS.E. from three replicate samples.

lower level in the control fruit than in the low O2 stored fruit at

20 C (Fig. 3A).

The ethylene production of thecontrol fruit reached the climac-

teric peak on day 3 of post-storage ripening at 20C (Fig. 3B). Fruit

stored in low O2 at 20C had lower production rates and reached

the climacteric peak with lower peak values in comparison with

the control fruit (Fig. 3B).

3.3. Ethanol contents and ADH activity during post-storage

ripening

After initiation of ripening with ethylene and transfer to air

at 20 C, the ethanol concentrations increased rapidly (Fig. 4A). In

spite of higher ethanol concentrations in the fruit stored in low O2atmospheres at 20C in green bananas, the build up during post-

storage ripening at 20C was much slower than in control fruit,

which reached 210L L1 onday 7 of ripening, fromtrace levels on

day0to30L L1 onday4at20 C (Fig.4A). Similarly, there wasan

increase in ADH activity with time during the post-storage ripen-

ing,but theincreased levels of ADHactivity persistedin banana fruit

from all treatments on return to air at 20C (Fig. 4B). In contrast to

low O2 treatments at 20C of green banana fruit, the activity was

lower in low O2 pretreated fruit than in air-stored fruit, although

differences were significant only for fruit treated under 0.5% O2at

20 C (Fig. 4B).

0

50

100

150

200

250

1 4 7

Ethanol(g100g-1FW)


a a

b

aa

a

a

b

c

0

50

100

150

1 4 7

ADH(molNADHmin-1mg-1protein)


a

b

a

b

a

a

b

b

b

A

B

Fig. 4. Changes in ethanol content (A) and alcohol dehydrogenase activity (B) in

banana fruits during post-storage ripening. Fruits were pretreated with 21% O2(whitebars), 2% O2(shaded bars) or0.5% O2 (black bars) for 7 days at 20C prior to

triggeringoff ripening by ethylene. Data represent meansS.E.from three replicate

samples. Values labeled with thesame letter arenot differentat the5% level.

3.4. Ester biosynthesis during ripening of bananas after storage

under low O2atmospheres

Until the end of the storage, ester production was almost not

detectable regardlessof O2 levelsin the storage atmosphere at20C

(Fig. 5). Four days after initiating ripening, ester production rapidly

increased and theincrease continued (Fig. 5). However, production

of esters in fruit stored in low O2 atmospheres at 20C increased

slowly in the first four days and speeded up later (Fig. 5). Ester pro-

duction and activity of related enzymes during ripening differed

according to storage conditions at 20

C. Fruit stored under low


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0

5

10

15

20

25

1 4 7

Isoamylacetate

(g100g-1FW)

a a a

a a

b

a

a

b

0

2

4

6

8

10

12

1 4 7

Isobutylacetate

(g

100g-1FW)

a

ab

b

a

b b

aa a

0

5

10

15

20

25

30

35

1 4 7

Ethylacetate(g100g-1FW)


a

b

b

ab b

a ab

C

0

10

20

30

40

50

1 4 7

AAT(unitsmg-1protein)


a

b

b

a

bb

a

bc

D

Days at 20C after treatment Days at 20C after treatment

A B

Fig. 5. Changes in isoamyl acetate (A), isobutyl acetate (B) and ethyl acetate (C) contents, and alcohol acetyltransferase activity (D) in banana fruits during post-storage

ripening. Fruitswere storedin 21% O2 (white bars),2% O2 (shaded bars) or 0.5% O2 (black bars) for 7 daysat 20C prior to triggering offripeningby ethylene. Data represent

meansS.E. from three replicate samples. Values labeled with thesame letter arenot differentat the5% level.

O2 conditions at 20C showed significantly lower ester produc-

tion during ripening (Fig. 5). AAT activity increased gradually with

storage time in all treatments, being significantly lower in the fruit

exposed to lowO2pretreatments at 20C (Fig.5D). TheAAT activity

was low before ripening and increased as ripening progressed.

4. Discussion

4.1. Low O2 directly or through ethanol accumulation inhibits

triggering of ripening in mature green bananas

Wills et al. (1982) showed that exposure of mature green

Williams bananafruit to 0.11.0% O2for 23days, prior to storage

in air, extended the time required for the fruit to ripen. Simi-

larly, Pesis et al. (2001) found that application of 3% O2 to mature

green banana fruit for 48h effectively delayed ripening. It is well-

known that storage in various CA treatments results in a general

retardation of metabolism of many fruit (Wills et al., 1982). The

retardation of ripening during storage in low O2 treatment at

20 C can be attributed directly to an effect of low O2 itself which

reduces respiration ratesand ethyleneproduction,and slows ripen-

ing metabolism. However, it is also possible that the induced

production of ethanol metabolites delays ripening. Both storage

under relatively low O2 conditions or exogenous application of

ethanolvapor in mature greenbanana fruithas beenshownto delay

ripening and decay (Yi et al., 2006). Therefore, it could be hypoth-

esized that the retardation of fruit ripening by low O2treatment at

20 C was related to levels of ethanol fermentative metabolism in

the mature green banana fruit.

Imahori et al. (1998) showed thatwhen storing ethylene treatedpre-climacteric bananas in low O2 atmospheres, ethanol accumu-

lated in the fruit and ripening was delayed. Pesis et al. (2001) also

showed that compared to 3% O2, mature green bananas exposed

to 1.8% accumulated levels of ethanol, and the fruit maintained a

better appearance and a lower decay incidence.

Exogenous application of ethanol to fruit inhibits the ripening

and extends the storage life of many climacteric and non-

climacteric fruit (Pesis, 2005). Kelly and Saltveit (1988) reported

that ethanol application inhibited color development, lycopene

production and ripening in tomato fruit. Bai et al. (2011) observed

that ethanol vapor treatment inhibited total anthocyanin accumu-

lation and softening of non-climacteric sweet cherry fruit. Bai etal.

(2004) applied ethanol to intact apples and Plotto et al. (2006)

applied it to mangoes showing that treating the intact fruit with


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Wills, R.B.H., Klieber, A., David, R., Siridhata, M., 1990. Effects of brief pre-marketing holding of bananas in nitrogen on timeto ripen. Australian Journal of Experimental Agriculture 30,579581.

Yahia, E.M.,1998. Modified and controlled atmospheres for tropical fruits. Horticul-ture Review, 123183.

Yang, X.,Song,J., Fillmore,S., Pang, X.,Zhang, Z.,2011.Effect of high temperature oncolor, chlorophyll, fluorescence and volatile biosynthesis in green-ripe bananafruit. Postharvest Biology and Technology 62, 246257.

Yi, C., Jiang,Y.M., Sun,J., Luo,Y.B., Jiang,W.B.,Macnish,A., 2006.Effectsof short-termN2 treatment on ripening of banana fruit. The Journal of Horticultural Scienceand Biotechnology 81, 10251028.

imahori 2013 postharvest biology and technology

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