Film wrapping delays ageing of `Minneola' tangelos under shelf-life conditions

Postharvest Biology and Technology 14 (1998) 107–116

Film wrapping delays ageing of ‘Minneola’ tangelos undershelf-life conditions1,2

S. D’Aquino a,*, A. Piga b, M. Agabbio b, T.G. McCollum c

a Istituto per la Fisiologia della Maturazione e della Conser6azione del Frutto delle Specie Arboree Mediterranee, CNR,Via dei Mille 48, Sassari, 07100, Italy

b Dipartimento di Scienze Ambientali e Biotecnologie Agroalimentari, Uni6ersita degli Studi di Sassari, V. le Italia 39, Sassari,07100, Italy

c Horticultural Research Laboratory, US Department of Agriculture, ARS, 2120 Camden Rd., Orlando, FL 32803, USA

Received 17 June 1997; accepted 7 April 1998

Abstract

Fruits of ‘Minneola’ tangelo (Citrus paradisi ‘Duncan’×Citrus reticulata ‘Dancy’) were dipped in water, 500 ppmsodium hypochlorite or 500 ppm imazalil and then left either unwrapped or wrapped with three plastic films ofdifferent permeabilities. The fruit were stored at 20°C and 60% relative humidity (RH) and sampled at 10-dayintervals for 1 month. Changes in characteristics of the juice (pH, titratable acidity, total soluble solids, vitamin C,acetaldehyde, ethanol, methanol and ethyl acetate), weight loss, ageing, decay, firmness, respiration, ethyleneevolution, and in-package gas composition, generally were delayed by the less permeable film. Decay caused byPenicillium digitatum was inhibited by imazalil, but not by sodium hypochlorite. An untrained test panel rated thefruits wrapped with the less permeable film the most acceptable, and the combination of this film with imazalilresulted in best overall fruit quality. © 1998 Elsevier Science B.V. All rights reserved.

Keywords: Decay; Ethylene; ‘Minneolas’; Modified atmosphere; Plastic film; Quality; Respiration; Storage; Tangelo;Volatile

1. Introduction

Although low temperature storage is of primaryimportance in postharvest technology (Harden-burg et al., 1986), the response of citrus fruits totemperature is much less substantial than that ofclimacteric fruits, such as avocados, apples, or

* Corresponding author. Tel.: +39 79 233466; fax: +39 79232047; e-mail: [email protected]

1 Trade names are used in this publication solely to providespecific information.

2 The authors contributed equally to this study.

0925-5214/98/$ - see front matter © 1998 Elsevier Science B.V. All rights reserved.

PII S0925-5214(98)00019-2

S. D ’Aquino et al. / Posthar6est Biology and Technology 14 (1998) 107–116108

pears. Citrus fruits do not undergo rapid chemicalor physical changes after removal from the tree(Ting and Attaway, 1971). El-Zeftawi (1976)found no relevant differences in total acidity,ascorbic acid or total soluble solids (TSS) in‘Valencia’ oranges stored at 5 or 15°C after 24weeks storage. Similar results have been reportedby Arras and Schirra (1988) for ‘Valencia’ or-anges stored at 2, 7 or 15°C for 12 weeks plus 1week at 20°C, and by Schirra and Chessa (1985)for ‘Tarocco’ oranges stored at 6 or 12°C for 8weeks.

Transpiration (Ben-Yehoshua, 1969; Ben-Ye-hoshua et al., 1985) and decay are the majorcauses of commercial and physiological deteriora-tion of citrus fruits, especially in areas with humidclimates, where commercial losses of 40–50%within 2 or 3 weeks from harvest can occur with-out adequate decay control measures (Brown,1988). The use of plastic films for citrus fruits canbe beneficial in maintaining fresh quality duringpostharvest storage and transportation. Filmwrapping reduces moisture loss, retards softening,and maintains characteristic freshness. But if thepermeability of the films is not appropriate, thereis the risk of off-flavour and excessive losses fromdecay (Miller and Risse, 1988). Ben-Yehoshua etal. (1979) were able to reduce decay by curingindividually sealed citrus fruits in plastic films for3 days at 36°C. D’Aquino et al. (1996), bycombining film wrapping with exposure of fruitfor 48–72 h in high humidity air, were able toreduce decay in ‘Miho’ satsumas after 24 days atroom temperature.

When citrus fruit are intended for the freshmarket, and the period from harvest to consump-tion is only a few weeks, the use of plastic filmsmight conveniently replace refrigeration. How-ever, effective control of micro-organism develop-ment needs to be achieved. Therefore, we wantedto evaluate the feasibility of substituting plasticfilms for refrigeration for 30 days under shelf-lifeconditions, using imazalil or sodium hypochloriteas fungicide treatments. For this, we used a veryperishable cultivar (‘Minneola’ tangelos) andstringent conditions (20°C and 60% RH).

2. Materials and methods

2.1. Fruit

‘Minneola’ tangelo (Citrus paradisi ‘Duncan’×Citrus reticulata ‘Dancy’) fruits were harvested thefirst week of February from the research stationof the National Council of Research (CNR) situ-ated in Oristano (Sardinia). A total of 2260 fruit(100 fruit were used for analysis at harvest) free ofvisual defects, were selected, weighed individuallyand divided into three lots of 720 fruit.

2.2. Treatments

One lot of fruit was dipped in water, the sec-ond dipped in a solution containing 500 ppm offree chlorine (commercial bleach), and the thirdin a water solution of 500 ppm imazalil (1-[2-(2,4-dichlorophenyl)-2-(2-propenyloxy)-ethyl]-1H-imidazole). Each dipping treatment was for 2min. Fruit were then allowed to dry at roomtemperature overnight and the following dayeach lot was subdivided into four sub-lots of 180fruit. One sub-lot was left unwrapped and theremaining three were sealed in polystyrene trayseach containing six fruits using three differentplastic films. Two of the films, Cryovac microp-erforated PY85 (MF) and Cryovac MR 19 mmthick (MR) (Grace Italiana, Cryovac Division,Milan) were heat-shrinkable and were applied us-ing a Minipack-R.A.S. wrapping machine. Thethird film, a 15 mm thick extensible PVC film(CX) (Coop Box, Italy), was applied manually,by stretching the film over the fruits until itsealed on the bottom of the tray. Film character-istics are reported in Table 1. A drop of siliconewas placed on the wrap to serve as a septum forrepeated gas sampling from the atmospherewithin the package.

2.3. Assessments and measurements

The fruit were placed at 20°C and 60% RH for30 days and inspected at 10-day intervals there-after. At each inspection time 60 fruits were re-moved for quality assessments.

S. D ’Aquino et al. / Posthar6est Biology and Technology 14 (1998) 107–116 109

Table 1Properties of the films used

Plastic filmProperty

Coop box CX 15 Cryovac PY 85Cryovac MR 15

15 mmThickness – –15 mm23 g/24 h m2 at 38°C and 100% 350 g/24 h m2 at 38°C and 100%Water transmission 585 g/24 h m2 at 23°C and 50%Delta RHrate Delta RHDelta RH

18 000 cm3/24 h m2 bar9500 cm3/24 h m2 bar – –O2 permeance47 000 cm3/24 h m2 barCO2 permeance – –26 500 cm3/24 h m2 bar– –– – 1.1 mmHole diameter

Number of holes/ – – – – 0.09mm2

– – – –Percentage of perfo- 8.5rated area

Composition of the atmosphere inside the pack-ages was determined on five packages containinghealthy fruits, using an analyser equipped with aninfrared detector for CO2 and a paramagneticdetector for O2 (Servomex 1450B3, O2/CO2 analy-ser). Ethylene was measured by gas chromatogra-phy (Varian 3300). Evolution of CO2 and C2H4

from unwrapped control fruit was determined bysealing ten single fruits from each fungicidal treat-ment in 1-litre jars for 1 h. Samples of 2 and 20ml of headspace gases were withdrawn for C2H4

and CO2 determination, respectively.At each inspection, the fruits were reweighed,

the number of decayed fruits recorded and thefruits rated for appearance on a scale from 1 to 5,where 5 was very fresh, 3 the limit of marketabil-ity, and 1 very old (fruit severely shrivelled). Thepercentage of marketable fruits was quantified asthe percent of fruits rated as 3, 4 or 5.

Firmness, expressed as deformation of thetransverse axis of non-peeled and peeled fruits,was determined by the use of a device developedin our laboratory. The basic components are ahollowed parallelepiped, whose weight can bevaried by adding sand in the cavity, a verticalruler, and a base. Deformation was measured asthe difference between the readings of the trans-verse diameter of the fruit measured before andafter applying the parallelepiped for 5 s; the paral-lelepiped weighed 1 kg.

Three replications of ten fruits for each treat-ment were juiced and the juice centrifuged for 3

min at 2000×g. Total soluble solid (TSS) and pHwere measured in the juice with a hand refrac-tometer and pH-meter, respectively. A total of 10ml of juice was titrated against 0.1 N NaOH tothe end point (8.2), and titratable acidity calcu-lated in terms of citric acid. Vitamin C content ofthe juice was determined by the indophenol titra-tion method (Ting and Rouseff, 1986). A maturityindex was calculated as the °Brix/titratable acidityratio.

Acetaldehyde, ethanol, methanol and ethyl ac-etate were measured as reported by Davis andChace (1969). Samples of 10 ml of juice wereplaced in 50-ml tubes and incubated for 20 min ina shaking bath (100 shakes/min) at 30°C; a 2-mlgas sample was withdrawn from the headspaceand injected into a Varian 3300 GC fitted with a2 m×2 mm glass column packed with 6.6%Carbowax 20M on 80/120 Carbograph 1 AW(run conditions were: N2 carrier gas at 20 mlmin−1, injector at 110°C, oven temperature 80°C,detector at 200°C). Volatiles were identified andquantified by comparison of retention times andpeak areas with those of external standards.

Twenty fruits from either wrapped or non-wrapped control treatments were peeled and di-vided into segments for sensory quality evaluationby seven untrained panellists. Sweetness, acidity,off-flavour and overall preference were rated us-ing a scale ranging from 1 to 9, according to theintensity of the attributes.


2.4. Statistical analysis

The experiment was designed as a 4 (storageperiods)×4 (films)×3 (fungicides) factorial ar-rangement of treatments in a complete ran-domised block design. However, for CO2 andC2H4 production of non-wrapped fruit the designwas a 4 (storage periods)×3 (fungicides) com-pletely randomised arrangement. A 4 (storage pe-riods)×4 (films) factorial randomised blockdesign was used for deformation and sensoryevaluation (previous experiments showed that nosensory differences could be detected among thedifferent kinds of fungicides used). Comparisonsamong the means are expressed as LSDs.

3. Results and discussion

3.1. In-package atmospheres

The in-package CO2 and O2 concentrationswere significantly influenced by the storage pe-riod, the fungicide treatment and the film wrap-ping (Table 2). In particular, fruit treated withchlorine had average in-package CO2 and O2 con-centrations of 3.9 and 17%, respectively, against3.3 and 17.9% for untreated control fruit, and 3.4and 17.4% for imazalil-treated fruits (data notshown). Composition of the atmosphere inside thepackages wrapped with the MF film changed verylittle during storage and was similar to air, whilethe concentrations of in-package CO2 decreased(Fig. 1A) and O2 increased (Fig. 1B), for CX andMR film by the 2nd day of storage.

The in-package C2H4 concentration did notchange very much in packages wrapped with MFand CX films, while a progressive increase wasdetected with MR film (Fig. 1C).

3.2. Respiration acti6ity and ethylene production

There was a significant interaction betweenstorage period and respiration activity of non-wrapped fruit (Table 2). Both CO2 and C2H4

production increased from harvest to the end ofstorage, with the exception of the first 10 days,

when C2H4 production was not different fromthat at harvest (Fig. 2). There was also a signifi-cant influence of the fungicide treatment on bothCO2 and C2H4 production, which was generallyhigher in chlorine-treated fruit than in controluntreated or imazalil-treated fruit (Fig. 2).

3.3. Internal quality

The factors which most contributed to changesin internal quality were the storage period and the

Fig. 1. Influence of the used films on the in-package concentra-tion of carbon dioxide (A), oxygen (B), and ethylene (C) of‘Minneola’ tangelos, held at 20°C and 60% relative humidity,at 2, 10, 20 or 30 days after wrapping. Vertical bars representthe standard errors.


Table 2Analysis of variance of respiration rate (ml CO2 kg−1 h−1), ethylene production (m l C2H4 kg−1 h−1), in-package CO2 (%), O2 (%),and C2H4 (ppm) of ‘Minneola’ tangelos held 30 days at 20°C and 60% RH

ANOVA summary

Respiration rate EthyleneSource In-package CO2 In-package O2 In-package C2H4

production

Mean df Mean dfdf Mean Meandf df Meansquare squaresquare squaresquare

Storage period (P) 3 382*** 3 1.54*** 3 7.56*** 3 56.6*** 3 0.24 NS25*** 2 0.12 NS 2 6.33***2 2Fungicide (F) 11.26** 2 0.53**

— — — 2 897***Film (W) 2— 1287*** 2 4.98***6.9* 6 0.06 NS 6 0.13 NS6 6P×F 0.62 NS 6 0.05 NS

P×W —— — — 6 3.27*** 6 2.69 NS 6 0.46***— — — 4 2.99***— 4F×W 9.75** 4 0.18 NS

3.0 63 0.07 156 0.50 156 2.14 156 0.10Error 63

Significant at *PB0.05, **PB0.01, or ***PB0.001, respectively; NS, non-significant; df, degrees of freedom.

film wrapping, while there was no effect of thefungicide treatment (Table 3). These changes didnot negatively affect internal quality, with theexception of the content of vitamin C which de-creased progressively from harvest to the end ofthe 30-day storage period (Table 3). The juice ofthe fruits wrapped with the MR film had thehighest loss of TA and largest increase in pH(Table 3). TSS underwent few changes duringstorage, although wrapped fruits always had thelowest values. The maturity index increasedsharply from harvest to the first inspection time,but then changed little, and in general was higherin MR-wrapped fruits. Other researchers havereported either beneficial or no effects in main-taining TA by modified atmosphere for othercitrus fruits (Ben-Yehoshua et al., 1979; Goriniand Testoni, 1988). Our data indicate, as a gen-eral trend, that high CO2 and low O2 concentra-tion inside the packages leads to a faster decreasein TA. However, the differences in TA and pH ofthe juice for the different treatments may be duein part to less weight loss of fruits wrapped inMR film. At the end of the trial, the non-wrappedfruits lost almost 14% of their initial weight, asagainst 1% for those sealed with MR film, andthis might result in concentration of the TA in thejuice of the non-wrapped fruits. Juice volatiles

were affected mainly by the storage period andthe film wrapping (Table 4).

The levels of acetaldehyde declined during stor-age for all treatments after the first 10 days ofstorage, with the exception of fruits wrapped withMR film (Table 4); after 20 days, acetaldehyde inthe juice of non-wrapped and MR-wrapped fruitwas significantly higher than in the juice of MF-and CX-wrapped fruit (data not shown), and at30 days for all the treatments it dropped to thesame values as at harvest (Table 4). An increase inethanol content was detected only after the 2ndweek of storage, and the only factor which con-tributed to ethanol changes was the storage pe-riod (Table 4). Methanol had a progressive andsignificant rise from harvest to the end of thestorage period, although the differences amongthe different plastic films were significant onlyafter the 2nd week of storage, and in particular,the highest values were detected in non-wrappedfruit, followed by the MR-wrapped fruit, whileMF and CX fruits had the lowest levels (Table 4).With the exception of the first inspection time,when no significant differences were found amongthe treatments, ethyl acetate was always higher inthe juice of MR-wrapped fruits (Table 4).

As a general trend, the non-wrapped and MRfruits had the highest increase in volatiles in the


juice during the storage period. This can be ex-plained by lower permeability to gases of the peel(non-wrapped fruit) or of peel plus film (MR-wrapped fruits). Probably in MF- and CX-wrapped fruit, the films, which had no oppositionto gas movement in the case of MF film, or a veryhigh permeability to gases in the case of CX film,reduced weight loss and desiccation of the peel,but did not alter the permeability of the pericarptissues. McDonald et al. (1993) reported a de-crease in gas permeability in ‘Marsh’ grapefruitafter 4 weeks of storage. The changes in volatilecontent that we have observed were similar to, orin the same range as, those reported by otherauthors for other citrus fruits (Schirra andChessa, 1988; Pesis and Avissar, 1989; Nisperos-Carriedo et al., 1990).

3.4. Sensory analysis

The results of the sensory analysis are reportedin Table 5. During storage, the loss of acidity

made the fruit more acceptable, especially forthose wrapped in MR film. However the positiveeffect of the decreased acidity was counteractedby an increased soft consistency of the segments,rapid senescence and build up of off-flavour innon-wrapped fruit and those wrapped in MF film.This led the panellists to prefer the fruit wrappedin CX and MR film over the storage period.

3.5. Decay

Decay, principally caused by Penicillin digi-tatum (data not shown), was not significantlyinfluenced by the storage period (Table 6), sug-gesting that the incidence of decayed fruit wasmainly caused by preharvest infection.

The effect of the fungicide treatment was im-portant in determining the fruit decay. The treat-ment with chlorine helped micro-organismgrowth, probably by weakening the peel tissues.Imazalil was effective in inhibiting the develop-ment of decay. Fruits wrapped with MR film hadthe highest losses, followed by those wrapped inCX film, although in this last case there were nosignificant differences between fruit wrapped inMR film and non-wrapped fruits. However, fruitstreated with imazalil, either wrapped or non-wrapped, showed no decay (data not shown).

3.6. Weight loss, o6erall appearance andmarketable fruits

All factors had a significant influence on weightloss, overall appearance and percentage of mar-ketable fruits (Table 6). The most striking effectof the film wrapping was reducing ageing andweight loss, with respect to non-wrapped fruits;the lower the permeability to water vapour thehigher the positive influence of the films. Thus,fruits wrapped in MR film appeared almost asfresh and sound after 1 month of storage at 20°Cas they were at harvest, and the weight losses wereonly about 1%, as against 14% of the non-wrapped fruits (data not shown). The influence ofthe other two films on weight loss and overallappearance was intermediate, with the response ofthe MF film more similar to that of the non-wrapped fruits. Responses to the CX and MR

Fig. 2. Effect of fungicide treatments on respiration (A) andethylene production (B) of ‘Minneola’ tangelos at harvest andafter 10, 20 and 30 days of storage at 20°C and 60% RH.Vertical bars represent the standard errors.


Tab

le3

Eff

ect

offil

mw

rapp

ing

onch

emic

alpa

ram

eter

sof

‘Min

neol

a’ta

ngel

osaf

ter

10,

20an

d30

days

ofst

orag

eat

20°C

and

60%

RH

TSS

(°B

rix)

Mat

urit

yin

dex

(TSS

/tit

rata

ble

acid

ity)

Vit

amin

C(m

g/10

0m

l)T

ime

inst

orag

epH

Tit

rata

ble

acid

ity

(%ci

tric

acid

)6.

5134

.53.

011.

7311

.26

Har

vest

10D

ays

7.42

a33

.6a

3.10

a1.

63a

Con

trol

12.1

5a

7.39

a33

.0a

3.12

b1.

61a

11.8

8aM

Pfil

m33

.2a

1.61

a7.

43a

3.10

a11

.89a

CX

film

7.71

a33

.1a

3.12

b1.

55a

11.9

6aM

Rfil

m

30D

ays

11.9

1c7.

48a

30.1

aC

ontr

ol3.

17a

1.59

d

30.3

a11

.71a

7.55

a1.

55b

MP

film

3.17

a

11.8

2bc

7.54

a30

.5a

CX

film

3.18

a1.

57c

29.6

a1.

51a

7.81

bM

Rfil

m11

.76a

b3.

30b

AN

OV

Asu

mm

ary

dfSo

urce

Mea

nsq

uare

s 0.25

7**

3.24

***

10.4

***

34.4

***

Stor

age

peri

od3

0.24

1**

(P)

0.01

8N

S0.

139

NS

2.73

NS

Fun

gici

de(F

)2

0.00

2N

S0.

005

NS

3.40

*0.

186*

*0.

95**

*0.

04**

*W

rapp

ing

(W)

0.02

***

30.

009

NS

0.09

4N

S1.

38N

S0.

001

NS

P×

F0.

003

NS

62.

98*

0.03

2N

S0.

185

NS

P×

W0.

008

NS

90.

01**

*0.

059

NS

61.

30N

S0.

01**

*0.

002

NS

0.09

2*F

×W

114

0.10

11.

210.

002

0.00

6E

rror

0.03

3

Mea

nsin

colu

mns

for

each

stor

age

peri

odfo

llow

edby

the

sam

ele

tter

are

not

sign

ifica

ntly

diff

eren

tat

the

5%le

vel

byth

eL

SDm

ulti

ple

rang

ete

st.

df,

degr

ees

offr

eedo

m.

Sign

ifica

ntat

*PB

0.05

,**

PB

0.01

,or

***PB

0.00

1;N

S,no

n-si

gnifi

cant

.


Table 4Effect of film wrapping on juice volatile content of ‘Minneola’ tangelos after 10, 20 and 30 days of storage at 20°C and 60% RH

Acetaldehyde (ppm) Ethanol (ppm) Methanol (ppm) Ethyl acetate (ppm)Time in storage

5.0 46.29 38.19Harvest 0.21

10 Days3.5a 46.17aControl 64.00a 0.35a

3.8a 45.66a 50.44aMP film 0.31a

CX film 3.3a 50.75a 47.27a 0.19a

6.1b 46.96a 78.37a 0.32aMR film

30 Days5.9a 71.57a 146.01cControl 0.38a

MP film 3.5a 44.24a 95.39a 0.40a

4.8a 83.04a 91.62aCX film 0.47a

MR film 5.4a 53.50a 110.37b 1.40b

ANOVA summary

Mean squaresSource df

0.123* 39663*** 2897**Storage period (P) 0.962**30.118 NS 774 NS2 2262*Fungicide (F) 0.461 NS0.234** 3250 NS 1199 NSWrapping (W) 1.45***30.024 NS 875 NS6 456 NSP×F 0.124 NS0.067 NS 2890 NSP×W 896 NS9 0.83***0.036 NS 2216 NS6 517 NSF×W 0.094 NS

114Error 0.041 1438 666 0.208

Means in column followed by the same letter for each storage period are not significantly different at the 5% level by the LSD test.Significant at *PB0.05, **PB0.01, or ***PB0.001, respectively; NS, non-significant; df, degrees of freedom.

films were very similar. The positive effect of filmwrapping is also shown by the amount of mar-ketable fruit, which after 30 days storage washigher than 80% for fruit wrapped in CX and MRfilms, but only 47 and 17%, respectively for fruitswrapped with MF film or non-wrapped (data notshown). Moreover, the percentage of marketablefruits was 100% for those treated with imazaliland wrapped in MR and CX films. Miller andMcDonald (1989) and Chun et al. (1990) havereported similar results with individually wrapped‘Minneola’ tangelos.

3.7. Firmness

Deformation of entire fruits, which was 1.35mm at harvest, in non-wrapped fruits increaseduntil the 2nd week of storage (8.41 mm) thendecreased (5.6 mm at the end of storage), proba-

bly due to the leathery consistency of the peelcaused by the excessive weight loss. In wrappedfruit there was a progressive increase in deforma-tion, and at 30 days it was 5.5, 4.3, and 1.8 mm inMF-, CX-, and MR-wrapped fruits, respectively.Deformation of peeled fruit (4.3 mm at harvest)increased over the storage period and at 30 dayswas 11.2, 9.5, 8.2, and 5.1 mm in control non-wrapped fruits and in MF-, CX-, and MR-wrapped fruits, respectively. Reduction ofsoftening in oranges, grapefruits and lemonssealed in HDPE film is reported by other authors(Ben-Yehoshua et al., 1979).

4. Conclusion

Film wrapping can delay ageing of fruits evenin non-refrigerated conditions, but can also be


Table 5Effect of film wrapping on sensory evaluation of ‘Minneola’ tangelos after 10, 20 and 30 days of storage at 20°C and 60% relativehumidity

AcidityTime in storage Off-flavourSweetness Overall preference

9.4Harvest 1.15.6 4.8

30 Days7.7cControl 1.4a5.42a 4.3a

7.6bc 1.6a5.7ab 4.7aMP film7.2abCX film 1.9a6.4ab 7.1b

6.9a 1.4a6.7b 7.7bMR film

Fruits evaluated subjectively for sweetness, acidity, off-flavour and overall preference on a scale based on the intensity of theattributes and ranging from 1 to 10.Means in columns for each storage period followed by the same letter are not significantly different at the 5% level.

detrimental in preserving internal quality whenanaerobic conditions occur and high RH pro-motes micro-organism development. In our condi-tions, wrapping had an overall beneficial effectnot only in maintaining the quality of the fruit,but also in improving their sensory attributes; infact the panellists scored CX- and MR-wrappedfruit at the end of the trial better than they did atharvest. At 30 days the appearance of the fruitwrapped in MR film was as fresh as at harvest,and fruit quality could have been maintained forlonger than 1 month. The modified compositionof the in-package atmosphere did not negativelyaffect the flavour and anaerobiosis did not occur.However, no positive effect on the incidence ofdecay, was found from the modified atmosphere

as observed for other species. On the contrary, thehighest losses were detected in fruit wrapped inCX and MR films. Imazalil (500 ppm) was veryeffective in inhibiting micro-organism develop-ment. The response to chlorine was disappointing,because there was no reduction in decay and thefruit aged more rapidly. The results obtained en-courage extending the use of film wrapping ofcitrus fruits for the fresh market. It would beworth testing plastic films less permeable to gases,which should create an in-package atmospherewith elevated levels of CO2 and reduced concen-trations of O2 at the threshold of anaerobic respi-ration, thus avoiding conversion of pyruvate toacetaldehyde and ethanol, while, at the same time,reducing pathogen growth.

Table 6Analysis of variance of decay incidence, overall appearance, marketable fruit and weight loss of ‘Minneola’ tangelos held at 30 daysat 20°C and 60% RH

Decay Overall appearance Marketable fruit Weight lossSource

df Mean square dfdf Mean square Mean squaredf Mean square

11 633*** 2Storage period (P) 2 5.92 NS 3 25.6*** 3879***321720***Fungicide (F) 8***2 2609*** 2 0.12*

3 8700*** 3Wrapping (W) 951***3 61.5* 3 23.5***329*** 4P×F 4 17.6 NS 6 0.46*** 6 6.70*

62789***P×W 428***6 924.5 NS 9 3.14***6 110* 6 21***F×W 6 35.1 NS 6 0.10*

45 1776Error 84 18.1 114 0.043 2.19114

df, degrees of freedom.Significant at *PB0.05, or ***PB0.001, respectively; NS, non-significant.


Acknowledgements

This research was supported in part by ‘Pro-getto speciale INC Agro-Industria — Migliora-mento della qualita dei prodotti agroalimentari’,National Research Council of Italy. The authorswish to thank Dr L. Garavaglia from Grace Ital-iana (Cryovac Division, Milan Italy) and DrsTorrisi and Coniglione (Elf Atochem Agri, Bel-passo, CT) for providing the heat-shrinkable filmsand imazalil, respectively.

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Film wrapping delays ageing of `Minneola' tangelos under shelf-life conditions