combined effects of hot water treatment (hwt) and modified atmosphere packaging (map) on quality of...

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INTRODUCTION Modified atmosphere packaging (MAP) in combi- nation with low temperature storage is a promis- ing and inexpensive way to improve the shelf life of fresh fruits and vegetables. 1–3 Packaging of fresh fruits and vegetables with plastic films results in the creation of a modified atmosphere that has higher levels of CO 2 and water vapor and a lower level of O 2 than ambient levels due to the respira- tion of and moisture loss from the commodity. 4 By using an appropriate film and an appropriate storage temperature, the ratio of carbon dioxide (CO 2 ) to oxygen (O 2 ) will continuously adjust itself by the interaction of the fruit respiration and gas diffusion through the packaging film. A reduced level of O 2 or elevated level of CO 2 inside the package can reduce respiration and ethylene pro- duction rate, delay ripening, retard softening, and slow down various compositional changes associ- ated with ripening. However, exposure of fresh fruits or vegetables to levels above their CO 2 tol- erance limits may cause physiological damage, and exposure to levels below their O 2 tolerance PACKAGING TECHNOLOGY AND SCIENCE Packag. Technol. Sci. 2003; 16: 171–178 DOI:10.1002/pts.626 Combined Effects of Hot Water Treatment (HWT) and Modified Atmosphere Packaging (MAP) on Quality of Tomatoes By Suparlan* and Kazuhiko ITOH Graduate School of Agricultural Science, Hokkaido University, Kita 9, Nishi 9, Kita-ku, Sapporo 060-8589, Japan. Effects of hot water treatment (HWT) and modified atmosphere packaging (MAP) on quality of tomatoes were studied. Prior to packaging with low-density polyethylene (LDPE) film (0.02 mm in thickness), tomatoes were immersed in hot water (42.5°C) for 30min. Control tomatoes were not treated and were stored for 2 weeks at 10°C and then for 3 days at 20°C without packaging. Steady states of O 2 and CO 2 concentrations inside the package were about 5 and 8%, respectively, and were reached after 6 and 4 days of storage, respectively. MAP reduced weight loss of tomatoes to about 41% of that of unpackaged fruit during a 2-week storage period. The use of a combination of HWT and MAP reduced weight loss and decay, inhibited color development and maintained firmness of tomatoes but had no effect on soluble solids content or titratable acidity. HWT slightly reduced mold growth of tomatoes stored in MAP. Packaging of control fruit in MAP resulted in stimulation of mold growth around the stem end of the fruit after about 1 week of storage and also resulted in cracking and decay. HWT could be used as disinfectant for tomatoes prior to storage in MAP in order to reduce microbial growth, cracking and decay that may be caused by excessive water vapor inside the package. Copyright © 2003 John Wiley & Sons, Ltd. Received 11 April 2003; Revised 11 July 2003; Accepted 26 July 2003 KEY WORDS: hot water treatment; packaging; weight loss; decay; mold growth * Correspondence to: Suparlan, Graduate School of Agricultural Science, Hokkaido University, Kita 9, Nishi 9, Kita-ku, Sapporo 060-8589, Japan. Tel: +81-11-706-2558; Fax: +81-11-706-3886. Email: [email protected] Copyright © 2003 John Wiley & Sons, Ltd.

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INTRODUCTION

Modified atmosphere packaging (MAP) in combi-nation with low temperature storage is a promis-ing and inexpensive way to improve the shelf lifeof fresh fruits and vegetables.1–3 Packaging of freshfruits and vegetables with plastic films results inthe creation of a modified atmosphere that hashigher levels of CO2 and water vapor and a lowerlevel of O2 than ambient levels due to the respira-tion of and moisture loss from the commodity.4 Byusing an appropriate film and an appropriate

storage temperature, the ratio of carbon dioxide(CO2) to oxygen (O2) will continuously adjust itselfby the interaction of the fruit respiration and gasdiffusion through the packaging film. A reducedlevel of O2 or elevated level of CO2 inside thepackage can reduce respiration and ethylene pro-duction rate, delay ripening, retard softening, andslow down various compositional changes associ-ated with ripening. However, exposure of freshfruits or vegetables to levels above their CO2 tol-erance limits may cause physiological damage,and exposure to levels below their O2 tolerance

PACKAGING TECHNOLOGY AND SCIENCEPackag. Technol. Sci. 2003; 16: 171–178DOI:10.1002/pts.626

Combined Effects of Hot Water Treatment(HWT) and Modified Atmosphere Packaging(MAP) on Quality of Tomatoes

By Suparlan* and Kazuhiko ITOHGraduate School of Agricultural Science, Hokkaido University, Kita 9, Nishi 9, Kita-ku, Sapporo 060-8589, Japan.

Effects of hot water treatment (HWT) and modified atmosphere packaging (MAP)on quality of tomatoes were studied. Prior to packaging with low-densitypolyethylene (LDPE) film (0.02mm in thickness), tomatoes were immersed in hotwater (42.5°C) for 30min. Control tomatoes were not treated and were stored for 2weeks at 10°C and then for 3 days at 20°C without packaging. Steady states of O2

and CO2 concentrations inside the package were about 5 and 8%, respectively, andwere reached after 6 and 4 days of storage, respectively. MAP reduced weight lossof tomatoes to about 41% of that of unpackaged fruit during a 2-week storageperiod. The use of a combination of HWT and MAP reduced weight loss and decay,inhibited color development and maintained firmness of tomatoes but had no effecton soluble solids content or titratable acidity. HWT slightly reduced mold growthof tomatoes stored in MAP. Packaging of control fruit in MAP resulted instimulation of mold growth around the stem end of the fruit after about 1 week ofstorage and also resulted in cracking and decay. HWT could be used as disinfectantfor tomatoes prior to storage in MAP in order to reduce microbial growth, crackingand decay that may be caused by excessive water vapor inside the package.Copyright © 2003 John Wiley & Sons, Ltd.Received 11 April 2003; Revised 11 July 2003; Accepted 26 July 2003

KEY WORDS: hot water treatment; packaging; weight loss; decay; mold growth

* Correspondence to: Suparlan, Graduate School of Agricultural Science, Hokkaido University, Kita 9, Nishi 9, Kita-ku, Sapporo060-8589, Japan. Tel: +81-11-706-2558; Fax: +81-11-706-3886.Email: [email protected]

Copyright © 2003 John Wiley & Sons, Ltd.

limits may increase anaerobic respiration and thedevelopment of off-flavors due to accumulation ofethanol and acetaldehyde.1

In addition, since the plastic film acts as barrierto movement of water favor and helps to maintaina high level of relative humidity (RH), the weightloss of fresh produce kept in MAP is reduced.However, maintenance of an excessively high levelof RH inside the package can result in moisturecondensation on the commodity, thus creating con-ditions favorable for pathogen growth and increas-ing the risk of fruit decay.2,5 For this reason,fungicidal treatment of packaged fruits and veg-etables is important. Ben-Yehoshua6 reported thatif film-wrapped fruits are not treated with appro-priate fungicides the incidence of decay to be high.However, there are various restrictions and banson the use of chemical treatment in post-harvesthandling of fruits and vegetables. Therefore, theinterest in the use of non-chemical treatment suchas heat treatment to control insect pest, preventfungal rots and affect the ripening becomesincrease during the past few years.7

Heat treatment has been used as a disinfestationtreatment for fruits and vegetables and also forincreasing the resistance of fruit to chilling injuryin low temperature storage.8–10 In addition, MAPhas been effective in reducing chilling injurysymptoms in chilling-sensitive crops such as avocados,11 cucumbers,12 and mangos.4 Moreover,D’Aquino et al.13 reported that the combination offilm wrapping with imazalil reduced weight lossand the severity of chilling injury of ‘Nova’ tangelofruit during cold storage. Therefore, the aim of thisstudy was to determine the effectiveness of a com-bination of hot water treatment and MAP forreduction of mold growth and for maintenance ofquality of tomato fruit during storage.

MATERIALS AND METHODS

Tomatoes

‘Maru’ tomatoes (Lycopersicon esculentum, Mill.)that had been grown in a greenhouse and directlypurchased from a commercial grower in Chitose,Hokkaido were used in this experiment. The toma-toes were hand-harvested from July to Novemberin 2002 at the breaker stage of maturity with a

mean a*/b* ratio of -0.23. The average weight ofthe tomatoes was 139.4 ± 33.6g. Tomatoes ofuniform shapes and sizes and free from damageand fungal infection were selected. The averagedensity of the tomatoes was about 0.995 ± 0.004kg.dm-3. Tomato samples were divided into threegroups: the first group treated with hot water andpackaged with polyethylene film, the secondgroup not treated and packaged with polyethylenefilm and the third group not treated and not pack-aged with polyethylene film.

Packaging film

Low-density polyethylene (LDPE) plastic film of0.02mm in thickness was used to package the fruit.The rate of permeation of O2 and CO2 through thefilm at 10°C were 197.2 and 650.6mLmil.m-2 h-1

atm-1, respectively.

Hot water treatment (HWT)

The HWT was conducted by submerging the fruitinto a water bath (T22S Thomas Kagaku Co., Ltd.)at a temperature of 42.5°C for 30min. These con-ditions were based on the results of preliminaryexperiments showing that this was the optimalcombination of temperature and exposure time ofHWT to prevent damage to the fruit. After treat-ment, the tomatoes were immediately cooled withtap water (23 ± 0.5°C) for about 20min and thencleaned with tissue paper.

Packaging and storage conditions

Packaging of tomato samples was conducted byplacing the tomatoes into the square acrylic boxesthat its one upper side was opened. This open sidewas then covered with plastic film and equippedwith a silicone rubber septum for gas analysis.Film areas of the packages ranged from 0.01 to 0.02m2 and free volume of the packages rangedfrom 1050 to 2400mL. Each package containedabout 230–550 grams of tomatoes depending onthe space volume of the package. Each package was stored in an incubator at a temperature of 10°C for 2 weeks. The package was then opened,

SUPARLAN AND K. ITOHPackaging Technologyand Science

Copyright © 2003 John Wiley & Sons, Ltd. 172 Packag. Technol. Sci. 2003; 16, 171–178

and the fruit was transferred to a room with thetemperature set at 20°C for 3 days to allow subse-quent ripening. After the subsequent ripening, thetomatoes were examined for color, weight loss,soluble solid content, firmness, and decay or moldgrowth.

During the period of storage at 10°C, concentra-tions of gases such as O2, CO2 and ethylene insideeach package were monitored using gas chro-matography. The O2 and CO2 concentrations weredetermined by measuring the headspace gas con-centrations of each package. A 2.0-mL gas samplewas withdrawn from each package through therubber sampling port using a gas-tight syringe.Analyses were performed on a gas chromatograph(Shimadzu, GC-14B) with a thermal conductivitydetector (TCD) maintained at 50°C. Gas chromato-graph equipped with a stainless steel column(WG-100 SUS O.D. 1/4≤ dia. ¥ 1.8m) at tempera-ture of 50°C. The carrier gas was helium at flowrate of 33mL/min. Ethylene (C2H4) productionwas measured by using a procedure similar to thatused for measurement of O2 and CO2 concentra-tions by using a gas chromatograph fitted with aflame ionization detector (FID) maintained at100°C and equipped with stainless steel columnfilled with activa alumina (30/60 mesh, SUS col. 3dia. ¥ 4m). The temperature of the column wasmaintained at 70°C, and helium was used as thecarrier gas at flow rate of 55mL/min.

Quality analysis

Quality characteristics of the tomatoes such asweight loss, color, firmness, and SSC were ana-lyzed before packaging, at the end of MAP, andafter the subsequent 3-day period without packaging.

Surface color of each tomato was measured at 4points on the shoulder, at one point near theblossom end and at one point near the stem end.Color was measured with a reflectance colorime-ter (Chroma Meter CR-200, Minolta Corp.) usingthe L* a* b* color system, where L* indicates light-ness on a scale of 0 (= black) to 100 (= white), a*indicates green (-) to red (+), and b* indicates blue(-) to yellow (+). The color of each tomato wasexpressed as the ratio a*/b*. The reported valuesrepresented the average of 12 samples for eachgroup.

Firmness was measured using a rheo meter(NRM-2002J, Fudoh Kogyo Co., Ltd.) connected toa computer. Firmness was measured at 4 points onthe shoulder of each of 6 tomatoes from each groupby applying a plunger of 3mm in diameter. Theamount of force (kg.f) required to compress theradial pericarp surface of each tomato at a constantspeed of 30cm/min was recorded. The firmnessvalue of the fruit was expressed as force per unitarea (MPa). The reported values represented theaverage of six samples with four measurementsper sample.

The soluble solids content of the fruit was measured using a digital refractometer (PR-100).Each whole tomato was sliced in half. Each halfwas further divided into 3 parts, so there were 6parts (replications) for each measurement per fruit.The juice from each part was extracted manually(>2 drops) and put into the refractometer. Thevalue of soluble solids content was expressed as %Brix. The reported values represented theaverage of six samples with six measurements persample.

Titratable acidity (TA) was determined using the AOAC method. About 100 grams of tomatosample was liquefied in an osterizer blender. TenmL of liquid sample was mixed with 90mL of dis-tilled water, and then about 0.3mL of an indicatorsolution was added. TA was determined by titrat-ing liquid samples with 0.1M NaOH until a pinkcolor that did not change had developed. TA wasexpressed as % of citric acid. The reported valuesrepresented the average of six samples for eachgroup.

Microbial count (mold and yeast) was deter-mined by the general procedure. Each tomato wasweighed, and then mixed with about 200mL ofsterile 0.85% sodium chloride solution in a sterilepolyethylene bag and homogenized with a stomacher for 2min at high speed. Then wash fluid was serially diluted, and 1mL of dilution was mixed with approximately 15mL of eachmedium, consisting of YM agar (Difco) plus 0.1g/L of chloramphenicol (Wako, Osaka, Japan),and incubated at 25°C for 3–5 days. Microbialanalysis was performed after 2 weeks of storage inMAP. All samples were prepared in duplicate, andeach microbial count was the mean of three pack-ages. Microbial counts were expressed as logcolony-forming units per gram of sample (log10

CFU/g).

Copyright © 2003 John Wiley & Sons, Ltd. 173 Packag. Technol. Sci. 2003; 16, 171–178

MODIFIED ATMOSPHERE PACKAGING OF TOMATO Packaging Technologyand Science

Statistical analysis

The effects of the combination of HWT and MAPon the quality characteristics of tomatoes (weightloss, surface color, firmness, SSC, TA, and moldcount) were assessed using analysis of variance(ANOVA), and mean values (n = 6) of variable datawere compared using the least significant differ-ence (LSD) test at the 5% level of significance.

RESULTS AND DISCUSSION

Changes in gas concentrations withinthe package and C2H4 production

Tomatoes packed with LDPE film showed a mod-ification of internal atmosphere, the concentrationof O2 decreasing rapidly and that of CO2 increas-ing rapidly, during the first few days of storage(Fig. 1). The patterns of change in gas concen-trations within the packages were similar for both treated and untreated tomatoes, though thechanges within the packages of treated tomatoeswere slightly faster than those within the packagesof untreated tomatoes. Steady states of O2 and CO2

concentrations were reached after 6 and 4 days ofstorage, and equilibrium concentrations of O2 andCO2 were about 5% and 8%, respectively. However,based on our preliminary results indicated that

equilibrium times and steady states of O2 concen-tration inside the packages were affected by theratios between weight of fruit, internal free volumeand permeable surface area as shown in Fig. 2. Thehigher the ratio between film surface area andweight of fruit was, the higher the steady-state O2

concentration inside the package.The CO2 concentration increased to about 8% in

4 days, remained at that level for 3 days, and thendecreased to about 5%. The decrease in CO2 con-centration may have been caused by an excessivelyhigh level of relative humidity inside the package,which could cause dissolution of CO2 in waterbecause CO2 has high solubility in water.14 The sol-ubility of CO2 is highly dependent on temperature.Moreover, at the steady-state concentration of CO2,the concentration of O2 was low (about 6%), a con-dition in which the respiration process of tomatoeswould be inhibited and the evolution rate of CO2

would thus decrease. Therefore, the productionrate of CO2 was lower than the rate of permeationof CO2 through the film. Henig and Gilbert15

reported that the respiration rate of tomato fruitwas constant when the O2 concentration inside thepackage ranged from 21–12.08% but that the res-piration rate decreased linearly with the slope of1.815 cc.kg-1.h-1 %O2 when the concentration of O2

decreased to below 12%.Ethylene concentration inside the packages

increased with storage time for both treated anduntreated tomatoes (Fig. 3). The rates of ethyleneproduction inside the packages of hot water-

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Copyright © 2003 John Wiley & Sons, Ltd. 174 Packag. Technol. Sci. 2003; 16, 171–178

0

5

10

15

20

25

0 3 6 9 12 15Duration of storage

Con

cent

ratio

ns o

f ga

sses

(%

)

CO2 (Control) O2 (Control)

CO2 (HWT) O2 (HWT)

Figure 1. Changes in O2 and CO2 concentrations intomatoes packaged at 10°C.Weights of tomatoes per

package: 0.231kg (control) and 0.239kg (HWT). Packagearea: 0.01m2. Free volumes: 817.8mL (control) and

809.8mL (HWT).

0369

1215182124

0 2 4 6 8 10 12 14 16

Duration of storage (days)

O2 c

once

ntra

tion

s (%

) 0.04290.0350

0.04400.0228

0.0213

Figure 2. Effect of the ratio of film surface area andweight of fruit (m2/kg) on steady-state O2 concentrations

inside the package.

treated tomatoes were slightly higher than thoseinside the packages of untreated tomatoes. Themaximum concentrations inside the packages oftreated and untreated tomatoes, which werereached after 4 days of storage, were 28.4ppm and 23.1ppm, respectively. The concentrationsdecreased to about 13.3ppm and 14.6ppm, respec-tively, at the end of the storage period. Thedecrease in the amount of ethylene produced maybe correlated with the reduction in respiration ratedue to the decrease in O2 concentration inside thepackage. As stated above, the O2 concentrationinside the package had decreased to less than 9%after 4 days of storage, and this decrease in O2 con-centration would have suppressed respiration rateand thus reduced the amount of ethylene pro-duced. On the other hand, the diffusion of ethyl-ene through the polymeric film may have beenrelatively constant. The presence of ethylene insidethe package did not affect the ripening process oftomatoes. Color development of both treated anduntreated tomatoes packaged with plastic film wassuppressed during the 2-week period of storage.The action of ethylene on tomato ripening mightbe inhibited by the presence of CO2 and lack of O2

inside the package.

Fruit quality

The use of modified atmosphere packaging (MAP)significantly reduced the weight loss of tomatoesduring storage for 14 days at 10°C. There was a sig-nificant difference between weight losses of pack-

aged and unpackaged fruit, but no significant dif-ference was found between treated and untreatedfruit packaged in polyethylene film (Table 1).During the 14-day storage period, the weight lossof tomatoes packaged in polyethylene film wasless than 0.7%, while that of unpackaged fruit wasmore than 1.2%. These results suggest that MAPwas an effective method for reducing weight lossof tomatoes, in agreement with results reported byZagory and Kader.1 The weight loss of tomatoescould be reduced by as much as 41%. After the sub-sequent 3-day ripening period at 20°C, the weightloss of tomatoes that had been subjected to HWTand MAP was less than that of tomatoes that hadbeen subjected to other treatments, but the differ-ences between weight losses of tomatoes subjectedto different treatments were not significant (Table1).

Changes in the surface color of tomatoes wasexpressed as the a*/b* ratio, a higher a*/b* ratioindicating a redder surface color of the tomato. Thechanges in surface color of the tomatoes during thestorage period and the subsequent ripening periodwere shown in Fig. 4. The combination of HWT

Copyright © 2003 John Wiley & Sons, Ltd. 175 Packag. Technol. Sci. 2003; 16, 171–178

MODIFIED ATMOSPHERE PACKAGING OF TOMATO Packaging Technologyand Science

0

5

10

15

20

25

30

35

0 3 6 9 12 15Duration of storage (days)

Eth

ylen

e co

ncen

trat

ion

(ppm

)

Control

HWT

Figure 3. Ethylene production inside the package during a2-week storage period.

Table 1. Effects of HWT and MAP on weightloss, SSC, titratable acidity, decay and

mold growth

CharacteristicsStorage period (d)

of quality Treatments 14 14 + 3d

Weight loss HWT-MAP 0.60a 1.74a

(%) C-MAP 0.68a 1.87a

C-Air 1.21b 2.05a

SSC HWT-MAP 6.47a

(%Brix) C-MAP 6.46a

C-Air 6.32a

Titratable HWT-MAP 0.63a

Acidity (%) C-MAP 0.66a

C-Air 0.66a

Decay HWT-MAP 0.0a

(%) C-MAP 17.1b

C-Air 0.0a

Mold growth HWT-MAP 2.57a

(log CFU/gr) C-MAP 3.44a

C-Air 0.81b

HWT: hot water treatment; MAP: modified atmosphere packaging; C: control, means followed by the same letter werenot significantly different at P £ 0.05 by analysis of variance.

and MAP significantly inhibited color develop-ment of the tomatoes during the 14-day storageperiod at 10°C. The color development of unpack-aged tomatoes was greater than that of packagedtomatoes. However, after the subsequent 3-dayripening period at 20°C, there was no significantdifference between surface color of treated anduntreated tomatoes in film packaging. Fruitripened normally under this condition. This resultindicated that MAP is useful for suppressing theripening rate of tomatoes. Suppression of theripening rate may be correlated with reduction inrespiration rate due to the reduced level of O2 andelevated level of CO2 inside the package.

The firmness of hot water-treated tomatoespackaged with plastic film was significantlygreater than that of untreated tomatoes packagedwith plastic film (Fig. 5). The degree of firmness of unpackaged tomatoes was even lower. Theseresults clearly demonstrated that the combinationof hot water treatment and plastic packagingimproved the firmness of the fruit compared withthe firmness of untreated fruit packaged withplastic film. A similar result has been reported for“Oroblanco” fruit.16 The firmness of tomato fruitmay be correlated with the weight loss rate and thedegree of injury due to decay or microbial growthduring storage and the ripening process. Excessivehumidity inside the package stimulated moldgrowth near the stem end and decay of untreatedfruit, resulting in the lower degree of firmness.

The “Maru” tomatoes used in this study have ahigh SSC and therefore relatively sweet taste. Asshown in Table 1, the SSC of the control andunpackaged tomatoes was about 6.32 %Brix, whilethose of treated and untreated tomatoes pack-aged in plastic film were 6.47 %Brix and 6.46%Brix, respectively. As a comparison, the SSC of“Momotaro” tomato was reported to range from4.68 to 5.56 %Brix,17 that of “Durinta” tomatoeswas reported to be about 4.6 %Brix,18 and that ofSunbeam tomatoes was reported to be 4.5 %Brix.19

The combination of HWT and MAP had no signif-icant effect on SSC. The use of MAP alone also hadno effect on SSC. Moreover, McDonald et al., 1999reported that HWT without packaging had noeffect on SSC. In addition, the combination ofHWT and MAP had no effect on TA. The two vari-ables SSC and TA are often used to determine theeffect of heat treatment on quality of fruits andvegetables. It has been shown that the effects ofheat treatment on those variables, most oftenacidity, depend on the temperature used and theduration of treatment.20 The temperature andduration of HWT used in our study were 42.5°Cand 30min, respectively, which has been deter-mined in a preliminary experiment to be theoptimal conditions for prevention of damage totomatoes.

Storage of tomatoes in MAP resulted in a highlevel of relative humidity (RH) due to fruit respi-ration. The high level of humidity inside thepackage stimulated mold growth near the stemend of untreated tomatoes from the seventh day of

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Copyright © 2003 John Wiley & Sons, Ltd. 176 Packag. Technol. Sci. 2003; 16, 171–178

-0.5

0.0

0.5

1.0

1.5

2.0

0 14 14+3

Duration of storage (days)

a* /b* r

atio

HWT-MAP C-MAP C-Air

aaa

b

b

ca

a

Figure 4. Color development of tomatoes during thestorage period. Results are means ± SDs.Values with

different letters are significantly different at P £ 0.05 byanalysis of variance.

0.5

0.7

0.9

1.1

1.3

1.5

1.7

C-Air C-MAP HWT-MAP

Treatments

Fir

mne

ss (

MP

a)

bc

a

Figure 5. Firmness of tomatoes after storage. Results aremeans ± SDs.Values with different letters are significantly

different at P £ 0.05 by analysis of variance.

the storage period. Some of the untreated tomatoeshad also become cracked and had decayed afterstorage for 14 days. These defects may have beencaused by excessive water vapor inside thepackage. However, hot water treated tomatoesprevented from those defects even though the levelof relative humidity inside the package of HWTtomatoes was as high as of that of untreated toma-toes. The same results have been reported foruntreated tomatoes stored in a modified atmos-phere at temperatures of 15 and 20°C.17 Burmeis-ter et al.21 reported that high RH inside the storagechamber could increase the incidence of chillinginjury (CI). Therefore, the observed decay ofuntreated tomatoes packaged in plastic film maybe one of the manifestations of CI. Forney andLipton22 suggested that large amount of water lossearly in the storage period might reduce the devel-opment of CI in various fruit species. Our initialresearch on hot water treatment has shown thatHWT reduce the incidence of chilling injury oftomatoes stored at low temperatures. Reductionsin the degrees of sensitivity to CI by heat treatmenthave been investigated in avocados,23 cucumbers,24

‘Fuyu’ persimmons,24 and tomatoes.19,25

The results of the present study indicated thatthe application of HWT before storage in MAP pre-vents decaying and cracking of tomatoes. A signif-icant difference was found between decay of hotwater-treated tomatoes and that of untreatedtomatoes packaged with plastic film (Table 1).Moreover, HWT prior to storage in MAP slightlyreduced mold growth. However, both treated anduntreated tomatoes packaged with plastic filmresulted in higher microbial count than unpack-aged tomatoes. There was significant differencebetween microbial counts of packaged andunpackaged tomatoes. Further, there was no sta-tistically significant difference between microbialcounts of treated and untreated tomatoes pack-aged in polyethylene film. The microbial count ofheat-treated tomatoes packaged in polyethylenefilm was 2.57 logcfu/g, that of untreated tomatoespackaged in polyethylene film was 3.44 logcfu/g,and that of unpackaged tomatoes was 0.81 logcfu/g. The lower microbial count of the hot water-treated tomatoes indicated that treatment with hotwater prior to packaging in plastic film and storagehas a disinfectant effect, resulting in reductions ofmicrobial growth and decay. Afek et al.26 reportedthat steam treatment prior to packaging and

storage at 0.5°C reduced spoilage or decay ofcarrots. The heat generated during hot water treat-ment destroys pathogens on the tomato’s surface,as was found in other studies on heat treatment offruits and vegetables.26–27

CONCLUSION

The use of MAP reduced the O2 concentration andincreased the CO2 concentration inside thepackage, with equilibrium concentrations of O2

and CO2 (5% and 8%, respectively) being reachedafter 6 and 4 days of storage, respectively. The useof a combination of HWT and MAP reducedweight loss, decay and mold growth, inhibited theripening process, maintained firmness and pre-vented decay and cracking of tomatoes stored at10°C and hence improved the storage life of toma-toes. HWT could be used as a disinfectant fortomatoes prior to storage in MAP in order toreduce decay and microbial growth. The use of acombination of HWT and MAP has no effects onSSC and TA.

ACKNOWLEDGEMENTS

We thank Dr Shigenobu Koseki for his help in the mea-surement of microbial count.

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