Effects of Continuous Application of CO2 on Fruit Quality Attributes and Shelf Life during Cold Storage in Cherry Tomato

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Effects of Continuous Application of CO

2

on

Fruit Quality Attributes and Shelf Life during Cold

Storage in Cherry Tomato

Adanech Melaku Taye, Shimeles Tilahun, Do Su Park, Mu Hong Seo, and Cheon Soon Jeong* Department of Horticulture, Kangwon National University, Chuncheon 24341, Korea

*Corresponding author: [email protected]

‘Unicon’ cherry tomato (Solanum lycopersicum) is one of the most highly perishable horticultural crops due to its high water content and respiration rate. This study was carried out to assess the effect of continuous application of CO2 (control [air], 3%, and 5%) on the quality

and shelf life of cherry tomato fruits stored at 10°C and 85 ± 5% relative humidity (RH) at two maturity stages (pink and red). Continuous application of CO2 did not affect the soluble solids

content (SSC) or titratable acidity (TA) of the fruit at either maturity stage during storage. However, there was a significant difference among treatments in terms of flesh firmness, cell wall thickness, pectin content, vitamin C content, skin color, lycopene content, weight loss, ethylene production rate, respiration rate, and acetaldehyde and ethanol production. Fruits treated with 5% CO2 maintained their high quality with regards to vitamin C, skin color (a*),

lycopene content, weight loss, physiological parameters (ethylene production rate, respiration rate, and volatile compounds), flesh firmness, cell wall thickness, and pectin content at both maturity stages compared with 3% CO2 treatment and the control. Continuous application of

CO2 (5%) reduced the ethylene production rate and the production of volatile compounds during

storage. Therefore, cherry tomato ‘Unicon’ fruit can be stored for two weeks without losing fruit quality at both maturity stages under continuous application of 5% CO2 as a postharvest

treatment.

The work was supported by the Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, Forestry, and Fisheries (IPET) through the Agri-Bioindustry Technology Development Program, funded by the Ministry of Agriculture, Food, and Rural Affairs (MAFRA) (314086-3) and by a 2015 Research Grant from Kangwon National University (No. 520150123).

HORTICULTURAL SCIENCE and TECHNOLOGY 35(3):300-313, 2017

URL: http://www.kjhst.org

pISSN : 1226-8763 eISSN : 2465-8588

This is an Open-Access article distributed under the terms of the Creative Commons Attribution NonCommercial License which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Additional key words: cell wall thickness, maturity stage, perishable, postharvest, volatile compounds

Introduction

Tomatoesareconsumedbroadlythroughouttheworld, andtheirconsumptionhasrecentlybeenshown tohavehealthbenefitsduetotheirhighphytonutrientcontents (LevyandSharoni, 2004; Hsuetal., 2008). Postharvestrecommendationsindicatethattomatoes, includingcherrytomatoes, shouldbestoredat10°C orhighertoavoidchillinginjury (JimenezandCantwell, 1996andRobertsetal., 2002) andthateven10°C maybeharmfultotomatoflavor (Mauletal., 2000). Oneofthemostcharacteristicphytonutrientsin tomatoislycopene, acarotenoidwithahighcapacityforreducingtheriskofchronicdiseasesthat represents -80% ofthetotalcarotenoidcontentsintomatofruit (Raoetal., 1998). Lycopeneaccountsfor

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thereddeningoftomatoesduetothedifferentiationofchloroplastsintochromoplasts (Egeaetal., 2011). Hence, thiscarotenoid isfundamentalforthenutritionalqualityandcommercialvalueofthisfruit (Dumasetal., 2003).

ThestorabilityofapplescanbeincreasedbytreatingfruitswithhighconcentrationsofCO2forashortperiodoftime. Burg

andBurg (1967and1969) foundthatCO2functionsasacompetitiveinhibitorofethyleneaction. Beyer (1979) reportedthat

suchanactionisrelatedtoethylenemetabolism; CO2canaffectthismetabolismbyinhibitingethyleneoxidation. Theactivity

ofCO2indelayingtheagingrateisassociatedwithreducedrespiratorymovementandahindranceofthesuccinicoxidase

complex, particularlysuccinicdehydrogenase (Ransonetal., 1960andShipwayandBramlage, 1973). Inadditiontoits respiration - blockingactivity, CO2athighlevelsdiminishesethyleneevolutioninfruits, suchasapple, pears, andtomato (Bramlage, etal., 1977; Buescher, 1979; Looney, 1975; MarcellinandChaves, 1983andWangandMellenthin, 1975). According toFarber (1991), theoptimumconditionsformodifiedatmospherepackaging (MAP) storageoffruitsandvegetablesare3 - 8% CO2

and2 - 5% O2.

Duetothelowstorabilityofcherrytomatofruit, manystudieshavefocusedondesigningvariouspracticalapproachesfor extendingthestorageperiod, includingcontrolledatmosphere (CA) storage. Short - termexposureoftomatofruitto80% CO2

stimulatestheethylenebiosyntheticpathwayduetotheinhibitionoftheripeningprocess (Hirofumietal., 1998). Treatmentwith 60% CO2for24hrreducedethyleneproductionintomatofruit, butitsharplyincreasedimmediatelyaftertheCO2treatment.

Surfaceblemishes, increasedsoftening, andunevenripeningwerealsoobservedinfruitsafterremovalfromelevatedCO2

levels (Kuboetal., 1990andMorris, 1977). However, nostudieshaveinvestigatedtheeffectsofcontinuousapplicationof CO2

atlowtemperatureonfruitqualityattributesandshelflifeincherrytomato. Maintainingfruitqualityandaddingcommercial valuewillbenefitbothproducersandconsumers. Tomatofruitisperishable, chillingsensitive, andeasilyaffectedbynumerous fungaldiseases (Hoeberichtsetal., 2002). Inaddition, tomatofruithasashortshelflifeduetoitshighwatercontent, andits climactericnatureleadstoethyleneproductionandahighrespirationrateafterharvest. Therefore, inthecurrentstudy, we examinedtheeffectsofcontinuousapplicationof CO2onfruitqualityattributesandshelflifeincherrytomato.

Materials and Methods

Plant Material and Treatments

Cherrytomato (Solanum lycopersicum) ‘Unicon’ fruitswereharvestedatthepinkandredmaturitystagesfromacommercial farminKangwonProvince, RepublicofKoreaonOctober15, 2015. ThefruitswereimmediatelytransportedtothePostharvest QualityManagementLaboratory, DepartmentofHorticulture, KangwonNationalUniversityinanair-ventilatedautomobile within30minofharvest. Uponarrival, defect- freefruitsofuniformcolorweresorted, washedwithcoldwater, andair- driedfor 6hrs. Thesortedfruitwerecarefullytransferredto0.75Lplasticcontainers (16fruitspercontainer) forCO2treatment. The

treatmentswereconductedusingacontinuousapplicationofCO2 (control [untreated, air], 3%, and5% ) withtwomaturitystages

offruit (pinkandred) inacompletelyrandomizeddesign (CRD). CO2wastakenfromagascylinderusingasyringeand

immediatelyinjectedintothecontainer, andtherequiredpercentageofCO2wasconfirmedusingahandheldPBIDansensor

gasanalyzer (CheckMate9900, Ringsted, Denmark). Thetreatedfruitswerestoredat10°Cand85 ± 5% RH. Evaluationswere madeoncherrytomatofruitstoredinanevaluationroom, anddatawerecollectedfromeachtreatmentat2- dayintervals.

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Weight Loss, Flesh Firmness, Surface Color, Titratable Acidity, Soluble Solids Content, Ethylene Production Rate, and Respiration Rate

Weightlosswasdeterminedbymeasuringthefreshweightoffruitandcomparingthevaluetotheinitialfreshweight. Fresh weightwasmeasuredeverytwodaysfor15d, andweightlosswascalculatedbysubtractingfreshweightsfromtheinitial weightofthefruit. FleshfirmnesswasmeasuredusingaRheometer (modelcompact-100II, Meschede, Germany) witha maximumforceof10kganda3mmdiameterroundstainlesssteelprobewithaflattip. Surfacecolor (a* value) wasmeasured onfruitsmarkedalongtheirequatorregions, withthreereadingstakenusingaChromameter (modelCR- 400, MinoltaCo., Tokyo, Japan). Cherrytomatojuicewasanalyzedforsolublesolidscontent (SSC) usingarefractometer (Model-AtagoInc., Tokyo, Japan); theresultswereexpressedin °Brix. Titratableacidity (TA) wasanalyzedusingaDL22FoodandBeverage Analyzer (MettlerToledoLtd., Zurich, Switzerland). Dilutedjuice (1mLofjuice: 19mLofwater) wastitratedwith0.1Nsodium hydroxideandtheresultswereexpressedasmg·100g-1_of_citric_acid_._The_ethylene_production_rate_was_measured_using_a_GC-

2010Shimadzu (ShimadzuCorporation, Tokyo, Japan) fittedwithaBP20waxcolumn (30m × 0.25mm × 0.25µm) andaflame ionizationdetector (FID). Thedetectorandinjectorwereoperatedat127°Candtheovenwassetat50°C. Thecarriergas (N) flow ratewas0.67mL· s-1₍_Park_et_al_.,₂₀₀₀_)._The_respiration_rate_was_measured_with_a_PBI_Dan_-_sensor₍_CheckMate₉₉₀₀_,_Ringsted_,

Denmark).

Vitamin C and Lycopene Content, Ethanol and Acetaldehyde Production

VitaminCwasanalyzedusinghighperformanceliquidchromatography (HPLC) (model: WatersAssociates, Milford, MA, USA) througha717plusautosamplerusingaZORBAXEclipseXDB-C18analyticalcolumn (4.6cm × 250mm × 5μm, Agilent

Co., Torrance, USA), aWaters600controllerpump, andaWaters486tunableabsorbancedetectorat265nm. Themobilephase was1: 9and100% MeOH: 0.1MKH2PO4, andtheflowratewas1.0mL· min-1 (LiandChen, 2001). Frozenfruittissue (1g) was

mixedwith10mLof 5% metaphosphoricacidandhomogenizedusingaT25Ultra-Turrax (IKAKorea. Ltd., Seoul, Republic ofKorea) untilcombined. Themixturewascentrifugedat20,000rpmfor10minutesat4°Candfilteredthrougha0.45μmfilter membrane. Thesample (1mL) wasanalyzedbyHPLCwiththreereplicates (Kimetal., 2011). Thelycopenecontentofthefruit wasanalyzedasdescribed, withslightmodifications (Fishetal., 2002). Frozenfruitwasgroundwithamortarandpestle, and1 ggroundsamplewashomogenizedwith1mLdistilledwaterusingaT25Ultra - Turraxstainlesssteelblender (IKAKorea. Ltd., Seoul, RepublicofKorea). Tubescontaininghomogenizedsampleswerecoveredwithaluminumfoilandplacedoniceand combinedwith20mLofhexane - ethanol - acetone ( 2 : 1 : 1 ), followedbygentleshaking. Thesampleswerecentrifugedat 15,000rpmfor20min, followedbytheadditionof3mLdistilledwaterpervial. Thesampleswereagitatedfor2min, incubated atambienttemperatureforafewmin, andreadusingaspectrophotometer (ThermoFisherScientific, Madison, WI, USA) at503 nm. Hexanewasusedasablank. Ethanolandacetaldehydeweremeasuredusingthesameprocedureusedtomeasurethe ethyleneproductionrate.

Cell wall Thickness and Water-soluble Pectin

Cellwallthicknesswasmeasuredunderascanningelectronmicroscope (SEM, Supra55VP, CarlZeiss, Germany) as describedbyIslametal. (2016). WatersolublepectinwasanalyzedbasedontheprotocolofBlumenkrantzandAsoe - Hansen

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Statistical Analysis

Significancetestswereconductedbyanalysisofvariance (ANOVA) usingSASVersion9software (SASInstitute, Cary, NC, USA) andExcel2010 (MicrosoftCo., WA, USA). Meancomparisonsweremadeusingleastsignificancedifference (LSD) at5% probability.

Result and Discussion

Weightlossleadstoquantitativecroplosses, aswellasareductioninqualityduetoshrivelingandwilting, softeningoftissue, andalossofcrispness (Kader, 1986). Wedetectedasignificant ( p < 0.05) differenceincherrytomatofruitqualityamong treatmentsatbothmaturitystages(Fig. 1AandB). Thehighestweightlosswasfoundinthecontrol, followedby3% CO2

treatment, whiletheleastweightlosswasobservedinfruitsafter5daysof5% CO2treatmentatthepinkmaturitystage.

However, therewasnodifferencebetween3% CO2and5% CO2treatmentsuntilday13, afterwhichweightlossincreased

significantlyinfruitstreatedwith3% CO2. Thecontrolfruitsatbothmaturitystagesshowedmoreweightlossthanthetreated

fruitsduetohigherrespirationratesandethyleneproduction(Fig. 3CandD, 4AandB), whichinturnresultedinwaterlossor shrinkageofthefruitsurface. Theseresultsindicatethatthecontinuousapplicationof5% CO2reducesweightlossintomato

fruitduetoreducedethyleneproductionandrespirationduringcoldstorage.

Therewassignificantdifference ( p < 0.05) infleshfirmnessamongtreatmentsatbothmaturitystages(Fig. 1CandD). Fruits treatedwith5% CO2weremuchfirmerthanthosetreatedwith3% CO2andthecontrolatbothmaturitystagesduringtheentire

storageperiod(Fig. 1CandD). Attheredmaturitystage, untreatedfruitwerethesoftest, followedbyfruitsunder3% CO2

treatmentandthoseunder5% CO2treatment. Atthepinkmaturitystage, however, therewasnosignificantdifferencebetween

fruitstreatedwith3% CO2anduntreatedfruitsthroughoutthestorageperiod. Atbothmaturitystages, fruitstreatedwith5%

CO2maintainedfirmnessthroughoutthestorageperiod. Similarly, PorrittandMeheriuk (1977) reportedthattreatmentwith20 - 30% CO2at 0°Cfortwoweeksreducedthesofteningof ‘Newton’ applefruitwithoutinducingCO2injury. Inthecurrentstudy,

5% CO2 -treatedfruitswerefirmerthanthosetreatedwith3% CO2andthecontrol. Atthepinkmaturitystage, fleshfirmnesswas

reducedfrom9.80Nto5.48Nand7.85Nincontroland5% CO2-treatedfruits, respectively. ThehigherthelevelofCO2

treatment, thefirmerthefleshandthehigherthecellwallthickness. Treatmentwith10to20% CO2for10- 14daysreducedthe

degradationoffleshfirmnessin ‘GoldenDelicious’ applefruit (Lauetal., 1977). Asthestorageperiodincreases, thethicknessof thefruitcellwalldecreases, alongwithcellwallbreakage (KashmireandKader, 1978).

Continuousapplicationof CO2treatmentsignificantly ( p < 0.05) affectedthesurfacecolorchangeoftomatofruitduringcold

storage(Fig. 2AandB). Fruitcolorpeakedearlierinuntreatedfruitsthanintreatedfruits. After11days, thecolorvaluesof controlfruitsandfruitstreatedwith3% CO2weresignificantlylowerthanthoseof5% CO2-treatedfruits. ContinuousCO2

applicationdelayedthecolorchangeatthepinkmaturitystage. Thisresultissupportedbythefindingof Sozzietal. (1999) that redcolordevelopedslowlyintomatofruitatthebreakerstageasaresultof CO2treatment. Aharonietal. (1989) andMitcham (1997) alsoreportedthathighCO2concentrationssignificantlyreducedchlorophylldegradationingreenvegetablescompared

withtheuntreatedcontrol. Similarly, thefruitsmaintainedtheirredcolorattheendofstorage. Colordevelopmentincherry tomatoesatthepinkstagebeganonday3and5under3% and5% CO2treatment, respectively. Bycontrast, colordevelopment

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earlierthaninuntreatedfruitandincreasedslowlyuntilitreachedaclimactericpeakonday11. Similarly, attheredmaturity stage, fruitunder5% CO2treatmentmaintainedbettercolorthanfruitundercontroland3% CO2treatmentthroughoutthe

storageperiod(Fig. 2B).

Therewasnosignificantdifference ( p < 0.05) intitratableacidityamongtreatmentsatbothmaturitystages, althoughthe acidityvaluesofthefruitsdecreasedwithincreasingstorage(Fig. 2CandD). Riquelmeetal. (1994) reportedthatstoring strawberriesunderlowO2andhighCO2concentrationsdidnotaffecttitratableacidity. Similarly, Biale (1960) reportedthat

treatmentwith60% CO2hadnoeffectontitratableacidityin ‘Valencia’ orangefruit, whereasstorageunderhighCO2levels

increasedtheorganicacidcontentsinlemon. Atthepinkmaturitystage, wedetectedadecreaseinaciditylevelsfromday3to day7inthecontrolgroup, whichsubsequentlybecamesimilartothoseoftheothertreatments. Therewasreductioninacidity Fig. 1. Effect of continuous application of CO2 on weight loss and flesh firmness in ‘Unicon’ cherry tomato fruit at two maturity

stages stored at 10°C for up to 15 days. A and C=pink and B and D=red maturity stages. Vertical bars represent mean +/- SE (n=5) when larger than the symbols.

W eight loss (%) W eight loss (%) 0 0.5 1 1.5 2 2.5 3 3.5 0 2 4 6 8 10 12 0 1 3 5 7 9 11 13 15 0 1 3 5 7 9 11 13 15

A

C

B

D

Storage time (days) Storage time (days) Control

3% CO2 5% CO2

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levelfrom0.89mg·100g-1_to₀_.₅₉_mg_·₁₀₀_g-1_in_untreated_fruit_,_from₀_.₈₉_mg_·₁₀₀_g-1_to₀_.₅₇_mg_·₁₀₀_g-1_in_fruits_treated_with₃_%

CO2, andfrom0.89mg·100g-1to0.65mg·100g-1infruitstreatedwith5% CO2. Thisresultisinagreementwiththefindingsof

CouveyandOlsen (1977).

Nosignificantdifference ( p < 0.05) wasobservedbetweentreatmentswithregardtosolublesolidscontent (SSC) atboth maturitystages(Fig. 3AandB). RyallandPentez (1982) reportedthatSSCwasnotaffectedbyCO2levelorlong- termapplication

ofCO2. However, SSClevelsshowedadecreasingtrendonthelastdayatbothmaturitystages, whichmightbeassociatedwith

utilizationof SSCduringrespiration.

AnalysisofvarianceoftheeffectsofcontinuousapplicationofCO2onethyleneproductionrevealedasignificantdifference

( p < 0.05) amongtreatmentsatbothmaturitystages (Fig. 3CandD). Theethyleneproductionratewaslowerinfruitstreatedwith

5% CO2fromthebeginningoftheexperiment, followedby3% CO2treatment, comparedtountreatedfruitsatbothmaturity Fig. 2. Effect of continuous application of CO2 on surface color (a* value) and titratable acidity in ‘Unicon’ cherry tomato fruit at

two maturity stages stored at 10°C for up to 15 days. A and C=pink and B and D=red maturity stages. Vertical bars represent mean +/- SE (n = 9 for surface color and n = 5 for titratable acidity) when larger than the symbols.

Surface color (Hunter

a *) Titiratable acidity (mg · 100g -1 ) -5 0 5 10 15 20 0 0.2 0.4 0.6 0.8 1 1.2 0 1 3 5 7 9 11 13 15 0 1 3 5 7 9 11 13 15

A

C

B

D

3% CO2 5% CO2

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stages. TheseobservationsaresimilartothoseofBurgandBurg (1967), whodetectedinhibitedethyleneproductionunderCO2

treatmentduetoitscompetitiveaction, whichinturnhelpsregulateethylenebiosynthesisduringstorage. Eventhoughall treatedfruitsatbothmaturitystagesexhibitedpeakethyleneproductiononthesameday, 5% CO2-treatedfruitsproducedthe

lowestethylenelevels, whichdeclineddrastically. Indeed, areducedO2uptakerateduringhighCO2treatment, accompaniedby

inhibitedethyleneproduction, wasfoundtoextendtheshelflifeoftomatofruit (Kuboetal., 1985). Atthepinkmaturitystage, bothcontroland3% CO2-treatedfruithadahighethyleneproductionrateuntilday5, followedbyaslightdecrease. Asimilar

trendwasobservedattheredmaturitystageaswell. Therespirationratewaslowerunder5% CO2treatmentcomparedwith3%

CO2andthecontrolthroughouttheentirestorageperiod, regardlessoffruitmaturity(Fig. 4AandB). Therespirationrate

reacheditspeakonday1inalltreatments. Eventhoughtherespirationratedecreasedafterday1underalltreatments, therateof reductionwashigherundercontroland3% CO2treatmentsthanunder5% CO2treatmentthroughouttheexperimentalperiod. Fig. 3. Effect of continuous application of CO2 on soluble solids content (SSC) and ethylene production rate in ‘Unicon’ cherry

tomato fruit at two maturity stages stored at 10°C for up to 15 days. A and C=pink and B and D=red maturity stages. Vertical bars represent mean +/- SE (n=5 for SSC and n=3 for ethylene production rate) when larger than the symbols.

Ethylene production (μL · kg -1 · hr -1) 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 3 5 7 9 11 13 15 0 1 3 5 7 9 11 13 15

3% CO2 5% CO2

Soluble Solids content (

°Brix)

A

C

B

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ThisresultisinagreementwiththefindingsofKader (1986), whodetectedreducedrespirationratesduetoelevatedCO2

concentrations, whichisresponsibleforchangesintheactivitiesofvariousenzymesthathastenfruitripeningandsenescence. Therewasasignificantdifference ( p < 0.05) invitaminCcontentamongtreatmentsatbothmaturitystages(Fig. 5AandB). Continuousapplicationof 5% CO2delayedthedecreaseinvitaminCcontentfor7daysatthepinkmaturitystage. Thevitamin

Ccontentsoffruitsunder3% CO2andcontroltreatmentwerehigherthanthoseof5% CO2-treatedfruitsonday1atthepink

maturitystage. Subsequently, vitaminClevelsdecreasedinboth3% CO2-treatedandcontrolfruitsattheendofstorageatboth

maturitystages. Thisresultindicatesthatasfruitripeningadvances, organicacidcontentsdecline. Similarly, Islametal. (1996) detectedincreasedascorbicacidcontentsintomatofruitwithincreasingmaturity, withhighconcentrationsofvitaminCfound atthepinkmaturitystage, followedbyaslightdecreasewhenthefruitsreachedtheredmaturitystage. AsshowninFig. 5B, vitaminCcontentsweremaintainedunder5% CO2treatmentcomparedwiththecontroland3% CO2treatmentthroughoutthe

storageperiod. Attheendofstorage, thehighestvitaminCcontent (31.78mg·100g-1_and₃₀_.₀₆_mg_·₁₀₀_g-1_at_both_maturity

stages, respectively) wasfoundinfruittreatedwith5% CO2. Atbothmaturitystages, vitaminClevelsremainedstableinfruit

treatedwith5% CO2comparedto3% CO2andthecontrolthroughoutthestorageperiod. Theseresultsindicatethattherateof

vitaminClosswaslowerinthe5% CO2-treatedgroupthaninthe3% CO2-treatedandcontrolgroupsatbothmaturitystages

throughouttheentirestorageperiod(Fig. 5AandB). VitaminCisgenerallyconsideredtobeagoodindicatorofnutritional qualityduringtheprocessingandstorageoffruits; ifvitaminClevelsarewellmaintained, theotherfruitqualityparametersare alsowellmaintained (Uddinetal., 2002).

Therewassignificantdifference ( p < 0.05) inlycopenebiosynthesisand / orcontentamongtreatmentsatbothmaturitystages

(Fig. 5CandD). Atthepinkmaturitystage, thelycopenecontentsatharvestweresimilarforalltreatmentsbutincreasedover timeuntilreachingapeakonday7 (24.96mg·kg-1₎_and_day₁₁₍₂₃_.₆₈_mg_·_kg-1₎_after_control_and₃_%_CO₂_treatment_,_respectively_.

Similarly, in5% CO2-treatedfruitatthepinkmaturitystage, lycopenecontentsincreasedfrom6.65mg·kg-1onday1to20.65

mg·kg-1_on_day₁₅₍_Fig_._5C₎_._At_the_red_maturity_stage_,_no_significant_change_in_lycopene_content_was_observed_under_any Fig. 4. Effect of continuous application of CO2 on respiration rate in ‘Unicon’ cherry tomato fruit at two maturity stages stored at

10°C for up to 15 days. A=pink and B=red maturity stages. Vertical bars represent mean +/- SE (n=3) when larger than the symbols.

0 1 3 5 7 9 11 13 15 0 1 3 5 7 9 11 13 15

A

B

Storage time (days) Storage time (days) Control 3% CO2 5% CO2 Respiration rate (mg · kg -1 · hr -1 ) 0 0.2 0.4 0.6 0.8 1 1.2 1.4

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treatmentuntilday11ofstorage. Thelycopenecontentstronglydecreasedfrom28.31mg·kg-1_on_day₁₁_to₈_.₆₅_mg_·_kg-1_on_day

15andfrom28.31mg·kg-1_on_day₁₁_to₉_.₇₂_mg_·_kg-1_on_day₁₅_in_control_and₃_%_CO₂_-_treated_fruit_,_respectively_,_whereas_the

lycopenecontentunder5% CO2treatmentdecreasedonlyslightlyduringthisperiod, from30.11mg· kg-1onday11to20.88

mg·kg-1_on_day₁₅_._Untreated_fruit_showed_an_immediate_decline_at_both_pink_and_red_stages_._Therefore_,_treatment_with_high

levelsof CO2 (5%) delayedtheformationoflycopeneand/ormaintainedthelycopenecontentattheendofthestorageperiod.

Similarly, Sozzietal. (1999) reportedadelayintotalcarotenoidandlycopenebiosynthesisunderelevatedCO2levels.

Volatilecompounds, suchasacetaldehydeandethanol, wereaffectedbythecontinuousapplicationofCO2atbothmaturity

stages. Wedetectedverylowlevelsofethanolformationincherrytomatofruitduringcoldstorageunderalltreatments regardlessoffruitmaturity(Fig. 6AandB). Afterday9, ethanollevelsinfruitsinthecontrolgroupwerelowerthanthoseof fruitstreatedwith3% and5% CO2atthepinkmaturitystage. Acetaldehydeformationwasaffectedbythecontinuousapplication Fig. 5. Effect of continuous application of CO2 on vitamin C and lycopene contents in ‘Unicon’ cherry tomato fruit at two maturity

stages stored at 10°C for up to 15 days. A=pink and B=red maturity stages. Vertical bars represent mean +/- SE (n=3) when larger than the symbols.

Lycopene content (mg · kg -1) 0 10 20 30 40 50 60 0 1 3 5 7 9 11 13 15 0 1 3 5 7 9 11 13 15

A

C

B

D

Storage time (days) Storage time (days) Control 3% CO2 5% CO2 Vitamin C (mg · 100g -1 ) 0 5 10 15 20 30 40 25 35

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ofCO2(Fig. 6CandD). Therateofacetaldehydeformationwaslowuntilday1foralltreatmentsatbothmaturitystages, after

whichthelevelsofthiscompoundinthecontroland3% CO2treatmentgroupsincreaseduptoday5andthendecreasedslowly

atthepinkmaturitystage. Bycontrast, attheredmaturitystage, acetaldehydelevelsincontroland3% CO2-treatedfruits

decreasedafterday3. Irrespectiveoffruitmaturity, acetaldehydeformationdecreasedafterafewdaysunderalltreatments. Theseresultsindicatethatfruitripeningleadstotheincreasedproductionofvolatiles, suchasethanolandacetaldehyde, infruits storedforlongperiodsoftimewithoutanti-agingpostharvesttreatment. Indeed, JanesandFrenkel (1978) andNanosetal. (1992) found thatfruitssuchaspearandstrawberryproduceethanolandacetaldehydewhentheyareallowedtoripen.

Therewassignificantdifference ( p < 0.05) incellwallthicknessamongtreatmentsatbothmaturitystages(Fig. 9A, B, C, D, E,

andF). Cellwallthicknessdecreasedwithincreasingstorageatbothmaturitystages, exceptforfruitstreatedwithCO2. Atboth

maturitystages, wedetectedrapiddegradationofcellwallthickness (outer, middle, andinner) inthecontrol, followedby3% CO2treatment, throughoutthestorageperiod. Fruitstreatedwith5% CO2appearedmorecompactthantheotherfruitsatboth

maturitystages(Fig. 7and8). Theseresultsareinagreementwiththefindingthat5% CO2treatmentaffectstheactivitiesof

enzymes, suchaspolygalacturonase (PG) andpectinmethylesterase (PME), whichareresponsibleforfruitsofteningduring storage ( GoulaoandOliveira, 2008 ).

Fig. 6. Effect of continuous application of CO2 on ethanol and acetaldehyde production in ‘Unicon’ cherry tomato fruit at two

maturity stages stored at 10°C for up to 15 days. A and C=pink and B and D=red maturity stages. Vertical bars represent mean +/- SE (n=3) when larger than the symbols.

Acetaldehyde (μL · kg · hr -1 ) Ethanol (μL · kg · hr -1 ) 0 1 3 5 7 9 11 13 15 0 1 3 5 7 9 11 13 15

A

C

B

D

Storage time (days) Storage time (days) Control 3% CO2 5% CO2 0 1 1.5 2 1.5 2.5 3 4 3.5 4.5 0 0.04 0.02 0.08 0.06 0.1 0.12 0.16 0.14

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Fig. 7. Effect of continuous application of CO2 on cell wall thickness in ‘Unicon’ cherry tomato fruit at the pink maturity stage.

0 day 7th_day ₁₅th_day

Cell wall

20 μm 20 μm

20 μm

Fig. 8. Effect of continuous application of CO2 on cell wall thickness in ‘Unicon’ cherry tomato fruit at the red maturity stage.

Control 5% CO 2 0 day 7th day 15th day 20 μm 20 μm 20 μm 20 μm 20 μm Control 5% CO 2

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ThecontinuousapplicationofCO2significantly (p < 0.05) affectedwater-solublepectincontentsatbothmaturitystages(Fig. 10A

andB). Water- solublepectinlevelsincreasedmorerapidlyincontrolfruitthaninCO2-treatedfruitatbothmaturitystages. At

thepinkmaturitystage, water - solublepectinlevelsincreasedfrom40mg· kg-1_to₇₀_mg_·_kg-1_and_from₄₀_mg_·_kg-1_to₆₀_mg_·_kg-1

incontroland3% CO2 - treatedfruits, respectively. However, 5% CO2treatmentreducedtherateofsolubilizationofpectinat

bothmaturitystagescomparedwiththecontroland3% CO2treatments. TreatingfruitswithhighCO2levelsdelayedtheonset

oftheclimactericriseandprolongedtomatofruitripening, resultingindelayedfruitsoftening. Thisresultisinagreementwith thefindingofWillsetal. (1981) thatelevatedCO2levelsreducethebreakdownofpecticsubstancesresponsibleformaintaining

afirmtextureinfruitforalongperiodoftime.

Basedontheoverallresults, weconcludedthat ‘Unicon’ cherrytomatofruitcanbestoredfor15daysat10°Cundercontinuous applicationof 5% CO2, comparedto3% CO2andcontrolfruits. Toobtainthebestsurfacecolorquality, alongwithanacceptable

textureandothertomatoqualityparameters, werecommendthecontinuousapplicationof 5% CO2asapostharvesttreatment

duringstorage..

Fig. 9. Effect of continuous application of CO2 on cell wall thickness in the outer (A, D), middle (B, E), and inner (C, F) cortex in

‘Unicon’ cherry tomato fruit at the pink (A, B, C) and red (D, E, F) maturity stages stored at 10°C for up to 15 days. Vertical bars represent mean +/- SE (n=3) when larger than the symbols.

Cell wall thickness (um)

0 2 4 6 8 10 14 12 16 0 2 4 6 8 10 14 12 16 0 2 4 6 8 10 14 12 16

Storage duration (days) Storage duration (days) Storage duration (days)

Outer Middle Inner

Control 5% CO2 0 10 5 20 15 25 30 35 0 10 5 20 15 25

A

D

C

F

B

E

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