Quality characterization of gamma-irradiated fresh oyster mushrooms (Pleurotus ostreatus) during low temperature storage

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Quality characterization of gamma-irradiated fresh oyster mushrooms (Pleurotus ostreatus) during low temperature storage

Kashi fAkr am,Jae- Jun Ahn,Joong- HoKwon

^*

Depar t mentofFoodSci ence& Technol ogy,KyungpookNat i onalUni ver s i t y,Daegu702- 701,Republ i cofKor ea

Abs t r a c t

Fresh oyster mushrooms (Pleurotus ostreatus) were gamma-irradiated at 0, 1, 2, and 3 kGy. The effects on various quality attributes were determined during storage at 5 ± 1℃. Color changes were more prominent in the cap region than the stem part. At the start of storage increase of Hunter’s L-value (lightness) was observed in the caps of 2 and 3 kGy-irradiated samples. The L-value was higher in the all irradiated samples during storage. The trend was different in the case of stem region, where L-value decreased upon irradiation, but remained high throughout storage. The a-value declined, whereas the b-value increased following irradiation. Irradiation showed a dose-dependent effect on the firmness, which was clearer during storage, but the samples irradiated at 1 kGy maintained an overall better texture than other irradiated samples. The weight loss was also higher in the all irradiated samples during storage. The samples irradiated at 1 kGy showed good physical appearance without any fungal attack at the end of storage; however color change in cap region was quite apparent. The ultra-structural drastic effect of irradiation was understandable using scanning electron microscopy. E-nose analysis demonstrated a clear change in the volatile profiles of all irradiated samples. Although the effect of irradiation on quality characteristics was quite clear but the all irradiated samples were free from fungal attack that was observed in the case of control sample.

Ke ywo r ds

：Gamma irradiation; Oyster mushroom; Quality Storage; Volatile profile E-nose analysis

I nt r oduct i on

Foodirradiationismostextensivelystudiedfood preservation technique.Severalwell-reputed health authoritiesexaminedtherelatedsafetyconcernsand endorsedthewholesomenessofthisadvancedtechnique (WHO 1999;Farkas& Mohácsi-Farkas2011).Food irradiation,servingasmodernpostharvesttechnologies, can increase marketability of fresh agricultural commoditieswiththeextensionofstorageperiodand improvedhygienicquality.Consideringthetechnical applicability and nutritionalsafety,more than 55 countrieshavepermittedthecommercialuseofthis

wholesome technology (Farkas & Mohácsi-Farkas 2011).Freshagriculturalproductsareusuallyexposed tolow doseofirradiationaimingimprovedhygienic qualitywithreducedenzymeactivityandrespiration rate(Arvanitoyannis2010).

Mushroomshavehighmarketdemandalloverthe worldduetotheiruniquetasteandexclusivefunctional properties(Cheung2008).Pl

e u r o t u ss p p.i

sthirdmost producedvarietyofmushroom intheworld(Royse 2003).Variousscientificreportshavedemonstratedthe high consumer demand due to its functional characteristics(Lo2008;Oke& Aslim 2011)andneed ofadvancedpreservationtechnologyforanincreased

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marketability(Xiaoe

ta l

.2011).Theshortpost-harvest lifeoffreshmushroomsduetoitsperishablenature andpoorhygienicqualityaremainconstraintsfor cost-effective long distance supply to different consumermarkets(Akram & Kwon2010).Different preservation methodologies, including modified atmospherepackaging(Gonzalez-Fandose

ta l

.2001;

Jacxsense

ta l

.2001)andchemicaltreatments(Brennan etal.2000)weredevelopedtomaintainpostharvest qualityoffreshmushrooms(Koorapatie

ta l

.2004). Recently,Xiaoe

tal

.(2011)reportedthecombined effectofchemicaltreatmentandmodifiedatmosphere toextendshelf-lifeofPl

e u r o t u so s t r e a t u smu

shrooms.

Inseveralcountries,includingKorea,freshanddried mushroomsarepermittedforfoodirradiation.Allowed doserangesforfreshmushroomsisgenerally1–3kGy andthatofdriedonesis1–10kGy(Akram & Kwon 2010).Ag

ar i c u sb i s p o r us(

Byune

ta l

.1990;Beaulieu

e tal

.2002;Akram & Kwon2010),Le

n t i n u se do d e s

(Jiange

ta l

.2010),andP.e

r y n g i i(

Akram e

ta l .2

012) showedtheimprovedpostharvestqualityandenhanced shelf life following irradiation. However, other mushroomsstillneeddetailedinvestigationproviding thebasicscientificdataforgeneralapplicabilityof irradiationtechnology.

Inthisstudytheappearance,color,texture,andweight loss of gamma-irradiated Pl

e u r o t u s o s t r e at u s

mushroomswereevaluatedduringstorage.Thechanges uponirradiationinthevolatilecompoundprofileand micro-structurewerealsoinvestigatedusingE-nose analysisand scanning electron microscopy (SEM), respectively.

Mat er i al sand met hods

Mushr ooms,i r r adi at i on,and st or age

Freshoystermushrooms(

Pl e u r o t u so s t r e a t u s

)of uniform sizeandfreeofphysicaldamage,werefilled inpolystyrenetrays(about300±10g)andwrappedwith foodgradepolyvinylchloridefilm.48mushroom trays weregroupedforeachirradiationtreatmentandcontrol.

Thesampleswerestoredat5±1℃ beforeirradiation treatment.Thenextday,gammairradiationtreatment (0,1,2,and3kGy)wasperformedusingaCo-60 gamma-ray source (AECL,IR-79,MDS Nordion InternationalCo.Ltd.,Ottawa,ON,Canada)atthe KoreanAtomicEnergyResearchInstitute(Jeongeup, Korea). The treatment was conducted at room temperaturewithadoserateof2.1kGy/handalanine dosimetersofadiameterof5mm (BrukerInstruments, Rheinstetten,Germany)wereattachedwiththesamples tocalibratetheabsorbeddoses.Allirradiatedand controlsampleswerestoredat5±1℃ inalaboratory refrigeratorfor4weeks.Threesampletrayswere randomlyselectedfrom eachgroupfordifferentanalysis asdescribedbelow.

Col ordet er mi nat i on dur i ng st or age

Chromameter(ModelCR-200,MinoltaCameraCo., Osaka,Japan)wasusedtodeterminethecolorchanges uponirradiationandduringsubsequentstorage.Color characteristics(L^*representinglightness,a^*rednessto greenness,and b^* yellowness to blueness) were determinedforeachsamplegroup(n=9).Thetotal changeincolor(ΔE)withrespecttothatofcontrol group atday firstwasalso determined using the expressionΔE=√ΔL²^°+^°Δa²^°+^°Δb²^°.

Text ur alchanges and wei ghtl oss dur i ng st or age

Sixsampleswereanalyzedfrom eachtreatmentgroup andcontroltodeterminethechangeinfirmnessusing aSunrheometer(Compac-100,SunScientificCo.,Ltd., Tokyo,Japan)asdescribedearlierbyAkram e

ta l

. (2012).Ninesampletraysfrom eachgroupweremarked withtheirrespectiveweightandthechangeswere confirmedbyweighingweeklyduringstorage.The percentageweightlosswithrespecttotheinitialweight wasreported.

Scanning electron microscopy

Ultra-structuraldeterminationswereconductedupon

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smallpieces(n=3)ofthemushroom stem surfaceand internaltissuesectionsasdescribedAkram e

ta l

.(2012). Hitachiscanningelectronmicroscope(ModelS-570, Tokyo,Japan)at1000×magnificationwasusedfor theSEM investigation.

Eval uat i on ofvol at i l epr of i l e

The volatile compound profiles ofcontroland irradiatedsampleswereinvestigatedusingazNose (ElectronicSensorTechnology,NewburyPark,CA, USA),equippedwithasurfaceacousticwave(SAW) sensorandVaporPrint^TM (Misrosense4.88)software. Crushedsample(2g)wasfilledina40mL vial (Supelco,Bellefonte,PA,USA)thatwassealedusing acapfittedwithaTeflonseptum (PTFE/siliconesepta, Supelco).Theheadspaceequilibrium wasattainedby leavingsampleatroom temperaturefor4hr.The analysiswasperformedataSAW sensortemperature of30℃;column,60℃;valve,120℃;inlet,150℃;and trap,220℃ (Akram e

tal

.2012).Tofindatrendin E-nosenumericaldata,principalcomponentanalysis (PCA)wasusedasdescribedbyKeshrie

ta l

.(2003).

Resul t sand Di scussi on

Col orat t r i but esdur i ng st or age

Tables1and2aredemonstratingthechangesinthe keycolorparameters,uponirradiationandsubsequent storage,inthestem andcappartsofmushrooms, respectively.Atthesamedayafterirradiation,the decrease in Hunter’sL-value (lightness)following irradiationwasobservedinthestem regionthatwas mostprominentin2and3kGy-irradiatedsamples, whereas1kGy-irradiatedsampleshadaboutsimilar valuesasthatofcontrolgroup(Table1).Theeffect ofirradiationwasmostprominentduringstorage,where allirradiatedsamplesshowedincreasedL-values.The control samples showed a decrease in L-value (lightness)duringstorage.Similareffectwasobserved incaseofb-value,whereasa-valueshowedanegligible effectuponirradiationandduringsubsequentstorage.

Thecapregion(Table2)showedmoredifferences than the stem partofthe mushrooms following irradiationtreatment.Atthesamedayafterirradiation treatment,thecontroland1kGy-irradiatedsamples showed similarcolorcharacteristics.However,the differenceswereprominentin2and3kGy-irradiated samples,whichshowedadecreaseina-valueand increaseinb-valueascomparedtothecontrolgroup. AllirradiatedsamplesshowedhigherL-valueswith slightdecrease in a-values during storage.Most significantdifferenceswereobservedincaseofb-value, whichwasmuchhigherforcappartsofirradiated samplesduringstorage.Microbialspoilageanddifferent physiologicalactions(enzymeactivityandrespiration) canaffectthecolorpropertiesofnon-irradiatedsamples (Simone

ta l

.2005).Irradiationcanimprovehygienic qualityandcanretarddifferentphysiologicalprocesses leadingbettercolorattributes.However,irradiationcan alsobleachthecolorpigment(Morenoe

ta l

.2007)and effectcellstructureresultinginchangedcolorproperties ofasample.Koorapatie

ta l

.(2004)showedthat1kGy gammairradiationimprovedL-valuesinslicesofA.

b i s p o r u sh

oweverthedrasticeffectwasapparentat higherdoses(3.1and5.2kGy).

Physicalappearance,firmness,and weight lossduring storage

Nonoteworthyapparentdifferenceswerefoundin thetreatedsampleswithrespecttothecontrolgroup (Fig.1)atthesamedayafterirradiationtreatment. However,irradiatedsampleswereeasilydistinguishable duringstorageduetothecapcolorthatturnedyellowish from originalgreencolor.Inthecontrolsamples,the greencolorbecamedarkerduringstoragemakingthe colordifferencemoreprominent.However,themold attackwasalsoobservedonthenon-irradiatedsamples atthethirdweekofstorage,whichwasabsentinthe allirradiatedsamples.Microbialspoilageduringstorage in non-irradiated samples of A. b

i s p o r u s s

lices (Koorapatie

ta l .2

004)andP.eryngii(Akram e

ta l

. 2012)wasalsoreportedpreviously.Dose-dependent softeninginthemushroomswasobservedforall

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Ta bl e1 .Ef f e c tofga mmai r r a di a t i ononc ol o rc ha r a c t e r i s t i c si nt hes t e m r e g i ono fPl e ur ot usos t r e at usmus hr o omsdur i ng s t o r ag e .

Hu nt e r

p a r a me t e r

^†

St or a ge ( da y) I r r a di a t i ondo s e( kGy )

0 1 2 3

L

0 8 3. 2 3±3 . 01

^‡a^x

82 . 05 ±2. 56

^a^x^y

75 . 18 ±2. 6 7

^b^z

79 . 10 ±3. 35

^b^y

7 80 . 84 ±4. 73

^a^b^x

80. 19±5 . 14

^a^x

81 . 18 ±2. 37

^a^x

83. 64±2 . 49

^a^x

14 76 . 86 ±5. 86

^b^c^y

81. 98±3 . 27

^a^x

79. 08±2 . 91

^a^x^y

81. 53±4. 2 8

^a^b^x^y

21 7 4. 5 9±4 . 27

^c^y

79. 13±2 . 94

^a^x

81 . 92 ±5. 22

^a^x

79 . 28 ±2. 89

^b^x

28 77 . 43 ±3. 54

^b^c^y

80 . 79 ±2. 44

^a^x^y

79 . 39 ±2. 92

^a^y

84 . 01 ±2. 76

^b^x

a

0 - 1. 2 1±0 . 22

^c^x

- 1 . 41 ±0. 37

^b^x

- 1. 23±0 . 39

^d^x

- 2 . 01 ±0. 32

^b^y

7 - 0. 9 7±0 . 36

^c^y

- 0. 52±0 . 46

^a^x

- 0. 8 0±0. 36

^c^d^x^y

- 0 . 69 ±0. 19

^a^x^y

14 - 0 . 39 ±0. 37

^b^x

- 0. 34±0 . 41

^a^x

- 0. 25±0 . 29

^a^b^x

- 0. 59±0 . 21

^a^x

21 0. 3 0±0. 39

^a^x

- 0. 1 8±0 . 29

^a^yz

0. 0 4±0 . 44

^a^xy

- 0 . 51 ±0. 4 3

^a^z

28 - 0 . 16 ±0. 62

^b^x

- 0. 39±0 . 29

^a^x

- 0. 71±0 . 59

^b^c^x

- 0. 68±0 . 28

^a^x

b

0 10 . 20 ±0. 54

^b^y

11 . 74 ±1. 23

^a^x^y

12. 11±2 . 51

^b^x

10 . 14 ±0. 77

^b^y

7 9 . 05 ±1. 3 9

^b^c^x

12. 57±1 . 07

^a^y

10. 08±0 . 76

^b^x

10 . 04 ±1. 58

^b^x

14 7. 90±2 . 04

^c^z

12. 48±1 . 31

^a^x

1 1. 5 6±1. 78

^b^x^y

9 . 68 ±1. 6 7

^b^y^z

21 10 . 59 ±2. 37

^b^x

9 . 27 ±1. 1 6

^b^x

12. 05±3 . 39

^b^x

10 . 43 ±1. 77

^b^x

28 1 5. 6 5±2 . 37

^a^x

11. 83±0 . 76

^a^y

17 . 49 ±1. 98

^a^x

17. 27±2 . 78

^a^x

ΔE

0 0. 0 0±0. 00

^c^y

1 . 96 ±1. 1 8

^b^y

8 . 27 ±2. 0 7

^a^x

4 . 20 ±5. 4 2

^a^b^x

7 3. 7 5±4 . 03

^bx^y

5. 8 9±1 . 55

^a^x

2 . 76 ±1. 5 7

^c^y

2. 4 4±1 . 52

^c^y

14 6 . 82 ±77 . 81

^a^x

4 . 12 ±1. 2 4

^a^b^y

5. 0 3±2 . 35

^bc^y

3 . 88 ±2. 7 7

^b^c^y

21 9. 0 9±4. 17

^a^x

4 . 65 ±2. 5 9

^a^b^y

5 . 60 ±3. 19

^b^x^y

4 . 46 ±2. 7 0

^a^b^c^y

28 8. 7 6±2. 04

^a^x

3 . 34 ±2. 1 0

^b^y

8 . 78 ±1. 5 6

^a^x

7. 7 3±2 . 24

^a^x

†L^*representslightness,a^*rednesstogreenness,b^*yellownesstobluenessandΔEtotaldifferencewithrespecttoacontrolgroup.

‡Mean± standarddeviation(n=9).

a-e

Valueswithinthesamecolumnwithdifferentsuperscriptlettersaresignificantlydifferentatρ <0.05.

w-zValueswithinthesamerowwithdifferentsuperscriptlettersaresignificantlydifferentatρ <0.05.

Fi g .1 .Phy s i c a la ppe ar a nc eo fPl e ur o t uso s t r e a t usmus hr o o msupo ng ammai r r a di a t i o n( 0 - da y;a bo v e )a nds t o r a ge( 28 - da y ; be l ow) .

Colorchangesweremostprominentinmushroom caps.

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Ta bl e2 .Ef f e c tofga mmai r r adi at i ononc ol orc har a c t e r i s t i c si nt hec apr e g i o no fPl e ur ot usos t r e at usmus hr o omsdur i ng s t o r ag e .

Hu nt e r

p a r a me t e r

^†

St or a ge ( da y) I r r a di a t i ondo s e( kGy )

0 1 2 3

L

0 68 . 67 ±3. 30

^‡b^x

68 . 72 ±4. 13

^b^x

71. 36±1 . 27

^b^x

70 . 55 ±2. 72

^b^x

7 7 3. 8 3±2 . 81

^a^x

76. 41±2 . 56

^a^x

75 . 71 ±3. 80

^a^x

75. 00±4 . 35

^a^x

1 4 6 3. 0 4±3 . 82

^a^y

70 . 78 ±2. 97

^b^x

73. 30±2 . 90

^a^b^x

74 . 08 ±5. 15

^a^b^x

2 1 68 . 00 ±2. 92

^b^y

75. 27±4 . 87

^a^x

74. 10±1 . 89

^a^b^x

76. 65±2 . 36

^a^x

2 8 6 8. 5 7±4 . 58

^bz

77. 22±2 . 17

^a^x

72. 88±2 . 96

^a^b^y

74. 57±3. 4 1

^a^b^x^y

a

0 0 . 55 ±0. 8 3

^b^x

0. 5 8±0 . 93

^a^x

0. 1 3±0 . 69

^bx

0 . 22 ±0. 6 7

^b^x

7 0 . 95 ±0. 5 0

^a^b^x

0. 9 9±0 . 56

^a^x

- 0. 01±0 . 52 0 . 82 ±0. 6 2

^a^b^x

1 4 0 . 96 ±0. 4 9

^a^b^x

1. 0 1±0 . 59

^a^x

1 . 09 ±0. 4 6

^a^x

1. 2 8±0 . 71

^a^x

2 1 1. 4 7±0. 97

^a^x

0. 8 9±1 . 00

^a^x

1 . 08 ±0. 5 3

^a^x

1. 1 5±0 . 59

^a^x

2 8 1. 8 0±0. 72

^a^x

0. 1 7±0 . 59

^a^y

0. 5 6±0 . 53

^a^by

0 . 74 ±0. 6 9

^a^b^y

b

0 11 . 43 ±1. 48

^b^y

12. 35±0 . 57

^c^y

13. 54±1 . 38

^b^x

11. 66±0 . 43

^c^y

7 1 0. 0 7±1 . 12

^bc^z

15 . 02 ±2. 40

^b^x

11 . 01 ±0. 7 5

^c^y^z

12. 25±1 . 25

^c^y

1 4 9. 0 5±2. 04

^c^y

14 . 58 ±2. 04

^b^c^x

13. 87±2 . 21

^b^x

15 . 58 ±1. 79

^b^x

2 1 1 1. 2 9±1 . 51

^bz

14. 31±3. 0 3

^b^c^x^y

12. 85±1 . 03

^b^yz

16 . 03 ±1. 93

^b^x

2 8 1 4. 6 3±2 . 08

^a^y

19. 93±2 . 07

^a^x

17 . 64 ±2. 19

^a^x

18. 52±1 . 85

^a^x

ΔE

0 0. 0 0±0. 00

^c^y

3 . 88 ±1. 2 9

^c^d^x

3. 7 3±1 . 24

^bx

2 . 60 ±2. 1 0

^b^x

7 5 . 56 ±2. 6 1

^a^b^x

8 . 76 ±2. 8 7

^b^x

7 . 23 ±3. 5 8

^a^x

7. 0 2±3 . 30

^a^x

1 4 6. 1 3±4. 13

^a^x

4 . 41 ±2. 7 8

^d^x

5. 8 3±2 . 45

^a^bx

7. 4 4±4 . 54

^a^x

2 1 2. 9 1±1. 84

^b^z

7. 98±4 . 47

^b^c^xy

5. 8 3±1 . 54

^a^by^z

9. 3 1±2 . 81

^a^x

2 8 5. 5 1±2. 05

^a^b^z

12. 17±2 . 54

^a^x

7. 6 4±3 . 37

^by^z

9 . 54 ±2. 9 1

^a^x^y

†L*representslightness,a^*rednesstogreenness,b^*yellownesstobluenessandΔEtotaldifferencewithrespecttoacontrolgroup.

‡Mean± standarddeviation(n=9).

a-e

Valueswithinthesamecolumnwithdifferentsuperscriptlettersaresignificantlydifferentatρ <0.05.

w-zValueswithinthesamerowwithdifferentsuperscriptlettersaresignificantlydifferentatρ <0.05.

Fi g.2 .Ef f e c tofg ammai r r a dai t i ono nf i r mne s s( abo ve )andwe i g htl os s( be l ow)ofPl e ur ot usos t r e a t usmus hr oo msdur i ng

s t o r ag e .

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irradiatedsamples(Fig.2A).Thechangeinfirmness wasapparentatthesamedayafterirradiationtreatment; however,differenceswere more prominentduring storage.Allsamples,includingthecontrolgroupsoften duringstorage,wherethesamplesirradiatedat1kGy showedacomparablefirmnesstothatofcontrolgroup duringstorage.Texturalchangesweremostprominent in2and3kGy-irradiatedsamples.Irradiationcaneffect enzymaticandmicrobialactions(Byune

ta l

.1990) thatmightbethemajorcausesoftexturalchangesin thecontrolsamplesduringstorage(Zivanovice

ta l

. 2000).However,irradiationcandisturbthemembranous cellstructuresresultinginleakageofcellfluidand collapseofcellintegrity(Koorapatie

ta l

.2004).The lossofcellturgidityandoverallpoorproductfirmness werealsonotedbyotherscientists,studyingirradiated freshmushrooms(Beaulieuetal.2002Akram e

ta l

. 2012).

Allirradiated samplesshowed increased weight lossduringstorage,wheretheeffectwasdependentupon theappliedirradiationdose(Fig.2B).Theeffectof irradiationoncellmembraneresultingineasyescape ofwaterfrom the mushroom surfaces mightbe responsibleforthisobservation.Thecollapsedphysical texture(shrinkage),whichwasvisibleinstemsof2 and 3 kGy-irradiated samplesduring storage,also supporttheseresults.Ourresultswerecontrarytothose providedbyRiverae

ta l

.(2011)andAkrame

ta l

.(2012) forothermushrooms,whichshowedbeneficialeffect of1kGyirradiationprovidingalowerweightlossand higherfirmness.ThesmallsizeofPl

e u r o t u so s t r e a t u s

mushroomswithanincreasedsurfaceareaexposedfor waterevaporation and difference in physiological processesmightbethecauseofthisvariation(Akram

& Kwon2010).

Micro-structuralevaluation

The scanning electron microscopy (SEM) was conducted to investigate the effectofirradiation treatmentonmicro-structureofmushrooms.Irradiation caused enlarged intercellular spaces due to the breakdownoffibrousstructuredependinguponthe

appliedirradiationdose.Thecleardiscriminationwas possible forthe samplessubjected to 3irradiation treatmentwithrespecttothecontrolgroup(Fig.3). Thecellstructurescancollapseduetoradiation-induced degradation ofcellmembranesproducing enlarged spaces(Evered& Burton1995Beaulieue

ta l

.2002). Thecomparablemicro-structuralchangeswerefound instem skinandinternaltissuesamples,wheremore cleardiscriminationwaspossibleusinginternaltissue micrographs.Theultra-structuralevaluationprovided thebetterunderstandingofradiation-induceddrastic changesinphysicalappearance,color,firmnessand weightlossobservations,wherethedetrimentalquality characteristics were also related to the applied irradiationdose.Gamma-irradiatedP.e

r y n gi i(

Akram

e ta l

.2012)andelectron-beam irradiatedblueberries (Maria e

t a l

. 2007) also provided the similar micro-structuralcharacteristics.

Changesin volatilecompound profile Radiation-induced subtle changes in sensory characteristicsofmushroomsaredifficulttopredictby sensorypanelistsduetolow thresholdofflavoring compoundsindifferentmushrooms(Laie

tal

.1994; Maue

ta l

.2006).Theeffectofirradiationtreatment wasinvestigatedusingE-noseanalysisandnumerical dataweresubjectedtoPCAtechniquetofindatrend intheexperimentalresults(Keshrie

ta l

.2003).Figure 4demonstratesthePCA resultsofthecontroland irradiated samples.Allsamplesfollowed different patternsascircledinFig.4.Theresultsshowedthat thevolatilecompoundprofilesofmushroomswerenot onlysensitiveforirradiationtreatmentbutalsodepend upon applied irradiation dose,as dose-dependent discriminationwasalsopossible.Theresultswerein goodagreementwith thoseofreportedearlierfor gamma-irradiatedP.e

r y n g i imu

shrooms(Akram etal. 2012).

In conclusion, gamma irradiation showed dose-dependenteffectuponthequalitycharacteristicsof themushrooms.Theeffectbecamemoresignificant duringstorage.The1kGy-irradiatedsamplesprovided

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Fi g .3 .Sc a nni nge l e c t r o nmi c r o s c o py( a bo ve :i nt e r na lt i s s ue ;be l o w:s ur f a c et i s s ue )s ho wi ngt hee f f e c to fg a mmai r r a di a t i on o nmi c r o - s t r uc t ur eo fPl e ur o t uso s t r e at usmus hr oo ms .

Fi g.4 .Pr i nc i palc o mpone ntanal ys i s ofE- no s e dat a de mo ns t r at i ng t he do s e - de pe nde nt di s c r i mi nat i o n i n v ol at i l epr o f i l e so fPl e ur o t usos t r e a t usmus hr o o msf o l l o wi ng ga mmai r r adi a t i on.

comparableresultstothoseofcontrolsamples.The colorbleachingeffectofirradiationthatwasquite apparentinthecapregionofallirradiatedmushrooms and fungalattack in non-irradiated sampleswere importantobservations.Thedifferentqualityattributes,

suchaschangedcolor,softtexture,andincreasedweight losswereexplainablethroughSEM analysisshowing drastic dose-dependent effect of irradiation on mushroom micro-structure.Irradiationtreatmentalso changedthevolatilecompoundprofilesofmushrooms. Theresultsshowedthatfurtherinvestigationsareneeded forprovidingbetter methodology to getimproved hygienicqualitybyirradiationwithminimum quality losses.

Acknowl edgement s

ThisresearchwassupportedbytheNationalResearch Foundation(NRF)ofKoreain2012.

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o u r n a loft heKo r e a n

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r i c us b i s p o r u s .Rad i a t i o nPh y s i c san dCh e mi s t r y6

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