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主 Ninagawaetロ.1/Cryobiology73ρ016)30-39 (B)
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Fig.l0.pHitransitionsinjerusalemartichoke(HelianthusωberosusL.)tubertisuesandonion(AliumcepロL.)bulbscaleepidermaltisueswithorwithoutelectriccurentloading at-1oCJmin(A)pHitransitioninjerusalemartichoketubertisueswithorwithoutelectriccurentloadingat-1oCfmin.Diamond:0~A (noload);square:1~A; triangle:10ドA. ηlepHivaluesarethemean:tSE(n=12).(B)pHitransitioninonionbulbscaleepidermaltisueswithorwithoutelectriccurentloadingat-1oCJmin.Diamond:0μA(noload); square:1~A; triangle:10ドA.ThepHivaluesarethemean:tSE(n=9).
intracelularfrezingocuredlowered.Nakagawaetal.reported thatthetemperatureaticenucleationinfluencedthesizeoftheice crystalalthoughultrasoundwasusedtoinduceicenucleation[20]. Therefore，itwasfirstsupposedthatthedecreaseinthegrainsizeof the intracel lular ice crystals with electric cur rent loading was relatedtotheincreaseinthedegreofsupercolingwiththatin thisstudy.However，thegrowingrateofintracelularicecrystal decreasedwithanincreaseinthevalueoftheelectriccurentload (Fig.8).FurukawaandShimadareportedthatthegrowthrateon theedgeofdendriticicecrystalsincreasedwithanincreaseinthe degre e of superco oling when water changed to ice crystals at frezing[5].Xanthakiseta.lreportedthatthetemperatureofice nucleation increased when pork meats were frozen in a static electric field，although the ice crystal sizes were reduced [29]. Therefore，itissupposedthattheincreaseinthedegreofsuper- colingduetothemicroelectriccurentloaddoesnotdecreasethe grainsizeofintracelularicecrystalsbutthattheelectricstimula- tion impedes the I IF. However， that mechanism could not be elucidatedinthisstudy.
Ontheotherhand，thetemperatureatwhichthedistiledwater betweencoverglaseswasfrozenwasnotchanged，althoughthe degreofsupercolingatwhichintracelularfrezingocured increasedalitle(namely，thetemperatureatwhichintracelular frezingocuredloweredalitle)withanincreaseinthevalueof electriccurentload(Fig.5).Thecolingrateswerethesame-10(/ min，irespectiveofmicroelectriccurentloading.However，the degreofsupercolingatintracelularfrezingwithelectriccur- rentloadingwas0.7O( higherat1同 or1.8O( higherat10μA，as compared with no electric curent load. In other words，the ocurenceofintracelularfrezingafterextracelularfrezingwith electriccurentloadwasdelayed42sat1μAor108sat10~lA， as comparedwithnoelectriccurentload.Thetemperaturegradualy loweredevenduringthedelayedtime.Itisexpectedthatthemicro electriccurentloadcouldreducetheocurenceofintracelular frezinginthelivingmaterialundertemperatureslowenoughto inducefrezing.
Furthermore，thisstudyindicatedthatthemicroelectriccur- rent load-could reduce the decline ofpHi with temperature lowering.T
reducedgradualywithtemperature、lowering(Fig.9).Although the co oling rate condition and the co oling start temperature difered，thisresultwassimilartotheresultofMuraiandYoshida [19]. However，the decline ofpHi with temperature lowering reducedwithanincreaseinthecolingrate.Thetemperature decreased rapidly owing to the increased coling rate.It is assumedthatthedeclineofpHiduetocolingcouldnotfolow aftertemperatureloweringrapidly.
Ontheotherhand，thisstudyshowsthatthemicroelectric curent load reduced the decline ofpHi due to temperature loweringandthattheefectivevalueoftheelectriccurentloadto reducethedeclineofpHiduetotemperatureloweringdifersac- cordingtotheplantspecies(Fig.10).ThedeclineofplantpHidueto temperatureloweringnotonlyrelatestocelsurvival[31]butalso causeschilinginjuriesincludingwitheringanddiscoloration[25]. Therefore，themicroelectriccurentloadontheplantunderlow temperaturehasthepotentialtoreducechilinginjuries.Inadi- tion，theocurenceofchilinginjuriesisrelatedtoadeclineof plasmamembranefunction[7，17.25]，andthedeclineofplantpHi duetotemperatureloweringocursduetoaninflowofprotons fromstoragevacuoles[32].Therefore，itissupposedthatthemicro electriccurentloadcouldworkonatonoplastandmightreduce theinflowofprotons.
Rapidfrezingcanreducethedeclineoffodqualitycausedby frezing[6，16].Anincreaseofthecolingrateincreasesthedegre ofsupercolingandthisdecreasesthegrainsizeofintracelularice crystalsandthedegreofceldeformation.Itisconsideredthata decreaseinthegrainsizeofintracelularicecrystalsanddegreof celdeformationwithanincreaseofthedegreofsupercoling contributetotheimprovementoffrozenfodquality[21].Onthe otherhand，thepresentstudyshowsthatamicroelectriccurent loadduringcolingcouldhavethesimilarefectonintracelularice crystalbehaviorstothoseathighercolingrateexceptingthe growingrate.Furthermore，thisstudyindicatesthatamicroelectric cur rent load could maintain intracel lular superco oling even at temperatureslowenoughtocauseintracelularfrezingandmight reducechilinginjuries.(onsequently，webelievethattheuseofa microelectriccurentloadisefectiveandusefulinthe