Persimmon (Diospvros kaki L.) fruit arehost to various quarantined pests, includingvarious fruit flies, Iightbrown apple moth,and longtailed mealybug (Dentener et al.,1996: Paull and Armstrong, 1994), whichlimit fruit export and marketability. Forpersimmon fruit grown in Southern Califor-nia, the Mexican fruit fly (Anastrepha in-dens), a sporadic pest, can disrupt export offruit from the local area. A reliable quaran-tine treatment is needed to prevent disrup-tions in trade and may require Probit 9security, a mortality rate of 99.9968%.

Quarantine control can be met with chem-ical treatments, most commonly with methyl

Received for publication 19 June 2006. Acceptedfor publication 26 Aug. 2006.This research was supported by the CaliforniaDepartment of Food and Agriculture (CDFA) un-der Research Agreement 02-0652 and USDA-NRI(05-35503-16223).We thank Stan Tuffs of Tuffs Ranch for providingthe persimmon fruit. We also thank Adel Kader andMarita Cantwell of the University of California,Davis, for their review and suggestions.'To whom reprint requests should be addressed;e-mail ejmitcham@ucdavis.edu .

bromide fumigation. There is increased in-terest in finding alternatives to the use ofmethyl bromide as a postharvest fumigant,mostly because of its damage to the ozonelayer and phytotoxicity to some fruits. Con-trolled atmosphere treatments have beenstudied for 'Fuyu' persimmons as an alterna-tive treatment. 'Fuyu' persimmon fruit toler-ated exposure for 7 d to 40% CO2 , whichcould be a potential insecticidal treatment(Mitcham et al., 1997), but tests of thistreatment to meet quarantine security levelsmust still be conducted for a range of pests.Gamma irradiation has also been tested withlimited success. 'Fuyu' persimmons wereirradiated with 300 and 1000 Gy. The treat-ments with 1000 Gy in polybags stimulatedCO, and ethylene production compared withcontrol fruit (Wheeler and Packer, 1989),indicating fruit stress. Skin browning wasalso observed after 2 weeks of cold storage onfruit that had been y-irradiated with 1000 Gyin polybags (Wheeler and Packer, 1989).Cold treatment has been used commerciallyas a quarantine treatment to control Mediter-ranean fruit fly (Ceratitis capitata) infesta-tions in persimmon fruit exported from Italy

or Jordan (Paull and Armstrong, 1994). Coldstorage is a possible quarantine treatment tocontrol the Mexican fruit fly. Cold treatmentsthat may achieve Probit 9 control of Mexicanfruit fly include 18 d at 0.55 °C, 20 dat I °C,or 22 d at 1.7 °C (APHIS, 2003; Hallman,1999). However, these long-term coldstorage treatments require significant timeand may have deleterious effects on fruitquality by causing chilling injury (Cl),thereby limiting fruit marketability.

Hot water dips and hot air treatments havebeen reported as possible quarantine treat-ments to control I ightbrown apple moth(Epiphvas posll'ittana) and longtailed mealy-bugs (Pscudoc'occtis longi.spinus) on persim-mon fruit exported from New Zealand toJapan (Detitener et al., 1996: Lay-Yee et al.,1997). These pests are likely found on thesurface of persimmon fruit or underneath thecalyx. Consequently, they are directly ex-posed to heat in short-time surface heattreatments that may have little effect on fruitquality. On the other hand, the Mexican fruitfly is an internal pest that would requirelonger heat treatments with hot water or hotair to heat the center of the fruit to desiredlethal temperatures. These longer exposuretimes are the result of the slow transfer ofheat by conduction, sometimes resulting ina very small window between fruit qualityand efficacy against pests: thus, shorter heattreatments are desired.

Radiofrequency (RF) energy involvesvolumetric heating of commodities, in whichelectromagnetic waves directly interact withthe commodity interior to generate heatthrough molecular friction, consequentlyraising temperatures much faster and moreevenly (Tang et al. 2000). For fresh fruits, RFheating would have the advantage of directheating of internal pests (Wang et al., 2003),thus shortening the exposure of fruits to hightemperatures that could reduce fruit damage.Recently, Hallman et al. (2005) reported invitro thermal mortality of third instar Mexicanfruit fly larvae using a heating block system.The heating block system heated the insectsin a controlled narrow heating space betweentwo metal plates closely mimicking the heat-ing rate of insects generated by RF energytreatments (Wang et al., 2002). These in vitroheating block system tests provided thetemperature and timeframe necessary to gen-erate the thermal death mortality curve forthe Mexican fruit fly (Hallman et al., 2005),which can be used as a guide to conductfurther heat treatments. The objective of thisstudy was to determine the tolerance of'Fuyu' persimmons to RF heating treatmentsbased on the thermal death mortality curvefor the Mexican fruit fly and determine ifa RF insect control treatment would befeasible.

Materials and Methods

Fruit availability and storage he/öretreatment. Persimmon fruit were harvestedfrom a commercial orchard in Winters, Calif.,

HOR I S( 11 N( F 42(1):125-129. 2007.

Effect of Radiofrequency Heatingon the Quality of 'Fuyu' PersimmonFruit as a Treatment for Controlof the Mexican Fruit FlyMaria E. Monzon, Bill Biasi, and Elizabeth J. Mitcham'Department of Plant Sciences, Univeiwitv of Calitirnia, !V1S2, One ShieldsAvenue, Davis, CA 95616-8780

Shaojin Wang and Juming TangDepartment of Biological Si 'stems Engineering, Washington StateUniversity, 213 Smith Hall, Pullman, WA 99164-6120

Guy J. HallmanUSDA —ARS, Crop Quality and Fr, at Insect Research Unit, 2413 E. Highway83, Building 200, Weslaco, TX 78596

Additional i,id(!x holds. Aitactiep/ia Inc/ens, commodity treatment. Diosptmos kaki, heat.phytosanitary, quarantine

Abstract. The external and internal quality of 'Fuvu' persimmon fruit (Diospyros kaki L.)was evaluated after heating with radiofrequency (RF) energy to 48, 50, or 52 °C, holdingat the target temperatures for durations ranging from 0.5 to 18 minutes, hydrocooling,and ripening at 20°C for 12 days. These treatment conditions were identified for controlof third instar Mexican fruit fly larvae (Anastrep/za ludens). The treatments had nocommercially significant effect on firmness, soluble solids content, titratable acidity, orweight loss of the fruit. RF-treated persimmon fruit attained a deeper orange—red skincolor than control fruit. There as a greater incidence of slight to moderate fleshbrowning in fruit heated to 50 and 52 °C as compared with 48 °C. Calyx browningincreased slightly in all RF-treated fruit and was the highest in the longer treatments ateach temperature. Heating persimmon fruit ith RF to 48°C and then holding for 6 or 12minutes showed the least damage, and the latter treatment was longer than should berequired for a quarantine treatment against the third instar Mexican fruit fly. Holdingpersimmons for 6.6 minutes at 48 °C should provide control of the Mexican fruit fly andmaintain fruit quality. Confirmation tests with infested fruit should be conducted.

Eli\4211 1 F.20II 25

on 5 and 12 Nov. 2003. After harvest, fruitwere transported to the Postharvest Labora-tory at the University of California, Davis,where they were sorted for size (150-200 g),color uniformity, and absence of calyx dam-age and surface defects. A total of 352 fruitper harvest was stored in chambers ventilatedwith humidified, ethylene-free air at 20 °C.The fruit were divided into two groups, onegroup was treated after 24 h and the secondgroup after 48 h of harvest, because it was notpossible to conduct all treatments and repli-cates on the same day. At harvest, persimmonfruit had an average of 16.6 ± 0.1% total sol-uble solids content, a hue angle of 69.9 ± 4.0denoting an orange—yellow skin color, andthe firmness was 66 ± 7.5 N penetration force.

Treatments. Persimmon fruit were heatedwith a 27-MHz, 12-kW batch RF machine(Strayfield International Limited, Woking-ham, U.K.). A 13-L container was used tohold the fruit submerged in a saline (NaCI)solution of distilled water while circulatingduring RF exposure (Birla et al., 2004). Thesaline solution was used as a medium to avoidoverheating of fruit at the contact points withother fruits and to assure heating uniformityby matching the dielectric properties of thefruit with those of the water based on itselectrical conductivity (EC). Persimmon fruitwere placed into the container and coveredwith an acrylic top plate to ensure fruitsubmersion in the 20 °C saline solution andproper fruit rotation. A centrifugal transferpump (245 W, 0.0031 ATM BronzeCentrifigal Pump, American Machine andTool Co.. Royersford, Pa.) permitted solutionrotation inside the container. Water jetsmounted on the periphery of the containerforced the fruit to rotate on their own axiswhile circulating in the container. Thesemotions helped to improve RF heating uni-formity (Birla et al., 2004).

Initial tests showed that with a water ECof 56 mSm (0.035% NaCl at 20 °C), thesaline solution and the fruit would heatevenly at a rate of 6.0 ± 0.5 °C min' andRF power of 9.6 kW with low temperaturevariation (2 °C) within and among the fruit.Water temperature at the end of RF treat-ments was 1.5 to 2 °C higher than the fruittemperature. For the final experiments, thetime when fruit temperature should havereached the target temperature was deter-mined by monitoring the heating rate of thesaline solution, which was heated 1.5 to 2 °Cwarmer than the target fruit temperature sothat the coolest temperature within the fruitwould be at or higher than the target temper-ature. A fiberoptic probe (FISO Technologies,Quebec) with ±0.5 °C accuracy and responsetime of less than 1.5 s inserted in the container3 cm below the water level was used tomonitor the saline solution temperature. Foreach treatment, eight persimmon fruit wereheated at one time because of space limita-tions inside the container; each of these heatexposures was considered as a treatment rep-lication. To increase the replicates, eachtreatment was repeated two times within eachof the two harvest dates and each of the two

delay periods (24 and 48 h) to have a total ofeight replicates per treatment.

Research by USDA ARS, Weslaco, Texas,and Washington State University. Pullman,using a heating block system determined thein vitro thermal-death mortality curve (timeat each temperature required for 100% mor-tality) for 600 third instar Mexican fruit flylarvae, the most heat-resistant life stage(Hallman et al., 2005). Preliminary in vitrothermal death kinetic data for third instarMexican fruit flies indicated that the requiredminimum times for 100% mortality of 600insects were 6.0, 1.5, and 0.5 min at 48, 50,and 52 °C, respectively. We selected a totalof nine treatments to determine the toleranceof persimmon fruit to RF heating. The expo-sure times at each temperature were based onthe minimum time required for 100% mor-tality (phytosanitary control) plus two longerexposure times to determine the upper limitof fruit tolerance (Table I). During RFtreatment, the saline solution and fruit wereheated from 20 °C to 48, 50, or 52 °C (Fig. 1).After reaching the target temperature, thefruit were held in the hot water for theselected holding times. Untreated fruitand fruit treated in water at 24 °C for 6 mm(approximate time to RF-heat fruit from20 °C to target temperature) were includedas controls.

Immediately after RF heating and thedesired holding time at the target tempera-ture, fruit were hydrocooled by pumping 0 °Cwater into the container while draining thehot water until the water temperature decreasedto 30 °C (Fig. I). Fruit were then transferredto a 15 °C cold water bath and held for 20 mmto promptly remove heat from the fruit. Theinternal temperature decreased to 25 °Cafter 20 min and the fruit were fan-dried toremove surface moisture. All fruit from eachtreatment replication were placed together ina 3.78-L jar connected to a flow board, whichsupplied a uniform flow of humidified (90%to 95% RH), ethylene-free air at 20 °C, and150 mLmin for 12 d at 20 °C to determineeffects of the heat treatment on fruit ripeningand condition. During ripening, the outletgases were monitored for CO 2 (daily) andC2 H4 (every 2 d). CO, concentrations weremeasured with an IR gas analyzer (HoribaVIA 510; Horiba Instruments Inc., Irvine,Calif.), and C,H 4 concentrations were mea-sured using a gas chromatograph (Carl GasChromatograph model 211; Chandler Engi-neering, Tulsa, Okla.) with a flame ionizationdetector using N 2 as the carrier gas at 80 T.The column used was 8% NaCl on aluminaF-I (Supelco, Bellefonte, Pa.).

Quality evaluations. Fruit skin color wasmeasured on opposite sides of each fruitusing a Minolta Chromameter (model CR-300; Ramsey, N.J.). The Chromameter wascalibrated with a Minolta white calibrationplate (No. 22,633,012). The readings werereported as hue values, in which color anglesare classified as red (0°), yellow (90°), green(180°), blue (270°), or an intermediate colorbetween any pair of these colors. The skin ofeach fruit was removed on two opposite sides

Table 1. Target temperatures and holding times forradiofrequency treatments designed to provide100% mortality of Mexican fruit fly third instarlarvae in 'Fuyu' persimmon and two extratimings designed to test the upper limit offruit tolerance to the treatment.

Holding times (mm)Target ExtraExtratemp (°C) Control TDT' timing I timing 2Untreated024648 6121850 1.534.552 0.5I2'Thermal death time (TDT) necessary to reach100% mortality of 600 third instar Mexican fruitfly larvae (Hallman ci al., 2005).

o 50

40

30I-

200246810

Time (mm)

Fig. 1. Temperature of saline water solution duringradiofrequency heating and hydrocooling of'Fuyu' persimmon fruit. Fruit temperature wassimilar to water temperature after treatment.Water and fruit were heated from 20 to 50 + 0.5°C, held at 50 °C for 3 min, and hydrocooled to30 °C before transfer to a 15 °C water bath.Heating rate was 6 °C min.

and fruit firmness was measured as resistanceto penetration with an 8-mm probe using aFruit Texture Analyser (Giiss, South Africa).Juice was extracted from wedges cut frontstem to blossom end from a composite of twofruit from the eight fruit used for eachreplication per harvest, delay period, andtreatment for determination of soluble solidscontent (SSC) and titratable acidity (TA);these data were averaged within each treat-ment replication to have a total of eightreplicates per treatment. Percent SSC wasdetermined by a digital refractometer (Abbemodel 10.450; American Optical, Buffalo,N.Y.) and TA (malic acid equivalents) by anautomatic titration system (TIM 850; Radi-ometer, Copenhagen, Denmark).

After ripening at 20 °C for 12 d, persim-mon fruit were evaluated for external andinternal quality, and a hedonic scale was usedto determine the severity score for the fruitthat had damage. Skin browning and shrivelwere evaluated on a scale of 0 to 3 in which0 = none, I = slight 0% to 10% of fruitsurface). 2 = moderate (11% to 25% of fruitsurface), 3 = severe (>25% of fruit surface).Calyx browning or drying was evaluated ona scale of 0 to 4 in which 0 = none, I = veryslight (slight browning at the edges, 1% to10%), 2 = slight (11% to 30% of surfacearea), 3 = moderate (31% to 60% of surface

126

HORTSC ri±c e Voi. 42(1) FIIRRLARY 2007

area), 4 = severe (>60% surface area). Fruitwere cut in half at the equator and fleshbrowning was evaluated on the cut surfaceof one half on a scale of 0 to 4 in which 0 =none, 1 = very slight (1% to 10% of surfacearea, very center of the fruit), 2 = slight (11%to 20% of surface area). 3 = moderate (21% to40% of surface area), 4 = severe (>40%surface area). Internal browning of fleshbegan in the fruit center and spread outward.Decay development was evaluated as 0none and 1 = some decay. For all externalsubjective scales, except decay, ratingsgreater than 2 (slight) were considered com-mercially unacceptable.

Statistical anah'sis. Fruit quality wasanalyzed using a randomized complete blockdesign consisting of two harvest dates, eachbeing subjected to two delay periods beforetreatment (24 and 48 h after harvest). Thesetwo variables were considered as blocks.Within each harvest delay period combina-tion, there were a total of nine RF treatmentsand two controls (Table 1), which werereplicated twice, giving a total of eightreplicates per treatment. For each qualitytrait, the average of the eight fruit from eachexperimental unit was considered as a repli-cate. Analysis of variance was computed bySAS Version 9 (SAS Institute, Cary, N.C.).Least square means were used when therewere missing values in the treatments. Meancomparisons between the untreated controlfruit and each treatment were performedusing Dunnett with a low experiment-wiseerror rate ((x = 0.05).

Results and Discussion

Harvest I and harvest 2 showed similarethylene production and respiration rate pat-terns. Ethylene production was lower than0.3 pL kg'h throughout the ripening periodat 20 °C and was not different among thetreatments (data not shown). The respirationrate of untreated persimmon fruit was 8.9 to9.2 mL CO 2 kg-h-' throughout the ripeningperiod at 20 °C. The maximum mean respi-ration rate (n = 8) was 6, 5, and 10 mL CO2kgh higher in RF-treated than in untreatedfruit 2, 6, and 12 d after treatment, respec-tively (Table 2). After 2 dat 20 °C, all the RF -

treated fruit had higher respiration ratescompared with the untreated fruit, but therespiration rate decreased after day 6 in sometreated fruit indicating that the fruit hadbegun to recover from the heat stress. Man-goes also recovered from heat stress after 4 dat 20 °C after vapor-heat treatment at 46 °Cfor 4 h (Mitcham and McDonald, 1993).Persimmon respiration rates were highest infruit heated to 52 °C, particularly after 12 dat20 °C, and these remained significantly ele-vated. However, fruit heated to 50 °C for 1.5ruin also showed higher respiration rates after12 d at 20 °C compared with the untreatedfruit. The higher respiration rates resultingfrom RF treatments indicate fruit stress andcorrelates with the internal damage observedfor the same treatments. Heat stress has also

been observed in vapor-heated mangoes inwhich it was attributed to higher respirationrates after treatment (Mitcham and McDonald,1993) and to the physiological damage of theinternal tissues (Mitcham and McDonald,1997).

Analysis of variance showed that persim-mon skin color (hue), firmness, SSC, calyxbrowning, and flesh browning were signifi-cantly different (a = 0.05) among the treat-ments (Table 3, Figs. 2 and 3). Calyxbrowning and flesh browning were bothhighly significant for treatment (P <0.0001).

Treatment of persimmon fruit at 48 °C,especially the longer exposure times, resultedin an increase in orange-red color as in-dicated by a decrease in hue angle comparedwith the untreated fruit (Table 3). This in-crease in orange-red color was also seen infruit heated to 50 °C for 1.5 or 3 ruin and to 52°C for 2 ruin. Similarly, an increase in yellowskin color intensity was observed in heat-treated 'Kensington' mangoes in which it was

TreatmentTemperature (°C)Time (mm)

24 648 6

1218

50 1.534.5

52 0.5

2

attributed to enhanced ripening (Jacobi andGiles, 1997; Jacobi et al., 1995). An increasein skin color of'Fuyu' persimmon fruit frombrilliant orange yellow to deep orange in-dicates changes in fruit maturity (Beede,1983) or ripeness. RF-treated fruit alsotended to be softer.

RF treatment had no effect on fruit TA orweight loss and had little effect on SSC(Table 3). Although the analysis of varianceshowed a significant overall effect of treat-ment on fruit firmness (P = 0.04), there wereno significant differences between the un-treated control fruit and the RF treated fruit(Table 3). There was a trend toward lower fruitfirmness with RF treatments at the higher tem-peratures (50 and 52 °C), but our results showthat fruit from all treatments were greater than22 N penetration force, the firmness mini-mum threshold acceptable to consumers of'Fuyu' persimmons (USDA, 2005). Fruitheated to 50 °C for 1.5 nun and 52 °C for 2ruin had the lowest firmness. Fruit treated at

Respiration Rate (mL CO kg h 1)

Day Day 12

Table 2. Mean values for Fuyu' persimmon fruit respiration rate (ii = 8) after radiofrequency treatmentafter 2, 6. or 12 d of ripening at 20 °C.

9.2 8.9 8.9

9.2 8.7 8.3

1 1.4* y10.6 12.112 . 6* 10.9 11.313 . 2* 12.0* 11.913 . 6* 13.6* 16.4*

12 . 7* 11.1 12.513 . 3* 12.3* 12.914 . 9* 13.1 16.1*

14 . 9* 13.8* 19.1*

15 . 2* 14.3* 19.0*

Overall P value <0.0001 <0.0001 <0.0001

Control vs. treatment iso' 1.9 2.8 5.4

'Untreated control fruit.Asterisk (*) denotes treatment mean was significantly different from untreated control at a = 0.05 based

on Dunnett minimum significant difference.'Dunnctt mean significant difference (Mso) used to compare the untreated control versus a given treatment.

Table 3. Mean values for quality traits (n = 8) on the effect of radiofrequency treatments on persimmonskin color, firmness, soluble solids, iitratable acidity, and weight loss after 12 d of ripening at 20 °C.

Treatment Skin ColorFirmnessTemperature (°C)Time (mm)(Hue)(Newtons)SSC' (%)TA (%)Wt loss (%)

61.244.617.10.100.7

24 661.346.217.30.081.1

48 658.642.617.10.090.8

12577*41.417.10.100.8

18573*41.417.10.120.8

50 1.557.6*34.016.70.101.1

358.2'38.517.10.100.8

4.559.137.516.70.110.8

52 0.558.836.417.00.131.0

58.937.116.50.120.9

2579*34.615.7*0.111.3

Overall P value <0.0010.04<0.0010.790.08

Control vs. Treatment vIsu'2.811.00.90.070.6

'Soluble solids content.'Titratable acidity.'Untreated control fruit."Asterisk )*) denotes treatment mean was significantly different from untreated control at a = 0.05 basedon Dunnett minimum significant difference.'Dunnett mean significant differences (usD) used to compare the untreated control versus a giventreatment.

HORTSCiENCE VOL. 42(1) FEBRUARY 2007 127

Untreated24 C48 °C50 °C52 Ccontrolcontrol

A

100

2 'E75

ca

('050

o.

oU)

25

BControlV//I1.21.1

Phytosanitary

Extratiming 1F:

timing 2

52 °C for 2 min alsoalso had significantly lowerSSC compared with the untreated fruit. Theseresults indicate that the longest treatment atthe highest temperature (52 °C for 2 min)caused the greatest amount of fruit stress.

RF treatments had little effect on theexternal appearance of persimmon fruit. Skinbrowning was not significantly affected bytreatments (P = 0.1) but was observed insome fruit treated at 52 °C for 1 or 2 mm (datanot shown). The browning was slight (<10%surface area), and symptoms were localizedsunken areas with tissue softening that werenot uniformly distributed on the surface ofthe fruit. Skin browning appeared to resultfrom overheating at contact points betweenfruit likely incited by slow rotation within thetreatment container, possibly because of non-spherical fruit shape (Birla et al., 2004).

Calyx browning manifested as very slightto moderately brown and dry areas on thecalyx. For all RF treatments, the averagecalyx browning severity of affected fruitwas slight to moderate compared with theuntreated fruit that had very slight calyxbrowning (Fig. 2B). There was a higherpercentage of calyx browning on all RF-treated fruit as compared with untreatedcontrol fruit (data not shown). However, onlyfruit heated to 52 °C for I or 2 mm, 50 °C for

1.82.01.8

1.91.92.1

2.21.92.5

1.5 min, or 48 °C for 18 min hadhad significantlyless acceptable fruit based on the percentageof fruit with calyx browning severity scores:!^2 compared with the untreated control fruit(Fig. 2A). Fruit heated to 48 °C for up to 12min had more than 85% of commerciallyacceptable fruit based on calyx browning. Webelieve that the NaCI solution oror the dryingprocess may have resulted in some damage tothe calyx, and these parameters should becontrolled in future studies.

RF treatments had no significant effect onshrivel or decay symptoms (P = 0.8 and 0.5,respectively). Shrivel was not observed inthis study, perhaps because fruit were imme-diately hydrocooled after RF treatments andwere then ripened immediately at 90% to95% relative humidity. A low level of decayincidence was observed when fruit wereheated to 52 °C for 2 mm (6.3%), but thiswas not significantly different from controlfruit that had no decay (data not shown).

Some RF treatments affected flesh qual-ity, resulting in internal browning begin-ning in the center of the fruit and expandinginto the middle of the flesh as severityincreased. Persimmon fruit did not tolerateRF heating to 52 °C, even with a holdingperiod as short as 0.5 mm, resulting ina significantly lower percentage of accept-

able fruit (62%) compared with the controlfruit (100%) (Fig. 3A). Treatments at 50°Cresulted in higher percentages of acceptablefruit compared with the fruit heated to 52°c, and the average severity score foraffected fruit was lower than for fruit heatedto 52 °c (Fig. 3B). Although heating thefruit to 50 °C and holding for a period of 3or 4.5 min resulted in >80 0/0 acceptable fruitbased on flesh browning, holding for 1.5min at 50 °C resulted in only 60% accept-able fruit with all unacceptable averageseverity score. The reason for this variabil-ity in response is unknown but may indicatethat RF treatment at 50 °C has the potentialto cause significant fruit damage. Addi-tional work is needed to clarify this point.The percentage of acceptable fruit based onflesh browning scores 2 when fruit wereheated 1o48 °C was more than 94% and wasnot significantly different t'rom untreatedcontrol fruit. The severity scores averaged1.5, within the range of commercial accept-ability (Fig. 3).

RF heat treatments may reduce Cl symp-touts during subsequent cold storage andshipping. Many authors have reported thatheat treatments can induce chilling tolerancein fruits (Burmeister et al., 1997; Woolf et al.,1997) perhaps as a result of formation of heatshock proteins (HSPs), as has been shown intorniato (Lurie and Klein. 1991) and 'Hass'avocado (Woolf et al., 1995). It has beensuggested that development ofHSPs could bethe reason for C1 alleviation in hot water-treated 'Fuyu' persimmons (Lay-Yee et al.,1997). Additional work is needed to deter-mine if RF-heated persimmon fruitfruit haveadditional protection from CI resulting fromHSP formation.

The RF treatment at 48 °c designed forphytosatiitary control of the Mexican Fruit flydid not significantly injure or reduce market-ability of 'Fuyu' persimmon fruit, but treat-ments at 50 °c were over the limit of fruitmarketability as a result of internal browning.Moderate to severe skin browning symptomshave been reported for persimmon fruitheated with air at 47 °c for more than 3 h(Woolf et al., 1997) or hot water dips at 47 °cfor more than I h (Burmeister et al., 1997). incontrast, our results showed that there wasonly a very slight development of skinbrowning, likely resulting from fruit-to-fruitcontact during treatment, which should beavoided with constant fruit movement ina larger commercial treatment system. Theseresults indicate that RF heating may be lessdamaging than hothot air or hot water treat-ments, perhaps as a result of the shorterexposure to heated environments. Severityof skin browning, calyx browning, andshrivel were relatively minor after RF treat-ments but were moderate to severe in hot airand hot water-treated fruit (Burmeister et al.,1997; Woolf et al., 1997). In addition to themuch shorter treatment time and heat expo-sure, immediate hydrocooling of persimmonfruit after the heat treatment likely reduceddamage from heat compared with air coolingat room temperature as reported in other

Fi g . 2. (A) Percent acceptable fruit based oil browning ses erity scores 2 after radiofrequencytreatment and 12 d of ripening at 20 °C for 'Fuyu' persimmon fruit. Fruit were heated from 20 °C to48°C (6, 12, 18 min). 50°C (1.5,3,4.5 min), or 52 °C (0.5, 1,2 min). An asterisk (*) denotes treatmentmean was significantly different from untreated control at = 0.05 based on Dunnett minimumsignificant difference (M5D 21.3). (B) Average calyx browning severity score: 0 = none. I = veryslight (slight browning at the edges, I -- I 0%), 2 = slight (II 30% of surface area), 3 = moderate(31-60% of surface area), 4 = ses ere (>6)1° surface area).

128 HORTSC'iENCE VOL. 42(1) FEBRUARY 2007

Untreated24°C48°C50°C52°Ccontrolcontrol

A

100

.-. C,

j:80

W .=60

U.

CCo

40

20

BControl 0.00.0

Phytosanitary

Extratiming I

timing 2 -

studies (Burmeister et al.. 1997; Lay-Yeeet al., 1997; Woolf et al., 1997).

Conclusions

The most promising RF protocol to obtainphytosanitary control of the third instar Mex-ican fruit fly in 'Fuyu' persimmon fruitappears to be RF heating to 48 °C for 6mm, and fruit also tolerated exposure of 12min without significant injury. The com-pleted heating block studies indicate thatthe required holding time to achieve Probit9 security for the third instar Mexican fruit flyshould be 6.6 min after RF heating to 48 °C(Hallman et al., 2005), indicating that Probit9 security could be met at 48 C within theholding times tolerated by the fruit. There-fore, heating with RF shows potential asa treatment to control the Mexican fruit flyin 'Fuyu' persimmon fruit. However, moreefficacy tests are needed to confirm that RFheating of persimmon fruit to 48 °C wouldkill Mexican fruit fly larvae within the fruit.

1.62.42.2

1.41.92.8

1.51.92.5

Literature Cited

APHIS. 2003. USDA APHIS Treatment ManualDec. 2004. http://www.aphis.usda.gov .

Beede. R. 1983. The storage performance ofFuyu Persimmon and its susceptibility to chill-ing injury. University of California, Davis.MS Diss.

Birla, S.L., S. Wang, J. Tang, and G. Hallman.2004. Improving heating uniforntity of freshfruits in radio frequency treatments for pestcontrol. Postharvest Biol. Technol. 33:205-217.

Burmeister, D.M., S. Ball, S. Green, and A.B.Woolf. 1997. Interaction of hot water treat-ments and controlled atmosphere storage onquality of 'Fuyu' persimmons. PostharvestBiol. Technol. 12:71-81.

Dentener, P.R., S.M. Alexander, P.J. Lester, Ri.Petra. J.H. Maindonald, and R.M. McDonald.1996. Hot air treatment for disinfestation oflightbrown apple moth and longtailed mealybug on persimmons. Postharvest Biol. Technol.8:143-152.

Hallman,, G. 1999. Lethality of cold to thirdinstars, pupae, and pharate adults of the Mex-ican Fruit Fly (Diptera: Tephritidae). J. Econ.Entomol. 92:480-484.

Hallman, G.J., S. Wang, and J. Tang. 2005. Re-action orders for thermal mortality of third-instar Mexican Fruit Fly (Diptera: Tep/o'iti-due). J. Econ. Entomol. 98:1905- 1910.

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Fig. 3. (A) Percent acceptable fruit based on the flesh browning severity scores 2 after radiofrequencytreatment and 12 d of ripening at 20 °C for 'Fuyu' persimmon fruit. Fruit were heated from 20 °C to48 'C(6, 12, 18 mm), 50 'C( 1.5, 3.0, 4.5 mm), or52 'C'(0.5, 1,2 mm). An asterisk (5) denotes treatmentmean was significantly different from untreated control at w = 0.05 based on Dunnett minimumsignificant difference (uso = 30.25). (B) Internal browning severity score: 0 = none, I = very slight10% of surface area), 2 = slight (11-20% of surthce area), 3 moderate (21-40% of surface area).4 = severe (>40% surface area). Severity scores >2 were considered commercially unacceptable.

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