Radiation Physics and Chemistry 81 (2012) 697–704

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Radiation Physics and Chemistry

0969-80

doi:10.1

n Corr

CA 9286

E-m

journal homepage: www.elsevier.com/locate/radphyschem

Commercial scale irradiation for insect disinfestation preserves peach quality

Heather McDonald a, Mary McCulloch a, Fred Caporaso a, Ian Winborne b, Michon Oubichon b,Cyril Rakovski a, Anuradha Prakash a,n

a Chapman University, One University Drive, Orange, CA 92866, USAb United States Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine, Plant Health Programs, 4700 River Road,

Riverdale, MD 20737, USA

a r t i c l e i n f o

Article history:

Received 8 October 2011

Accepted 11 January 2012Available online 30 January 2012

Keywords:

Irradiation

Phytosanitary

Peaches

Commercial

Sensory

6X/$ - see front matter & 2012 Elsevier Ltd. A

016/j.radphyschem.2012.01.018

esponding author at: Chapman University, O

6, USA

ail address: prakash@chapman.edu (A. Prakas

a b s t r a c t

Irradiation is approved as a generic quarantine treatment by the US Department of Agriculture, Animal

and Plant Health Inspection Service. Due to the effectiveness of irradiation in controlling insects on

commodities, there is a growing need to understand the effects of low dose irradiation on fruit quality.

The goal of this study was to determine the sensitivity of peaches (Prunus persica) to irradiation, and

secondly, to determine the effect of commercial scale treatment on shelf-life, overall quality and

consumer liking. Six varieties of peaches were irradiated in small batches at 0.29, 0.49, 0.69 and

0.90 kGy to observe the sensitivity of peaches at different dose levels. Changes in quality were

evaluated by 8 trained panelists using descriptive analysis. Sensory characteristics (color, smoothness,

aroma, touch firmness, mouth firmness, graininess, overall flavor and off-flavor) were evaluated at 2–4

day intervals and untreated samples served as control. To simulate commercial treatment, peaches

were irradiated in pallet quantities at a target dose level of 0.4 kGy. The average absorbed dose was

0.66 kGy with an average dose uniformity ratio of 1.57. Commercially treated peaches were evaluated

by 40–80 untrained consumers for acceptability routinely throughout the shelf life. Titratable acidity,

Brix, texture and weight loss were also monitored for both commercial and small scale irradiated

peaches. There was no dose effect on TA, Brix and weight loss due to irradiation. Peaches irradiated at

0.69 and 0.90 kGy were darker in flesh color, more juicy and less firm as determined by the trained

panel and analytical pressure tests. Commercial scale irradiation did not adversely affect shelf life but

was seen to enhance ripening. This, however, was perceived as a positive change by consumers. Overall,

consumers rated the acceptability of irradiated peaches higher than untreated peaches. Statistical

analysis was performed using linear mixed models to find determinates of irradiation on peaches.

& 2012 Elsevier Ltd. All rights reserved.

1. Introduction

The goal of quarantine or phytosanitary treatments is toprevent the introduction and spread of regulated pests (ISPM,2009). Phytosanitary treatments allow for the destruction orremoval of pests or for making the pest reproductively sterile.These treatments are particularly important for internationaltrade. Various types of disinfestation treatments include cold,hot water immersion, heated air, methyl bromide fumigation andirradiation (Hallman, 2011).

Fresh horticultural commodities in the US can be irradiated upto 1 kGy (FDA, 2008). Irradiation has been approved as a quar-antine treatment for Tephritidae family fruit flies and all otherpests (except for Lepidoptera order) at minimum doses of 0.15 kGy

ll rights reserved.

ne University Drive, Orange,

h).

and 0.40 kGy, respectively. Processors need to achieve the mini-mum dose for successful quarantine security while not exceedingthe maximum dose of 1 kGy and treatment should occur in anapproved facility following the American Society for Testing andMaterials (ASTM) standards (APHIS, 2011; Follett, 2009).

The benefits of using irradiation are that the cold treatmentallows quality to be maintained, it leaves no residue on theproduct, reduces use of fumigants and pallet loads can be treatedat a time. Low dose gamma irradiation (1 kGy or less) has beenshown to control insect pests with little quality loss to freshcommodities (Maxie et al., 1971); however, energy is impartedinto metabolically alive tissues of the commodities, so undesir-able damage can occur (Ferrier 2010).

The 2011 US peach production was forecasted at 1.13 million tons(NASS, 2011). Twenty-three US states currently produce Freestonepeaches (Prunus persica), a temperate fruit grown and producedprimarily in California, Georgia and South Carolina (NASS, 2011;Boriss and Brunke, 2006). In 2007, 112,352 metric tons of freshpeaches were exported (NASS, 2009). The 1996 Food Quality

H. McDonald et al. / Radiation Physics and Chemistry 81 (2012) 697–704698

protection Act (FQPA) and the Montreal Protocol have placed restric-tions on the types and amounts of fumigants that can be used onpeaches for pest control (Hallman, 2011). Although methyl bromidefumigation is approved for postharvest phytosanitary peach fumiga-tion for surface pests, peaches do not tolerate methyl bromide well.Irradiation is effective against pests common to peaches, such as plumcurculio (Hallman, 2003) and the oriental fruit moth (Hallman, 2004).

A major consideration in determining the feasibility of irradiationfor peaches is the effect on quality, especially under commercialconditions of distribution and storage. Various factors, such ascultivar and maturity stage, can affect the tolerance of fruit toirradiation. Peaches are a climacteric fruit that exhibit a dramaticincrease in respiration rates and ethylene production just prior tothe onset of ripening. For these fruits, the physiological state or stageof maturity often has a marked effect on the response to irradiation.At dose levels above 1 kGy, irradiation has been shown to stimulatethe onset of the climacteric in peaches through radiation-inducedethylene production (Maxie and Kader, 1966; Thomas, 1986) lead-ing to loss of firmness, and color development. Different peachvarieties have been found to respond differently to irradiationtreatment, but the greatest impact seems to be on firmness. Kimet al. (2009) noticed a dose effect in Danguemudo peaches. Allirradiated peaches (0.50, 1.0, 1.5 and 2.0 kGy) exhibited softeningcompared to control. Similar to these findings, Hussain et al. (2008)observed a dose dependent loss of firmness of Elberta peachesirradiated at doses between 1 and 2 kGy. Drake and Neven (1998)studied Regina peaches treated with low dose irradiation up to0.90 kGy. Breakdown, softening and color changes were observedamong peaches treated at doses greater than 0.60 kGy.

In 2006, the US Department of Agriculture-Animal and Plant HealthInspection Service (USDA-APHIS) approved generic treatments of0.15 kGy for fruit flies and 0.40 kGy for all insects except pupal andadult Lepidoptera (APHIS, 2006). Thus, under US regulations, peacheswould be subjected to a minimum dose of 0.40 kGy and a maximumof 1.0 kGy. Given a target dose of 0.40 kGy, under commercialconditions of treatment, the fruit will be subjected to a range of dosesbetween 0.40 and 0.80 kGy, based on a dose uniformity ratio (DUR) of2.0. However, most studies on peaches have been conducted underlaboratory conditions at dose levels exceeding 1 kGy (Maxie and Kader,1966; Thomas, 1986; Kim et al., 2009; Hussain et al., 2008, 2010). Also,while softening of peaches as a result of irradiation has beendocumented, there is a lack of data regarding consumer acceptability.

Thus, in this study we evaluated the dose response of qualityfactors of six varieties of peaches to irradiation levels below1 kGy. Also, we evaluated the effect of commercial scale irradia-tion treatment and distribution on quality and consumer accept-ability of irradiated peaches.

2. Materials and methods

2.1. Sample procurement

Six varieties of fresh peaches (P. persica) were provided byTitan Farms (July Prince, Flame Prince, August Lady) in Ridge

Table 1List of varieties and texture readings at each shipment.

Shipment Varieties Maturity

1 Encore Firm, green–yellow

1 Blaze Prince Firm, red

2 July Prince Soft, red, fully ripe

2 Red Globe Soft, red, fully ripe

3 Flame Prince Firm, yellow

3 August Lady Firm, yellow–red

Spring, SC and Lane Southern Orchards (Blaze Prince, Encore, RedGlobe) in Fort Valley, GA during June–August 2010 (Table 1). Thepeaches were bulk packed in 25 lb cardboard cartons withapproximately 70 peaches per carton after being hydrocooled.One day after the harvest, peaches were transported by refriger-ated trucks to the Food Technology Service, Inc. (FTSI) inMulberry, Florida, for gamma irradiation treatment.

2.2. Gamma irradiation

Peaches of each variety were divided into two sets. One setwas used for a small scale study designed to determine dosedependent effects of irradiation on peach quality. Thus, smallbatches of fruits were exposed to multiples doses as describedbelow to enable uniform treatment and allow precise determina-tion of the effects of irradiation dose on quality. The second set ofpeaches was used to conduct a larger scale treatment wherepeaches were irradiated in pallets to mimic commercial irradia-tion of peaches at a minimum target dose of 0.40 kGy.

2.3. Dose response Studies

For each peach variety, 30 cardboard cartons of peaches with anet weight of 25 lbs each were obtained as described above. Six ofthe 30 cartons from each grower were not irradiated and wereused as control. The remaining 24 cartons were exposed togamma radiation from a Co60 source (E1 million Ci) at FTSI(Mulberry, FL). For treatment, cartons were arranged in a singlefile stack, three cartons in height. To ensure uniformity of dose,turntables were utilized for rotating carton stacks in the irradia-tion field at a dose rate of �0.1 kGy/min. Alanine pellet dosi-meters (Far West Technology, Inc., Goleta, CA 93117, USA) wereplaced at minimum and maximum dose locations, which hadbeen previously determined by dose mapping. The target doseswere 0.25, 0.4, 0.7 and 1 kGy, and the average doses achievedwere 0.29, 0.49, 0.69 and 0.90 kGy, respectively. The observeddose uniformity ratio (Dmax/Dmin) for the turntable irradiationranged from 1.07 to 1.19.

2.4. Commercial scale irradiation

For each peach variety, 42 cardboard cartons of peaches with anet weight of 25 lbs each were obtained as described above.Eighteen cartons from each grower were not irradiated andserved as control. The remaining 24 cartons were irradiated ingroups of 12 cartons arranged in a configuration that was 1 cartonwide, 4 cartons long and 3 cartons placed high along the center-line of a 42�48 in pallet so irradiation passed through a productwidth of 20 in. Alanine pellet dosimeters manufactured by FarWest Technology Inc. were placed at the location of the minimumand maximum doses previously been determined through dosemapping. Pallets of peaches were then placed in aluminumcarriers and exposed to gamma radiation from a Co60 source(�1 million Ci) at FTSI (Mulberry, FL). Each carrier dwelled for149 s at each of the 9 stations within the irradiator. The target

Texture (lbs) Notes

�12 Did not soften during storage

�12 Flavor developed during storage

�3.5 Temperature abuse during shipment, full flavor

�3.5 Temperature abuse during shipment, full flavor

�16 Flavor developed during storage, did not soften

�16 Flavor developed during storage, did not soften

H. McDonald et al. / Radiation Physics and Chemistry 81 (2012) 697–704 699

dose was 0.40 kGy; the average absorbed dose was 0.66 kGy withan average dose uniformity ratio (Dmax/Dmin) of 1.57.

On the day following the irradiation treatment, peaches weretransported to Chapman University (Orange, CA) by refrigeratedtrucks (1–6 1C). Commercial shipment from Mulberry, FL, toOrange, CA, took 4 days. Temperatures were recorded duringshipment and storage using DeltaTRAK temperature data loggers(Pleasanton, CA). Once received at Chapman University, peacheswere stored at 2–3 1C for up to 27 days. The peaches wereremoved from cold storage 2 days prior to each test day andallowed to ripen under ambient conditions.

2.5. Sensory evaluation

2.5.1. Sensory trained panel

Panelists’ selection was based on interest and performance onpreliminary screening tests. Eight panelists were selected toevaluate peaches using descriptive analysis. Four 60-min trainingsessions were utilized to establish vocabulary describing keypeach characteristics: smoothness, bruising, flesh color (cut),peach aroma (whole and cut), whole peach firmness (usingfingertips), cut peach firmness (in mouth), mealiness, ripeness,juiciness, peach flavor, sweetness and tartness. These character-istics were rated from none to intense on a 15-point unstructured,anchored scale (15-cm horizontal lines) (Chambers and Wolf,1996). Reference points were identified by anchors placed on thescale and defined as ‘‘Gold standards’’ and ‘‘Green Controls’’. ‘‘Goldstandards’’ were defined as perfectly ripe peaches, with a break inground color from green toward yellow. ‘‘Green Controls’’ weredefined as freshly picked peaches that have reached appropriatematurity for harvest, but have characteristic light green groundcolor. The panelists evaluated all varieties of small scale irradiatedpeaches (0, 0.49, 0.69 and 0.90 kGy) throughout the investigation.

Peach slices were cut using a peach pitter (Williams-Sonoma;San Francisco, CA). Each panelist evaluated the slices for fleshcolor, firmness in mouth, mealiness, ripeness, juiciness, peachflavor, sweetness and tartness. The remaining attributes: smooth-ness, bruising, peach aroma and firmness were scored using awhole peach. Peaches were presented monadically on whitepaper plates marked with 3-digit random codes. Samples wereevaluated at 2–4 days intervals up to 27 days of storage. Panelistswere provided with unsalted soda crackers and filtered water ateach evaluation for palate cleansing between samples.

2.5.2. Consumer panel

All commercially treated (0.66 kGy) varieties of peaches wereevaluated by consumers at the beginning of storage and near theend of shelf life (up to 16 days after harvest). Consumers ratedoverall appearance, overall flavor, overall texture, overall juicinessand overall liking on a 9-point hedonic scale (like extremely¼9,dislike extremely¼1). Samples were served on white paper plateslabeled with 3-digit numbers. Samples were served to consumersmonadically in a balanced order to prevent any position bias. Themajority of consumers asked to have their peach cut; a peachpitter (Williams-Sonoma; San Francisco, CA) was used. Consumerswere asked to cleanse their palates with an unsalted soda crackerand filtered water between samples (Chambers and Wolf, 1996).

2.6. Texture analysis

Ten peaches were randomly selected from each dose level fortexture measurements. Texture was measured using an Effegi penet-rometer (QA Supplies; Norfolk, VA) with an 8 mm plunger tip.Measurements were taken on opposite sides of each peach. For eachtexture measurement, a piece of skin was peeled off and the plungertip was pressed into the peach flesh to determine force in lbs.

2.7. Chemical analysis

2.7.1. Sample preparation for titratable acidity, Brix.

Six peaches were sliced using a peach pitter (William-Sonoma;San Francisco, CA), blended for 30–45 s (Kitchen Aid; St. Joseph,MI), and filtered through 2 layers of cheesecloth to producepeach puree.

2.7.2. Titratable acidity and pH.

Ten grams of peach puree was combined with 90 ml of deionizedwater. Initial pH of the peach puree solution was measured(pH200 Hannah Instruments; Woonsocket, RI) and titrated topH 8.2 with 0.1 N NaOH. The final result was calculated asfollows: % malic acid¼ml NaOH�0.1 N NaOH�67.04/mlsample�10.

2.7.3. Brix.

A drop of the peach puree was placed on the prism of an AbbeRefractometer (LR45227 Milton Roy Co.; Ivyland, PA) todetermine 1Bx.

2.7.4. Weight loss.

Six peaches from each dose level were set aside for shelf lifetesting to determine overall weight loss. Weight measurements(g), along with photographs, were taken every 4–7 days.

2.8. Statistical analysis

We implemented linear mixed modeling to detect and assessthe effects of statistically significant variables (irradiation dose,variety and age) on various measures for quality attributes (Lairdand Ware, 1982). Model building and goodness-of-fit analysiswere carried out using the R statistical software package (RDevelopment Core Team, 2011). For the sensory data analyses,regression models were built for each of the following dependentvariables, smoothness, bruising, flesh color (cut), peach aroma(whole and cut), whole peach firmness (using fingertips), cutpeach firmness (in mouth), mealiness, ripeness, juiciness, peachflavor, sweetness and tartness. For the consumer data analyses,regression models were built for each of the following dependentvariables measuring the degree of liking of peaches in regards tooverall appearance, overall flavor, overall texture, overall juicinessand overall liking. The appropriate complex correlation structureinduced by the repeated measurements corresponding to indivi-dual panelists were modeled via random effects. Fixed effectsregression models with dependent variables measuring texture,Brix and TA were used for the analytical quality analyses wherethe classical assumptions of independence and homogeneity holdgood. Model diagnostics such as Q–Q plot, fitted versus residualplot and goodness of fit indicate no departures from the linearregression model assumptions.

3. Results and discussion

3.1. Sensory trained panel

Irradiation did not affect the following sensory attributesthroughout the shelf life of 27 days: smoothness, bruising, firmnessof the whole peach, overall peach flavor, overall peach aroma (cutand whole), mealiness, sweet, tart and ripeness (data not shown).

However, irradiation target doses with an average absorbeddose of 0.69 and 0.9 kGy significantly (pr0.05) affected fleshcolor (more orange/red), juiciness (more juicy) and mouth firm-ness (less firm) (Table 2). These differences were apparentimmediately after irradiation treatment. On any given day, the

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H. McDonald et al. / Radiation Physics and Chemistry 81 (2012) 697–704700

peaches treated with 0.69 or 0.9 kGy dose were about 0.4 unitsmore orange/red compared to control. The mouth firmness of thepeaches treated with 0.69 and 0.9 kGy doses were 0.4 and0.7 units, respectively, softer on any given day compared to thecontrol. Trained panelists found 0.69 and 0.9 kGy treated peachesabout 0.6 units juicier than control. Age (or storage time) was alsoa significant factor affecting all sensory attributes except foroverall peach flavor. Variety was a significant factor affecting allsensory attributes except for overall peach aroma.

The darkening of color and increased ripeness caused byirradiation may be due an increase in respiration rate and to theinitial burst of stimulatory amounts of ethylene by the freshlyharvested, less mature peaches (Maxie and Kader, 1966). Aparallel increase in phenylalanine ammonia-lyase activity due toirradiation has been observed in a variety of plants and plantproducts (Chalker-Scott and Fuchigami, 1989), and has beenconnected with color development in peach skin (Hussain et al.,2010). Trained panelists’ scores for mouth firmness and analyticaltexture readings were significantly lower (softer) for peachestreated at the higher dose levels of 0.69 and 0.9 kGy. Loss offirmness can occur due to irradiation enhanced ripening and alsosolubilization of pectin. Maygold, Suwanne, Southland and Loringpeach firmness was reduced at dosesZ1000 Gy, regardless ofstorage temperature (Shewfelt et al., 1968). Loring and Dixilandpeaches were substantially softer than control fruit immediatelyafter treatment when treated with 1500 and 3000 Gy (Ahmedet al., 1972). Previous studies also support the suggestion thatirradiation dependent loss of firmness appears to be dependentupon variety (Drake and Neven, 1998; Hussain et al., 2008; Kimet al., 2010). Southland peaches experienced softening at 500 Gywhereas Maygold, Loring and Dixieland peaches experiencedsoftening the day after the treatment at 1000 Gy or above(Braddock et al., 1966). Cardinal and Red Globe experiencedsoftening at 2000 Gy whereas Suncrest, Fay Elberta and Hallow-een peaches treated with up to 3000 Gy did not experiencesignificant softening (Bramlage and Couey, 1965).

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3.2. Consumer panels

In general, peaches treated commercially in pallet size loads,receiving a target dose of 0.4 kGy (average absorbed dose of0.66 kGy) showed no negative effect on consumers’ acceptability(Fig. 1(a)–(f)). Moreover, consumers’ liking of irradiated peacheswas similar to control peaches throughout the shelf life.

Acceptability scores for flavor, texture, juiciness and overallliking of irradiated fruits were significantly higher as compared tocontrol fruits for Blaze Prince, Encore, August Lady and FlamePrince varieties 7 or 8 days after harvest, 1 day after treatment(pr0.05). These varieties showed no significant differences for allattributes between irradiated and control peaches 13–16 daysafter harvest. Red Globe and July Prince varieties experiencedtemperature abuse, where the fruit was exposed to temperaturesof 14–21 1C, which are not optimal for peaches. This resulted insignificant softening of the peaches and decrease in shelf life.Higher temperatures increase the activity of ripening enzymes andin general, a peach can ripen as much in a day at 21 1C as it wouldin a week at 0 1C (Taylor and Rushing, 2011). Thus, consumertesting was performed only until days 7 and 14. The temperatureabuse, however, did not exacerbate negative effects as bothcontrol and irradiated fruits had similar liking scores across allattributes. Consumers scored irradiated peaches higher initiallybecause irradiation increased ripeness in the freshly picked, veryfirm peaches. This preliminary data shows that consumers findvery firm peaches less acceptable than ripe peaches.

H. McDonald et al. / Radiation Physics and Chemistry 81 (2012) 697–704 701

3.3. Texture analysis

Instrumental texture was not affected by doses of 0.29, 0.49and 0.69 kGy immediately after treatment and through 27 days ofstorage (Table 3). The highest dose of 0.9 kGy showed a significant(pr0.05) softening effect on peach texture immediately after

Fig. 1. Hedonic scale data (like extremely¼9, dislike extremely¼1) for six varieties

treatment and throughout 27 days of storage. The sensitivity ofpectic components to the irradiation treatment, specifically pectinsolubilization, is thought to be a main factor in the softening ofpeaches as discussed previously in the Sensory Trained Panelresults section. Age was a significant factor (pr0.05) affectinganalytical textures for all varieties, although the magnitude of

of peaches evaluated by consumers at the beginning and end of storage time.

Fig. 1. (continued)

H. McDonald et al. / Radiation Physics and Chemistry 81 (2012) 697–704702

difference was quite small. Peaches were softened by 0.17 lbs foreach day of storage. The significant variety effect was most likelydue to fruits harvested at different stages of maturity. Encore andBlaze Prince varieties were harvested at typical firmness readingsof 9–13 lbs of pressure and only demonstrated a softening effectat 0.9 kGy. July Prince and Red Globe varieties experienced

temperature abuse during transport and thus all fruits werereceived very soft (3–4 lbs of pressure); however, irradiationshowed no effect on temperature abused peaches. Flame Princeand August Lady varieties were received at very high, a typicalfirmness readings of 13–22 lbs of pressure. The impact of peachmaturity at harvest on quality of irradiated peaches has been

Table 3Change in texture for 6 varieties of peaches as measured by an Effegi

penetrometer.a

Irradiation dose (kGy) Firmness (lb)

Day 7 Day 14 Day 27

Encore0 12.91 abx 11.58 aby 9.11 abz

0.29 13.31 bx 11.98 by 9.51 bz

0.49 13.13 bx 11.80 by 9.33 bz

0.66 (commercial) 11.95 bcx 10.62 bcy 8.15 bcz

0.69 12.14 bcx 10.81 bcy 8.34 bcz

0.9 11.13 cx 9.80 cy 7.33 cz

Blaze Prince0 10.83 abx 9.50 aby 7.03 abz

0.29 11.23 bx 9.90 by 7.43 bz

0.49 11.05 bx 9.72 by 7.25 bz

0.66 (commercial) 9.87 bcx 8.54 bcy 6.07 bcz

0.69 10.06 bcx 8.73 bcy 6.26 bcz

0.9 9.05 cx 7.72 cy 5.25 cz

July Prince0 5.21 abx 3.88 aby 1.41 abz

0.29 5.61 bx 4.28 by 1.81 bz

0.49 5.43 bx 4.10 by 1.63 bz

0.66 (commercial) 4.25 bcx 2.92 bcy 0.45 bcz

0.69 4.44 bcx 3.11 bcy 0.64 bcz

0.9 3.43 cx 2.10 cy 0.00 cz

Red Globe0 4.51 abx 3.18 aby 0.71 abz

0.29 4.91 bx 3.58 by 1.11 bz

0.49 4.73 bx 3.40 by 0.93 bz

0.66 (commercial) 3.55 bcx 2.22 bcy 0.00 bcz

0.69 3.74 bcx 2.41 bcy 0.00 bcz

0.9 2.73 cx 1.40 cy 0.00 cz

Flame Prince0 16.57 abx 15.24 aby 12.77 abz

0.29 16.97 bx 15.64 by 13.17 bz

0.49 16.79 bx 15.46 by 12.99 bz

0.66 (commercial) 15.61 bcx 14.28 bcy 11.81 bcz

0.69 15.80 bcx 14.47 bcy 12.00 bcz

0.9 14.79 cx 13.46 cy 10.99 cz

August Lady0 17.31 abx 15.98 aby 13.51 abz

0.29 17.71 bx 16.38 by 13.91 bz

0.49 17.53 bx 16.20 by 13.73 bz

0.66 (commercial) 16.35 bcx 15.02 bcy 12.55 bcz

0.69 16.54 bcx 15.21 bcy 12.74 bcz

0.9 15.53 cx 14.20 cy 11.73 cz

a Predicted means of 6 varieties at 4 dose levels. Values in the same row/

column that are followed by the same letter are not significantly different.

Columns are designated with a,b,c and rows are designated with x,y,z.

H. McDonald et al. / Radiation Physics and Chemistry 81 (2012) 697–704 703

observed previously. Dixieland Peaches treated at the hard stage(438 N) experienced a significant decrease in sensory qualityand were described as mealy and flat-tasting; however, panelistsdid not find a significant impact on sensory quality of peachestreated at the hard-ripe stage (16–38 N) (Merkley et al., 1968).

3.4. Titratable acidity

Irradiation did not demonstrate a large effect on TA except at0.9 kGy. Peaches treated with a 0.9 kGy dose had lower TAcompared to untreated peaches (pr0.05); even though thisdifference was statistically significant, the magnitude of thedecrease was negligible. Initial TA values for irradiated anduntreated peaches ranged from 0.49%–0.69%. After 27 days ofstorage, TA values for irradiated and untreated peaches rangedfrom 0.33%–0.53%. Age was a significant factor affecting TA for allvarieties yielding a decrease of 0.008% in TA with each day ofstorage. Again, there was a significant varietal effect on TA most

likely due to differences in maturity stages at harvest. Encore,Blaze Prince, Flame Prince and August Lady varieties wereharvested early in the maturity stage and were found to haveslightly higher TA values while the July Prince and Red Globevarieties had lower TA values. The lower TA values for July Princeand Red Globe fruits may also have been affected by thetemperature abuse and accelerated ripening of fruits duringdistribution.

Previous studies on other climacteric fruits such as mangoesand apricots have reported a slight decrease in total acidity as afunction of time but showed no effects of irradiation (Sabato et al.,2009; Egea et al., 2007).

3.5. Brix

Brix values for all irradiated peaches ranged from 10.29 to13.95 while untreated peaches had Brix values ranging from10.84 to 14.20. Irradiation did not appear to have a dose responseeffect on Brix. At initial storage and throughout the shelf-life,peaches treated at 0.49 kGy were found to have significantly(pr0.05) lower Brix values compared to untreated peaches butyielding a very small decrease of 0.68 units on any given day. Asexpected, there was a significant (pr0.01) effect of age; for eachday of storage, Brix values increased by 0.03. There were nosignificant effects of variety on Brix.

Others have observed a general increase in total soluble solidsin peaches irradiated at dose ranges of 1.0–2.0 kGy. This increaseis TSS has also been observed as a function of storage time. Theincrease of TSS over time can be explained by the rapid ripeningand softening of pulp, dissolution of starch, increase of sweettaste and volatile flavor components and decrease of organic acidas the fruit ages or is stored (Hussain et al., 2008; Kim et al.,2010). In other climacteric fruits, like mangoes, Sabato et al.(2009) found that values for total soluble solids were independentof radiation or storage.

3.6. Weight loss

There was no effect of irradiation on weight loss of peaches.The average weight loss of 1% was observed with all peaches.(data not shown).

4. Conclusion

Although trained sensory data and instrumental textureshowed a softening effect at the higher dose level of 0.9 kGy,consumer liking of commercially treated peaches (target dose of400 Gy) was not different from untreated peaches even at the endof shelf life 13–27 days after harvest. Furthermore, immediatelyafter treatment, consumers appeared to find commercially irra-diated peaches more acceptable. Texture appears to be the mostimportant attribute in consumer acceptance of peaches with mostconsumers preferring slightly soft peaches. This study shows thatthe effect of irradiation depends upon maturity stage. This studyindicates that commercial scale irradiation at a target dose of400 Gy and DUR of 1.67 for phytosanitary treatment preservespeach quality.

Acknowledgments

The project was funded by a TASC Grant from USDA-FAS. Theauthors wish to thank Titan Farms and Lane Southern Orchardsfor the peaches, the Peach Council of Georgia and South Carolinaand FTSI, Mulberry FL, for the irradiation treatment.

H. McDonald et al. / Radiation Physics and Chemistry 81 (2012) 697–704704

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