Alternative Sanitizing Methods to Ensure Safety and Quality of Fresh-Cut Kiwifruit

ALTERNATIVE SANITIZING METHODS TO ENSURE SAFETY ANDQUALITY OF FRESH-CUT KIWIFRUITjfpp_730 1..10

SARA BEIRÃO-DA-COSTA1, M. CONCEIÇÃO MOURA-GUEDES2, M. MANUELA FERREIRA-PINTO2,JOSÉ EMPIS3 and MARGARIDA MOLDÃO-MARTINS1,4

1CEER – Biosystems Engineering, ISA, Technical University of Lisbon, Tapada da, Ajuda, 1349-017 Lisboa, Portugal2IICT/ECOBIO, Instituto de Investigação Científica Tropical, Apartado 3014, Lisboa, Portugal3IBB – Institute for Biotechnology and Bioengineering, Instituto Superior Técnico, Technical University of Lisbon, Avenida Rovisco Pais, Lisboa,Portugal

4Corresponding author.TEL: 351-21-3653246;FAX: 351-21-3653200;EMAIL: [email protected]

Received for Publication March 2, 2011Accepted for Publication April 22, 2012

doi:10.1111/j.1745-4549.2012.00730.x

ABSTRACT

The effect of different sanitizing methods as alternative decontamination treat-ments to chlorinated-water, on microbiological counts, packaging atmospherecomposition, color and firmness of fresh-cut kiwifruit under refrigerated con-ditions was evaluated. The fruits were subjected, within minimal processing, towater, chlorinated water (150 ppm free chlorine), ozonated water (0.2 ppm),UV-C (1 kJ/m2) or heat-shock treatment (95C/30 s). Results showed that UV-Cand heat-shock treatments were efficient with respect to microbial quality offruits, by maintaining the microbial loads below the legal or recommended limitsduring 10-day storage. No significant (P < 0.05) reduction of the initial microbialflora was observed in kiwi slices treated with ozonated water and chlorine. UV-Ctreatment was also effective in reducing respiration rate of kiwifruit slices. No sig-nificant changes (P < 0.05) in color parameters (L*, c and h°) were observed inkiwi slices submitted to different sanitizing methods. UV-treated fruits showed asignificant (P < 0.05) increase in firmness value.

PRACTICAL APPLICATIONS

In minimally processed vegetables, namely in sliced fruits, chlorine solutions havebeen widely used by the industry for sanitization purposes. However, reducedmicrobiological efficiency allied to the sensory alteration and eventual formationof carcinogenic chlorinated compounds pointed out the need for alternativedecontamination methodologies. Also, the evermore conscious consumers aredemanding minimization of the potentially negative impact of food processing onhuman health and the environment.

INTRODUCTION

Decontamination is an important unit operation inminimal processing of fresh-cut fruits and vegetables. Someof the key characteristics of minimally processed fruitsand vegetables influencing the microbial quality are theincreased cutting surfaces or damaged plant tissues, whichsupply nutrients for microbiological growth and tissues thatremain metabolically active, together with a degree of pro-cessing, which is less than that required to ensure microbio-logical stability (Nguyen and Carlin 1994).The nonexistence

of further processing prior to consumption implies thatthe packaged product must meet both quality and safetycriteria, especially as several outbreaks already occurred inthe past associated with fresh-cut fruits and vegetables(NACMCF [National Advisory Committee on Microbio-logical Criteria for Foods] 1999).The most commonlyused decontaminant in fresh-cut fruits and vegetables ischlorine supplied as hypochlorite or chlorine dioxide, itsmicrobicidal activity depending on the amount of freeavailable chlorine, as hypochlorous acid (Beuchat 1998,Beuchat 2000, Sapers 2001). However, chlorine shows a low

Journal of Food Processing and Preservation ISSN 1745-4549

1Journal of Food Processing and Preservation •• (2012) ••–•• © 2012 Wiley Periodicals, Inc.

sanitizing efficacy as its availability is dependent on: (1) thepresence of organic matter; (2) pH; and (3) temperature(Parish et al. 1993). Besides, it is known that it can beharmful because of the formation of carcinogenic chlori-nated by-products, such as trichloromethanes and chlo-ramines (Sapers 2001). Therefore, alternative sanitizingmethods are needed with improved efficiency andsafety.

Heat-shock blanching by hot water immersion (80–95Cfor 1–2 min) proved to be an effective methodology inreducing microbial growth in apples (Fleischman et al.2001) and oranges (Pao et al. 2001) but according to Sapers(2001), the feasibility of the treatment is dependent ofthe absence of heat injury. A washing treatment at 50Cfor 60 s was also effective in maintaining low counts ofbacteria during storage of ready-to-use lettuce (Baur et al.2005).

The use of nonionizing germicidal UV-C light seems tobe another alternative sanitizing methodology for fresh-cutproducts. The exposure of bacteria, viruses and spores toUV light alters bonds within the DNA double helix, yield-ing either mutation or lethal effects on cells (Morgan1989).UV-C radiation applied at proper doses and to bothsides of baby spinach leaves could reduce microbial growthand extend shelf life without adversely affecting the qualityof fresh-cut (Escalona et al. 2010). The effectiveness ofUV-C treatments in reducing microbial loads and improv-ing quality has also been reported for lettuce (Allende andArtés 2003; Allende et al. 2006), pepper (Vicente et al.2005), cantaloupe melon (Lamikanra et al. 2005), pome-granate arils (López-Rubira et al. 2005) and watermelon(Fonseca and Rushing 2006). In addition, the use of thistreatment was approved by the Food and Drug Adminis-tration (FDA), which alleged that it does not leave anyresidue in the final product (Allende et al. 2006).

The FDA also approved the use of ozone as an antimicro-bial agent for the treatment, storage and processing offoods, either as ozone gas or as an aqueous solution, indirect contact with minimally processed fruits and veg-etables. Ozone is a strong oxidizing agent with antimicrobialproperties that rapidly attacks bacterial cell walls with lethaleffects (Beuchat 2000; Mahapatra et al. 2005). The effects ofozone as sanitizing agent have been reported, among others,on fresh-cut celery (Zhang et al. 2005), lettuce (Baur et al.2004; Beltrán et al. 2005) and rocket leaves (Martínez-Sánchez et al. 2006).

The objective of the present work is to study the effi-ciency of sanitizing methods alternative to chlorine for thedecontamination of fresh-cut kiwifruit and to evaluate theeffects of the applied treatments on the main qualityparameters and physiology, assessed by a respiratoryindex and pectin methyesterase (PME) activity, of fruitslices.

MATERIALS AND METHODS

Raw Material

Kiwifruit (Actinidia deliciosa [A Chev] Liang et Fergusonvar deliciosa cv Hayward) from the center of Portugal (Bair-rada region), were purchased at a local market, transportedto the laboratory and selected for uniform size (about 70 g),absence of wound, and commercial maturity stage (basedon external color and firmness). Fruits were stored at 4Cprior to minimal processing operations.

A physicochemical characterization of unprocessed kiwiwas performed to provide a comparison basis for the pro-cessing effects. Main physical and chemical fruit characteris-tics were: total soluble solids content (11.0%), firmness(1.10 N/mm2) and pH (3.5).

Fruit Preparation

Fruits were sanitized by one of four different methods: (1)150 ppm free chlorine supplied as sodium hypochloritesolution at pH 6.5 (2 min, 10C); (2) 0.2 ppm ozone sup-plied as an ozone solution in water (2 min, 10C); (3) UVradiation at a dose of 1 kJ/m2; and (4) heat shock by immer-sion in hot water at 95C/30 s. Heat-treated samples werecooled in ice-cold potable water (5 min, 0C), paper driedand then sliced. Fruits washed in water were usedas control. Experimental scheme of fruit preparation issummarized in Fig. 1. Hand-peeling operation was per-formed with sharpened knives. The UV-C apparatusincluded a closed box, equipped with germicidal lamps(TUV 15W/G15 T8, Philips, Eindhoven, Holland) emittingat 254 nm and placed 17 cm above the product, coveredwith a reflector inner layer to promote homogeneous distri-bution of light and to avoid shaded areas. UV-C radiationintensity was determined with a photo-radiometer (DeltaOhm LP9021 UVC, Padova, Italy) as a mean of 16 readings,and the applied energy (1 kJ/m2) was obtained by multiply-ing the measured intensity by the exposure time. UV-Ctreatment was performed on slices instead of whole fruit asit is a surface treatment with low penetration into tissues(50–300 nm). The flat shape of slices, in opposition to ovoidshape of the whole kiwifruit, also avoids the shadow effectassuring treatment uniformity. The aqueous ozone solutionwas prepared with an ozone gas generator SPO3 (modelOZ5, Santo Tirso, Porto, Portugal), using oxygen as feed gas.The ozone generator system (maximum O3 productioncapacity of 5 g/h) was equipped with a 120 L reservoir.O3-water was impelled out by a pump at a flow rate of1.5 m3/h. Concentration of ozonated water was set to 1 ppmO3 and monitored continuously by measuring the redoxpotential (Redox probe pH 7,685, calibrated with RedoxBuffersolutions of 220 mV and 468 mV from Hanna

SANITIZING METHODS FOR FRESH-CUT KIWIFRUIT S. BEIRÃO-DA-COSTA ET AL.

2 Journal of Food Processing and Preservation •• (2012) ••–•• © 2012 Wiley Periodicals, Inc.

Instruments, Woonsocket, MA). The ozone solutionwas used immediately after ozone concentration wasreached.

To minimize mechanical damage of the fruits duringminimal processing, and as a washing procedure afterkiwifruit peeling is needed to remove peel and trichomeresidues, all the sanitation procedures were conducted afterthat operation, with exception to heat shock, in order toavoid outer pericarp vitality loss. Moreover, kiwifruit has alow microbial risk as the crop is grown above ground.

Peeled kiwifruits were sliced (1.5 cm) with sharpenedknives. Samples were, respectively, pooled to minimizeheterogeneity (sanitized pincers) and 100 g portions ofslices were packed in bags (200 ¥ 220 mm) made fromlow-density polyethylene and vinylidene chloride (AmcorFlexibles Neocel – Embalagens Lda., Lisboa, Portugal) with3,000–4,000 and 11,000–15,000 (mL/m2/24h/atm) perme-ability to O2 and CO2, respectively. The bags were then heat-sealed (Tish-400 impulse sealer, Tew Electric HeatingEquipment Co., Ltd., Taipei, Taiwan) and stored at 4C (S600Pharma, Fitoclima, Aralab – Equipamentos de Laboratórioe Electromecânica Geral Lda., Sintra, Portugal) for 10 days.Analytical procedures were carried out on five samplingdates, i.e. days 1, 3, 6, 8 and 10.

Quality Measurements

Microbiological Analysis. Microbiological loads offresh-cut kiwifruit subjected to the different sanitizingmethods were analyzed during the 10-day storage. Formicrobiological analysis, at each sampling day, three bags

per treatment were analyzed for total aerobic mesophilic,psychrotrophic microorganisms, moulds and yeasts, andlactic acid bacteria. Kiwifruit samples (50 g) were removedfrom the packaging and homogenized in 450 mL of sterileRinger solution (Sigma, St. Louis, MO) with a sterilizedhomogenizer (IKA Labortechnik homogenizer, Staufen,Germany) for 1 min. Appropriate serial 10-fold dilutionswere prepared with Ringer solution and used for platingon agar media. Total aerobic mesophilic count was per-formed according to NP-1409 (1987). Samples (1 mL/plate) were plated onto 15 mL/plate of plate count agar(PCA – Merck, Darmstadt, Germany) using the pour-platemethod and incubated at 30C for 72 h. Yeasts and mouldswere determined on 15 mL/plate of yeast extract glucosechloranphenicol agar (Merck) by surface plating ofsamples (0.2 mL/plate) followed by incubation at 25Cduring 5 days (NP 3277-1 1987). Lactic acid bacteria werequantified according to ISO 15214 (1998). Samples (1 mL/plate) were deposited by pour-plate method onto Lactoba-cilli De Man, Rogosa and Sharpe agar (MERCK) andincubated under anaerobic and moist conditions at 30Cfor 5 days. Psychrotrophic microorganisms were countedon 15 mL/plate of PCA by the spread-plate technique(0.1 mL/plate) followed by incubation at 5C for 10 daysaccording to NP 2307 (1987).

Results of microbial counts were expressed as Log10(cfu/g).

Gas Composition. Packages of gas composition wereevaluated throughout the storage period. At each samplingdate, three new packages were analyzed for gas composition.

Kiwifruit, 4 ºC

Peeling Heat treatment 95 ºC/30 s

Washing 150 ppm Chlorine

10 ºC/2min

Washing 0.2 ppm Ozone

10 ºC/2 min

Washing Water

10 ºC/2 min

Rinsing

Peeling

Draining

Cutting (≈ 1.5 cm)

UV Treatment 1 kJ/m2

Packaging

Rinsing

FIG. 1. FRESH-CUT KIWIFRUIT PRODUCTIONDIAGRAM ACCORDING FIVE DIFFERENTSANITIZING PROCESSES

S. BEIRÃO-DA-COSTA ET AL. SANITIZING METHODS FOR FRESH-CUT KIWIFRUIT


Headspace gas samples were taken with a hypodermicneedle through an adhesive septum previously fixed on thebags and were analyzed using a checkmate 9900 O2/CO2 gasanalyzer (PBI-Dansensor, Ringsted, Denmark).

Color Measurement. Color of minimally processedkiwi was evaluated on the outer pericarp (green section) ofslices with a CR 300 Minolta colorimeter (Minolta, Tokyo,Japan) by measuring L*, a* and b* (Commission Internatio-nale d’Eclairage) parameters. From those, chroma (c) andhue angle (h°) were determined, defined as

c a b= +* *2 2 (1)

hb

a° = ⎛

⎝⎞⎠arctan (2)

where a* and b* are the color readings.A white tile (L* = 97.46, a* = -0.02 and b* = 1.72) was

used for equipment calibration. The C illuminant and a10° observer were employed. Thirty measures were per-formed for each of 15 slices obtained under each sanitizingtreatment.

Firmness Measurement. Firmness was evaluated byperforming a puncture test on kiwi slices outer pericarpusing a TA-XT Plus texture analyzer (Stable Micro Systems,Surrey, UK) with a 5 kg load cell. Firmness measurementswere taken as the medium force value obtained during thetest using a stainless steel probe with 4 mm diameter topenetrate the fruit to a depth of 4 mm, at 1 mm/s. Meanvalues were calculated from results of at least 20 measure-ments in different slices, for each sample.

PME Extraction and Assay. About 12 g of kiwifruitouter pericarp (without seeds) was homogenized with40 mL of cold 1.5 M NaCl in a T25 basic, IKA Labortechnikhomogenizer. The homogenate was then stirred for 30 minat 4C and centrifuged at 15,000 ¥ g for 10 min, at 4C. Theresulting supernatant was used for PME activity assay. PMEactivity was assayed titrimetrically, using a pH-meter con-nected with a pH-electrode, measuring protons from thecarboxyl groups obtained from the hydrolysis of methylesters of pectin. A 100 mL of substrate solution (0.25%[w/v] citric pectin in 0.2 M NaCl) was mixed with 5 mL ofPME extract and the pH adjusted to 7.5 with 1 M and0.05 M NaOH. After the pH reached 7.5, 0.2 mL of 0.02 MNaOH was added and the time required to reach pH 7.5again was recorded. PME activity was measured at 25C. Oneunit of PME activity was defined as the amount of enzymethat can cause the release of 1 mmol of COO-/ g of freshtissue and per minute (mmol/g/min).

Statistics

Analysis of variance (ANOVA) was applied to the results, aswell as a mean comparison test (Fisher’s least significantdifference), to analyze significant differences (P < 0.05)between treatments along storage time. “Statistica” v. 6.1software from Statsoft, Inc. (Tulsa, OK) was used.

RESULTS AND DISCUSSION

Microbiological Growth

Microbiological loads of fresh-cut kiwifruit subjected to thedifferent sanitizing methods were analyzed during the10-day storage period (Fig. 2). No moulds growth wasdetected in any of the samples, the data just beingaccounted for because of yeasts.

After minimal processing operations, fruits rinsed withwater showed a microbial load of about 3.5 log units, for allstudied groups of microorganisms. Neither ozone nor chlo-rine treatment was effective in reducing initial population,yielding similar figures. Sanitation with UV-C light and heatshock yielded a reduction of the initial population of 1 logunit for total mesophylic and lactic acid bacteria. For yeast,the observed reduction was 1.1 and 1.6 log units for UV-Clight and heat shock, respectively. No differences wereobserved between the initial psychrotrophic populations ofkiwifruit slices subjected to different sanitizing methods.

During storage, microbial counts of fresh-cut kiwifruitincreased. Total mesophilic population is similar in water-rinsed and chlorine- or ozone-containing water, throughoutstorage but, at the end of 10-day storage, UV-treated fruitsshowed a population reduced by 1.6 log units while heat-shocked fruits maintained the initial total mesophyliccounts. The same pattern was found for the growth of totalpsychrotrophic microorganisms. There was no Portugueseregulation establishing microbial limits to fresh-cut fruitsand vegetables. However, the Spanish legislation establishes6 log cfu/g and 7 log cfu/g as the limit of total aerobic meso-philes at processing day and the end of the shelf life, respec-tively (Boletín Oficial del Estado [BOE] 2001). In thepresent work, no sample ever exceeded these limits duringthe studied period. For psychrotrophic microorganisms,values of 5 and 8 log units after processing and at consump-tion date, respectively, is pointed out as indicative (Debevere2006).

O’Conner-Shaw et al. (1994) reported that microbialgrowth did not appear to contribute to spoilage in slicedkiwifruit. Nevertheless, water washed fruits achieved therecommended limit for yeasts (5 log units) after 6 days ofstorage and exceeded them after 8 days. Fruits sanitized withchlorine and with ozonated water exceeded the recom-mended limits but only at the end of the analysis period,



while yeast loads in UV and heat-shock-treated fruits alwayskept below the recommended value. Yeast growth oftenaffects product shelf life as yeasts can be responsible for thedevelopment of off-flavors because of production of CO2,ethanol, organic acids and volatile esters (Fleet 1992; Jacxs-ens et al. 2003; Ragaert et al. 2007).

The initial population of acid lactic bacteria was low, notexceeding the recommended limits (3–4 log units) by Debe-vere (2006) in all samples, and no significant growth wasregistered during the 8-day period of storage. After 10 days,an increase in lactic acid bacteria was observed mainly forthe fruits rinsed with water, and with chlorinated and ozon-ated water; however, the achieved microbial loads stillremained 1 log unit lower than the indicative values. UVand heat-shock samples showed lactic acid bacteria growthof 3 and 4.5 log units, respectively, below the indicativelimit.

The observed inefficiency of chlorine in reducing initialmicrobial loads and minimizing microbial growth withinstorage of fresh-cut produce had also been reported byParish et al. (1993), namely for rocket leaves, when used atthe concentration of 100 mg/L (Martínez-Sánchez et al.2006), and for carrots at 200 mg/L (Ruiz-Cruz et al. 2007).For fresh-cut watermelon, the initial reduction of themicrobial population by chlorine was only effective for a5-day long period according to Fonseca and Rushing 2006.The efficiency of the treatment depends on various factors,including pH, temperature and contact with organic mate-rial (Beuchat 2000). In the present work, despite the mainte-nance of the theoretical optimum conditions of pH andtemperature, no advantage was evidenced by chlorine in thesanitizing treatment, when compared with the water treat-ment. This is in accordance to preliminary results (data notshown) in which a mere 0.2 log units lowering was observed

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FIG. 2. MICROBIOLOGICAL GROWTH ON FRESH-CUT KIWIFRUIT SLICES SUBJECTED TO DIFFERENT SANITIZING METHODS AND STORED AT 4CFOR UP TO 10 DAYS(A) Total aerobic mesophylic bacteria. (B) Moulds and yeasts. (C) Lactic acid bacteria. (D) Total psychrotrophic bacteria. The horizontal line indicatesthe Spanish legal limit ([29] A) or indicative values (B, C and D) from (34). Error bars indicate the standard deviation, n = 3.



for the chlorine washing treatment. The similar observedinefficiency of treatment with ozonated-water treatment isnot in agreement with several published works. Total bacte-rial counts on fresh-cut celery treated with 0.03, 0.08 and0.18 mg/L were significantly lower than those of the samewashed with tap water (Zhang et al. 2005). Baur et al. (2004)reported that a reduction in total aerobic mesophiles,pseudomonades and Enterobacteriaceae on shreddedlettuce was observed when comparing ozone treatment(1 mg/L) to tap water wash, but the treatment was not aseffective in reducing the initial counts as the chlorine treat-ment (200 mg/L). In addition, ozonated water (0.5 ppm)was not also effective in reducing mesophylic and yeasts andmoulds in fresh-cut carrots (Alegria et al. 2009). The resultsfor ozone efficiency were strongly dependent on numerousvariables, such as the number and kind of contaminatingmicroorganisms, physiology of vegetables, reactor design,water quality, temperature, and pH. According to Hassen-berg and Idler (2005), the competition between bothorganic load and inorganic matter and microorganisms forthe available ozone contributes to reduce its availability.In the present study, the rapid redox potential decreaseobserved (Redox probe pH 7,685) during treatment indi-rectly equates to the use of available ozone by the organicload present.

UV-C and heat shock were the most effective treatmentsin microbial population decrease. Martín-Diana et al.(2007) reported the effectiveness of a steamer jet-injectiontreatment as a reduction of 1.8 log units in the mesophylicload of fresh-cut lettuce, while a blanching treatmentallows a 3 log cfu/g mesophylic reduction in leafy salads.The present results are also in agreement with severalauthors, which report that UV-C treatment is a usefulmethodology in fresh-cut product decontamination. UV-Cradiation on fresh-cut lettuce (2.37, 4.06, 7.11 and 8.14 kJ/m2) and watermelon cubes (4.1 kJ/m2) led to lower loadsof total aerobic mesophylic and psychrotropic microorgan-isms when compared with nontreated samples (Allendeet al. 2006; Fonseca and Rushing 2006). However, no ben-efits were found in the application of 0.56–13.62 kJ/m2

UV-C radiation as regards the microbial population reduc-tion of minimally processed pomegranate, probably due tosome protection of the microorganisms by the aril surfacecomposition or topography (López-Rubira et al. 2005).Lamikanra et al. (2005) referred that microbial loads offresh-cut cantaloupe were significantly reduced whenUV-C light was applied after cutting, the effect being morepronounced if the minimal processing operations takeplace under light exposure. The initial microbial reductionachieved by the heat treatment (100C/45 s) as a precutprocedure in minimally processed carrot (shredded) wassignificantly higher than that attained by chlorinated wateraccording to Alegria et al. (2010).

Gas Compositions within Packages

To determine if the different sanitizing methods affectthe physiology of kiwifruit slices, gas composition withinpackages was monitored during storage (Fig. 3).

As expected, CO2 partial pressure inside the packagesincreased in all samples, at a higher rate during the first 3days of storage, as a consequence of incremented metabolicactivity because of minimal processing operations. Thepassive modified atmosphere formed reduced the fruitrespiration rate and therefore the equilibrium levels wereachieved. O2 partial pressure inside the bags decreased,showing an inverse evolution, the differences noted betweentreatments being similar to those observed for CO2, reach-ing final partial pressures between 4 and 6%. The differenttreatments affect CO2 production by fresh-cut kiwifruit.The higher CO2 accumulation occurred within packages offruits washed in water or subjected to heat-shock. The high-CO2 levels revealed pronounced metabolic activity and arenot due to microorganisms’ CO2 production because heat-shock-treated samples showed the lowest microbial loads.Slices treated with UV-C nonionizing radiation displayedthe lowest production of CO2, denoting a decreased respira-tion rate and a lower microbial growth.

The effects of UV-C radiation in respiratory activitydepend upon the species treated. The results obtained are inaccordance with those from other authors reporting adecrease in respiration rate of peppers (Vicente et al. 2005),minimally processed pomegranate arils (López-Rubira et al.2005), fresh-cut cantaloupe melon (Lamikanra et al. 2005)and broccoli florets (Costa et al. 2006), as a consequenceof UV-C treatments. In tomatoes, the climacteric peak of

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FIG. 3. CO2 CONCENTRATION WITHIN PACKAGES OF FRESH-CUTKIWIFRUIT SLICES SUBJECTED TO DIFFERENT SANITIZING METHODSAND STORED AT 4C FOR UP TO 10 DAYSError bars indicate the standard deviation, n = 3.



respiration is lowered and delayed when fruits were sub-jected to UV-C radiation, probably due to the maintenanceof higher levels of putrescine, an antisenescence agentinhibitory of ethylene synthesis as suggested by Maharajet al. (1999). It is known that kiwifruit is highly sensitive toethylene (Crisosto and Mitchell 2007), therefore thispathway could explain the reduction of the respiration ratein UV-C-treated slices. The inhibition of fresh-cut celeryrespiration rate when subjected to ozonated-water treat-ments, and the efficiency of the inhibition increased withincreasing concentration of ozone in water, from 0.08 to0.18 ppm, were also reported by Zhang et al. (2005). Never-theless, fresh-cut iceberg lettuce respiration rate was notaffected by ozonated-water wash treatment, as sampleswashed in 1, 10 and 20 mg/L ozone in water exhibited respi-

ration rates similar to that of water-washed samples (Bauret al. 2004; Beltrán et al. 2005).

Color Parameters

No significant differences in c and h° were observed amongslices of the different treatments (Table 1). ANOVA showedthat only storage time had a significant effect on these colorparameters.

Small differences where also noted in h° during storage. Adecrease in c values, indicative of some yellowing, can beobserved during the storage period in all samples. Fruitslices washed in water or subjected to ozone treatment werethose that showed a higher decline in chromaticity.

Both treatment and storage time significantly affectedslices luminosity (L*) (Table 1). A decline in L* values wereobserved for all samples. As occurred for h°, fruit slicestreated with UV radiation maintain initial luminosity valueswithin the first 6 days of storage.

Firmness

The effect of the different sanitizing methods on kiwifruitslices firmness was monitored during the 10-day storageperiod (Fig. 4). After minimal processing, UV-treated fruitsshowed a significantly higher firmness, comparing withother samples, value maintained until the third day ofstorage. The better retention of firmness explains theobserved L* value preservation within the first days ofstorage as a decrease in the luminosity of kiwifruit slices isdue to an induction of translucent water-soaked tissue

TABLE 1. EVOLUTION OF COLOR PARAMETERS OF KIWIFRUIT SLICES,SUBJECTED TO DIFFERENT SANITIZED TREATMENTS, DURINGSTORAGE AT 4C

Storage day Treatment L* c h°

1 Heat-shock 42.35a 18.96a 113.65ab

Cl 43.54aA 17.10a 114.09a

Water 43.12aA 18.86a 114.78a

Ozone 42.51aA 18.58a 114.48a

UV 44.19aA 19.02a 114.93a

3 Heat-shock 41.07b 15.22bc 114.95a

Cl 41.45bB 16.62a 114.21a

Water 41.62bA 17.22a 114.12ab

Ozone 41.86abAB 16.92ab 114.72a

UV 43.85aA 17.05ab 114.07a

6 Heat-shock 40.53b 14.29c 113.88ab

Cl 39.21bC 15.80ab 114.56a

Water 39.21bB 14.78b 115.38a

Ozone 40.51bB 14.66c 114.48a

UV 42.88aA 15.27bc 114.20a

8 Heat-shock 38.75a 14.04c 113.05b

Cl 38.92aC 14.29b 113.39a

Water 38.37aB 12.78b 113.03bc

Ozone 40.05aB 14.93bc 114.06a

UV 39.41aB 14.58c 114.98a

10 Heat-shock 38.66bc 14.46c 112.59b

Cl 40.24abBC 14.16b 114.31a

Water 38.20cB 12.98b 112.38c

Ozone 37.72cB 12.83c 112.36b

UV 40.87aB 14.20c 113.46a

ANOVA effect P

Treatment 0.000 0.422 0.664Storage time 0.000 0.000 0.000Treatment ¥ storage time 0.199 0.127 0.409

For L* column, different lowercase indicate significant differences ateach time for different samples and different uppercase indicate signifi-cant differences of each sample at different times, at P < 0.05.For c and h° columns, for each sample, different letter indicate signifi-cant differences at P < 0.05.ANOVA, analysis of variance.

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FIG. 4. FIRMNESS EVOLUTION OF FRESH-CUT KIWIFRUIT SLICESSUBJECTED TO DIFFERENT SANITIZING METHODS, STORED AT 4C FORUP TO 10 DAYSAbove each bar: different lowercase indicates significant differencesfor each sample along storage time; different uppercase indicatessignificant differences between samples at the same storage time(Fisher’s least significant difference test, P < 0.05).



resulting from structure loss instead of browning as con-firmed by Agar et al. (1999), Beirão-da-Costa et al. (2006)and Beirão-da-Costa et al. (2008a,b).

The other four treatments did not show any effect onfruit slices firmness as no differences were noted amongfruit slices during all storage period. The results are inaccordance to previously published works reporting that,wash treatments with tap water, chlorinated and ozonatedwater also did not influence texture parameters of shreddedlettuce (Baur et al. 2005).

Better firmness retention of fruits and vegetables as con-sequence of UV-C light exposure was reported for fresh-cut cantaloupe melon (Lamikanra et al. 2005), peppers(Vicente et al. 2005), strawberries (Marquenie et al. 2002)and tomato (Maharaj et al. 1999; Barka et al. 2000). Themechanism involved in fruit firmness preservation couldbe related to the increased level of polyamines observed inUV-C-treated fruits as a correlation was observed betweenthese compounds and the suppression of cell wall soften-ing enzymes polygalacturonase and PME (Barka et al.2000).

PME Activity

In order to understand the mechanism underlying the dif-ferences found in UV-treated and water washed (control)fruits firmness, the activity of PME was measured (Table 2).

Several works refer to the influence of UV treatments inenzymes activity. It was observed by Lamikanra et al. (2005)that UV treatment increased peroxidase activity whilelowered esterase and lipase activity. Studies reported byBarka et al. (2000) indicated that 3.6 kJ/m2 UV-C treat-ments minimize the activity of cell wall degrading enzymes,inducing their proteolysis or reducing their synthesis, delay-ing softening and tomato firmness decay. In a previous work(Beirão-da-Costa et al. 2008a,b), it was found that a firmingeffect provided in fresh-cut kiwifruit was due to the activa-tion of PME as a reaction against physical stresses. Never-theless, a 73.8 mJ/cm2 UV-C treatment did not influenceorange juice PME activity (Tran and Farid 2004). Ourresults did not show any significant differences betweenPME activity of the water washed and the UV-treated slices;

so, it is therefore hypothesized that the mechanism involvedin kiwifruit firmness preservation was the one described for“McIntosh” apples and strawberries (Ponappa et al. 1993).These authors reported that exogenous polyamines effec-tively suppressed cell wall softening and activity of polyga-lacturonase. This mechanism is similar to that of calciumions, involved in the formation of cationic cross-links withpectic acid and other polysaccharides, promoting binding ofthe cell walls, limiting accessibility to degrading enzymes.

CONCLUSIONS

UV and heat shock were efficient treatments concerningmicrobial quality of fruits, by maintaining the microbialloads below the legal or recommended limits for 10-dayrefrigerated storage. Ozone and chlorine treatments werenot effective in reducing microbiological growth as micro-bial counts were similar to those fruits just washed in water(control).

Fresh-cut kiwifruit slices metabolism, assessed as CO2

production, was affected by sanitizing treatments, the lowestrespiration rate having been observed in UV-C-treatedfruits.

When compared with the control treatment, colorparameters of fruit slices were not affected by the differenttreatments with exception for luminosity of UV-treatedsamples, which was nevertheless maintained during the first6 days of storage. L* value maintenance was correlated tothe lower existence of water-soaked tissues as, during thesame 6-day period, UV samples showed improved firmnessretention.

Therefore, UV-C light, even at a low dose (1 kJ/m2) seemsto be an interesting and promising methodology for fresh-cut kiwifruit sanitizing, allowing overall quality preserva-tion of fruit slices. Further studies are needed in order tobetter understand the mechanism behind fruit slices firm-ness preservation.

ACKNOWLEDGMENT

The first author acknowledges the financial support fromFundação para a Ciência e Tecnologia, Portugal, throughprogram POCTI, PhD Grant No. BD/10765/2002.

REFERENCES

AGAR, I.T., MASSANTINI, R., HESS-PIERCE, B. and KADER,A.A. 1999. Postharvest CO2 and ethylene production andquality maintenance of fresh-cut kiwifruit slices. J. Food Sci.64(3), 433–440.

ALEGRIA, C., PINHEIRO, J., GONÇALVES, E.M.,FERNANDES, I., MOLDÃO, M. and ABREU, M. 2009.Quality attributes of shredded carrot (Daucus carota L. cv.

TABLE 2. PME ACTIVITY OF FRESH-CUT KIWIFRUIT, 1 DAY AFTERMINIMAL PROCESSING

TreatmentPME activity (mmolCOO-/min/g)

Water 1.54 � 0.22a

UV 1.68 � 0.22a

Mean values � standard deviation. a indicate no significant differencesat P < 0.01.PME, pectin methyesterase.



Nantes) as affected by alternative decontamination processesto chlorine. Innov. Food Sci. Emerg. Technol. 10, 61–69.

ALEGRIA, C., PINHEIRO, J., GONÇALVES, E.M.,FERNANDES, I., MOLDÃO, M. and ABREU, M. 2010.Evaluation of a pre-cut heat treatment as an alternative tochlorine in minimally processed shredded carrot. Innov.Food Sci. Emerg. Technol. 11, 155–161.

ALLENDE, A. and ARTÉS, F. 2003. UV-C radiation as a noveltechnique for keeping quality of fresh processed “Lollo Rosso”lettuce. Food Res. Int. 36(7), 739–746.

ALLENDE, A., MCEVOY, J.L., LUO, Y., ARTÉS, F. and WANG,C.Y. 2006. Effectiveness of two-sided UV-C treatments ininhibiting natural microflora and extending the shelf-life ofminimally processed “Red Oak Leaf” lettuce. Food Microbiol.23(3), 241–249.

BARKA, E.A., KALANTARI, S., MAKHLOUF, J. and ARUL, J.2000. Impact of UV-C irradiation on the cell wall-degradingenzymes during ripening of tomato (Lycopersicon esculentumL.) fruit. J. Agric. Food Chem. 48(3), 667–671.

BAUR, S., KLAIBER, R., HAMMES, W.P. and CARLE, R. 2004.Sensory and microbiological quality of shredded, packagediceberg lettuce as affected by pre-washing procedures withchlorinated and ozonated water. Innov. Food Sci. Emerg.Technol. 5(1), 45–55.

BAUR, S., KLAIBER WEI, H.R., HAMMES, W.P. and CARLE, R.2005. Effect of temperature and chlorination of pre-washingwater on shelf-life and physiological properties of ready-to-use iceberg lettuce. Innov. Food Sci. Emerg. Technol. 6(6),171–182.

BEIRÃO-DA-COSTA, S., STEINER, A., CORREIA, L., EMPIS, J.and MOLDÃO-MARTINS, M. 2006. Effects of maturity stageand mild heat treatments on quality of minimally processedkiwifruit. J. Food Eng. 76(4), 616–625.

BEIRÃO-DA-COSTA, S., CARDOSO, A., LOURO-MARTINS,L., EMPIS, J. and MOLDÃO-MARTINS, M. 2008a. The effectof calcium dips combined with mild heating of wholekiwifruit for fruit slices quality maintenance. Food Chem.108(1), 191–197.

BEIRÃO-DA-COSTA, S., STEINER, A., CORREIA, L., LEITÃO,E., EMPIS, J. and MOLDÃO-MARTINS, M. 2008b. Influenceof moderate heat pre-treatments on physical and chemicalcharacteristics of kiwifruit slices. Eur. Food Res. Technol. 226,641–651.

BELTRÁN, D., SELMA, M.V., MARÍN, A. and GIL, M.I. 2005.Ozonated water extends the shelf life of fresh-cut lettuce.J. Agric. Food Chem. 53(14), 5654–5663.

BEUCHAT, L.R. 1998. Surface decontamination of fruits andvegetables eaten raw: A review. Food Safety Unit, WorldHealth Organization, WHO/FSF/FOS/98.2.

BEUCHAT, L.R. 2000. Use of sanitizers in raw fruit andvegetables processing. In Minimally Processed Fruits andVegetables (S.M. Alzamora, M.S. Tapia and A. López-Malo,eds.) pp. 63–78, Aspen Publishers Inc., Gaithersburg, MD.

BOLETÍN OFICIAL DEL ESTADO (BOE). 2001. Normas dehigiene para la elaboración, distribución y comercio de

comidas preparadas, Madrid, Spain. Real Decreto 3484/2000,1435–1441.

COSTA, L., VICENTE, A.R., CIVELLO, P.M., CHAVES, A.R. andMARTINEZ, G.A. 2006. UV-C treatment delays postharvestsenescence in broccoli florets. Postharvest Biol. Technol. 39(2),204–210.

CRISOSTO, C.H. and MITCHELL, F.G. 2007. Kiwifruit:Sistemas de Manejo Postcosecha: Frutas Pequeñas. InTecnología Postcosecha De Cultivos Hortofrutícolas, 3a Ed.,(A.A. Kader and C. Pelayo-Zaldivar, eds.) pp. 401–420,Universidad de California, Davis, CA.

DEBEVERE, J. 2006. Valeurs Microbiologiques Indicatives &Critères Microbiologiques Légaux., FAC. SCI. BIO-ING. Univ.Gent, Gent, Belgium.

ESCALONA, V.H., AGUAYO, E., MARTÍNEZ-HERNÁNDEZ,G.B. and ARTÉS, F. 2010. UV-C doses to reduce pathogenand spoilage bacterial growth in vitro and in baby spinach.Postharvest Biol. Technol. 56, 223–231.

FLEET, G. 1992. Spoilage yeast. Crit. Rev. Biotechnol. 12(1),1–44.

FLEISCHMAN, G.J., BATOR, C., MERKER, R. and KELLER,S.E. 2001. Hot water immersion to eliminate Escherchia coliO157:H7 on the surface of whole apples: Thermal effect andefficacy. J. Food Prot. 64(4), 45–455.

FONSECA, J.M. and RUSHING, J.W. 2006. Effect ofultraviolet-C light on quality and microbial population offresh-cut watermelon. Postharvest Biol. Technol. 40(2),256–261.

HASSENBERG, K. and IDLER, C. 2005. Influence of washingmethod on the quality of pre packed iceberg lettuce.Agricultural Engineering International: The CIGR Ejournal.Manuscript FP 05 003, vol. VII.

ISO 15214. 1998. Microbiology of food and animal feedingstuffs – horizontal method for the enumeration of mesophiliclactic acid bacteria – colony-count technique at 30 degrees.ISO/FDIS.

JACXSENS, L., DEVLIEGHERE, F., RAGAERT, P., VANNESTE,E. and DEBEVERE, J. 2003. Relation between microbiologicalquality, metabolite production and sensory quality ofequilibrium modified atmosphere packaged fresh-cutproduce. J. Food Microbiol. 83(3), 263–280.

LAMIKANRA, O., KUENEMAN, D., UKUKU, D. andBETT-GARBER, K.L. 2005. Effect of processing underultraviolet light on the shelf life of fresh-cut cantaloupemelon. J. Food Sci. 70(9), 534–539.

LÓPEZ-RUBIRA, V., CONESA, A., ALLENDE, A. and ARTÉS, F.2005. Shelf-life and overall quality of minimally processedpomegranate arils modified atmosphere packaged and treatedwith UV-C. Postharvest Biol. Technol. 37(2), 174–185.

MAHAPATRA, A.K., MUTHUKUMARAPPAN, K. and JULSON,J.L. 2005. Applications of ozone, bacteriocins and irradiationin food processing: A review. Crit. Rev. Food Sci. Nutr. 45(6),447–461.

MAHARAJ, R., ARUL, J. and NADEAU, P. 1999. Effect ofphotochemical treatment in the preservation of fresh tomato



(Lycopersicon esculentum cv. Capello) by delaying senescence.Postharvest Biol. Technol. 15(1), 13–23.

MARQUENIE, D., MICHIELS, C.W., GEERAERD, A.H.,SCHENK, A., SOONTJENS, C., VAN IMPE, J.F. andNICOLAÏ, B.M. 2002. Using survival analysis to investigatethe effect of UV-C and heat treatment on storage rot ofstrawberry and sweet cherry. Int. J. Food Microbiol. 2(3),187–196.

MARTÍN-DIANA, A.B., RICO, D., BARRY-RYAN, C.,FRÍAS, J.M., HENEHAN, G.T.M. and BARAT, J.M. 2007.Efficacy of steamer jet-injection as alternative to chlorine infresh-cut lettuce. Postharvest Biol. Technol. 45(1), 97–107.

MARTÍNEZ-SÁNCHEZ, A., ALLENDE, A., BENNETT, R.N.,FERRERES, F. and GIL, M.I. 2006. Microbial, nutritionaland sensory quality of rocket leaves as affected by differentsanitizers. Postharvest Biol. Technol. 42(1), 86–97.

MORGAN, R. 1989. UV “green” light disinfection. Dairy Ind.Int. 54(11), 33–35.

NACMCF (NATIONAL ADVISORY COMMITTEE ONMICROBIOLOGICAL CRITERIA FOR FOODS). 1999.Microbiological safety evaluations and recommendationson fresh produce. Food Control 10(2), 117–143.

NGUYEN, C. and CARLIN, F. 1994. The microbiology ofminimally processed fresh fruits and vegetables. Crit. Rev.Food Sci. Nutr. 34(4), 371–401.

NP 2307. 1987. Microbiologia alimentar. Regras gerais para acontagem de microrganismos psicrotróficos.1a edição, IPQ,Lisboa.

NP 3277-1. 1987. Microbiologia Alimentar. Contagem debolores e leveduras. Parte 1: Incubação a 25C. IPQ, Lisboa.

NP-1409. 1987. Microbiologia Alimentar. Frutos, produtoshortícolas e seus derivados. Contagem de microrganismos a30C. IPQ, Lisboa.

O’CONNER-SHAW, R.E., ROBERTS, R., FORD, A.L. andNOTTINGHAM, S.M. 1994. Shelf life of minimally processed

honeydew, kiwifruit, papaya, pineapple and cantaloupe.J. Food Sci. 59(6), 1202–1206.

PAO, S., DAVIS, C.L. and PARRISH, M.E. 2001. Microscopicobservation and processing validation of fruit sanitizingtreatments for the enhanced microbiological safety of orangejuice. J. Food Prot. 64(3), 310–314.

PARISH, M.E., BEUCHAT, L.R., SUSLOW, T.V., HARRIS, L.J.,GARRETT, E.H., PONAPPA, A.R., SCHEERENS, J.C. andMILLER, A.R. 1993. Vacuum infiltration of polyaminesincreases firmness of strawberry slices under various storageconditions. J. Food Sci. 58(2), 361–364.

PONAPPA, T., SCHEERENS J.C. and MILLER, A.R. 1993.Vacuum infiltration of polyamines increases firmnessof strawberry slices under various storage conditions.J. Food Sci. 58(2), 361–364.

RAGAERT, P., DEVLIEGHERE, F. and DEBEVERE, J. 2007. Roleof microbiological and physiological spoilage mechanismsduring storage of minimally processed vegetables. PostharvestBiol. Technol. 44(3), 185–194.

RUIZ-CRUZ, S., ACEDO-FÉLIX, E., DÍAZ-CINCO, M.,ISLAS-OSUNA, M.A. and GONZÁLEZ-AGUILAR, G.A. 2007.Efficacy of sanitizers in reducing Escherichia coli O157:H7,Salmonella spp. and Listeria monocytogenes populations onfresh-cut carrots. Food Control 18(11), 1383–1390.

SAPERS, G.M. 2001. Efficacy of washing and sanitizing methodsfor disinfection of fresh fruit and vegetable products. FoodTechnol. Biotechnol. 39(4), 305–311.

TRAN, M.T.T. and FARID, M. 2004. Ultraviolet treatmentfor orange juice. Food Sci. Emerg. Technol. 5(4), 495–502.

VICENTE, A.R., PINEDA, C., LEMOINE, L., CIVELLO, P.M.,MARTINEZ, G.A. and CHAVES, A.R. 2005. UV-C treatmentsreduce decay, retain quality and alleviate chilling injury inpepper. Postharvest Biol. Technol. 35(1), 69–78.

ZHANG, L., LU, Z., YU, Z. and GAO, X. 2005. Preservation offresh-cut celery by treatment of ozonated water. Food Control16(3), 279–283.



Alternative Sanitizing Methods to Ensure Safety and Quality of Fresh-Cut Kiwifruit

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