Innovative Food Science and Emerging Technologies 10 (2009) 61–69

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Innovative Food Science and Emerging Technologies

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Quality attributes of shredded carrot (Daucus carota L. cv. Nantes) as affected byalternative decontamination processes to chlorine

Carla Alegria a,1, Joaquina Pinheiro a,1, Elsa M. Gonçalves a,1, Isabel Fernandes a,1,Margarida Moldão b,2, Marta Abreu a,⁎a Departamento de Tecnologia das Indústrias Alimentares, Instituto Nacional de Engenharia Tecnologia e Inovação, Estrada Paço do Lumiar, 22, 1649-038 Lisboa, Portugalb Centro de Estudos de Engenharia Rural/Departamento de Agro-Indústrias e Agronomia Tropical, Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Tapada da Ajuda,1349-017 Lisboa, Portugal

⁎ Corresponding author. Tel.: +351 21 7127101; fax: +E-mail address: marta.abreu@mail2.ineti.pt (M. Abre

1 Tel.: +351 21 7127101; fax: +351 21 7127162.2 Tel.: +351 21 3653547; fax: +351 213 653 195.

1466-8564/$ – see front matter © 2008 Elsevier Ltd. Aldoi:10.1016/j.ifset.2008.08.006

a b s t r a c t

a r t i c l e i n f o

Article history:

The effects of alternative de Received 26 March 2008Accepted 31 August 2008

Editor proof receive date 30 September 2008

Keywords:Shredded carrotOzonated-waterUltrasonicationHot waterProcessingMicrobiological qualitySensory quality

contamination processes to chlorine: ozonated-water (1 ppm/5 min), hot water(100 °C/45 s) andultrasonication (45kHz/1min), applied pre- or post-cut in the technological diagramofminimalprocessing of carrots were tested. Ultrasonication in chlorinated-water and thermo-ultrasonication as combinedprocesses applied just in pre-cut carrot were also tested. The initial microbial load reduction, soluble solidscontent, pH and sensorial attributes of shredded carrot just after processing were evaluated. Decontaminationprocesses applied on pre-cut carrot provided maintenance of fresh-like sensorial quality, regardless the type oftreatment, due to diminished leaching phenomenawhich is critical for shredded carrot. Chlorination, ozonizationand ultrasonication achieved ca. 1 Log10 reduction of initial microbial load. No additional decontamination effectin combined processes was observed. The use of heat in pre-cut carrot proved to be the most efficient processregarding microbial reduction (3 Log10 units) providing, as well, an acceptable fresh-like quality product.Industrial relevance: The major constraint for marketability of minimally processed shredded carrot is its limitedshelf-life due to rapid microbial growth and colour loss (decrease of orange intensity and/or whitening of theshreds). These questions arise from the practical experience of a fresh-cut industry directly involved in the R&Dresearch project which supported this study. Chlorine solutions have been widely used to sanitize fruit andvegetables in the fresh-cut industry. However, reducedmicrobiological efficiency allied to the eventual formationof carcinogenic chlorinated compounds pointed out the need for alternative methodologies. The present workaimed the evaluation of clean alternative decontamination processes applied both to pre- and post-cut carrot forthe production of shredded carrot, operating under conditions of industrial practice at pilot-plant scale.

© 2008 Elsevier Ltd. All rights reserved.

1. Introduction

Minimally processed vegetables are experiencing an increasingpopularity mainly due to their convenience, freshness and associatedhealth benefits. The predominance of shredded carrot in fresh-cutvegetable production characterizes it as an important component in thismarket owing success to carrots pleasant flavour and nutritionalbenefits aswell as to versatility of use (Alasalvar, Grigor, Zhang, Quantick& Shahidi, 2001).

Usually shredded carrot presents a reduced shelf-life period of about7 to 8 days due to rapid microbial growth. The enhanced physiological/biochemical responses gathered with the great surface extent imposedby shredding, leads to increases inmicrobial and non-microbial spoilage

351 21 7127162.u).

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during storage with negative impact on sensory quality (Jacxsens,Devlieghere, Ragaert, Vanneste & Debevere, 2003). Losses in orangeintensity and/or whitening of the shreds (Barry-Ryan, Pacussi &O'Beirne, 2000; Li & Barth, 1998; Cisneros-Zevallos, Saltveit & Krochta,1995; Bolin &Huxsoll,1991), fresh-like flavour and aroma (Klaiber, Baur,Magel, Hammes & Carle, 2004; Seljåsen, Bengtsson, Hoftun & Vogt,2001; Carlin, Nguyen-The, Cudennec & Reich, 1989) and texture (Barry-Ryan et al., 2000) have been identified as the main quality changes inshredded carrot.

In general, total counts of microbiological populations on minimallyprocessed vegetables after processing are known to range from3.0 to 6.0Log10 units (Ragaert, Devlieghere & Debevere, 2007). Surface deconta-mination treatments during minimal processing acquire a primordialrole in the stability, safety and overall quality of minimally processedvegetables (Hagenmaier & Baker, 1998). Chlorine-based decontamina-tion procedures (50–200 ppm free chlorine) are used by a vast majorityof minimally processed product manufacturers (Beuchat, 1998). How-ever, the existing data about the real effect of chlorine solutions in direct

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contactwithvegetable surfaces to reduce initialmicrobial loadare in factvery limited, since the most that can be expected at permittedconcentrations is 1 to 2 Log10 population reductions. Furthermore,selective reduction in epiphytic microflora may result in an increase inthe potential growth of pathogens (Li, Brackett, Chen & Beuchat, 2002;Zagory, 1999; Beuchat, 1998), where chlorine action has proved to beboth limited (Parish et al., 2003) and unpredictable (Nguyen-The &Carlin, 1994).

On the other hand, chlorine efficiency is extremely dependent onthe amount of free available chlorine (as HOCl) in the wash-water butalso on the pH, temperature, treatment duration, organic matterpresent and vegetable tissue components (Beuchat, 1998). Hence,adequate chlorine treatments should be designed for each vegetableproduct (Simons & Sanguansri, 1997). Finally, the formation ofcarcinogenic chlorinated by-products such as chloramines andtrihalomethanes, called attention to several safety concerns regardingchemical hazard to both human and environment. These currentapprehensions have lead to an increased restriction on chlorine usewhereas in some European countries, including Germany, TheNetherlands, Switzerland and Belgium, its use for washing fresh-cutproducts is banned (Beltrán, Selma, Tudela & Gil, 2005).

Accordingly, the highlighted reasons point out the need to seek foralternative sanitizing technologies which should bemore efficient andclean (Soliva-Fortuny & Martín-Belloso, 2003). Ozone, ultrasoundsand heat treatments, used as single or in combined processes, havebeen studied as clean alternative technologies on the quality ofminimal processed fruits and vegetables (Lamikanra & Watson, 2007;Tsouvaltzis, Siomos & Gerasopoulos, 2006; Seymour, Burfoot, Smith,Cox & Lockwood, 2002; Howard, Griffin & Lee, 1994).

Theuse of ozonated-water as a disinfectant depends on the fact thatas an oxidizing agent, it is 1.5 times stronger and effective than chlorineover a much wider spectrum of microorganisms, including pathogens.In addition, ozonated-water in food processing is recognized asallowable by organic certification and regulatory bodies (Xu, 1999).

Power ultrasound (frequencies ranging from 20 to 100 kHz) haverecently been proposed has a potential application to fresh productdecontamination. The growth, collapse and oscillation of bubblesgenerate mechanical energy, known as cavitation, has a ‘cleaning’action on vegetable surfaces rather than a bacterial destruction effect(Seymour et al., 2002). Power ultrasound on its own is currentlyunfeasible due to impairment on product sensory quality and it mostlikely have to be used in combinationwith other treatments under thehurdle technology concept (Piyasena, Mohareb & McKellar, 2003).

In food processing, thermal treatments are generally effective inreducing microbial levels and inhibiting enzymatic reactions despite ofundesirable effects on texture, flavour, nutritional and fresh-like quality.The classical approach to overcome, or at least minimize, theseundesirable quality changes is the high temperature short time (HTST)concept. It is based on the fact that the inactivation of microorganismschiefly depends on the temperature of the heat treatment, whereasmany undesirable quality changes dependmainly on the duration of theheat treatment (Ohlsson, 1980).

Therefore, the aim of this work was to evaluate alternativedecontamination processes to chlorination testing the effects ofdifferent treatments (ozone, heat, ultrasound and combined treat-ments) and the application site in process diagram (pre- or post-cut)on reducing initial microbial load and quality attributes of shreddedcarrot immediately after minimal processing.

2. Materials and methods

2.1. Plant material

Carrots (Daucus carota L. cv. Nantes) of about 140–180 mm lengthand of 40 mm diameter (upper end) were obtained from a localprocessor (Campotec, S.A.) and transported to INETI in a refrigerated

truck. At the laboratory, carrots were hand-sorted to select unda-maged units and then stored in a dark cooling chamber at 5 °C untilprocessing (within 24 h).

2.2. Processing carrots

Decontaminating processes were conducted on pilot-plant scalewith semi-industrial equipment, carefully sanitized prior to proces-sing. All carrots were rinsed briefly under running tap water in orderto remove soil contamination and paper dried.

Raw material (hand peeled and topped) was processed accordingto the flow diagram shown in Fig. 1. Shredded carrot without anydecontamination procedure was assigned as untreated-control. Apreviously optimized chlorinated-water conditions (200 ppm freechlorine/1 min) as a post-cut procedure (Abreu et al., 2005) was usedas control treatment while its microbial efficacy should be overcome.

Five batches of 10 kg of carrots were used for each decontamina-tion set and processed as follows:

2.2.1. Single decontamination processesI. Chlorinated-water (200 ppm free chlorine/1 min, 5 °C) and

subsequent rinsing (ice-cold water for 2 min) in pre- and post-cut carrot;

II. Ozonated-water (1 ppm/5 min, 5 °C) in pre- and post-cutcarrot;

III. Ultrasonication (45 kHz/1 min, 80% power level) in pre- andpost-cut carrot;

IV. Hot water (100 °C/45 s) and subsequent cooling (ice-cold bathfor 5 min) in pre- and post-cut carrot.

2.2.2. Combined decontamination processesV. Ultrasonication (45 kHz, 80% power level) in chlorinated-water

(50 ppm) for 1 min (identified as US×HIPO samples) in pre-cutcarrot carried out alongwith the respective singular treatmentsof chlorinated-water (50 ppm/1 min) and ultrasonication(45 kHz/1 min, 80% power level);

VI. Ultrasonication (45 kHz, 80% power level) in warm water(50 °C) for 1 min (identified as US×HT samples) in pre-cutcarrot carried out alongwith the respective singular treatmentsof warmwater (50 °C/1min) and ultrasonication (45 kHz/1min,80% power level);

Treatments were carried out in baskets and immersed in therespective solutions during the established treatment time, paperdried for pre-cut treatments and centrifuged manually for post-cuttreatments. Processed shredded carrot was pooled to minimizeheterogeneity (sanitized pincers) and subsequently packed in bagsof 35 μm bioriented polypropylene (200×220 mm) (Amcor FlexiblesNeocel-Embalagens, Lda., Lisboa, Portugal). The permeability of thefilm was with oxygen and carbon dioxide transmission rates of1100 cm3 m−2 day−1 atm−1 and 3000 cm3 m−2 day−1 atm−1 at 23 °C,respectively. Each package contained 250 g of product, andwas kept at5 °C until analysis (within 2 h).

Untreated-control and all treated samples were evaluated for totalaerobic mesophilic and yeast and moulds counts, physical–chemicalattributes (soluble solids content, pH and CIELab colour parameters)and sensory analysis (colour, firmness, aroma and general acceptance).

2.3. Preparation of treatment solutions

Chlorinated-water was prepared by adding sodium hypochloritesolution (NaOCl) containing ≥5% active chlorine to distilled water toobtain a final solution containing 200 ppm or 50 ppm free chlorine(pH 8).

Ozonated-water was produced by circulating potable tap waterthrough an OZ5 ozone generator from SPO3 (Santo Tirso, Porto,

Fig. 1. Flow diagram of minimal processing for shredded carrots according to different decontamination processes (type and application site). a) Pre-cut decontamination treatments(whole carrot); b) Post-cut decontamination treatments (shredded carrot). 1 — Rinsing conditions for chlorinated-water treatments: ice-cold water for 2 min; 2 — cooling conditionsfor hot water treatments: ice-cold water for 5 min.

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Portugal) using oxygen as feed gas. The ozone generator system(maximum O3 production capacity of 5 g h−1) was equipped with a120 L reservoir. Ozonated-water was impelled out by a pump at a flowrate of 1.5 m3 h−1. Concentration of ozonated-water was set to 1 ppmO3 and monitored continuously by measuring the redox potential(Redox probe pH 7685, calibrated with Redox Buffer solutions of220 mV and 468 mV from Mettler, Toledo). The ozone solution wasused immediately after ozone concentration was reached.

Potable tap water was heated to 100 °C using a thermostatically-controlledwater bath of 50 L nominal capacity (Edelsthal Rost-Fret) andtemperature was monitored continuously with T-type thermocouples.

An Elma Transsonic TI-H-55 multi-frequency ultrasound tank(Elma GmbH& Co, Singen, Germany) with a 45 L nominal capacity wasused for ultrasonication trials. The equipmentwas set at a frequency of45 kHz (radiating 80% of power) in sweep mode to expand thegenerated ultrasound field. Prior to sample treatment, tap water wasdegassed for 5 min at operating frequency. For chemical combinedtreatments, the same ultrasonication conditions were maintainedusing chlorinated-water (50 ppm) instead. Ultrasonication combinedwith heat (thermo-ultrasonication) was preformed in tap water withthe ultrasonic equipment set at 50 °C (temperature controlled by T-type thermocouples) keeping ultrasonic conditions as described.

2.4. Analytical procedures

2.4.1. Microbial analysisTotal mesophilic aerobic count (TAPC) was preformed according to

EN ISO 4833 (2003). Yeasts & moulds (Y&M) were determined using

Rose Bengal Chloramphenicol Agar, surface inoculation, incubated at25 °C during 5 days. Microbial counts were expressed as Log10 (cfu g−1).Mean counts for each treatment were subtracted from mean initialmicrobial load to give an average Log10 reduction in the attachedmicroorganism groups.

2.4.2. Physical–chemical measurementsAll sampleswere analyzed forpHand total soluble solid content (SSC,

°Brix). The pHwasmeasured (room temperature) in thehomogenizedofminimally processed carrot in distilledwater (1:1,w:v) using a pHmeter(CrisonMicro pH 2001, Crison Instruments, Spain). Minimally processedcarrot was ground with a domestic blender to extract the juice and SSCwas measured with a digital refractometer (DR-A1, ATAGO Co Ltd.,Japan) equipped with a thermostatic water bath set at 20 °C. Theseprocedures were done in triplicate.

L⁎, a⁎, and b⁎ CIE values (Commission Internationale de l'Eclaireage)were determined in portions of 30 g of product, using a colorimeter(Colorgard®System/05 fromGardner,USA), on theCIELab colour systemusing the C illuminant. The instrument was calibrated using awhite tile(L⁎=92.85; a⁎=0.87; b⁎=0.19) and a black tile (L⁎=0.00; a⁎=0.00;b⁎=0.00) standards. Results were expressed as the calculated totalcolour difference, TCD=[(L⁎−L⁎0)2+(a⁎−a⁎0)2+(b⁎−b⁎0)2]0.5, whereL⁎0, a⁎0 and b⁎0 referred to the colour reading of untreated-control.Results are mean of 45 measurements taken per treatment.

2.4.3. Sensorial analysisA panel of 8–10 trained judges (members of our Department), who

met the basic requirements of sensory sensitivity according to ISO 8586-

Table 1Initial microbial contamination (total mesophilic aerobic count — TAPC and yeast andmoulds count —Y&M), and physico-chemical attributes of untreated shredded carrot

Quality measurements Mean±SD

Microbial loada

TAPC (Log10 [cfu g−1]) 6.4±0.3Y&M (Log10 [cfu g−1]) 3.8±0.1

Physico-chemical attributespHb 6.2±0.0SSC (°Brix)b 9.7±0.3Colour parametersc

L⁎ 52.83±1.30a⁎ 27.20±0.86b⁎ 45.60±0.93

a Data represents the mean of 5 values.b Data represents the mean of 3 values.c Data represents the mean of 45 values.

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1 (1993) in adequate conditions compliant to ISO 13299 (1995),identified and distinguished the sensory attributes, colour, firmnessand fresh-like aroma, of minimally processed carrot. Evaluations werescored based on a 5-point scale, and general acceptancewas also scoredin a 5-point hedonic scale according to the following scoring systems:

Colour: 1 = very light orange; 2 = light orange; 3 = orange; 4 = darkorange; 5 = very dark orange, corresponding the initial carrot freshappearance to anchor 3, immediately after cutting;

Firmness: 1 = very firm, 2 = firm; 3 = moderate; 4 = soft; and 5 =very soft, where anchor 1 corresponds to the perception of the fresh-cut carrot immediately after cutting;

Fresh-like aroma: 1 = very intense, 2 = intense; 3 = moderate; 4 =low; and 5 = absent, where anchor 1 corresponds to the perception ofthe carrots aroma immediately after cutting. Panellists are also askedto identify the presence of any off-odours in the comments section;

General acceptance: 1 = excellent freshly cut, 2 = good, 3 = limit ofmarketability, 4 = fair limit of usability and 5 = poor unusable.Panellists are also asked to enclose any relevant comment.

Fig. 2. The effects of treatment type (chlorinated-water: 200 ppm/1min; ozonated-water: 1 p(pre- or post-cut) on the decontamination efficiency of total aerobic plate counts ( ) and yeaat pb0.05. Different small case letters represent significant differences for TAPC reductionreductions at pb0.05.

Samples (±100 g) of minimally processed carrot were served inplastic dinner plates marked with three-digit code numbers andpresented in a randomized order. Panellists were requested to evaluateon the scale the level of difference in intensity perceived between thesample and the reference (freshly untreated shredded carrot) withrespect to each descriptor and respective acceptance level. The appliedcut-off for the general acceptance was fixed at 3 (limit of marketability)and scores above 3 indicated unacceptable samples.

2.5. Statistical analysis

Data were subjected to Multi- and One-Way ANOVA, and the meanscompared using Fisher Least Significant Difference (LSD) test (α=0.05),using the Statistica™ v.6.1 Software from Stasoft (StatSoft, Inc., 2002).

3. Results and discussion

3.1. Untreated-control

Untreated-control results for initial total mesophilic aerobic count(TAPC), yeast and moulds count (Y&M), pH, total soluble solid content(SSC), and colour parameters (L⁎, a⁎, b⁎) are shown in Table 1.

Initial contamination level of untreated-control was 6.4 Log10 and3.8 Log10 units for total mesophilic aerobic count (TAPC) and yeast &moulds (Y&M), respectively. These mesophilic contamination levelsare similar to those found by Nguyen-The and Carlin (1994) andChervin and Boisseau (1994) for the same vegetable. Y&M counts ofabout 4–5 Log10 have also been reported in shredded vegetables(Nguyen-The & Carlin, 1994).

The carrots' pH values close to 6 (Table 1), are also mentioned for cv.Nantes carrots (Lima,Grossi, Lima,Alves, Coneglian,Godoy&Sabaa-Srur,2001) as well as for cv. Flakee carrots (Carlin et al., 1989). The relativelyhigh soluble solids contentof 9.7°Brix,within thevalue reportedby Limaet al. (2001) (8.5°Brix), characterizes carrots perceived sweetness.Means values of L⁎=52.83±1.30, a⁎=27.20±0.86 and b⁎=45.60±0.9expresses the orange colour of untreated shredded cv. Nantes carrot.

pm/5min; hotwater 100 °C/45 s; and ultrasonication 45 kHz/1min) and application sitest andmoulds counts (□). Values aremeans of five replicates, and bars represent the LSDs at pb0.05 and different upper case letters represent significant differences for Y&M

Table 2Analysis of variance on minimal processed carrot decontamination data

Factor TAPC Log10 reduction Y&M Log10 reduction

df SS MS F p SS MS F p

Intercept 1 78.80 78.80 737.97 0.0000 91.23 91.23 3646.82 0.0000Treatmenttype (1)

3 56.44 18.82 175.76 0.0000 72.76 24.25 969.47 0.0000

Applicationsite (2)

1 0.08 0.08 0.76 0.3894 0.07 0.07 2.62 0.1155

1×2 3 4.94 1.65 15.37 0.0000 0.29 0.10 3.80 0.0194Error 32 3.43 0.11 0.80 0.03

df: degrees of freedom; SS: sum of squares; MS: mean squares; F: Fisher test.

Table 3The effects of combined treatments applied in pre-cut carrot (ultrasonication inchlorinated-water and thermo-ultrasonication) on the decontamination efficiency oftotal aerobic plate counts (TAPC) and yeast and moulds (Y&M)

Treatment TAPC Log10 reduction Y&M Log10 reduction

Ultrasonication in chlorinated-water 1.1b 1.0b

(US×HIPO)Thermo-ultrasonication 1.7c 1.2b

(US×HT)

Singular treatmentsUltrasonication 1.3b,c 0.9b

(45 kHz/1 min)Chlorinated-water 0.4a 0.1a

(50 ppm/1 min)Warm water 1.5b,c 1.2b

(50 °C/1 min)

In the same column, different letters represent significant differences at pb0.05.

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3.2. Microbial analysis

3.2.1. Single decontamination processesReductions in TAPC and Y&M populations as affected by treatment

type and treatment application site (pre- or post-cutting) in theminimal processing diagram of shredded carrot are shown in Fig. 2.

Main effects ANOVA results (Table 2) indicate a significant effect forthe treatment type on reduction of bothmicrobial groups tested, whiletreatment application site (pre- and post-cut) had a non significanteffect. An exception to this behaviour was found with ultrasoundtreatment given that post-cut application rendered the higher efficacy.

The decontamination level attained by chlorine-treated samples(Fig. 2) was about 1 Log10 relatively to both TAPC and Y&M populations.The effect of chlorinated-water as a decontamination process onpre-cutcarrot reported in literature seems to be inconsistent: Klaiber, Baur,Wolf,Hammes and Carle (2005) found reductions of 1.7 Log10 units usingchlorinated-water at 200 ppm free chlorine during 120 s on cv. Bangorcarrot, while no observable effect over initial microbial load wasreported by Sinigaglia, Albenzio and Corbo (1999) using a 100 ppm freechlorine solution. Likewise, studies carried out in other vegetablesreport diverse efficacy results linked to chlorinated-water use: Baur,Klaiber, Wei, Hammes and Carle (2005) achieved a 1.6 Log10 reduction(200 ppm/60 s) in iceberg lettuce; Cliffe-Byrnes and O'Beirne (2005)reached a one-Log10 reduction with 50 ppm/5 min in coleslaw mix;Martínez-Sánchez, Allende, Bennett, Ferreres and Gil (2006) alsoobserved reductions of about 1 Log10 on wild rocket leaves using100 ppm/1 min; and Beltrán et al. (2005) observed no decontaminatingeffect after chlorinated-water treatments (80 ppm/3 min) in potatostrips. Our results about chlorine efficiency (ca. 1 Log10 efficacy) aregenerally in agreement with the above mentioned data and acknowl-edge the reduced lethality in direct contact with vegetable cut tissues.The high antioxidant potential of carrots and the great surface areaexposed by cutting operations might explain chlorines' failure toinactive microorganisms.

The effect of ozonated-water treatments (Fig. 2) promoted amicrobial reduction up to 0.4 Log10 for TAPC and slightly higher oneswith regard to Y&M group (0.6–0.7 Log10), rendering it as less efficientthan chlorinated-water.

No decontaminating effect or a low reduction rate using ozonated-water have also been reported in studies with carrot and iceberglettuce: Klaiber et al. (2004) found no initial microbial reduction inaerobic plate counts on pre-cut carrot (cv. Bangor) at 1.3 ppm/2 min;Baur, Klaiber, Hammes and Carle (2004) and Hassenberg and Idler(2005) showed reductions up to 0.5 Log10 in iceberg lettuce leavesusing 1 ppm/2 min and 1.5 ppm/2 min, respectively. Kim, Yousef andChism (1999) found 1.2 Log10 reductions at 1.3 ppm/3 min also iniceberg lettuce. Even when ozonated-water treatments were per-formed in a closed system, achieving ozone concentrations of 10 and20 ppm, the efficacy level on iceberg lettuce did not exceed 1.6 Log10(Beltrán, Selma, Marín & Gil, 2005).

Contrary to initial expectations, the results of ozone efficacy werefound to be strongly dependent on numerous variables, such as thenumber and kind of contaminating microorganisms, physiology of

vegetables, reactor design, water quality, temperature, and pH (Kimet al., 1999). The competition between both organic load and inorganicmatter (Achen & Yousef, 2001; Hassenberg & Idler, 2005) andmicroorganisms for the available ozone, contributes to reduce itsavailability. In our study, the rapid redox potential decrease observed(Redox probe pH 7685) during treatment (0.08 and 0.32 ppmmin−1 forboth pre- and post-cut treatments, respectively), indirectly states theuse of available ozone by the organic load present.

Hot water treatments (100 °C/45 s) achieved the highest microbialreductions among the tested alternative treatments (Fig. 2). When itsapplication was made in pre-cut carrots, reductions of 3 Log10 unitswere found, and its use in post-cut carrot provided a 4 Log10 cfu g−1

reduction of TAPC. Both samples exhibit no counts for the Y&M group,demonstrating highest efficiency in regard to this microbial group.Furthermore, the efficiency of heat treatment at 100 °C/45 s onmicrobial reduction was quite above the control treatment (chlori-nated-water, 200 ppm/1 min) with a further 2–3 Log10 reduction inpre- and post-cut samples, respectively.

The use of heat as a decontamination treatment, albeit thedifference in time–temperature binomials used, has gathered fairlygood results. In a study by Klaiber et al. (2005), pre-washing wholecarrot (cv. Bangor) with warmwater (50 °C/120 s) promoted a 2 Log10reduction in the total aerobic bacterial population. Also, for iceberglettuce, warm water treatments (50 °C/1 min) were compared to200 ppm chlorinated-water (4 °C, 1 min) since c.a. 1.6 Log10 reductionwas attained by both decontamination procedures (Baur et al., 2005).A minimum of 2 Log10 decrease in initial microbial population wasreported by Park, Cho and Lee (1998) when a 60 °C/30 s treatment wasapplied on soybean sprouts and watercress (in cubes).

The mechanical effect exerted by sonication as a single treatment,was diminutive in shredded samples, never exceeding 0.5 Log10reductions for both mesophilic flora and Y&M group, as shown inFig. 2. Nonetheless, when sonication was preformed prior toshredding (pre-cut samples) the efficiency slightly increased (1Log10 reduction), which can be a result of diminished surface areaand lesser “protective sites” for contaminant flora, improvingmicrobial removal from the vegetable surface. Despite the furtherreductions observed in pre-cut ultrasonication, its efficiency did notsurpass chlorine performance, as expected for singular application.The great surface area associated to shredded carrot for microbialattachment and infiltration of microorganisms into points below thesurfaces provides some level of physical protection against cavitationwhich might explain these results.

3.2.2. Combined decontamination processesReductions in TAPC and Y&M populations as affected by combined

processes (ultrasonication in chlorinated-water or thermo-ultrasonica-tion) in pre-cut carrot are shown in Table 3. Treatments of lower

Fig. 3. The effects of treatment type (chlorinated-water: 200 ppm/1 min; ozonated-water: 1 ppm/5 min; hot water 100 °C/45 s; and ultrasonication 45 kHz/1 min) and applicationsite, pre-cut ( ) and post-cut (□), on soluble solids content (a), pH (b) and TCD values (c). Bars represent the LSD at pb0.05. Different letters represent significant differences atpb0.05.

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Table 5Effects of different decontamination processes on sensory attributes mean scores ofminimal processed shredded carrot

Treatment type Application site Colour Firmness Aroma General acceptance

Chlorinated-water Pre-cut 3.4d 2.3b 2.7b,c 2.8c

Post-cut 2.3b 2.3b 3.3d 3.2c

Ozonated-water Pre-cut 3.4c,d 2.5b 2.5a,b 2.9c

Post-cut 2.2a,b 2.4b 3.2d 3.1c

Hot water Pre-cut 3.1c 1.7a 2.1a 1.6a

Post-cut 1.9a 3.8c 4.3e 4.0d

Ultrasonication Pre-cut 3.1c,d 1.7a 2.4a,b 2.2b

Post-cut 2.1a,b 2.2a,b 3.1c,d 3.2c

Values are average of 8–10 observations. Within a column, different letters representsignificant differences at p=0.05.Colour scoring system: 1 = very light orange; 2 = light orange; 3 = orange; 4 = darkorange; 5 = very dark orange, corresponding the initial carrot fresh appearance toanchor 3, immediately after cutting.Firmness scoring system: 1 = very firm, 2 = firm; 3 =moderate; 4 = soft; and 5 = very soft,where anchor 1 corresponds to the perception of the fresh-cut carrot immediately aftercutting.Fresh-like aroma scoring system: 1 = very intense, 2 = intense; 3 = moderate; 4 = low;and 5 = absent, where anchor 1 corresponds to the perception of the carrots aromaimmediately after cutting.General acceptance scoring system: 1 = excellent freshly cut, 2 = good, 3 = limit ofmarketability, 4 = fair limit of usability and 5 = poor unusable.

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intensities (50 ppm/1 min, 50 °C/1 min and 45 kHz/1 min) were alsotested, as singular ones, to assess additional/synergic effects incombined processes.

Regarding the data in Table 3, we can see that achieved reductions inTAPCandY&Mpopulationsas affectedbyultrasonication in chlorinated-water (US×HIPO samples) were about 1 Log10 unit. Slightly higherreductions were found for thermo-ultrasonication (US×HT samples),with Log10 reductions of 1.7 and 1.2 for TAPC and Y&M, respectively.

The decontamination outcome of the combined treatments did notexceed the efficacy of the respective singular treatments or the controltreatment. As a result, the mechanical feat associated to cavitation as ameans to enhance the lethal effect of temperature or chlorine was notobserved in our results. It is difficult to compare our results since littleinformation on ultrasonication for fresh-cut decontamination purposesis available. However, Seymour et al. (2002) in an inoculation study iniceberg lettuce found that the lethal effect of chlorine over E. coli wasimproved by ultrasonication. In the same study, a further 1 Log10reductionwas assessedwhen the combination of 100ppmchlorinewith32 kHz for 10 min was performed relatively to the singular treatments.

3.3. SSC, pH and colour results

3.3.1. Single decontamination processesSolid soluble content changes (SSC, Fig. 3a) of minimally processed

carrot significantly decreased (pb0.05) by both independent variables(application site and treatment type). However, SSC losses in post-cutsamples (in the range of 4.3 to 5.7°Brix) were higher (pb0.05) thanthose calculated in pre-cut samples (in the range of 1.1 to 1.9°Brix).This behaviour could be explained by highest leaching rates on post-cut samples where surface area exposed to immersion treatments isgreater than in pre-cut ones. As a result of these considerable losses,namely in soluble sugars, sweet-taste perception could be affected.

The accounted pH values (Fig. 3b) were only significantly affected(pb0.05) by treatment type. On the other hand, differences between pHvalues from all treated samples and the untreated-control did notexceed 0.2 pH units. This value does not relate to any expressivephysiological outcome posting this significance as a non-existing effectover this quality attribute in minimally processed carrot.

Differences in the colour values (CIELab parameters) of minimallyprocessed shredded carrots and thereof deduced values for total colourdifferences (TCD, Fig. 3c) were significantly influenced (pb0.05) by bothindependent variables. Regardless treatment type, the TCD values ofpre-cut samples (ranging from 1.6 to 2.9) were always lower (pb0.05)than in post-cut samples (in the range of 3.4 to 5.6). Once again theintense leaching phenomenon can be observed by the increased TCDvalues in post-cut applications. Colour changes were minimized bychlorinated-water, ozonated-water and hotwater treatments applied inpre-cut carrot, with no differences found between them (pN0.05).

3.3.2. Combined decontamination processesAs shown in Table 4, SSC losses were higher (pb0.05) in US×HIPO

samples (7.5°Brix) than in US×HT samples (8.1°Brix). Even thoughtthere is no apparent reason for this significance, SSC variation ofcombined samples arewithin the range of singular pre-cut treatmentsand did not exceed 2.2°Brix relatively to the untreated-control.

Table 4The effects of decontaminating pre-cut carrot in ultrasonication in chlorinated-waterand thermo-ultrasonication on the soluble solids content and pH of minimallyprocessed carrot

Treatment SSC (°Brix) pH TCD value

Ultrasonication in chlorinated-water (US×HIPO) 7.5a 6.0a 4.1a

Thermo-ultrasonication (US×HT) 8.1b 6.0a 3.5a

In the same column, different letters represent significant differences at pb0.05.

Mean pH values (6.0 units) of both samples, did not reveal anysignificant difference among tested combinations and denote main-tenance in regard to the untreated-control pH value (Table 1).

Non-significant differences (pN0.05) were found between US×HIPOand US×HTsamples TCD values of 4.1 and 3.5, respectively. Despite TCDmean values of these samples are slightly above the observed TCD rangefor tested singular pre-cut treatments, both combined samples denoteda closeproximity to the lowest post-cut TCDvalue. This fact supports theprevious statement that pre-cut treatments are more effective to initialcolour preservation.

3.4. Sensorial analysis

3.4.1. Single decontamination processesDifferences in given scores for colour, firmness, aroma and also for

sample general acceptance (Table 5), as well as their impliedcomparison with the untreated-control, shows that the testeddecontamination processes significantly affected overall productquality just after minimal processing.

Significant and high correlations (r=0.94; r2=0.88; p=0.000625)between assessed colour and objective colour measurements (TCDvalues), demonstrates panel consistency and adequacy. Irrespective ofevaluated decontaminating treatment type, colour scores of pre-cuttreated samples were higher (pb0.05) to those decontaminated aftershredding. All pre-cut treated samples showed mean scores rangingfrom 3.1 to 3.4 (pN0.05), close to anchor 3 (untreated-control)implying colour maintenance of fresh product. In opposition, adeviation from anchor 3 (orange) to lower scores (from 1.9 to 2.3)was found in shredded-treated samples resulting in loss of perceptionin colour intensity from orange to light orange. This could beattributed to orange pigment leaching (carotenes) during immersiontreatments as observed in the washing solutions colour aftertreatment (not quantified). The significant higher TCD values(pb0.05) when treatments were applied post-cut, corroborates thisintense pigment leaching to the wash-water.

Mean scores forfirmnessof treated samples (from1.7 to3.8) denote adeviation fromanchor 1 (untreated-control) indicating a softeningeffectas a result of applied decontamination processes. Non-significantdifferences (pN0.05) between scores of chlorinated and ozonatedsamples, independently of treatment localization, and also for post-cutultrasonicated samples, were found (scoring from 2.2 to 2.5). Amongevaluated samples, pre-cut heat-treated and ultrasonicated carrots

Table 6The effects of decontaminating pre-cut carrot in ultrasonication in chlorinated-waterand thermo-ultrasonication on sensory attributes mean scores of minimal processedshredded carrot

Treatment Colour Firmnessns Aromans Generalacceptance

Ultrasonication in chlorinated-water(US×HIPO)

2.8a 1.7 2.6 2.8b

Thermo-ultrasonication (US×HT) 3.1b 1.7 2.4 2.3a

Values are average of 8–10 observations. Within a column, different letters representsignificant differences at p=0.05. ns — no significant differences were observed atp=0.05.Colour scoring system: 1 = very light orange; 2 = light orange; 3 = orange; 4 = darkorange; 5 = very dark orange, corresponding the initial carrot fresh appearance toanchor 3, immediately after cutting.Firmness scoring system: 1 = very firm, 2 = firm; 3 =moderate; 4 = soft; and 5 = very soft,where anchor 1 corresponds to the perception of the fresh-cut carrot immediately aftercutting.Fresh-like aroma scoring system: 1 = very intense, 2 = intense; 3 = moderate; 4 = low;and 5 = absent, where anchor 1 corresponds to the perception of the carrots aromaimmediately after cutting.General acceptance scoring system: 1 = excellent freshly cut, 2 = good, 3 = limit ofmarketability, 4 = fair limit of usability and 5 = poor unusable.

68 C. Alegria et al. / Innovative Food Science and Emerging Technologies 10 (2009) 61–69

showed the best fresh firmness perception (rating 1.7). Distinctively, asoftening effect was extremely evident in heat-treated shredded carrotas mean scores of 3.8 were significantly higher to all evaluated samples(pb0.05). This softening was due to the high exposed vegetablesuperficial area (shreds) in direct contact with a washing procedure ofhigh temperature.

The effect of decontamination processes on sample aroma scores(ranging 2.1 to 4.3) denoted losses in perceived fresh-like aromaimmediately after minimal processing. Regardless treatment type,shredded sample scores (3.1 to 4.3) were always significantly higher(pb0.05) than pre-cut samples (mean scores from 2.1 to 2.9), posingpost-cut procedures as critical to losses in aroma.

Aroma evaluation also enables the panellists to detect off-flavours(comments included in sensory form) caused by the treatment type, aswell as loss of aroma intensity. In post-cut decontamination processes,changes in fresh-like aroma reached an absolute maximum for heat-treated samples (mean score of 4.3) being this change attributed to thepresence of an off-odour recognized by the judges as “cooked”. Post-cut chlorinated, ozonated and ultrasonicated samples accountedsimilar scores close to anchor 3 (moderate aroma) and no significantdifferences were found between them (pb0.05). However, only inchlorinated samples the presence of an off-odour was detected andidentified as “disinfectant”. Decontamination treatments applied inpre-cut carrot (except for chlorinated samples) provided a similararoma score (from 2.1 to 2.5) without significant differences betweensamples (pN0.05) corresponding to an intense tomoderate perception.

The impact of decontamination processes on sample overallquality accomplished an acceptance level close to or above samplecut-off limit (anchor 3 — limit of marketability). Sensory acceptancereveals itself of extreme importance to ensure industrial processesviability. This proximity to acceptance cut-off level is at leastconcerning as it might indicate a shorter shelf-life of the product,since during storage further deterioration is expected.

In general, the determined correlations between general acceptanceand assessed sensory attributes showed that for minimally processedcarrot, the acceptance levels are more dependent on sample firmnessand aroma (correlations of 0.85; r2=0.72 and 0.93; r2=0.87, respectively)than in colour (correlations of −0.67; r2=0.45) of treated samples. Heat-treated shredded samples stand out among evaluated samples, sincethey reached the highest rejection level (mean score of 4.0) justified bythe significant loss in firmness and fresh-like aroma. Pre-cut heat-treated samples obtained the highest acceptance (mean score of 1.6)among all evaluated samples due to maintenance of fresh-like firmnessand aroma.

3.4.2. Combined decontamination processesMean sensory scores for combined decontamination treatments

applied in pre-cut carrot are summarized in Table 6. The sensoryimpact level of the combined treatments (US×HIPO and US×HT) inpre-cut carrot on colour, firmness and aroma was similar to that ofsingular pre-cut decontamination processes, as expected. Even thougharomatic losses were perceived, panellists did not identify any off-odour in these samples. The acceptance level for US×HIPO and US×HTsamples, of 2.3 and 2.8 respectively, also states sample closeness tocut-off level just after minimal processing.

4. Conclusion

Shredded carrot decontamination level showed to be treatmenttype dependent. Ozonated-water, ultrasonication and combinedtreatments, ultrasonication in chlorinated-water and thermo-ultra-sonication, did not provide suitable microbial reduction for minimalprocessing purposes, with reduction levels of ca.1 Log10 units. The useof heat (100 °C/45 s) achieved highest reductions surpassing chlorineperformance by 2–3 Log10.

Considering all tested decontamination processes on the quality ofshredded carrot just after minimal processing, application site provedto be critical when the treatment was applied after cutting (shred-ding), namely by the observed significant SSC losses, colour changesand impairment of aroma perception.

To the fresh-cut industry, post-cut decontamination treatments onshredded carrot should be disregarded, therefore the use of heat(100 °C/45 s) as a pre-cut decontamination treatment might havetechnological relevance and feasibility as an alternative decontamina-tion procedure to chlorine. Experimental research on its impact onproduct quality during storage is presently under study by the authors.

Acknowledgments

The authors wish to thank financial support provided by the POCTIMed. 2.3 — CLEANTECH Project.

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