Food Research International 44 (2011) 1224–1230

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Food Research International

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Combined effect of active coating and MAP to prolong the shelf life of minimallyprocessed kiwifruit (Actinidia deliciosa cv. Hayward)

Marianna Mastromatteo b, Marcella Mastromatteo a, Amalia Conte a,b, Matteo Alessandro Del Nobile a,b,⁎a Istituto per la Ricerca e le Applicazioni Biotecnologiche per la Sicurezza e la Valorizzazione, dei Prodotti Tipici e di Qualità, BIOAGROMED, Via Napoli, 52, 71100 Foggia, Italyb Department of Food Science, University of Foggia, Via Napoli, 25, 71100 Foggia, Italy

⁎ Corresponding author. Department of Food ScienNapoli, 25, 71100, Foggia, Italy. Tel./fax: +39 881 589 2

E-mail address: ma.delnobile@unifg.it (M.A. Del Nob

0963-9969/$ – see front matter © 2010 Elsevier Ltd. Aldoi:10.1016/j.foodres.2010.11.002

a b s t r a c t

a r t i c l e i n f o

Article history:Received 5 July 2010Accepted 1 November 2010

Keywords:KiwifruitMinimally processingAntimicrobial compoundsMAP

In this work different strategies aimed to prolong the shelf life of minimally processed kiwifruits arepresented. First, the effectiveness of several treatments in delaying the quality loss of the investigated producepackaged under passive MAP was addressed; afterward, the treatments that have shown the bestperformances were used to assess the effectiveness of active MAP in prolonging the packaged produceshelf life. Different treatments such as coating with sodium alginate in combination with dipping into anhydro-alcoholic solution (Coat-dipp-EtOH), dipping into an hydro-alcoholic solution (Dipp-EtOH) andcoating with sodium alginate containing grape fruit seed extract solution (Coat-GFSE) were investigated. Theuntreated samples were used as control. Headspace gas concentrations, pH, mass loss, sensory quality andviable cell load of main spoilage microorganisms were monitored in both the experimental steps. Resultssuggested that the best performances under passive MAP were recorded with the coating treatments,justifying the choice of this treatment in the second step. In fact, the coatings were more effective in delayingdehydration and slowing down respiratory activity of minimally processed kiwifruits both in passive andactive MAP. The combination of active compounds with alginate-based coating delayed the microbial growthwhereas the sole dipping treatment was inefficient. In particular, a viability loss of the mesophilic andpsychrotrophic bacteria of about 2 log cycle for the coated samples with respect to control and dipped sampleswas found. However, as the microbial load was always found below the threshold value imposed by law, thesensorial acceptability limit of the packaged fresh-cut produce coincided with its shelf life. Alginate-basedcoating reduced respiratory activity, as well as sensory decay, increasing the sensorial acceptability limit ofthe samples packaged under passive MAP up to 12 days with respect to the control (8 days). For the samplespackaged under active MAP, the coating treatments reduced the excessive dehydration of the produce due tothe MAP conditions. In fact, when the active MAP was used alone a very short shelf life of the uncoatedsamples occurred (2.7 days). Whereas, the combined use of active MAP and coating treatments prolonged theproduce shelf life up to 13 days.

ce, University of Foggia, Via,42.ile).

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© 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Minimally processed (MP) fruits are products that maintain theirattributes and quality similar to those of fresh products (Alzamora,Lopez-Malo, & Tapia, 2000). However, minimal processing alters theintegrity of fruit and induces wounding stress and spoilage. Physicaldamage or wounding caused by slicing, peeling, and/or othermechanical injuries in minimally processed fruits results in increasedrespiration rates and ethylene production within minutes (Abe &Watada, 1991). Increases occur in biochemical reactions related to

changes in color, flavor, texture, nutritional quality and susceptibilityto dehydration. These responses occur in disrupted tissues wherecellular decompartmentation leads to intermixing of enzymes andsubstrates, as well as the release of acid and hydrolyzing enzymes(Watada, Abe, & Yamuchi, 1990). During storage such products have avery limited shelf life (Brackett, 1994; O'Connor-Shaw, Roberts, Ford,& Nottingham, 1994).

Kiwifruit (Actinidia chinensis, Planch and Actinidia deliciosa, A.Chev.) is a native of the mountains of southern China. Commercialdevelopment of the fruit took place in New Zealand, with a number ofcultivars being selected from seeds of A. deliciosa. Long storage life wasregarded as essential for the development of an export industry inNew Zealand, so the cultivar Hayward, which has a storage life of atleast six months at 0 °C, was adopted for cultivation among others(Scott, Spraggon, & McBride, 1986). The firmness of a kiwifruitstrongly influences its sensory qualities at the moment of consump-tion, including perceived aroma intensity, sweetness, acidity and

1225M. Mastromatteo et al. / Food Research International 44 (2011) 1224–1230

ripeness (Stec, Hodgson, Macrae, & Triggs, 1989). Enzymatic activities,softening and ripening of kiwifruit are promoted by ethylene (Arpaia,Mitchell, Kader, &Mayer, 1985;Wegrzyn &MacRae, 1992). The loss ofcellular compartmentation, due to peeling and cutting, causes mixingof metabolites of the ethylene generating system stimulating ethyleneproduction (Mazliak, 1983; Watada et al., 1990). Therefore, it isdifficult to maintain the quality of minimally processed kiwifruit oncethey have been cut (Chien & Buta, 2003).

In order to extend the shelf life of minimally processed products anumber of technologies are available. Temperature and headspaceatmosphere are two important factors to prolong their shelf life.Modified atmosphere (MAP) can be interpreted as a dynamic systemwith two gas fluxes, the respiration rate of the fresh product and thegas exchange through the packaging film (Van de Velde & Kiekens,2002). In general, gas compositions inside a MAP package are low inO2 and high in CO2, depending primarily on temperature, productweight and respiration rate, O2 and CO2 film transmission rates andpackage total surface area. MAP and low temperature storage areusually not sufficient to extend the shelf life of pre-cut produce as theexcessive physiological stress and increased susceptibility towardsmicrobial spoilage caused by processing operations like cutting andslicing, reduce the shelf life significantly.

Edible coatings, containing antimicrobial agents, are gainingimportance as potential treatments to reduce the deleterious effectsimposed by minimal processing on fresh-cut fruit (Conte, Scrocco,Brescia, & Del Nobile, 2009; Del Nobile, Conte, Scrocco, Laverse, et al.,2009). The use of edible coatings for a wide range of food products,including fresh and minimally processed fruit, has received increasedinterest, because coatings can serve as carrier for a wide range of foodadditives, including anti-browning agents, colorants, flavors,nutrients, spices and various antimicrobials that can extend productshelf life and reduce the risk of pathogen growth on food surface(Cagri, Uspunol, & Ryser, 2004; Pranoto, Salokhe, & Rakshit, 2005).Incorporating antimicrobial compounds into edible films or coatingsprovides a novel way to improve the safety and shelf life of ready-to-eat foods (Cagri et al., 2004). Some of the more commonly usedantimicrobials include benzoic acid, sorbic acid, lysozyme, bacter-iocins (nisin and pediocins) and plant-derived secondarymetabolites,such as essential oils and phytoalexins.

Essential oils are regarded as alternatives to chemical preservatives,and their use in foods meets the demands of consumers forminimally processed natural products, as reviewed by Burt (2004).Essential oils can extend shelf life of unprocessed or processed foodsby reducing microbial growth rate or viability (Beuchat & Golden,1989). These compounds can be added to edible films and coatings tomodify flavor, aroma, and odor, as well as to introduce antimicrobialproperties (Cagri et al., 2004). However, there are a few studies aboutthe effectiveness of the incorporation of those compounds into ediblecoatings applied to fruit for ensuring quality and safety has beenpublished (Eswaranandam, Hettiarachchy, & Meullenet, 2006;Raybaudi-Massilia, Mosqueda-Melgar, & Martìn-Belloso, 2008;Rojas-Graü et al., 2007).

Ethanol is the most common microbiological and medicaldisinfectant. Recently, many studies dealing with table grapepreservation techniques have found that the use of ethanol, as acommon food additive with antimicrobial activity, suppressedmicrobial growth and prevented berry decay (Del Nobile, Conte,Scrocco, Brescia, et al., 2009; Del Nobile et al., 2008; Pinto, Lichter,Danshin, & Sela, 2006). Treatment of table grapes with ethanol has thepotential not only to kill spoilage microorganisms, but also to inhibithazardous food borne pathogens.

The objective of this work was to evaluate the effectiveness of thenatural essential oil, such as Grape Fruit Seed Extract (GFSE)incorporated into an edible coating, and ethanol on the shelf life ofpacked minimally processed kiwifruit under both passive and activeMAP.

2. Materials and methods

2.1. Sample preparation

Fresh italian kiwifruits (A. deliciosa cv. Hayward) kindly providedby a local farm (Ermes, Noicattaro, Italy), were transported within 2 hto the laboratory under refrigerated conditions (±4 °C) and imme-diately processed. Kiwifruit were washed with tap water, treated for5 min with chlorinated water (20,000 ppm) and peeled using amanual vegetable cutter. The minimally processed kiwifruit weresubjected to the following treatments:

a) Coat-dipp-EtOH: kiwifruits were dipped for 5 min into a hydro-alcoholic solution (30% v/v in ethanol) and then air-dried for10 min (Del Nobile, Conte, Scrocco, Brescia, et al., 2009; Del Nobileet al., 2008). Afterward kiwifruits were dipped into a sodiumalginate (4% w/v) water solution. The sodium alginate solutionwas prepared by dissolving sodium alginic acid in distilledwater at50 °C for 2 h. The coated samples were immersed into a 5% (w/v)calcium chloride (CaCl2) solution for 1 min to promote the alginategel forming process and then into a hydro-alcoholic solution (30%v/v in ethanol) for 5 min (Conte et al., 2009; Del Nobile, Conte,Scrocco, Laverse, et al., 2009). Sodium alginic acid and CaCl2 wereprovided by Sigma-Aldrich Co. Inc. (USA), Ethanol by Baker(Holland).

b) Dipp-EtOH: kiwifruit were dipped for 5 min into a hydro-alcoholicsolution (30% v/v in ethanol) and then air-dried for 10 min.

c) Coat-GFSE: kiwifruit were dipped into a sodium alginate (4%, w/v)solution containing grape fruit seed extract water solution (GFSE,5000 ppm) (Biocitro, Probena s.l., Zaragoza, Spain) and thenimmersed into a 5% (w/v) CaCl2 solution for 1 min (Cagri et al.,2004; Rojas-Graü et al., 2007).

After dipping or coating treatment, two kiwifruits per package(~200 g per pack) were packaged in an Oriented Polypropylene film(OPP thickness 20 μm) bags with a surface area of 396 cm2. Samplessimply peeled were also packaged and used as control (Ctrl). Thesamples were sealed by means of a S100-Tecnovac equipment(Tecnovac, San Paolo D'Argon, Bergamo, Italy) with the followingatmospheres: passive and active modified atmosphere packaging(MAP: 10% O2, 10% CO2). The main parameters of the Tecnovacequipment were: 99.0% gas, 99.0% vacuum, 2.3 min sealer. All sampleswere stored at 4 °C for about 15–21 days. Three samples for eachtreatment were randomly selected for analysis.

2.2. Headspace gas composition

The changes in headspace O2 and CO2 concentration of packagedminimally processed kiwifruit were measured using a PBI DansensorO2/CO2 analyzer (Checkmate 9900, Denmark). The volume taken fromthe package headspace for gas analysis was about 10 cm3. The packageheadspace volume was determined by the difference between thetotal volume of the packages and the volume of the sample. The totalvolume was measured by dipping the packages containing the fruitinto a graduated water container and by observing the increase in thewater level. Similarly, the volume of the samples was calculated byimmersion of the clusters in a graduated cylinder with water, and bymeasuring the increase in water level. To avoid modifications in theheadspace gas composition due to gas sampling, each package wasused only for a single measurement of the headspace gas composition.Three bags were used for each measurement.

2.3. Microbiological analysis and pH evaluation

For microbiological analysis, about 25 g of sample was asepticallyremoved from each package, placed in a stomacher bag, diluted with0.9% NaCl solution and homogenized with a Stomacher LAB Blender

Table 1Values of Oxygen Transmission Rate (OTR) and Carbon Dioxide Transmission (CDTR) ofOriented Polypropylene film (OPP thickness 20 μm).

Temperature (°C) OTR (cm3·m−2·day−1) CDTR (cm3·m−2·day−1)

23 2481.74±241.54 6982.53±574.1516 1674.61±125.87 4926.5±341.5210 1364.13±300.88 3552.0±268.555 1014.72±9.5 2700±176.7

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400 (Pbi International, Milan, Italy). Decimal dilutions were carriedout using the same diluent. Mesophiles and psychrotrophs weredetermined on Plate Count Agar (PCA) with incubation at 30 °C for24–48 h and 7 °C for 10 days, respectively. For Enterobacteriaceae,Violet Red Bile Glucose Agar (VRBGA) was used and plates wereincubated at 37 °C for 18–24 h. Lactic acid bacteria (LAB) were platedonMRS Agar and incubated anaerobically at 30 °C for 2–4 days. Yeastsand moulds were determined on Sabouraud Dextrose Agar (SDA),supplemented with chloramphenycol (0.1 g l−1) (C. Erba, Milan,Italy) with incubation at 25 °C for 48 h and 5 days, respectively.

The pHwas evaluated on the homogenized kiwifruit by a pHmeter(Crison Instruments, Barcelona, Spain). The pH measurement wascarried out twice, on two different batches.

2.4. Mass loss

The mass loss percent was determined according to the followingexpression:

%ML tð Þ = M0−M tð ÞM0

d100 ð1Þ

where: %ML(t) is the mass loss percent at time t, M0 is the initialsample mass and M(t) is the sample mass at time t. The sample masswas determined by a digital precision balance (±0.1 g) (GibertiniEurope, Italy). At each sampling time, the mass was measured twice,on two different batches.

2.5. Sensory evaluation

A panel consisting of seven untrained evaluators using a five pointhedonic scale (5: excellent; 4: good; 3: acceptable limit of market-ability; 2: poor and 1: extremely poor) (Larmond, 1977; Mastromat-teo, Danza, Conte, Muratore, & Del Nobile, 2010; Mastromatteo,Lucera, Sinigaglia, & Corbo, 2009; Nowak, Von Mueffling, Grotheer,Klein, & Watkinson, 2007) was used in this study to quantitativelydetermine the “overall quality” according to the procedure reportedby Gimenez et al. (2003). Panelists were asked to base their decisionon the sample “overall quality” only taking into account its color, odor,and firmness. Therefore, the samples “overall quality” has to beconsidered as an average of the above-mentioned sensorial attributevalues (i.e., color, odor, and firmness) as weighted by the panelist.Moreover, panelists were also asked to score color, odor, and firmnessof each sample. A score equal to 3 was used as the threshold forproduce acceptability. During the test sessions, two samples for eachtreatment were randomly presented for sensory analysis. To deter-mine the sensory acceptability limit (SAL) of the investigatedminimally processed produce, a first order kinetic equation (Conteet al., 2009) was fitted to the experimental data:

SA tð Þ = SAmin−SA0d exp −kd SALð Þ1− exp −kd SALð Þ

+ SA0−SAmin−SA0d exp −kd SALð Þ

1− exp −kd SALð Þ� �

d exp −kd tð Þ

ð2Þ

where: SA(t) is the kiwifruit sensory attribute at time t, k is the kineticconstant, SA0 is the initial value of the kiwifruit sensory attribute,SAmin is the limit for minimally processed produce acceptability, SAL isthe sensory acceptability limit (i.e., the time at which SA(t) is equal toSAmin), and t is the storage time.

Panelists were also asked to search for visual moulds, thusallowing determining the day between the latest storage time atwhich moulds were not visible and earliest storage time at whichmoulds were visible, hereinafter referred to as VMT (Visual MouldsTime) (Costa, Lucera, Mastromatteo, Conte, & Del Nobile, 2010). Dueto safety reasons, the evaluation of minimally processed kiwifruit

color, odor, firmness and overall quality by the panelists was stoppedas soon as visible moulds were detected.

2.6. Permeation tests

The Water Vapor Transmission Rate (WVTR) of the selected filmwas determined by means of a water vapor permeability analyser(Lyssy, Model 80-5000, Dansensor, Ringsted, Denmark). Two samplesof the filmwith a surface area of 5 cm2 were tested at 23 °C and 85% ofrelative humidity (RH). A flow rate of 100 ml/min of nitrogen wasused.

The Oxygen Transmission Rate (OTR) was determined bymeans ofan Ox-Tran (Mocon, Model 2/20). Two samples of the film with asurface area of 5 cm2 were tested at 10, 16 and 23 °C and 0% RH at theupstream and the downstream side of the sample.

The Carbon Dioxide Transmission Rate (CDTR) was determined bymeans of a Permatran (Mocon,Model C 4/41). Two samples of the filmwith a surface area of 5 cm2 were tested at 10, 16 and 23 °C and 0% RHat the upstream and the downstream side of the sample.

2.7. Statistical analysis

The values of the parameters relative to microbiological analysisand sensory quality were compared by one-way analysis of variance(ANOVA). A Duncan's multiple range test with the option ofhomogeneous groups (Pb0.05) was used to determine significancebetween treatments. To this aim, STATISTICA 7.1 for Windows(Stat-Soft, Inc, Tulsa, OK, USA) was used.

3. Results and discussion

3.1. Film barrier properties

The measured values of OTR and CDTR for the tested film are listedin Table 1. The gas permeation tests were conducted at temperaturesdifferent to 5 °C, that was the storage temperature of kiwifruit, as it isnot possible with the actual equipments to make permeation tests attemperatures lower than 10 °C. In order to determine the gas barrierproperties of the selected film in the real working conditions, theArrhenius equation was used:

P = P0d exp − EaRT

� �: ð3Þ

The tests were conducted at 23 °C, 16 °C and 10 °C and by using theabove equation the permeability values at 5 °C were obtained byextrapolation. As expected the permeability increased as thetemperature of the permeation test increased. A similar trend wasalso found for CO2 permeability. The extrapolated permeability values(mol·cm/cm2·atm·h) for both O2 and CO2 were then converted to therespective values of OTR and CDTR (cc/(m2·day)).

As far as the WVTR is concerned, the above-mentioned approachwas not adopted due to the fact that the apparatus devoted tomeasure water vapor transport properties cannot make measures atmore than two temperatures, thus not allowing any extrapolation. Forthis reason, the permeation tests to water vapor were carried out only

Table 2aEvolution of mesophilic and psychrotrophic bacteria (log cfu/g) for Step I kiwifruitpacked under passive MAP.

Samples Mesophiles Psychrotrophs

log cfu/ginitial log cfu/g8 days log cfu/ginitial log cfu/g8 days

Coat-dipp-EtOH 2.00±0.00a 2.10±0.17a 2.00±0.00a 2.33±0.58a

Dipp-EtOH 2.40±0.35a,b 4.13±0.84b 2.00±0.00a 3.76±0.24b

Coat-GFSE 2.00±0.00a 2.40±0.35a 2.00±0.00a 2.48±0.83a

Control 2.48±0.00a,b 4.20±0.25b 2.00±0.00a 4.21±0.53b

Mean values±standard deviation.a–dMeans in the same column followed by different superscript upper cases aresignificantly different (Pb0.05).

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at one temperature and the values recorded should be used to solecomparative purposes. WVTR value equal to 0.6 g m−2 day−1 wasobtained for Oriented Polypropylene film (OPP thickness 20 μm).

3.2. Step I: packaging under passive MAP

3.2.1. Headspace gas compositionFruit and vegetables consume oxygen and produce carbon dioxide

while packed, giving rise to a modification of the headspace gascomposition (Jayas & Jeyamkondan, 2002). The respiration of theproduct and the gas permeability of the film influence the change ingaseous composition of the environment surrounding the product.

Fig. 1a, b shows the evolution over storage of O2 and CO2

concentrations in the OPP20 bag headspace for Coat-dipp-EtOH,Dipp-EtOH, Coat-GFSE and Ctrl samples packaged in passive MAP. Asexpected, a decrease in the headspace oxygen concentration, as wellas an increase in the headspace carbon dioxide concentration wasobserved. In particular, a faster decrease in the headspace oxygenconcentration for Dipp-EtOH (5.55) and Ctrl (6.64) samples comparedto coated samples (about 10.0–11.0) was observed (Fig. 1a). Thesedata suggest that coating treatment can reduce the respiration activityof minimally processed kiwifruit. Similar results were also reported inthe literature for minimally processed lampascioni and fresh-cutapples. In fact, it was found that edible coating based on sodiumalginate, whey proteins concentrate, carrageenan or polysaccharides/lipid formulation, in combination with anti-browning agents, reducedthe respiration rate of minimally processed lampascioni and slicedapples (Conte et al., 2009; Lee, Park, Lee, & Choi, 2003; Wong, Tillin,Hudson, & Pavlath, 1994). In addition, Wong et al. (1994) indicatedthat the diffusion of the headspace oxygen to the tissue apple pieceswas slowed down by the oxygen resistance of the coating. Moreover, ahigher increase of carbon dioxide concentration for coated samples

Fig. 1. Evolution of oxygen (a) and carbon dioxide (b) plotted as a function of storagetime for minimally processed kiwifruit belonging to Step I.

(10.0) with respect to the uncoated samples (about 7.0–8.0) wasobserved (Fig. 1b). Olivas and Barbosa-Cánovas (2005) indicated thatcoatingswith selective permeability to gases are capable of decreasingthe interchange of O2 and CO2 between coated fruit and theenvironment, slowing down the metabolism by decreasing internalO2 concentration and increasing CO2 concentration.

3.2.2. Microbiological stability and pHTable 2a reports the cell load of mesophilic and psychrotrophic

bacteria at 0 and 8 days of sampling for treated and untreated samplespacked under passive MAP. The initial cell load for mesophiles andpsychrotrophs was the same for all samples and did not exceed 2.5 logcfu/g. It is interesting to note that at 8 days of sampling a viability lossof the mesophilic bacteria of about 2 log cycle for the coated samples(Coat-dipp-EtOH and Coat-GFSE) with respect to Dipp-EtOH and Ctrlsamples was found. The Dipp-EtOH samples showed the samebehavior of the untreated samples. Probably, the coating treatmentimproved the ethanol efficacy as it avoided its evaporation. For thepsychrotrophic bacteria, significant differences between the cell loadof the coated samples and uncoated samples were also observed(Pb0.05). Many studies have found that ethanol pre-treatment wasthe most effective as it successfully reduced the cell load of the mainspoilage microorganisms of minimally packed produce (Del Nobileet al., 2008; Del Nobile, Conte, Scrocco, Brescia, et al., 2009). Shapero,Nelson, and Labuza (1978) examined the inhibition of a strain ofStaphylococcus aureus by ethanol at low water activities (about 0.88)and concluded that the inhibition was due not only to the lowering ofwater activity by ethanol but also to some other effects on thebacteria. Ballesteros, Chirife, and Bozzini (1993) came to the sameconclusion in an electron microscopic study of two different strains ofS. aureus, which indicated that cell wall changes were partlyresponsible for the antibacterial action of ethanol. This is supportedby the work of Ingram (1981) and Ingram and Buttke (1984), andthese authors suggested that ethanol inhibits cross-linking duringpeptidoglycan biosynthesis by decreasing the strength of hydrophobicinteractions. Moreover, the inclusion of essential oils into ediblecoatings significantly inhibited the growth of psychrophilic aerobes,yeasts and moulds of fresh-cut apples (Rojas-Graü et al., 2007). It isworth noting that at 8 days the cell load of mesophiles was alwaysfound below the threshold value (5×107 log cfu/g) imposed by theFrench Regulation (Corbo et al., 2004) during the entire storage time.

Table 2bEvolution of mesophilic and psychrotrophic bacteria (log cfu/g) for Step II kiwifruitpacked under active MAP.

Samples Mesophiles Psychrotrophs

log cfu/ginitial log cfu/g8 days log cfu/ginitial log cfu/g8 days

Coat-dipp-EtOH 2.00±0.00a 2.20±0.35a 2.00±0.00a 2.00±0.00a

Coat-GFSE 2.00±0.00a 2.88±0.79a 2.00±0.00a 3.11±0.23b

Control 2.89±0.77a,b 4.00±0.26b 2.00±0.00a 4.16±0.18c

Mean values±standard deviation.a–dMeans in the same column followed by different superscript upper cases aresignificantly different (Pb0.05).

Table 3aMass loss percentage for Step I kiwifruit.

Time(day)

Samples

Coat-dipp-EtOH Dipp-EtOH Coat-GFSE Control

1 0.308±0.049a 0.310±0.063a 0.437±0.041b 0.145±0.027c

4 0.354±0.084a 0.535±0.074b 0.470±0.097a,b 0.186±0.049c

6 0.514±0.085a 0.519±0.101a 0.518±0.159a 0.175±0.099b

8 0.610±0.080a 0.492±0.063a 0.592±0.146a 0.256±0.058b

11 0.503±0.054a 0.517±0.117a 0.558±0.111a 0.283±0.028b

13 0.483±0.038a 0.528±0.029a 0.575±0.063a 0.327±0.256a

15 0.555±0.166a –⁎ 0.612±0.076a –

Mean values±standard deviation.a–cMeans in the same row followed by different superscript upper cases are significantlydifferent (Pb0.05).⁎ The samples were not acceptable.

Table 4aShelf life of Step I kiwifruit packaged under passive MAP assumed as the lowest valueamong the calculated microbial and sensorial acceptability limits (MAL, SAL) and visualmoulds time (VMT).

Samples SALOQ (day) VMT (day) Shelf life (day)

Coat-dipp-EtOH 12.30±0.55a N15 12.30±0.55a

Dipp-EtOH 10.20±1.07b 14 10.20±1.07b

Coat-GFSE 11.75±0.56a N15 11.75±0.56a

Control 8.22±0.52c 14 8.22±0.52c

Mean values±standard deviation.a–d Means in the same column followed by different superscript upper cases aresignificantly different (Pb0.05).

1228 M. Mastromatteo et al. / Food Research International 44 (2011) 1224–1230

Lactic acid bacteria and Enterobacteriaceae (b1 log cfu/g), yeasts andmoulds (b2 log cfu/g) were always below the level of detection.

The pH valueswere about 3.4 in all samples and remained constantduring the entire storage period (data not shown).

3.2.3. Mass lossConcerning the effect of different treatments on mass loss,

significant differences between the coated and dipped samples withrespect to the control samples were observed (Pb0.05). In particular,the higher mass loss percent of the coated and dipped samples wasprobably due to the high water content of the alginate coating and thedipping treatment. However, for these samples the mass loss percentdid not exceed 0.6% for the entire storage period (Table 3a).

3.2.4. Sensory evaluationFig. 3a shows the evolution during storage of the minimally

processed kiwifruit “overall quality” for all investigated samplespacked under passive MAP. As can be inferred from the figure, theuncoated samples packaged under passive MAP reached first the“overall quality” threshold value with respect to the coated samples.SAL values were determined for minimally processed kiwifruit“overall quality” following the procedure reported in the Materialsand methods section. Curves shown in the figure were obtained byfitting Eq. (2) to the experimental data, results are listed in Table 3a;whereas, the solid horizontal line is the “overall quality” thresholdvalue. SALOQ is the time at which the investigatedminimally processedproduce was nomoremarketable from a sensory point of view. As canbe inferred from the data listed in Table 4a, for the control and Dipp-EtOH samples, a SALOQ value of about 8–10 days wasmeasured, due toa general spoiling in terms of color, odor and consistence. Conversely,alginate-based coating reduced respiratory activity, as well as sensorydecay, increasing the SALOQ value up to 12 days. Also, the combinationof active compounds with alginate-based coating delayed theappearance of visible moulds. It is worth noting that as the microbial

Table 3bMass loss percentage for Step II kiwifruit.

Time(day)

Samples

Coat-dipp-EtOH Coat-GFSE Control

1 0.664±0.074a 0.775±0.204a 0.761±0.086a

4 0.644±0.099a 1.092±0.546a 0.928±0.146a

6 0.729±0.147a 1.141±0.189b 0.80±0.146a

8 0.796±0.037a 1.257±0.289b 1.094±0.204a,b

11 0.960±0.093a 1.49±0.053b 1.031±0.196a

13 1.209±0.155a 1.288±0.148a 1.119±0.171a

15 1.441±0.261a 1.288±0.055a –⁎

Mean values±standard deviation.a–bMeans in the same row followed by different superscript upper cases aresignificantly different (Pb0.05).⁎ The samples were not acceptable.

load was always found below the threshold value imposed by law(Corbo et al., 2004), in this study SALOQ coincides with minimallyprocessed produce shelf life. In particular, the highest shelf life valuewas obtained with coating treatments (12.3 and 11.75 for Coat-dipp-EtOH and Coat-GFSE, respectively) with respect to dipping treatment(10.2). For this reason, in the second step only the combined use ofcoating treatments with active MAP was investigated. The active MAPconditions were chosen on the basis on the headspace gasconcentration found at equilibrium for Coat-dipp-EtOH and Coat-GFSE samples; i.e., 10% O2 and 10% CO2. Nitrogen percent concentra-tion was set as complement of oxygen and carbon dioxide percentconcentration to 100.

3.3. Step II: packaging under active MAP

3.3.1. Headspace gas compositionFig. 2a, b shows the evolution over storage of O2 and CO2

concentrations in the OPP20 bag headspace for Coat-dipp-EtOH,Coat-GFSE and Ctrl samples packaged in active MAP. It is worth notingthat for control samples the oxygen concentration decreased rapidlyduring the first 12 days of storage. Whilst for the coated samples, asexpected, an appropriate equilibrium between the respiration of theproduct and the gas permeability of the film was obtained. Datasuggest that the coating treatment was effective to avoid a drasticreduction of oxygen concentration as it occurred in non-coatedminimally processed kiwifruit. This result is a direct consequence ofthe coating influence over the oxygen diffusion between the fruit andenvironment (Baldwin, Nisperos-Carriedo, Chen, & Hagenmaier,1996). The carbon dioxide headspace concentrations of the samplespackaged under active MAP level off to values higher than those of thekiwi stored under passive MAP. In fact, for coating and controlsamples a carbon dioxide final value of about 15 and 12% respectively,was obtained.

3.3.2. Microbiological stability and pHTable 2b reports the cell load of mesophilic and psychrotrophic

bacteria at 0 and 8 days of sampling for treated and untreated samplespacked under active MAP. Data show that by means the combined useof active MAP and active coating, no growth of mesophiles andpsychrotrophs at 8 days of storage was observed. On the contrary, thecontrol samples showed an increase of the cell load of about 2 log

Table 4bShelf life of Step II kiwifruit packaged under active MAP assumed as the lowest valueamong the calculated microbial and sensorial acceptability limits (MAL, SAL) and visualmoulds time (VMT).

Samples SAL OQ (day) VMT (day) Shelf life (day)

Coat-dipp-EtOH 11.45±1.13a N21 11.45±1.13a

Coat-GFSE 13.52±1.03b 18.5 13.52±1.03b

Control 2.70±0.67c 13 2.70±0.67c

Mean values±standard deviation.a–dMeans in the same column followed by different superscript upper cases aresignificantly different (Pb0.05).

Fig. 2. Evolution of oxygen (a) and carbon dioxide (b) plotted as a function of storagetime for minimally processed kiwifruit belonging to Step II.

Fig. 3. “Overall quality” of Step I (a) and Step II (b) minimally processed kiwifruit.

1229M. Mastromatteo et al. / Food Research International 44 (2011) 1224–1230

cycle. The combined use of active coating and active MAP was mosteffective as no growth was observed during the storage. Literaturedata report that the combined use of antimicrobial compounds andactive MAP affected significantly and positively the microbiologicalstability of the sliced strawberries and carrots (Amanatidou, Slump,Gorris, & Smid, 2000; Campaniello, Bevilacqua, Sinigaglia, & Corbo,2008). As reported for the samples packaged under passive MAP, alsoin this case the final cell load of mesophiles was always found belowthe threshold value (5×107 log cfu/g) imposed by the FrenchRegulation (Corbo et al., 2004).

3.3.3. Mass lossConcerning the effect of active MAP on mass loss, all samples

showed a sudden increase in themass loss percent at the early stage ofstorage. Most probably, this result is directly related to both theevaporation of moisture from produce during the severe initialvacuumization that was applied prior to injecting the gas in thepackage to realize the modified atmosphere, and to the absence ofhumidity in the gas mixture injected into the bag. However, the massloss percentage did not exceed 1.5 for all samples (Table 3b).

3.3.4. Sensory evaluationFig. 3b shows the evolution during storage of the minimally

processed kiwifruit “overall quality” for all investigated samplespacked under active MAP. Curves shown in the figure were obtainedby fitting Eq. (2) to the experimental data, whereas the solidhorizontal line is the “overall quality” threshold value. SAL valuesfor the minimally processed kiwifruit “overall quality” packagedunder active MAP were reported in Table 4b. As can be inferred fromthe data, for samples packaged under active MAP a SALOQ value of

11.45 and 13.52 days for Coat-dipp-EtOH and Coat-GFSE, respectively,was observed. The active MAP alone worse the shelf life; in fact, avalue of about 2.7 days for the control samples was obtained. This wasdue to a general spoiling in terms of overall quality such as color, odorand consistence. The coating allowed a good preservation of theproduct by reducing the respiratory activity, as well as sensory decay.The combined use of active coating and active MAP delayed themoulds growth until over 21 and 18.5 days for Coat-dipp-EtOH andCoat-GFSE, respectively. Dantigny, Guilmart, Radoi, Bensoussan, andZwietering (2005) reported that ethanol was an effective additionalbarrier to inhibit fungal growth in food products. Moreover, activeMAP involving reduced O2 levels and elevated levels of CO2, was usedin combination with other environmental factors to control growthand mycotoxin production by several moulds (El Halouat & Debevere,1997).

4. Conclusions

Results of this study suggested that the coatings were the besttreatments and could be used to control dehydration and respirationof minimally processed kiwifruits both in passive and active MAP,thus extending its shelf life. The combination of coating with hydro-alcoholic solution and GFSE inhibited the microbial growth whereasthe dipping samples showed the same behavior of the untreatedsample. Probably, the coating treatment improved the ethanol efficacyas it avoided its evaporation. Moreover, the microbial loads did notlimit the shelf life of the investigated produce. It is worth noting that,when the active MAP was used alone a very short shelf life of theuncoated samples occurred. However, the combined use of activeMAP and coating treatments allowed a good preservation of the

1230 M. Mastromatteo et al. / Food Research International 44 (2011) 1224–1230

product reducing the sensory decay. Moreover, this combinedapproach delayed the presence of visible moulds.

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