Innovative packaging for minimally processed fruits

PACKAGING TECHNOLOGY AND SCIENCEPackag. Technol. Sci. 2007; 20: 325–335Published online 27 October 2006 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/pts.761

Innovative Packaging for Minimally ProcessedFruits

By M. Avella,1,* G. Bruno,2 M. E. Errico,1 G. Gentile,1 N. Piciocchi,2A. Sorrentino2 and M. G.Volpe2

1Institute of Chemistry and Technology of Polymers, ICTP-CNR,Via Campi Flegrei, 34, 80078 Pozzuoli (NA), Italy2Institute of Food Science, ISA-CNR,Via Roma, 52 a/c, 83100 Avellino (AV), Italy

Novel nanocomposite films for use in the packaging of foods ready for consumptionand based on isotactic polypropylene (iPP) filled with innovative calciumcarbonate nanoparticles, as well as having spherical and elongated shape andcovered with appropriate coating agent able to better interact with the iPP matrix,were prepared and characterized. Morphological, thermal, mechanical andtransport characterizations on nanocomposite films were performed. The resultsevidenced a good dispersion of the nanofiller into the polymeric matrix as well asan increase in mechanical parameters such as modulus. Moreover, a drasticreduction of iPP permeability to both oxygen and carbon dioxide was alsorecorded. Migration tests evidenced that these nanocomposites are suitable for foodpackaging applications. Finally, the analysis of some shelf-life parameters carriedout on packaged minimally processed apples showed that these materials are ableto preserve for up to 10 days apple slices, limiting oxidation processes andmicrobiological growth. Copyright © 2006 John Wiley & Sons, Ltd.Received 3 January 2006; Revised 11 September 2006; Accepted 20 September 2006

KEY WORDS: nanocomposite; packaging; minimally processed fruits; food contact; migrationtests

*Correspondence to: M. Avella, Institute of Chemistry and Technology of Polymers, ICTP-CNR, Via Campi Flegrei, 34, 80078 Pozzuoli (NA), Italy.E-mail: [email protected]

Copyright © 2006 John Wiley & Sons, Ltd.

INTRODUCTION

Minimally processed (MP) fruits are spreading inanswer to the increasing demand for easy and fastproducts with fresh-like quality. The increasing useof foods ready for consumption is due to theirability to satisfy new food habits following lifestylechanges.

These products maintain their quality similar tothat of fresh products. In fact, washing, sorting,peeling and cutting of fruits and vegetables arecompletely automated in order to limit manipula-

tions and to guarantee the hygienic characteristicsof the product.1

The rapid darkening of many fruits is a seriousproblem during minimal processing operations.Appropriate steps must be taken during fruit pro-cessing against oxidation phenomena. Browningdamages the appearance, organoleptic propertiesand nutritional quality.2

Generally, the market for MP products belong tovegetables, but recently much attention has beenturned to the possibility of manufacturing alsofresh fruits.3 Truly, packaged MP fruits are already

available, but they represent niche productshaving high production costs and needing the coldchain for their commercialization.

The greater part of the literature on ready-to-eatfruits and vegetables is based on the use of modi-fied atmospheres, 4–8 where the air is replaced by agas mixture, or on the use of controlled atmos-pheres,9 where the proportions of the gases arekept under control during the whole storageperiod. Obviously, these methodologies increaseproduction costs.

Among several thermoplastics, polyolefins arethe most used plastic materials in the food pack-aging sector.10 Isotactic polypropylene (iPP) filmshold a prominent position in this field because oftheir transparency, brilliance, low specific weightand chemical inertness. Unfortunately, polypropy-lene, like other polyolefins, is characterized by lowbarrier properties, which results in poor protectionof the packaged food.11 One of the most usefulmethods to improve polypropylene drawbacks isto add a second component such as a polymer inblend or in multilayers, fillers, etc.12–14

Nowadays, polypropylene-based nanocompos-ites are a major industry challenge because theyrepresent the route to substantially increasing themechanical and physical properties of such awidely used thermoplastic commodity.15–19 In fact,conventional composites usually require a highcontent of microfillers to impart the desiredmechanical, thermal and barrier properties.Nanocomposites can achieve same or higher prop-erties with only a low percentage of filler (1–5wt%), thus preserving polymer processability andrecycling. The enhanced properties are due to thesynergistic effects of nanoscale structure and inter-action of fillers with polymers. The size and nanos-tructure of the dispersed phase significantlyinfluence the properties of polymer-basednanocomposites.20–25

The key factors in the preparation of high-performance nanomaterials are to obtain a fine and homogeneous dispersion of the nanoparticlesand to promote strong interfacial adhesionbetween matrix and nanofillers. Nevertheless,nanoparticles have a strong tendency to agglom-erate, giving rise to cluster formation, because oftheir high adsorption surface energies and the dif-ferent polarity with respect to that of commonpolymers.

Several studies have focused on preparationmethodologies of nanocomposites.26,27 Modifica-tion of the nanoparticle surface by using organiccoating agents represents an effective route toimproving the nanophase dispersion into the poly-meric matrix.

The goal of this research is the preparation andcharacterization of iPP-based nanocomposites forpotential use in the packaging of MP foods, suchas apple slices.

For this purpose, innovative modified calciumcarbonate (CaCO3) nanoparticles, characterized bya spherical and elongated shape, were tested.

EXPERIMENTAL

Materials

iPP [Moplen X 30 S (Mn = 4.69·104g/mol, Mw = 3.5·105g/mol and Mz = 2.06·106g/mol)], was kindlysupplied by Basell Polyolefins (Ferrara, Italy).Spherical and elongated CaCO3 nanoparticlescoated with polypropylene-maleic anhydride graftcopolymer (iPP-g-MA) were kindly supplied bySolvay Advanced Functional Minerals (Giraud,France) and coded as S-CaCO3 and E-CaCO3

respectively. Apple samples (Golden-Delicious)were from south of Italy. They were harvested onautumn and stored in air at 4°C. (+)-catechin, mol-ecular biology grade hydrochloric acid 38.0%,methanol, Folin–Ciocalteu phenol reagent,Na2CO3, bacteriological peptone and NaCl werepurchased from Sigma-Aldrich (Milan, Italy).Other chemicals for microbiological tests (platecount agar, violet red bile glucoses agar, violet redbile lactose agar) were purchased from Oxoid(Milan, Italy). Water was bidistilled using Milli-Qsystem (Millipore).

Preparation of iPP-basednanocomposites

iPP/CaCO3 nanocomposites were prepared bymixing components in a Brabender-like apparatus(Rheocord EC of HAAKE Inc., Karlsruhe,Germany, NJ, USA) at 200°C and 32rpm for 10min.The mixing ratios of iPP/CaCO3 (wt/wt) were:100/0, 99/1 and 97/3.

M. AVELLA ET AL.Packaging Technologyand Science

Copyright © 2006 John Wiley & Sons, Ltd. 326 Packag. Technol. Sci. 2007; 20: 325–335DOI: 10.1002/pts

Then, plain iPP and iPP/CaCO3 nanocompositeswere compression-moulded in a heated press at200°C for 2min without any applied pressure.After this period, a pressure of 100 bar was appliedfor 3min, then the press plates, equipped with coilsfor fluids, were rapidly cooled to room tempera-ture by cold water. Finally, the pressure wasreleased and the mould removed from the plates.

Morphological analysis

The surface analysis was performed by using ascanning electron microscope (SEM; CambridgeStereoscan microscope model 440, Cambridge,UK) on nanoparticle powders and on cryogeni-cally fractured surface of nanocomposites. Before observations, samples were metalled with a goldlayer.

Mechanical analysis

Tensile tests were performed on dumbbell speci-mens (4mm wide and 15mm long) by using anInstron machine (model 5564, Milan, Italy) at roomtemperature and a crosshead speed of 10mm/min(average 10 samples tested). Young’s modulus (E)was calculated from recorded curves in accordanceto the ASTM D256 standard.

Permeability tests

Permeability tests were performed in a gas-membrane-gas instrument based on the measure-ment of the downstream pressure increase at aconstant upstream side-driving pressure. Theapparatus and experimental procedures weresimilar to those reported elsewhere.28,29 In eachexperiment, sufficient time was allowed to ensureattainment of steady-state permeation. The mea-surements were carried out at a pressure of 1atmand at a temperature of 30°C. The permeabilitywas computed from the slope of the linear, steady-state part of the curve representing the permeatedgas volume as a function of time. The gas diffu-sivity was calculated from the ‘time lag’ deter-mined from the intercept of the steady-statepermeability curve on the abscissa.

Migration tests

iPP and iPP-based nanocomposites films (area ~30cm2, thickness ~100mm) were stripped in vacuumand placed in 30ml of bidistilled water, used as a simulant. Then, the films were placed in anoven and kept at 40°C for 10 days. After this treatment, the simulant was removed and samples were washed with a further 25ml of sim-ulant. The washings were added to the previouslyremoved solution of simulant and successivelyevaporated. Finally, the residue was dried at 110°Covernight and weighted after cooling to room temperature.30,31

Apple packaging

Apples were initially washed with chlorinatedwater (150ppm of active chlorine for 3min) toprevent surface contamination,32 peeled, cut inslices and then packed in the tested film. Beforepackaging, polymeric films were exposed to UVrays (30W, UV lamp) for 15min and then thermo-settled in order to obtain appropriate bags. Thepacked apples were stored at 4°C for 10 days.Microbiological analysis, Brix index and polyphe-nol determinations were performed on thesamples at 5 and 10 days of storage.

Microbiological analyses

Apple samples (10g) were homogenized with 90mlof sterile Ringer solution in a Stomacher 400 (LabBlender, Seward Medical, London, UK) and seri-ally diluted in the same diluent. Different dilutionswere plated on specific growth media, and afterincubation the colonies were counted. Totalmesophilic microflora was determined on platecount agar, incubated at 30°C for 72h. Moulds wereenumerated on 2% malt medium (malt extract 20g/l, yeast extract 3g/l, agar 15g/l) sterilized at120°C for 15min; the plates were incubated at 25°Cfor 3 days. Tests were carried out in triplicate.

Brix index measurements

The Brix (% soluble solids) of apples were mea-sured by using an Opteh refractometer before the


PACKAGING FOR MINIMALLY PROCESSED FRUITS Packaging Technologyand Science

packaging and after 5 and 10 days of storage into neat iPP and iPP-based nanocomposite filmskept at 4°C. Measurements were carried out intriplicate.

Determination of total phenoliccontent

The extraction of phenolics was carried out usingan acidic (concentrated HCl, 1%) water/methanol(30/70 v/v) solution.33,34 Apple samples (0.5g)were put into 25ml of the acidic water/alcoholsolution and homogenized (Ultra-Turrax IKA-WERK, Staufen, Germany) at room temperature.Then, the obtained mixture was centrifuged for 15min at 3500rpm. The supernatant was recoveredwhile the insoluble phase was re-extracted into 20ml of acidic water/alcohol solution for 30min atroom temperature and then centrifuged asdescribed earlier. The recovered supernatant wasadded to that obtained after the first centrifuga-tion, then the solution were combined, placed in a50ml volumetric flask, and the volume wasadjusted by adding in the right amount ofwater/methanol solution. This extraction proce-dure was carried out in triplicate for apple samplespacked in the tested films (neat iPP and iPP-basednanocomposites) and kept for 5 and 10 days at 4°C.

Polyphenol concentration was estimated by theFolin–Ciocalteau method.35 One milliliter of eachsolution described above was added to 5ml ofFolin–Ciocalteau reagent and 10ml of aqueousNa2CO3 (10% wt/wt). After 2h in the dark, thevolume of solutions was adjusted to 25ml by

adding bidistilled water. On these solutions spectrophotometric analysis was carried out byusing a Varian UV/Visible spectrophotometer (Shropshire, UK). Polyphenol concentration wasevaluated by measuring the absorbance at 760nmand the results were expressed as (+)-catechinequivalent.

RESULTS AND DISCUSSION

Morphological analysis

Generally, the presence of organic agents onnanoparticle surface can improve nanofiller dis-persion into the polymeric matrix because they candecrease the adsorption surface energy of particles,thus preventing agglomeration phenomena. Inparticular, CaCO3 nanoparticles of spherical andelongated shape, coated with iPP-maleic anhy-dride and characterized by different crystal modi-fication were used for nanoreinforcing of iPPpolymeric matrix. The main features and codes of selected CaCO3 nanoparticles are shown inTable 1.

iPP-g-MA coating agent was selected because ofits similar chemical nature to that of the polymericmatrix that could ensure strong coated nano-particles/iPP interactions, thus allowing goodmatrix/nanofillers interfacial adhesion.

The nanoparticle morphology was observed bySEM analysis (Figure 1). In Figure 1a, sphericalnanoparticles (S-CaCO3) characterized by anaverage diameter of 50nm are reported, while



Table 1. Codes and main properties of CaCO3 nanoparticles

Properties

Coating Average SpecificNanoparticles Coating agent content particle surface(code) Shape Crystal structure agent (weight%) size (nm) area (m2/g)

S-CaCO3 Spheres Calcite iPP-g-MA 10 50 75(Trigonal-rhombohedral)

E-CaCO3 Rods Calcite iPP-g-MA 10 250 (length) 10 ÷ 15(Trigonal-scalenohedral) 50 (thickness)

elongated nanoparticles (E-CaCO3) with a lengthof about 250nm and lateral thickness of 50nm areshown in Figure 1b. Moreover, in the micrographs,the coating agent can be clearly evidenced by thepresence of a polymeric film on the nanoparticlesurface.

The preparation of iPP-based nanocompositeswas performed by melt mixing, and structure–properties relationships were studied, with partic-ular attention to the influence of the amount andshape of nanoparticles on iPP properties.

The dispersion of nanoparticles and the adhe-sion between the phases was evaluated by SEManalysis performed on fractured surfaces of com-pression-moulded samples.

In Figure 2a,b, SEM micrographs of iPP-basednanocomposites containing the highest amount ofS-CaCO3 and E-CaCO3 nanoparticles (3% wt/wt)are shown, respectively. In both the cases, homo-geneous and fine nanoparticle dispersion into theiPP matrix was reached. The discrete nanoparticlesare completely covered by the iPP phase and novoids are evidenced due to the applied mechani-cal stress.

These morphological observations indicate thatthe presence of iPP-g-MA coating agent preventsnanoparticle clustering and promotes strong adhe-sion between polymer and nanofillers. This result



a

b

a

b

Figure 1. SEM micrograph of (a) S-CaCO3 nanopowders;(b) E-CaCO3 nanopowders.

Figure 2. SEM micrograph of fractured surface of iPP-based nanocomposites containing (a) 3% wt/wt of

S-CaCO3 nanoparticles; (b) 3% wt/wt of E-CaCO3

nanoparticles.

could be justified on the basis of the surface mod-ifier nature and consequently of the type of pre-dominant interactions (surface modifier–surfacemodifier and/or surface modifier–polymer) thatcan be generated in these multicomponent nanos-tructured materials.

In fact, the iPP-g-MA coating agent not onlymodifies the filler surface polarity, matching thatof iPP and improving in this way the dispersion ofnanoparticles into the matrix, but also promotesthe physical interactions of polymer-modifiednanoparticles occurring via entanglements. Thesefactors are both responsible for strong interactionsleading to the highest polymer/CaCO3 adhesionlevel.

Thermal properties

Previous papers36,37 focused on the influence ofCaCO3 nanoparticles on thermal properties of iPP-based nanocomposites. The crystallization behav-iour was analysed upon cooling from the melt atvarious rates, ranging from 1 to 8°C/min. Someparameters of crystallization properties are sum-marized in Table 2, in which other thermal prop-erty data are also reported.

Either the spherical or the elongated nano-particles can efficiently promote nucleation ofpolypropylene crystals, or an increase in the crys-tallization rate of iPP can be observed when at least

3% of CaCO3 is present in the nanocomposite.Despite the marked influence on crystallizationkinetics, no significant effect of CaCO3 on both thecrystalline content and melting behaviour can beobserved. The differences in crystallization tem-peratures, observed upon cooling from the melt,are masked by reorganization of the crystal phasethat occurs during the subsequent heating, and thefinal melting point results were unaffected by thepresence of the filler.

With regard to the glass transition temperature(Tg), a slight increase of the Tg was also recorded,unless it does not appear significantly influencedby the amount and shape of nanoparticles. Thisshift is mainly due to a restricted mobility of iPPchains in the presence of CaCO3 nanoparticlesbecause of the above-mentioned strong intercon-nection between the phases.

Finally, the thermal stability of iPP and iPP-based nanocomposites was analysed by thermo-gravimetry. The values of the degradationtemperature (Td), which corresponds to 50% loss ofinitial mass, are presented in the final column ofTable 2. The presence of nanoparticles induced anincrease in the Td of the material of about 20–25°C.This improved thermal stability can be attributedto the homogeneous distribution of nanoparticlesinto the iPP matrix. As a matter of fact, CaCO3

nanoparticles act as a barrier both for the diffusionof heat and for the volatile decomposition prod-ucts within nanococomposites.



Table 2.Thermal parameters of iPP and iPP/CaCO3

nanocomposites

Sample Tm (°C)* Xc* Tc (°C)† Tg (°C) Td (°C)

iPP 163 44 121 20 3681% S-CaCO3 163 43 118 26 3823% S-CaCO3 162 43 119 22 3781% E-CaCO3 163 43 121 24 3903% E-CaCO3 163 44 125 26 391

*Evaluated from first heating run of compression-moulded samples at a rate of 20°C/min.†Evaluated upon cooling from the melt at a rate of 8°C/min. Data from Avella et al.36 Tc,crystallization temperature;Td decomposition temperature;Tg, glass transition temperature;Tm, melting point; Xc crystalline fraction.

Mechanical properties

In Figure 3, results of tensile tests performed oniPP and iPP-based nanocomposites are shown. Theaddition of S-CaCO3 and E-CaCO3 was responsiblefor a significant increase in the nanocompositeYoung’s modulus of up to 30%. This increase is afunction of nanoparticle content and shape.

In fact, a comparison between Young’s modulusvalues of nanocomposites with the same amountsof CaCO3 but different shapes showed that spher-ical nanoparticles gave rise to a more pronouncedincrease of the modulus with respect to thatobtained with elongated nanoparticles. Moreover,it can be observed that the stiffness increaseinduced by the addition of E-CaCO3 nanoparticleswas slightly influenced by the filler content. In par-ticular, Young’s modulus value (~1320MPa with1% of E-CaCO3) remained almost unchanged aftera further addition of nanoparticles (~1380MPawith 3% of E-CaCO3), thus suggesting that this isthe maximum improvement obtainable with testedE-CaCO3.

A different behaviour was observed for theiPP/S-CaCO3 system. A dependence of modulusvalue on the filler content was recorded. In fact,modulus values (~1350MPa with 1% of S-CaCO3

and ~1460MPa with 3% of S-CaCO3) increased upto 30% with respect to that of neat iPP (~1100MPa).Moreover, these values are higher than thoseobtained for iPP/E-CaCO3 nanocomposites. These

results suggest that there is a significant influenceof the nanoparticle shape on the extent of themechanical improvement.

It is known that the incorporation of fillers intothe polymeric matrix results in a heterogeneoussystem and that these heterogeneities can act asstress concentration points when an externalmechanical load is applied. The relevance of thisphenomenon is strictly related to filler geometryand size and essentially to the interaction betweenfillers and polymeric matrix.

As observed by SEM analysis, in the investi-gated systems, both nanoparticles appeared wellwelded to the polymeric matrix and after an exter-nal mechanical load no voids were evident, thusindicating that a good adhesion level was reachedbecause of the strong interaction between thecoating agent and the polymer chains.

Therefore, the different specific surface area ofthe nanoparticles in contact with the polymermatrix was the main factor influencing theimprovement of the final properties. In fact, in thecase of spherical nanoparticles, the availablecontact surface area was higher than that of elon-gated nanoparticles (see Table 1), thus producing awider interfacial region through which themechanical stress can be transferred from the poly-meric matrix to the rigid filler.

Permeability properties

Generally, the addition of inorganic fillers into apolymer could affect the gas diffusion mechanismthrough the material because of the different per-meability properties of the matrix and the foreignparticles. This phenomenon is particularly stressedwhen a filler of nanometric size is dispersed intothe polymeric matrix because of the high specificsurface of nanoparticles responsible for widecontact area between the phases.

Moreover, the tortuous path that diffusing mol-ecules have to bypass because of the presence ofnanoparticles is an additional phenomenon thatmust be taken into account to study the nanocom-posite permeability property.38,39

As can be observed, nanoparticles (Figures 4 and5) significantly influenced iPP barrier propertieseither to oxygen or to carbon dioxide, reducingboth the coefficient permeability values by up to



Figure 3.Trend of the Young’s modulus as a function ofamount and shape of the CaCO3 nanoparticles: (a) iPP/S-CaCO3 nanocomposites; (b) iPP/E-CaCO3 nanocomposites.

about 30% as a function of the amount of nanopar-ticles. Furthermore, spherical nanoparticles wereresponsible for a slightly more pronounceddecrease of permeability with respect to thatobtained by the addition of elongated nanoparti-cles. This result could be explained by consideringthat S-CaCO3 nanoparticles are characterized by ahigher specific surface area than that of E-CaCO3,corresponding to a larger interfacial region.

Migration tests

Migration tests showed that all the nanocompositefilms undergo to migration values that are compa-rable, within the experimental errors, with thoserecorded for neat iPP, independently from theamount of nanoparticles (1% and 3% w/w) andfrom their shape. Therefore, all the tested films aresuitable for food packaging applications becausethe release of nanoparticles or other substances isnegligible and, in any case, lower than the allowedlimit of 10mg/dm2.40

Microbiological analyses

In Figure 6 the total mesophilic microflora enu-merated on apples stored for 5 and 10 days at 4°Cis reported. As can be observed, the totalmesophilic microflora increases as a function ofstorage time in the case of apples packaged in neatiPP films. Concerning iPP-based nanocomposites,CaCO3 nanoparticles caused a decrease of thisparameter with respect to that recorded at startingtime (t0), thus preventing the growth of naturalmicroflora. Moreover, the microorganism growthseems to be influenced by the shape and theamount of nanoparticles. In fact, S-CaCO3

nanoparticles led to a reduction of microflora of upto 65% as a function of time and nanoparticlecontent. On the other hand, the presence of elon-gated nanoparticles allows a slightly larger



Figure 4.Variation of the oxygen permeability as afunction of amount and shape of the CaCO3

nanoparticles: (a) iPP/S-CaCO3 nanocomposites; (b) iPP/E-CaCO3 nanocomposites.

Figure 5.Variation of the carbon dioxide permeability as afunction of amount and shape of the CaCO3

nanoparticles: (a) iPP/S-CaCO3 nanocomposites; (b) iPP/E-CaCO3 nanocomposites.

Figure 6.Total microbial counts on apple slices at timezero (t0) and after 5 and 10 days of storage at 4°C in

different packaging materials.

microorganism growth decrease than thatobserved with spherical nanoparticles after thefirst 5 days of storage, while a successive increasewas recorded in the next 5 days. Nevertheless, thismicroorganism growth increase assures smallervalues than those recorded on apples at t0. Thesefindings underline a strict correlation betweennanocomposite barrier properties and totalmesophilic microflora enumerated during storagetime. In fact, as described above, sphericalnanoparticles were responsible for a more pro-nounced improvement of barrier to oxygen incomparison with that obtained with E-CaCO3. Thisenhanced property can justify the reduction effectof CaCO3 nanoparticles on microorganism growth,particularly marked in the case of S-CaCO3.

In Figure 7, mould population on apples as afunction of storage time and nanoparticle shapeand amount is reported. This microbiologicalanalysis showed a reduction of mould growth dueto the presence of nanoparticles attributable, alsoin this case, to the increase of barrier to oxygenrecorded for nanocomposites.

Brix indices

In Figure 8, Brix index values are reported. As it isshown, during the first 5 days, a slight increase ofBrix index values was recorded for apples packedboth in neat iPP and in iPP-based nanocompositefilms. In the next 5 days, Brix values decreased forapples packed in nanocomposite films, consistent

with what has been reported in the literature.2 Onthe contrary, concerning iPP films, Brix valuesremained almost unchanged during the wholestorage period.

Moreover, the most interesting finding is thatapples stored in nanocomposite films containing3% by weight of S-CaCO3 show the lowest Brixindex values. This result could be attributed tobetter barrier properties of this nanocompositetowards gases, and possibly also to ethylene naturally developed during apple maturation,which, if retained in the packaging, facilitates maturation.41

Polyphenols

It is well known that determination of the polyphe-nol concentration, expressed as (+)-catechin, indi-cates oxidation phenomena occurring on the fruit.In particular, a more significant oxidative effectcorresponds to a drastic decrease of the catechinvalue.

The (+)-catechin concentration, after 5 days ofapple storage, as a function of nanoparticleamount and shape is reported in Figure 9. Thisvalue was drastically reduced in apples packed iniPP films and in nanocomposite films containing1% by weight of nanoparticles. In the case of iPP-based nanocomposites containing 3% by weight ofCaCO3, polyphenol concentration values almostsimilar to that of fresh apples were recorded. More-over, the nanoparticle shape did not seem to influ-



Figure 7. Mould counted on apple slices at time zero (t0)and after 5 and 10 days of storage at 4°C in different

packaging materials.

Figure 8. Brix indices measured on apple slices at timezero (t0) and after 5 and 10 days of storage at 4°C in

different packaging materials.

ence this value. These results suggest that the pres-ence of nanoparticles decreases apple oxidationphenomena, in particular at the highest loading ofnanoparticles, with respect to that obtained byapple storage in iPP films.

CONCLUSIONS

iPP-based nanocomposites filled with CaCO3

nanoparticles were prepared and characterized.The results can be summarized as follows:

1. S-CaCO3 and E-CaCO3 nanoparticles werehomogeneously and finely dispersed into theiPP matrix. The discrete nanofillers were com-pletely covered by the iPP phase.

2. The thermal stability of iPP is stronglyimproved by the presence of both S-CaCO3 andE-CaCO3 nanoparticles.

3. The Young’s modulus of iPP-based nanocom-posites increased in the presence of nanorein-forcements; the S-CaCO3 led to a higher increaseof the modulus than that obtained with E-CaCO3 nanoparticles.

4. CaCO3 drastically reduced the iPP permeabilityeither to oxygen or to carbon dioxide both in thecase of S-CaCO3 and in the case of E-CaCO3.

5. Contact test measurements have shown thatiPP/CaCO3 nanofiller films satisfy the fixedlimit of global migration of 60mg/kg requiredfor plastic materials.

6. Usual parameters used to determine the foodshelf life (Microbiological analysis, Brix indicesand polyphenol content) have demonstratedthat iPP-based nanocomposites are able to guar-antee the integrity of apple slices for up to 10days.

ACKNOWLEDGEMENTS

The authors are very grateful to Dr. Karine Cavalier andDr. Roberto Rosa of Solvay Advanced Functional Min-erals for kindly providing the CaCO3, as well as foruseful discussion. Moreover, the authors wish to thankMr. Manlio Colella for the precious technical assistancein the morphological analysis. Financial support fromRegione Campania, LR 28/5/02 n. 5, is gratefullyacknowledged.

REFERENCES1. Ahvenainen R. Novel food packaging techniques.

Woodhead Publishing: Cambridge, 2003.2. Rocha AMCN, Morais AMMB. Shelf life of mini-

mally processed apple (c.v. Jonagored) determinedby colour changes. Food Control. 2003; 14(1): 13–20.

3. Brody AL. Chilly is hot. Food Technology. 2002;56(4):102–105.

4. Anese M, Manzano M, Nicoli MC. Quality of mini-mally processed apple slices using different modi-fied atmosphere conditions. J. Food Quality. 1997; 20:359–370.

5. Soliva-Foruny RC, Martin-Belloso O. New advancesin extending the shelf-life of fresch-cut fruits: areview. Trends Food Sci. Technol. 2003; 14(9): 341–353.

6. Alley EW, Nathance PK, Donna AM. Factors affect-ing quality of fresch-cut horticultural products.Postharvest Biol. Tech. 1996; 9: 115–125.

7. Kader AA. L’applicazione dell’atmosfera controllataper il mantenimento della qualità della frutta fresca.Frutticoltura. 2000; 11: 44–47.

8. Rocculi P, Romani S, Della Rosa M. Effect of MAPwith argon and nitrous oxide on quality mainte-nance of minimally processed kiwifruit. PostharvestBiol. Tech. 2005; 35(3): 319–328.

9. Lanciotti R, Gianotti A, Patignani F et al. Use ofnatural aroma compounds to improve shelf-life andsafety of minimally processed fruits. Trends Food Sci.Technol. 2004; 15(3–4): 201–208.

10. Karger-Kocsis J (ed.). Polypropylene: An A–Z Refer-ence. Kluwer Academic Publishers: Dordrecht, 1999.

11. Karian HG (ed.). Handbook of Polypropylene andPolypropylene Composites. Marcel Dekker: New York,1999.



Figure 9. Polyphemol concentration of apples, expressed as(+)-catechin, measured at time zero and after 10 days of

storage in neat iPP and in iPP-based nanocompositesfilms.

12. Karger-Kocsis J (ed.). Polypropylene: Structure, Blendsand Composites. Chapman and Hall: London, 1995.

13. Deanin RD, Manion MA. Compatibilization of poly-olefin polyblends. In Handbook of Polyolefins, VasileC (ed.), 2nd edn. Marcel Dekker: New York, 2000;575–602.

14. Avella M, Laurienzo P, Malinconico M, MartuscelliE, Volpe MG. Functionalized polyolefins: synthesisand application in blends and composites. In Hand-book of Polyolefins, Vasile C (ed.), 2nd edn. MarcelDekker: New York, 2000; 723–771.

15. García-López D, Merino JC, Pastor JM. Influence ofthe CaCO3 nanoparticles on the molecular orienta-tion of the polypropylene matrix. J. Appl. Polym. Sci.2003; 88(4): 947–952.

16. Hasegawa N, Okamoto H, Kato M, Usuki A. Prepa-ration and mechanical properties of polypropylene-clay hybrids based on modified polypropylene andorganophilic clay. J. Appl. Polym. Sci. 2000; 78(11):1918–1922.

17. Svoboda P, Zeng C, Wang H, Lee LJ, Tomasko DL.Morphology and mechanical properties ofpolypropylene/organoclay nanocomposites. J. Appl.Polym. Sci. 2000; 85(7): 1562–1570.

18. Kawasumi M, Hasegawa N, Kato M, Usuki A,Okada A. Preparation and mechanical properties ofpolypropylene-clay hybrids. Macromolecules. 1997;30(20): 6333–6338.

19. Manias E, Touny A, Wu L et al. Polypropylene/montmorillonite nanocomposites. Review of thesynthetic routes and materials properties. Chem.Mater. 2001; 13(10): 3516–3523.

20. Novak BM. Hybrid nanocomposite materials –between inorganic glasses and organic polymers.Adv. Mater. 1993; 5(6): 422–433.

21. Alexandre M, Dubois P. Polymer-layered silicatenanocomposites: preparation, properties and uses ofa new class of materials. Mater. Sci. Eng. Reports.2000; 28(1–2): 1–63.

22. Avella M, Errico ME, Rimedio R. PVA/PTFEnanocomposites: thermal, mechanical and barrierproperties. J. Mater. Sci. 2004; 39(19): 6133–6136.

23. Avella M, Errico ME, Martuscelli E. NovelPMMA/CaCO3 nanocomposites abrasion resistantprepared by an in situ polymerization process.Nano. Lett. 2001; 1(4): 213–217.

24. Lu S, Melo M, Zhao J, Pearce EM, Kwei TK. Organic-inorganic polymeric hybrids involving novelpoly(hydroxymethylsiloxane). Macromolecules. 1995;28(14): 4908–4913.

25. Ahmadi SJ, Huang YD, Li JW. Synthetic routes,properties and future applications of polymer-layered silicate nanocomposites. J. Mater. Sci. 2004;39(6): 1919–1925.

26. Avella M, Cosco S, Errico ME, Rimedio R, Martus-celli E. Recent preparation methodologies to obtainpolymer based nanocomposites. In Recent ResearchDevelopments in Materials Science, Pandalai SG (ed.),Vol. 3. Research Sign Post: Trivandrum, India, 2003;375–399.

27. Yu YY, Chen CY, Chen WC. Synthesis and charac-terization of organic-inorganic hybrid thin filmsfrom poly(acrylic) and monodispersed colloidalsilica. Polymer. 2003; 44(3): 593–601.

28. Del Nobile MA, Mensitieri G, Nicolais L. Effect ofchemical composition on gas transport properties ofethylene-based ionomers. Polym. Int. 1996; 41(1):73–78.

29. Nicodemo L, Marcone A, Monetta T, Mensitieri G,Bellucci F. Transport of water dissolved oxygen inpolymers via electrochemical technique. J. Membr.Sci. 1992; 70(2–3): 207–215.

30. O’Brien A, Leach A, Cooper I. Polypropylene: estab-lishment of a rapid extraction test for overall migra-tion limit compliance testing. Packag. Technol. Sci.2000; 13(1):13–18.

31. Galotto MJ, Guarda A. Suitability of alternative fattyfood simulants to study the effect of thermal andmicrowave heating on overall migration of plasticpackaging. Packag. Technol. Sci. 2004; 17(4): 219–223.

32. Wardowski WF, Brown GE. Postharvest Decay ControlRecommendations for Florida Citrus Fruit. Circular 952.Institute of Food and Agricultural Sciences, Univer-sity of Florida: Gainesville, FL; 1991.

33. Tarozzi A, Marchesi A, Cantelli-Forti G, Hrelia P.Cold-storage affects antioxidant properties ofapples in Caco-2 cells. J. Nutri. 2004; 134: 1105–1109.

34. Sun J, Chu YF, Wu X, Liu RH. Antioxidant andantiproliferative activities of common fruits. J. Agric.Food Chem. 2002; 50(25): 7449–7454.

35. Osman H, Nasarudin R, Lee SL. Extracts of cocoa(Theobroma cacao L.) leaves and their antioxidationpotential. Food Chem. 2004; 86(1): 41–46.

36. Avella M, Cosco S, Di Lorenzo ML, Di Pace E, ErricoME. Influence of CaCO3 nanoparticles shape onthermal and crystallization behavior of isotacticpolypropylene based nanocomposites. J. Therm.Anal. Calorim. 2005; 80(1): 131–136.

37. Avella M, Cosco S, Di Lorenzo ML, Di Pace E, ErricoME, Gentile G. Nucleation activity of nanosizedCaCO3 on crystallization of isotactic polypropylene,in dependence on crystal modification, particleshape, and coating. Euro. Polym. J. 2006; 42(7):1548–1557.

38. Gorrasi G, Tammaro L, Tortora M et al. Transportproperties of organic vapors in nanocomposites ofisotactic polypropylene. J. Polym. Sci., Part B: Polym.Phys. 2003; 41(15): 1798–1805.

39. Ellis TS, D’Angelo JS. Thermal and mechanicalproperties of a polypropylene nanocomposite. J.Appli. Polym. Sci. 2003; 90(6): 1639–1647.

40. European Council Regulation No. 1935/2004 of theEuropean Parliament and of the Council of 27October 2004 on materials and articles intended tocome into contact with food and repealing Direc-tives 80/590/EEC and 89/109/EEC, Official JournalL 338, 13/11/2004, 0004–0014.

41. Ahvenainen R. New approaches in improving theshelf life of minimally processed fruit and vegeta-bles. Trends Food Sci. Technol. 1996; 7(6): 179–187.



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Innovative packaging for minimally processed fruits