Selasa, 24 Desember 2013

Effectiveness of a novel insect-repellent food packaging incorporating essential oils against the red flour beetle (Tribolium castaneum)



a b s t r a c t

Packaging represents a critical step in the food quality preservation and the ultimate defence against insect pests. Cereal-based foods may be infested by insects even during their packed life, i.e. during distribution, transportation and storage in warehouses or in retail stores. Many studies in the last years have concerned the development of active packaging with antioxidant and antimicrobial action, but very few studies have addressed insect-repellent packaging materials for foods. This work aimed at assessing the repellent efficacy of novel functional packaging materials containing three essential oils: citronella, oregano and rosemary. Re-pellent films were chemically characterized by MHS-SPME-GC-MS. The results obtained from area tests run in Petri dishes indicated that essential oils at concentrations higher than 0.005 μL/cm2 showed potential in terms of repellent activities against the red flour beetle, Tribolium castaneum. Assays performed with coated packages containing wheat semolina showed repellency results ranging from 53 to 87% for citronella and rosemary, respectively.

Industrial Relevance: The paper deals with the study carried out of several Essential Oils as repellent for in-sects in packaged food. Rejection of packaged food caused by insect pests is a great problem that affects the industry worldwide. Without any doubt the prevention of insect attack from the packaging material without affecting the packaged product is an environmentally friendly and economical advantage. The indus-try is demanding this type of solutions.


1. Introduction

Insect infestations are the main cause of loss of packed foodstuffs both in terms of direct damages or cost to preserve and package food ( Hanlon, Kelsey, & Forcinio, 1998). The issue of sustainment of the world population is generally considered in terms of the need to increase food productions. However measures such as the safeguard of stored foods from insect contamination could represent a solution for increasing food products availability.

Cereal-based dry foods such as pasta, flour, cakes, rice and others may be subject to insect infestations. The attack to packaged foods can occur during the production phases or in the following steps of the distribution, such as transportation and storage in warehouses or in retail stores. In any case, consumers frequently blame the man-ufacturers for any occurring insect contamination, independently from their real involvement, and the consequences on the image of the company can be severe ( Hou, Field, & Taylor, 2004).


 worldwide distributed in various climatic conditions ( Robertson,  2006). The search for tools to prevent infestations is crucial and current solutions involve the spraying of insecticides such as pyrethins and py-rethroids (e.g. resmethrin, sumithrin, tetramethrin, permethrin) in the environment where dry food is processed and packaged, after removing all food and utensils for food contact. Stored products safeguard has long relied on the employment of synthetic insecticidal molecules such as methyl bromide (MB) and phosphine as fumigants but whose use has been restricted lately due to adverse effects on the environment (e.g. ozone depletion caused by MB) and to pest resistance develop-ment of certain species with reiterated phosphine treatments ( Shaaya,  Kostjukovsky, Eilberg, & Sukprakarn, 1997).

The theme of the interaction between insect pests and packaged foods has been handled by several authors, who pointed out on the abil-ity of insects to penetrate into packages ( Essig, Hoskins, Linsley,  Michelbacher, & Smith, 1943; Gerhardt & Lindgren, 1954; Gerhardt &  Lindgren, 1955; Batth, 1970; Cline, 1978; Langbridge, 1970) and on the resistance of various packaging materials to insect attacks ( Dominichini & Forti, 1975; Licciardello, Cocuzza, Russo, & Muratore,  2010; Sreenathan, Iyengar, Narasimhan, & Majumder, 1960).
Being consolidated that packaging represents a critical point in the food quality preservation and the ultimate defence against insect

pests, efforts should be paid not only towards the design of effective systems which may retard the food quality decay, but also for the development of insect-proof packages, able to resist to insects pene-tration and/or to repel their presence from the food packages environment.

During the last 10 years, new technologies for food packaging have emerged and among them active packaging is one of the most prom-ising innovation. It consists of incorporating into the packaging material active compounds useful for the food protection in terms of antioxidant and/or antimicrobial effect. Several papers have been published dealing with different proposals of active packaging ( Goñi et al., 2009;  Gutiérrez, Escudero, Batlle, & Nerín, 2009; Gutiérrez, Sánchez, Batlle,  López, & Nerín, 2009; López, Sánchez, Batlle, & Nerín, 2007a, 2007b;  Rodríguez, Batlle, & Nerín, 2007, 2008) but only a few commercial solu-tions are available. Few papers in literature have dealt with the develop-ment of insect-repellent packaging systems.  Highland & Merritt, 1973;  Highland, Simonaitis, & Boatright, 1984; Highland & Cline, 1986) pub-lished the first attempts to reduce insects infestations by the use of repellent-treated packaging materials. More recently, Hou et al. ( Hou  et al., 2004) proposed the use of DEET and Neem contained in paper, Wong et al. ( Wong, Signal, Campion, & Motion, 2005) addressed the use of citronella essential oil in a coating for carton packages, whereas Germinara et al. ( Germinara, Conte, Lecce, Di Palma, & Del Nobile,  2010) embedded propionic acid into corn zein and policaprolactone. Apart from the mentioned papers, an in-depth survey only gave back a chapter on a book dedicated to active packaging ( Navarro, Zehavi,  Angel, & Finkelman, 2007) another chapter focused on essential oils in active packaging ( Nerín, 2012) and a few US patents concerning the de-velopment of slow-release repellent systems ( Calton, Siemer, & Wood,  2001; Domb, 1993; Tucci & Dry, 2000) while two patents are known to describe the incorporation of insect repellents into paper-based packaging ( Radwan & Allin, 1997; Whalon & Malloy, 1998). The use of natural plant extracts in this application could facilitate acceptance by food regulators as well as the general public.

The aim of the present work was to evaluate the repellent efficacy of citronella, oregano and rosemary essential oils against one of the most common stored food pests, Tribolium castaneum (Herbst) (Cole-optera, Tenebrionidae), and to assess the effectiveness of a novel functional active plastic material with repellent action containing the three essential oils.


2. Materials and methods

2.1. Essential oils and repellent films

Citronella (Cymbopogon nardus), oregano (Origanum vulgare) and rosemary (Rosmarinus officinalis) essential oils (EO) were purchased from Gutiérrez SAS Matières Premières Essentielles (Grasse Cedex, France). Such oils are GRAS (Generally Recognized as Safe) according to  FDA (21CFR182.20). In the following the gross composition of test-ed essential oils is reported:

Citronella
oil.  FDA:
182.20.  Citronellal  35 ÷ 40%;
geraniol
25 ÷ 30%;
citronellol
15 ÷ 20%, D-limonene
5 ÷ 10%;
linalool
0
÷ 5%; farnesol 0 ÷ 5%


Origanum
oil. Carvacrol 75 ÷ 80%; linalool
5 ÷ 10%;
thymol
5
÷ 10%; D-limonene 0 ÷ 5%









Rosemary oil. Beta pinene 10 ÷ 15%; camphor 10 ÷ 15%; camphene 5 ÷ 10%. D-Limonene 0 ÷ 5%; terpineol 0 ÷ 5%; linalool 0 ÷ 5%.

The formulations were suitably diluted for the bioassays described hereafter.

Repellent films were prepared by Artibal (Sabiñánigo, Spain) from corona-treated polypropylene (30 μm thickness), following a patent-ed procedure ( European Patent EP1657181). The coating included 4% (w/w) of the above-mentioned essential oils. Each film was analysed


for the volatile composition and tested for the repellent effectiveness in the bioassays described in the following after one-month storage in aluminium-polyethylene hermetically sealed bags.

2.2. Insects

The unsexed adults of T. castaneum used in the experiments were 24 weeks post-eclosion and were obtained from laboratory cultures maintained in incubators at 30 ± 1 °C and 70 ± 5% r.h. in the dark. The colonies had been cultured in laboratory for over four years on wheat flour mixed with 5% brewer's yeast.

2.3. Volatile composition of repellent films

A quantitative Multiple Headspace (MHS) SPME analysis was performed according to the method described by Ezquerro et al. ( Ezquerro, Pons, & Tena, 2003), which is based on the multiple head-space extraction (MHE) method developed by  Kolb (1982). This meth-od was previously applied for the study of the diffusion of volatile compounds in plastic films ( Licciardello, Del Nobile, Spagna &  Muratore, 2009; Licciardello, Muratore, Mercea, Tosa & Nerín, 2013).

MHS-SPME involves various SPME extractions of the same sample, and the total amount of the analyte can be calculated from the sum of the areas of the chromatograms relative to each extraction. The total area can be easily calculated from the following equation:

N
A1


AT ¼Ai ¼
ð1Þ

1β

i1




where: AT is the total area relative to multiple extractions, Ai is the area of the chromatographic peak relative to the i-th SPME extrac-tion), A1 is the area relative to the first extraction, β is a constant, and N is the total number of extractions. The latter value can be calcu-lated from the slope of the plot resulting from the following equation:

lnAi ¼ ði 1Þ lnβ þ lnA1                                                   ð2Þ

The fibre used was a polydimethylsiloxane (PDMS, 100 μm,), which gave the richest profiles for basil and rosemary essential oils in a previous work ( López, Huerga, Batlle, & Nerín, 2006). A 6.25 cm2 sample of each functional film was incubated into 20-mL
headspace vials at 80 °C for
30 min and extracted at 80 °C for
30 min.  Pre-incubation  and
extraction  temperature  and  times

resulted from preliminary experiments which considered incubation and extraction temperatures ranging from 60 to 80 °C and extraction time ranging from 15 to 35 minutes. After extraction, the fibre was desorbed for 5 min into the GC injector set at 270 °C in splitless mode, the temperature of the transfer line being set at 280 °C.

GCMS analyses were performed using an Agilent (Palo Alto, CA, USA) 6890 N GC equipped with a 5975B mass detector, and a HP-5 MS (30 m × 0.25 mm, 0.25 μm film thickness) 5% phenyl-methylsyloxane capillary column. The temperature program was as follows: initial tem-perature 40 °C for 2 min, raised by 10 °C/min to 300 °C and 300 °C for 2 min. The carrier gas was helium, 99.999% purity, supplied by Carburos Metálicos (Barcelona, Spain). Samples were analyzed in a Combi-Pal autosampler (CTC Analytics AG, Zwingen, Switzerland) coupled to the GC-MS, which allowed analytical reproducibility and precision.

Quantification of essential oil components was carried out by ex-ternal calibration, preparing appropriate solutions of pure standards in the same organic coating used to encapsulate the essential oils, and spiking virgin PP with suitable amounts (microliters) of such so-lutions. The spiked films, having the same size as the active film sam-ples, were analyzed as above described.

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175


2.4. Bioassays for the repellency of essential oils

Preference area assays ( Nerio, Olivero-Verbel, & Stashenko, 2010;  Ogendo et al., 2008) were run to evaluate the repellent effect of citro-nella, oregano and rosemary essential oils against T. castaneum, com-monly referred to as the red flour beetle.

Filter paper disks (11 cm diameter) were cut in halves, one half was treated with 0.5 mL of suitable dilutions of the essential oils in acetone and the other half was impregnated with 0.5 mL of acetone alone (con-trol). After solvent evaporation, disks were reconstituted in glass plates (11 cm diameter) by coupling one half treated with the essential oils and one half of control paper. Ten adults of T. castaneum were placed in the centre of each plate. Two repellency tests were carried out at 25 °C and 70% RH with the following essential oil concentrations:

Test#1: 0.001 and 0.01 μL/cm2
Test#2: 0.005, 0.01 and 0.02 μL/cm2

For each concentration and for each essential oil, four replicates were performed. Insects were enumerated after 0.15, 0.30, 1 and 3 h and re-sults were expressed as percent repellency (R%), calculated as follows:

R% ¼ ðC TÞ=ðC þ TÞ _ 100

where:

C          number of insects in the control area;

T          number of insects in the treated area


2.5. Bioassays for the effectiveness of repellent films

Sachets sized 52.5 × 74.25 mm were prepared with repellent films, with the coated side as the outer side of packages, and filled with 25 g durum wheat semolina.

For the preference tests, one sachet made with the control film and one made with the treated one were positioned at the sides of rigid polyethylene white boxes (20 × 10 × 7 cm). Twenty adults of the red flour beetle, unfeeded for 48 hours, were then released in the centre of the boxes, and maintained in the dark until the end of the trial, carried out at 25 °C and 70% RH. A control trial was also performed, consisting of two semolina sachets made with control film aimed at excluding other factors than the essential oil on the in-sect behaviour. Each test was carried out in triplicate.

Boxes were checked after 2, 24 and 48 h, and the percentage of re-pellency (R%) was calculated as aforementioned, with:

C = number of insects on the control package; T = number of in-sects on the repellent package.

2.6. Statistical analysis

All data were submitted to one-way analysis of variance (ANOVA), and post-hoc comparison of means was performed by the Tukey test (p b 0.05) through the statistical package SPSS® Statistics 13.0 (Armonk, NY, USA).

3. Results and discussion

3.1. Volatile composition of coated repellent films

A typical chromatogram of the PP film coated with citronella EO (film A) is shown in  Fig. 1a. The MHS-SPME analysis was able to quantify 6 major compounds, as shown in  Table 1: citronellol, gerani-ol and their acetates, together with citronellal and eugenol represent almost 50% of the total chromatographic area. Among the major com-pounds, elemol and δ-cadinene were not quantified as a commercial


standard was not available, while myrcene and trans-β-ocimene did not follow the linear relationship ln Ai versus i-1.

A typical chromatogram of B-type film B (PP coated with oregano EO) is shown in  Fig. 1b. The MHS-SPME analysis revealed the quanti-tative composition of linalool, thymol, carvacrol and β-caryophyllene ( Table 1), which represent more than 60% of the total chromato-graphic area, carvacrol being the major compound characterizing this EO, as shows  Table 1.

A typical chromatogram of film C (PP coated with rosemary EO) is shown in  Fig. 1c. The MHS-SPME analysis could quantify 5 major compounds ( Table 1), which represent almost 40% of the total chro-matographic area. Among the major compounds, camphor could not be quantified by the MHS-SPME technique, as it did not follow the lin-ear relationship ln Ai vs i-1.


3.2. Repellency of essential oils

Preliminary bioassays of the repellent effect of diluted EOs by the area preference tests ( Fig. 2) were carried out as a screening for the ef-fectiveness of natural substances to be incorporated in functional repel-lent packaging and for comparative purposes: this method is the most widely used for the assessment of the repellency of natural substances.
Test#1 ( Fig. 3ac) performed with two EO concentration (0.01 e 0.001 μL/cm2) showed a doseresponse effect, with special regards for citronella. For this oil, the repellency value reached 90 and 100% after 30 min-1 h in the trial performed with the highest concentration, and values below 50% in the trials at 0.001 μL/cm2. Citronella EO showed in the first hour of the test significantly higher repellency (p b 0.05) compared to the other EOs. It has to be noted that the repellency values decreased after 3 h, and this might be attributed to the loss of the essen-tial oils from the filter paper by evaporation. Rosemary essential oil also showed a concentration effect (p b 0.05), however at the lowest dilu-tion this oil seemed to exert an attractive action, especially at the latest time intervals, as evidenced by the negative R% values.

Test#2 ( Fig. 4ac) was performed with three EO concentration (0.005, 0.01 and 0.02 μL/cm2); this test confirmed the effect of concen-tration on the insect response. As for Test#1, repellency decreased after 3 h, possibly due to the essential oil evaporation from filter paper.

All of the tested essential oils at concentrations 0.0050.02 μL/cm2 were effective at repelling T. castaneum in preference area tests, while a lower concentration (0.001 μL/cm2) was not satisfactorily effective or, in the case of rosemary, it showed an attractive effect.

The evaporation of the EOs from the paper support was expected due to the fact that such volatiles compounds are not bound but only absorbed on paper. Also, this is one of the main reasons why a special formula is needed to incorporate EOs in packaging material, either in plastic or in paper and board. Thus, the resulting active ma-terials would act as reservoir of EO and the controlled kinetics of re-lease is the key point for proposing them as commercial active materials with repellent properties versus insects.


3.3. Effectiveness of the repellent films against the red flour beetle

Two hours after the start of the trials, most of the insects were found grouped close to the sachets made with the control film, while only 2 to 5 insects out of 20 were found on the treated sachet.  Fig. 5 shows the per-cent repellency after 2, 24 and 48 h of semolina packages made with films containing the tested essential oils. Values did not change signifi-cantly through the duration of the assays for oregano and citronella, while data referred to rosemary essential oil are slightly higher after 24 and 48 h. Repellency data for the control sachets were always signifi-cantly different (p b 0.05) from those referring to the coated sachets and, among test materials, no significant difference (p b 0.05) was ob-served. Insects tended to locate behind the sachets (this is a typical be-havioural aspect of the Tenebrionidae family) and in correspondence with the seal, which are known to be the most vulnerable points of

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177
Table 1

Quantitative composition, by MHS-SPME-GC-MS, of coated

PP films (film A = citronella EO, 4% w/w; film B = oregano

EO, 4% w/w; film C = rosemary, 4% w/w).

μg/cm2
Film A

Citronellal
134.22
Citronellol
40.78
Geraniol
94.90
Citronellyl acetate
12.74
Eugenol
6.00
Geranyl acetate
15.44
Film B

Linalool
8.88
Thymol
10.65
Carvacrol
174.26
β-caryophyllene
95.58
Film C

1,8 cineole
211.04
Linalool
5.21
α-terpineol
32.29
Carvacrol
3.28
β-caryophyllene
318.92




packages. Insects remained substantially in the same place chosen dur-ing the first 2 hours throughout the duration of the trials. No attempt to pierce packages was observed during the tests, however it is possible that a longer starvation of insects could determine an increased aggres-siveness towards packages.

Repellency data relative to the control trials were close to zero, as insects placed themselves randomly and choose one or another pack-age indifferently. The fact that the histograms for the control are neg-ative should be taken as a merely casual result.

The observed repellency of essential oils in the tests performed on filter paper and with treated packages can be attributed to the essen-tial oils components. It has been demonstrated that terpenoids pos-sess biological activity against several post-harvest Coleoptera ( Weaver, Dunkel, Ntezurubaza, Jackson, & Stock, 1991). In particular, citronellol and trans-geraniol, which are key components of the citro-nella EO, were found to have strong repellent effect on T. castaneum ( Zhang et al., 2011). Also, linalool, which is present in all of the tested EOs, has been demonstrated to effectively repel T. castaneum in repel-lency tests carried out in olfactometers ( Ukeh & Umoetok, 2011). An-other study assessed the potential of 1,8 cineole, one of the most representative terpenoid in rosemary EO, against T. castaneum ( Lee,  Annis, Tumaalii, & Choi, 2004). An interesting research by  Bekele  and Hassanali (2001) demonstrated that single components of essen-tial oils do not show comparable toxicity to the EO towards two stored food insects, but their combinations do provide bioactivity: the mixtures allowed to select 1,8 cineole, limonene and camphor among the most powerful components.


Compared to the repellency data obtained in the preliminary bio-assays conducted with essential oils on filter paper, where the effica-cy decreased drastically after 3 hours from the beginning of the experiments, coated films showed a durable efficacy, ranging around 60% for citronella- and oregano-based repellent packaging, and 87% for the rosemary-based coated film. The retention of effectiveness is due to the bonding of essential oil to the packaging film by the coating matrix which, while immobilizing the essential oil preventing its loss by evaporation, it guarantees a controlled release able to effectively repel insects. As previous studies demonstrated this coated polymers









Fig. 2. Detail of a plate during the preference test for the evaluation of repellency. In this case, all of the ten insects are found on the control half and as far a possible from the essential oil.


are stable for at more than 4 months and in some cases the activity remains even for more than one year ( Nerín, 2012). Further studies should address the shelf life of repellent packaging by the release ki-netics: indeed it is required that the effectiveness of such systems is at least as long as the product shelf life.

Finally, some studies ( Huang, Lam, & Ho, 2000; Huang, Tan, Kini, &  Ho, 1997; Rozman, Kalinovic, & Korunic, 2007) demonstrated that T. castaneum is less sensitive to some essential oils compared to Sitophilus spp., another frequent stored food pest. Therefore, our promising results obtained with T. castaneum let hypothesize an even stronger efficacy of the essential oils object of this research and of the repellent packaging films on other pest species.

4. Conclusion

Repellency for coated films ranging from 53 to 87% is to be considered a very promising result and encourage the study and application of repel-lent packaging materials for the safeguard of packaged foods and the reduction of packaged food losses due to insect attacks. Data obtained from the bioessays on filter paper supplied tentative information on T. castaneum response to citronella, oregano and rosemary essential oils, which were completed by the results coming from the tests run with coated films. The development of insect-repellent packaging should take into account that high doses might be required, with possible effects on the sensory quality of the produce, hence it is necessary to orient the diffusion of active components towards the outside of packages. This


Fig. 1. ac. Typical chromatograms relative to the MHS-SPME analysis of the coated PP film. (a): film A (citronella EO). 1) Myrcene; 2) α-Pinene; 3) trans-β-Ocimene; 4) Linalool; 5) allo-Ocimene; 6) Citronellal; 7) Isopulegol; 8) Citronellol; 9) Geraniol; 10) Geranial; 11) Thymol; 12) Carvacrol; 13) Citronellyl acetate; 14) Nerol; 15) Eugenol; 16) Geranyl acetate; 17) β-Elemene; 18) δ-Cadinene; 19) Elemol; 20) γ-Eudesmol; 21) t-Cadinol; 22) α-Eudesmol; 23) Germacrene; 24) trans-β-Farnesene; 25) α-Cubebene; 26) cis-α-Bisabolene; 27) β-Cubebene; 28) α-Amorphene; 29) β-Cadinene; 30) 1S,cis-Calamenene; 31) α-Cadinene. (b): film B (oregano EO). 1) Limonene; 2) Camphor; 3) endo-Borneol; 4) α-Terpineol; 5) Thymol; 6) Carvacrol; 7) Camphene; 8) Eugenol 9) β-Caryophyllene; 10) α-Humulene; 11) δ-Cadinene; 12) Caryophyllene oxide; 13) t-Cadinol. (c) film C (rosemary EO). 1) 1,8-Cineole; 2) Linalool; 3) Camphor; 4) Endo-borneol; 5) α-Terpineol; 6) Bornyl acetate; 7) Thymol; 8) Carvacrol; 9) α-Cubebene; 10) α-Ylangene; 11) α-Copaene; 12) Isocaryophyllene; 13) β-Caryophyllene; 14) Aromadendrene; 15) α-Humulene; 16) α-Amorphene; 17) δ-Cadinene; and 18) 1S,cis-Calamenene.

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 80

 60

 40

 20

 0










Fig. 3. Repellent effect, as repellency %, of citronella (a), oregano (b) and rosemary (c) essential oils, Test#1.














Repellency %




100




15 min  30 min  60 min  180 min














80



60



40



20



0



-20

0.005
0.01
0.02
0.005
0.01
0.02
0.005
0.01
0.021

Citronella


Oregano


Rosemary



µL/cm2


Fig. 4. Repellent effect, as repellency %, of citronella (a), oregano (b) and rosemary (c) essential oils, Test#2.










% repellency

F. Licciardello et al. / Innovative Food Science and Emerging Technologies 19 (2013) 173180
179

 Citronella   Oregano   Rosemary   Control
100.00

80.00



60.00



40.00



20.00



0.00



2
24
48

-20.00



-40.00
time (h)







Fig. 5. Repellency of semolina packages made with coated PP films, compared with packages realized with control PP, against Tribolium castaneum, in a preference test carried out with 20 adult insects.


could be attained by coupling active films, as outer layers, with materials having barrier properties to volatiles, as inner layers. Moreover, the breakdown of active components in the repellent films might occur, re-ducing their effectiveness with time, and innovative techniques of immobilisation (nanocomposite materials, microencapsulation, use of beta-cyclodextrins) could extend effectiveness for several years. Finally, it should be taken into consideration that repellent packages would re-duce the incidence of exogenous infestations and can only be synergistic with hygienic prevention measures, since they have no effect on insects already present in the packaged produce at any life stage. The widespread of repellent packaging is currently limited by the lack of scientific studies, therefore this work should encourage further investigation considering active substances, doses, modes of application and target insects. The adoption of repellent packaging could reduce the recourse to thick pack-aging films, which ensure a certain level of prevention against insects at-tacks to packages, and help fight overpackaging (i.e. the use of higher volumes of plastic than strictly necessary). The potential of essential oils could be the answer to the current search for environmental and health-friendly solutions for the safeguard of foods. If packaging is the last frontier against insect pests, then repellent packaging might repre-sent the ultimate weapon for producers and consumers against pests at-tacks to packages.


Acknowledgement

The authors acknowledge the company Artibal for supplying the active polymers. Thanks are given to Gobierno de Aragon and Fondo Social Europeo for the financial help through the GUIA group T-10

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