clove essential oil composite antimicrobial films for scrambled egg packaging

Food Packaging and Shelf Life 21 (2019) 100355

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Polylactide/poly(ε-caprolactone)/zinc oxide/clove essential oil composite antimicrobial films for scrambled egg packaging

T

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Jasim Ahmeda, , Mehrajfatema Mullaa, Harsha Jacoba, Giorgio Lucianob, Bini T.B.c, Abdulwahab Almusallamd a

Food and Nutrition Program, Environment and Life Sciences Research Center, Kuwait Institute for Scientific Research, P.O. Box 24885, Safat, 13109, Kuwait The Institute for Macromolecular Studies, CNR-ISMAC, Via De Marini 6 Torre Francia 16149, Genova, Italy c Nanotechnology Research Center, College of Engineering and Petroleum, Kuwait University d Department of Chemical Engineering, College of Engineering and Petroleum, Kuwait University b

A R T I C LE I N FO

A B S T R A C T

Keywords: Polylactide Poly(ε-caprolactone) Clove essential oil Polymer degradation Mechanical rigidity Weibull model

The aim of the present work was to develop an antimicrobial nanopackaging for food application by incorporating zinc oxide (ZnO) nanoparticles and clove essential oil (CEO) into polylactide/polyethylene glycol/ polycaprolactone (PLA/PEG/PCL) blend using the solution cast technique. The developed films were characterized by thermal, rheological, mechanical, structural and microbiological analysis. Rheological tests at melt revealed that reinforcement of ZnO significantly lowered the dynamic moduli by accelerating the polymer degradation. The CEO acts as an efficient plasticizer by facilitating the chain mobility in the blend, which reflected into the tensile and thermal properties. Reinforcement of ZnO into the PLA/PEG/PCL matrix did not change the thermogram. The efficacy of the composite films was verified against Staphylococcus aureus and Escherichia coli inoculated in scrambled egg, and results indicated that the PLA/PEG/PCL/ZnO/CEO film exhibited the highest antibacterial activity during 21 days storage at 4 °C. The Weibull model was employed to fit the inactivation kinetics of the test organisms, and it was found that the model fitted well for the developed packaging materials.

1. Introduction

is suitable for the use of automobiles, biomedical devices, and electrical appliances. The lack of flexibility, thermal stability, brittleness, and medium gas-barrier properties of PLA, however, preventing the polymer for the packaging applications (Paul et al., 2003). Furthermore, PLA is prone to hydrolytic degradation and found unsuitable for the extrusion. The best strategy for the development of PLA-based packaging is to blend with other flexible polymers [e.g., poly(butylene succinate), (PBS), poly(3-hydroxybutyrate) (PHB), and polycaprolactone (PCL)] or plasticizing with low molecular weight polymers (e.g., polyethylene glycol, PEG, polypropylene glycol, PG), or reinforcement of nanoparticles (e.g., clay-based or metallic) to improve various properties of the blend polymers. Poly(ε-caprolactone) (PCL) –a biodegradable polymer possesses low tensile strength and high elongation at break in contrast to the high modulus/tensile strength and low elongation at break of PLA (Nair & Laurencin, 2007). Therefore, melt blending of PCL with brittle PLA could impart the flexibility in the polymer blend, and also impede the transmission rates of oxygen, water vapor and carbon dioxide (Olewnik & Richert, 2015). Furthermore, reinforcement of nanoparticles (NPs) as the third component could improve the mechanical and barrier

The use of plastic, today is alarming and environmentalists around the globe are appealing to restrict the limit on the usage of plastic, which ends up in landfill and waters. Recently, it has been reported plastics release greenhouse gases namely, methane and ethylene when exposed to solar radiation (Royer, FerroÂn, Wilson, & Karl, 2018), and contributes a significant increase in plastic pollution and deposition, in particular, the non-biodegradable substances, which can lead to global warming. The probable solutions for controlling the conventional plastics in the environment could be either by reining the production, ensuring the maximum recycles of the polymers and the most important one is the substitute by biodegradable polymers. However, it is a hard reality that the polymeric materials cannot be replaced by biodegradable polymers entirely in the next decade or so because of the inherent poor mechanical, thermal and barrier properties of these materials for the packaging applications. Among biodegradable polymers, nature-derived poly(lactic acid) or polylactide (PLA) is undoubtedly the promising candidate for the food packaging. Because of the high modulus and mechanical strength, PLA

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Corresponding author. E-mail address: [email protected] (J. Ahmed).

https://doi.org/10.1016/j.fpsl.2019.100355 Received 25 December 2018; Received in revised form 10 June 2019; Accepted 27 June 2019 2214-2894/ © 2019 Published by Elsevier Ltd.

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360 g/L).

properties of the PLA/PCL blend. While working on the reinforcement of multi-walled carbon nanotubes (MWCNT) and titanium oxide (TiO2) into PLA/PCL matrix, various researchers (Ostafinska et al., 2015; Wu et al., 2011) found an improvement in the mechanical and electrical properties of the composites with a minimum change in the morphology. Conversely, reinforcement of ZnO into PLA/PCL matrix accelerated the polymer degradation (Ahmadzadeh, Babaei, & Goudarzi, 2018). To impart antimicrobial component in the packaging materials intended for food uses, essential oils (EO) (e.g., cinnamon, clove, menthol) have been incorporated into the films. Earlier we have investigated the fabrication of PLA/PEG/EO antimicrobial films focusing on the microbiological inactivation. Therefore, the approach has been extended to develop unique packaging materials based on PLA and PCL with the incorporation of PEG, ZnO, and clove essential oil (CEO) so that the developed films could retain the mechanical integrity with effective antimicrobial activities. The microstructure of polymer nanocomposites in the melt can be well characterized by the rheometry. Generally, the addition of low molecular weight polymer/s (e.g., PEG. PCL) to brittle polymers (e.g., PLA) acts as a plasticizer in the blend by transforming the solid-like behavior (G′ > G″) into the liquid-like characteristic (G″ > G′). Furthermore, the addition of essential oils lubricates the composite film with a significant reduction of the viscosity, and even sometimes the blend could not be shaped into a film. The introduction of NPs to the composite is believed to be restricted the polymer degradation, however, it depends upon the type of nanoparticles. For example, impregnation of carbon nanotubes (CNTs) and organoclays in the PLA/PCL blend influenced the phase morphology of ternary system and rheology, thereafter, improved the mechanical and electrical properties (Wu, Zhang, Zhang, & Yu, 2009, 2011). Conversely, a significant degradation of the PLA has been reported by our group while ZnO and Ag/Cu NPs were incorporated into PLA/PEG blend (Ahmed, Mulla, & Arfat, 2016, 2018b, Ahmed, Hiremath, & Jacob, 2016, 2018a; Arfat, Ahmed, Hazza, A., & Joseph, 2017). The PLA/PEG/Ag–Cu/CEO composites exhibited a complex rheological system with both plasticizing and antiplasticizing effects, which attributed by the constituents of the composite, namely, PEG, CEO, and NPs. The metallic oxide NPs acted as a catalyst for the degradation of the PLA, in particular, above the melting temperature because of the “unzipping” depolymerisation (Gerard & Budtova, 2012). The reinforcement of ZnO at a loading concentration of 4% (w/ w) into PLA or PLA/PEG resulted in a Newtonian fluid in melt with a drastic lowering of the viscosity, which was not even suitable for the fabrication of the film (Ahmed, Hiremath et al., 2016, 2016b). Therefore, the rheological properties of the nanocomposites with EO require a thorough investigation in a wide range of temperatures, in particular, at the vicinity of the melting point of the polymers. The objective of this work was to develop biodegradable nanocomposite films loaded with ZnO and CEO on the PLA/PEG/PCL matrix, and thereafter, characterize the thermal, rheological, optical and microstructural properties of the film. Finally, the antimicrobial properties of the films were tested against Staphylococcus aureus and Escherichia coli in contaminated scrambled egg samples.

2.2. Bacterial strains and media Culti-loops® of Gram-positive Staphylococcus aureus subsp. aureus (ATCC 25923) strain and Culti-loops® of Gram-negative Escherichia coli (ATCC 25922) strain were procured from Remel Europe Ltd. (Dartford, Kent, UK). Brain heart infusion agar (BHIA), and Tryptic soya broth (TSB) and Muller Hinton agar (MHA) was purchased from Conda Laboratories (Torrejón de Ardoz, MD, Spain) and TM Media (Bhiwadi, India), respectively. Baird-Parker Agar (ISO) Base, Egg yolk Tellurite Emulsion and Brilliance E.coli/Coliform Selective Medium were purchased from Oxoid (Basingstoke, HM, UK). 2.3. Preparation of PLA/PEG/PCL based films The PLA/PEG/PCL (1:1:0.25 wt.%) films, and ZnO, CEO loaded composites (PLA/PEG/PCL/ZnO, PLA/PEG/PCL/CEO and PLA/PEG/ PCL/ZnO/CEO) were prepared by solvent cast technique. About 1.6 g PLA was mixed with 0.4 g PEG in dry condition and dissolved in DCM (30 mL/g of PLA), furthermore, 1.6 g PCL was dissolved separately in DCM (30 mL/g of PCL) by vigorous mixing on a magnetic stirrer at room temperature (˜25 °C) for about 1 h. Completely dissolved PLA/ PEG and PCL solutions were then mixed and kept for an hour on a magnetic stirrer for proper mixing. ZnO (3% w/w) in 15 mL DCM were sonicated separately for 30 min (Branson Ultrasonics, CT, USA). This ZnO suspension was then mixed with PLA/PEG/PCL solution followed by sonication for 30 min. Finally, the 25% CEO (% w/w, PLA + PCL) were transferred to the PLA/PEG/PCL and PLA/PEG/PCL/ZnO solutions, and blended for another 15 min to ensure the oil incorporation into the film (Ahmed, Mulla, & Arfat, 2017). The mixture was evenly poured onto glass petri-dishes (100-mm diameter and 15-mm depth). The solvent evaporated at room temperature under a fume hood. The resultant films were peeled from the glass petri-dishes after 12 h, stored in a desiccator for further analysis. 2.4. Determination of film properties and characterization 2.4.1. Film thickness and color The thickness of the films was measured at several locations randomly around the film (n = 10) using a micrometer (Mitutoyo, Kawasaki-shi, Japan). 2.4.2. Fourier transform infrared (FTIR) FTIR spectra of the films were recorded using an FTIR spectrometer (Nicolet™ iS™5, Thermo Scientific, Waltham, MA, USA) in the range of 600–4000 cm−1 at a resolution of 4 cm−1.

2.1. Materials

2.4.3. Mechanical properties The tensile strength (TS) and elongation at break (EAB) were determined using a Texture Analyzer TA.XT plus (Stable Micro Systems, UK) with a 50 N load cell equipped with tensile grips (A/TG model) (D882, ASTM, 2001). The initial distance of the grip was set at 50 mm, and the cross-head speed was 50 mm/min. TS and EAB were evaluated in ten samples from each type of film.

PLA (Ingeo™ 4043D) pellets were procured from NatureWorks LLC (Minnetonka, MN, USA). Polycaprolactone (PCL) beads (Avg. Mn 80, 000), polyethylene glycol (PEG) powder (avg. MW 1,500 g/mol), clove essential oil (CEO) (RI at 20 °C: 1.532) were procured from SigmaAldrich (St. Louis, MO, USA). Dichloromethane (DCM) was purchased from Fisher Scientific (Loughborough, LE, UK). Commercially accessible ZnO nanofillers were generously provided by Umicore Zinc Chemicals (Belgium) as Zano 20 Plus-3 (surface treated by 3- methacryloxypropyltrimethoxysilane; ZnO content ∼98.8%, bulk density:

2.4.4. Rheological measurement The melt rheology of the composite films was measured using an ARES-G2 rheometer (TA Instruments, New Castle, DE, USA) equipped with a plate accessory (25-mm diameter) in a 1-mm gap at the selected temperature range (140, 150, 160 and 170 °C). The frequency-sweep (0.1–10 Hz) measurements were performed at a constant strain of 0.5% within linear viscoelastic range (LVR). Rheological tests were repeated twice, and the parameters were acquired from the instrumental software (TRIOS, TA Instruments, New Castle, DE, USA).

2. Materials and methods

2

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microbial population.

2.4.5. Differential scanning calorimetry (DSC) Thermal analysis was performed with a Q2000 DSC (TA Instruments, New Castle, DE) under a nitrogen atmosphere in the temperature range of -80 to 160 ℃ at 10 ℃ /min following the method described by Ahmed, Varshney, Auras, and Hwang (2010)) for PLA/ nanoclay composite. Thermal properties were calculated from the instrumental software (Universal Analysis version 4.5A, TA Instruments, USA).

log

N t p = −⎛ ⎞ N0 ⎝δ ⎠

(1)

Where t is the time and N is the number of microbial counts at time t. The performance of the Weibull model was assessed based on the statistical indicators, namely, residual sum of squares (RSS) and residual standard error (RSE) (Oliveira et al., 2013). 2.5. Statistical analysis

2.4.6. Measurement of water vapor permeability (WVP) The WVP was determined using Permatran W3/31 (Mocon, Inc., Minneapolis, MN, USA) (F1249, ASTM, 1995).

Data were presented as the mean ± standard deviations and analysis of variance (ANOVA) at a 95% confidence level using Excel software (Microsoft Corporation, USA). The fitting of Weibull models was carried out using R-software package NLS tools (R package, Foundation for Statistical Computing, Austria, 2013).

2.4.7. Scanning electron microscopy (SEM) The SEM images were visualized using an SEM (JEOL, JCM-6000 Plus, Tokyo, Japan) at an accelerating voltage of 15 kV. Prior to imaging, the film samples mounted on the brass stub and sputtered coated under a flow of argon to improve the conductivity of the sample and the photographs were taken at 500× magnification.

3. Results and discussion 3.1. Film thickness

2.4.8. Evaluation of in vitro antibacterial effectiveness of films The antimicrobial effectiveness of the composite films was evaluated against Staphylococcus aureus (Gram-positive) and E.coli (Gramnegative) using the liquid culture method (Ahmed, Hiremath et al., 2016, 2016b). A film disc was dipped in a test tube containing 10 mL of TSB where 0.1 ml of the S. aureus and E.coli inoculums adjusted to a cell concentration of 1 × 108 CFU/ml. The test tubes were shaken at room temperature (25 °C) at 200 rpm. After 24 and 168 h, aliquots (1 ml) were withdrawn from the test tubes and serially diluted with buffered peptone water and spread onto BHIA plates. Plates were incubated at 37 °C for 24 h, and the colony-forming units (CFU) were counted. A film-free inoculated TSB medium and PLA/PEG/PCL film served as controls.

The thickness of PLA/PEG/PCL film was 0.075 ± 0.001 mm, which increased to 0.083 ± 0.001 mm with the reinforcement of ZnO because of the increase in solid content in the film. The addition of the CEO did not improve the thickness of the film. The PLA/PEG/PCL film reinforced with both ZnO and CEO exhibited an increase in the film thickness (0.090 ± 0.001 mm). The presence of CEO could interfere with the dispersion of ZnO into the polymer matrix and orderly alignment of polymer chains resulting in a less compact network and therefore, increase the thickness. Similar observations were made by other researchers for composite films (Lee, Kim, & Park, 2018; Shankar, Wang, & Rhim, 2018). 3.2. Mechanical properties

2.4.9. Antimicrobial confirmation test and microbial inactivation kinetics modelling The antimicrobial effectiveness of the composite films was tested against S. aureus and E. coli using scrambled egg as a model food. Two sets of freshly prepared scrambled eggs (≈10 g) were placed in two separate petri dishes. To each petri dish, an aliquot of a 1 × 107 CFU/ mL inoculum of S. aureus and E. coli were transferred separately, thoroughly spread over the egg sample, and hold for 30 min for the attachment. Afterward, inoculated scrambled egg (≈1 g) contaminated with S. aureus or E.coli were wrapped individually with composite film (3 × 3 cm), heat sealed and stored in petri dishes at 4 °C. Wrapped samples were analyzed for the survival of S. aureus and E.coli by enumeration at 0, 7, 14 and 21 d during the storage. Egg samples wrapped with PLA/PEG/PCL films served as a control. For enumeration, the egg samples were carefully transferred from the packet to 9 mL of sterile buffered peptone water (0.1% w/v) and homogenized then for 1 min on a vortex. From this homogenate, serial dilutions were made in peptone water and spread-plated on BairdParker agar for S. aureus and Brilliance E.coli/Coliforms selective agar for E.coli. Baird-Parker agar and Brilliance E.coli-Coliforms agar plates were incubated at 37 °C for 48 h and 24 h, respectively before the bacterial enumeration and expressed as log CFU/g of the egg sample. All samples were analyzed in duplicate and repeated two times (n = 4). The inactivation kinetics of S. aureus and E.coli in scrambled eggs in the developed composites packaging were fitted by the Weibull model (Eq. 1), which mostly used to describe microbial nonlinearity survival curves in inactivation by thermal and non-thermal processes (Albert & Mafart, 2005; Mafart, Couvert, Gaillard, & Leguerinel, 2002; Oliveira, Soares, & Piccoli, 2013). The model consists three parameters, namely, N0 is the initial number of microorganisms, p indicates the shape of the curves (dimensionless) (p > 1: convex curves and p < 1: concave curves), and δ represents to the time for the 1st decimal reduction in the

Reinforcement of ZnO into the PLA/PEG/PCL leads to improve on the tensile strength (TS) significantly from 13.97 to 21.38 MPa, whereas, the EAB dropped from 25.48 to 17.72% (P < 0.05). This observation is consistent with the earlier observation for the ZnO impregnated polymers (Castro-Mayorgaa, Fabraa, Pourrahimib, Olssonb, & Lagarona, 2017; Murariu et al., 2011; Shankar et al., 2018). The improvement in tensile properties is mostly associated with lower interfacial energy between the polymer matrix and nanoparticles, and also the finer dispersion of the nanoparticles (Murariu et al., 2011). Additionally, the surface coating of ZnO by silane prevents the catalytic effect of ZnO and responsible for reducing the extent of unzipping reactions. The incorporation of CEO, on the contrary, plasticized the PLA/ PEG/PCL films by lubricating the film surfaces resulting in a drop in the TS to 10.93 MPa and a significant improvement in the EAB (204%). Incorporation of both ZnO and CEO into PLA/PEG/PCL, however, maintained the TS value (13.96 MPa) similar to PLA/PEG/PCL/ZnO with a significant improvement in the EAB (136.1%). 3.3. Water vapor permeability (WVP) The WVP value of the PLA/PEG/PCL film was 13.75 ± 1.84 g mm/ m2 day atm., and the value is consistent with the values reported in the literature (Jain, Reddy, Mohanty, Misra, & Ghosh, 2010; Plackett et al., 2006). Reinforcement of ZnO lowered the WVP value drastically to 1.47 ± 0.17 g mm/m2 day atm. Shankar et al. (2018) found a similar trend, and they advocated the drop was due to the elevated tortuous path, which eventually impedes diffusion of H2O across the composite film. Incorporation of CEO increased the WVP to 16.16 ± 0.20 g mm/ m2 day atm for the composite films. The PLA/PEG/PCL/ZnO/CEO film exhibited a WVP slightly higher (2.97 ± 0.02 g mm/m2 day atm) than the PLA/PEG/PCL/ZnO film which indicates a good dispersion of the 3

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Fig. 1. Rheograms of the PLA/PEG/PCL blend and its composites in melt (3% ZnO, 25% CEO and 3% ZnO and 25% CEO) (a). the elastic(G′) and viscous modulus (G″) against frequency at 140 °C; the complex modulus (G*) and phase angle (δ) at the selected temperature (b). PLA/PEG/PCL (c). PLA/PEG/PCL/25%CEO, (d). PLA/PEG/PCL/3% ZnO and (e). PLA/PEG/PCL/3%ZnO/25%CEO.

rheometry and tensile measurements (Ahmed et al., 2017; Murariu et al., 2011). In our earlier study, it was demonstrated that the rheological measurement of the melt was not possible by incorporating ZnO into PLA/PEG matrix. A comparison between the mechanical rigidity between PLA/PEG/ZnO and PLA/PEG/PCL/ZnO films at 160 °C and 1 Hz demonstrated that the PCL impregnated film resulted in a significantly higher η* value (199.9 Pa.s) than the PLA/PEG/ZnO (0.18 Pa.s) at the equal concentration level of ZnO. It supports the advantages of PCL incorporation into the blend by restricting the degradation of PLA significantly. A combination of ZnO and CEO impregnation resulted in an intermediate value for the moduli. To investigate the influence of the temperature of PLA/PEG/PCL nanocomposites at melt, the complex modulus, G* (sum of the squares of dynamic moduli) and the phase angle, δ (ratio between moduli) was graphed against the frequency, ω (Fig. 1b-e). The G* increased with increasing frequency while the δ decreased at a similar condition. The G*- ω rheograms of the melt decreased and the corresponding δ- ω increased with increasing the temperature. These rheograms exhibited a change in the fluidity which was measured by calculating the slope (n) of the power-type equation (G * = kωn ) . For PLA/PEG/PCL (Fig. 1b), the n value was increased from 0.84 to 0.90 with increasing the temperature from 140 to 170 °C, and thus, confirming the shear-thinning behavior. The G* values of the PLA/PEG/PCL melt dropped significantly from 12634 Pa to 8102, 1873 and 4199 Pa with the reinforcement of CEO, ZnO and a combination of CEO and ZnO, respectively at 140 °C and at a frequency of 1 Hz. Among the tested samples, the maximum reduction of G* (85%) was recorded for the PLA/PEG/PCL/ZnO melt (n = 0.91-0.92), which is contrary to the tensile data. The difference could be associated with the ‘unzipping’ depolymerisation in the melt induced by ZnO as reported by Ahmadzadeh et al. (2018) for PLA/PCL/

ZnO into PLA/PEG/PCL matrix.

3.4. Rheological properties To impart flexibility into the film, PEG was incorporated into the PLA/PCL blend and the blend PLA/PEG/PCL used as a base material for the film development. Replacement of PLA by PCL into the blend was further quantified by the melt rheology. At 170 °C, the complex viscosity (η*) of PLA/PEG/PCL (4:1:4) improved significantly (633.6 Pa.s) against the PLA/PEG (9:1) blend (302.4 Pa.s). It indicates a significant property improvement in the melt. Rheograms of the PLA/PEG/PCL and the composites with CEO and ZnO as a function of frequency at 140 °C are illustrated in Fig. 1a. The melt composite exhibited liquidlike property (G″ > G′) in the studied frequency range with shorter relaxation time, λ. Both the dynamic moduli showed strong frequencydependency although the increase of the G′ was higher than that of the G″. The polymers, however, did not show any plateau region indicating there was no entanglement occurred in the melt and the transition happened entirely to the Maxwell region. Incorporation of CEO into PLA/PEG/PCL dropped both moduli significantly (35–41%) because of the lubrication/plasticization effect attributed by the CEO. Reinforcement of ZnO into the PLA/PEG/PCL further dropped both the magnitudes of G′ (≈ one log cycle) and G″ (about 1/6). The obtained rheological data demonstrated that the polymeric chain segment mobility improved significantly with the reinforcement of ZnO and CEO into the PLA/PEG/PCL. The reinforcement of ZnO to PCL improved the mechanical rigidity (Young’s modulus) of the composites by restricting the mobility of the polymer matrix near the surface (Elen et al., 2011). On the contrary, the thermal degradation of PLA induced by ZnO is supported in the literature by various analytical tools, including GPC, 4

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Table 1 Thermal properties of nanoparticle and essential oil impregnated PLA/PEG/PCL films. Sample

Tg (°C)

Tm (°C)

Onset

Mid

PLA PCL PEG PLA/PCL

52.96 ± 0.83 −64.35 ± 1.01 – −65.45 ± 0.89

56.40 ± 0.75 −61.08 ± 1.00 – −62.5 ± 0.85

58.93 ± 0.68 −57.86 ± 0.97 – −57.95 ± 0.91

PLA/PEG/PCL

−63.85 ± 1.04

−61.91 ± 0.93

−58.97 ± 1.03

PLA/PEG/PCL/EO

−65.85 ± 0.97

−63.84 ± 0.90

−61.32 ± 0.98

PLA/PEG/PCL/ZnO

−63.61 ± 0.95

−60.49 ± 0.89

−57.71 ± 0.79

PLA/PEG/PCL/ZnO/EO

−66.10 ± 0.95

−63.99 ± 0.94

−61.53 ± 1.00

Hm (J/g)

Tc (°C)

Hc (J/g)

End 146.2 56.25 50.64 56.16 148.1 46.18 56.14 148.4 29.02 45.52 134.5 46.28 55.59 148.9 37.16 48.25 140.2

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

1.15 0.87 0.78 0.77 1.34 0.67 0.79 1.46 0.55 0.67 1.19 0.60 0.59 1.45 0.63 0.72 1.32

21.78 ± 0.77 39.55 ± 0.68 155.5 ± 1.22 16.73 ± 0.90 2.67 ± 0.03 1.29 ± 0.04 12.75 ± 0.14 8.64 ± 0.12 1.86 ± 0.03 15.92 ± 0.13 6.59 ± 0.13 0.39 ± 0.00 11.46 ± 0.15 8.08 ± 0.10 4.27 ± 0.08 14.62 ± 0.15 7.38 ± 0.11

111.14 ± 0.89 29.03 ± 0.55 17.94 ± 0.34 30.31 ± 0.33 – −7.72 ± 0.10 30.24 ± 0.37 79.7 ± 1.02 – 21.32 ± 0.33 63.65 ± 0.58 −21.34 ± 0.33 29.56 ± 0.53 83.05 ± 0.88 −4.64 ± 0.10 25.14 ± 0.22 81.12 ± 0.79

22.74 ± 0.24 48.71 ± 0.44 149.0 ± 1.23 21.37 ± 0.35 – 1.16 ± 0.04 22.75 ± 0.32 8.01 ± 0.12 – 21.07 ± 0.03 5.72 ± 0.10 0.35 ± 0.12 18.13 ± 0.33 7.70 ± 0.13 3.76 ± 0.08 30.84 ± 0.15 4.86 ± 0.01

Tm and Tc. values, because of the lubricating or plasticizing effect attributed to the CEO. The Tm of the PEG, PCL, and PLA drastically dropped to 29.02, 45.52 and 134.47 °C, respectively. No crystallization peak for the PEG was detected in the blend whereas the Tc for the PCL and the PLA lowered to 21.32 and 63.65 °C, respectively. This abrupt drop in the thermal properties could be attributed by the improved chain mobility induced by the CEO acting as a plasticizing/lubricating agent in the polymer blend matrix. In our earlier work (Ahmed, Hiremath et al., 2016, 2016b) on PLA/PEG/CEO films, a similar drop of Tg and Tm was observed. The Tg values of CEO added PLA/PEG films decreased from 17 to -9.2 °C, and the Tm values dropped from 147 to 127 °C. Some other researchers also observed a similar decrease in thermal properties when thymol and cinnamaldehyde were incorporated into PLA films (Qin et al., 2015; Ramos, Jiménez, Peltzer, & Garrigós, 2014; Wu et al., 2014). Reinforcement of 3% ZnO into the PLA/PEG/PCL matrix did not change the thermogram (P > 0.05), which is consistent with the observation of Murariu et al. (2011) using surface-treated ZnO. However, this observation differed from our earlier observation on PLA/PEG/ZnO film using untreated and silane-treated ZnO (Arfat et al., 2017). The silane-treated ZnO improved the Tg and the Tm of the composites by 0.5 to 2.5 °C and 1 to 1.9 °C, respectively. The presence of PCL in the matrix could make the difference in the blend. The minor improvement in the thermal properties of PLA could be attributed to the reinforcement of ZnO that restrict the segmental mobility of the polymer chain. The thermal properties of PLA/PEG/PCL/ZnO/CEO composite significantly differed from other composites (Table 1). The Tg of the PCL dropped to a value of about -64 °C. The Tm values for PEG, PCL, and PLA were detected at 37.16, 48.25 and 140.17 °C and the corresponding Tc values were -4.64, 25.14 and 81.12 °C, respectively. The obtained values were ranged between the values obtained for the PLA/PEG/PCL/ CEO and the PLA/PEG/PCL/ZnO films. Overall, the CEO effect was more pronounced over the ZnO in the composites, and the plasticizing effect facilitated more flexibility on the polymer chains and produced a film with a lower melting point and enthalpy than the original. A similar change in thermal properties of biopolymer/EO films are reported (Javidi, Hosseini, & Rezaei, 2016; Qin, Li, Liu, Yuan, & Li, 2017). However, the lower change in the Tc of PLA and PCL in the blend could be influenced by the molecular structure and composition of the essential oils (Eucalyptol, Camphor, and α-pinene), which could have played an important role in the chain mobility of the polymers, and therefore, it showed a different behavior from other EO loaded polymer matrix (Yahyaoui, D´ıaz, & Labidi, 2016).

ZnO composites. They found a significant drop in the G′ and the complex viscosity in the melt with the incorporation of ZnO because of the degradation and scission of polymeric chains (e.g., PLA) accelerated by the ZnO. The scission of polymeric chains was further confirmed by the decrease in the molecular weight of PLA (Ahmadzadeh et al., 2018). Conversely, the addition of CEO restricted the chain scission by forming a protecting layer around the melt surface at 140 °C (n = 0.82-0.85), and therefore, the degradation of the polymer restricted to 36 and 67% in PLA/PEG/PCL/CEO and PLA/PEG/PCL/ZnO/CEO composites, respectively. The G* value of those composites reduced further (25–76%) with increasing the temperature from 140 to 170 °C because of the Newtonian flow behavior of the composite and also degradation of polymers, in particular, PLA above the melting point. The δ- ω rheograms followed the G*- ω rheograms accordingly. 3.5. Thermal analysis The thermal analysis data [glass transition temperature, Tg, melting temperature, Tm, crystallization temperature, Tc, and associated enthalpies (ΔHm and ΔHc)] of each polymer and their blend are reported in Table 1. The Tg (midpoint) values for the PLA and PCL were detected at 56.40 and -61.08 °C, respectively and the corresponding Tm and Tc were 146.18 and 111.14 °C (cold crystallization); and 56.25 and 29.03 °C, respectively. These values are consistent with the literature values (2016b, 2018b, Ahmed, Hiremath et al., 2016, 2018a). The addition of 50% PLA content had a little effect on the Tg, Tm, and Tc of the PCL. The significant drop in the process enthalpy, in particular, the ΔHm of the neat PCL dropped from 32.17 to 16.68 J/g in PLA/PCL blend, indicates the interactions between the two constituents. The Tg and the Tc values of the PCL were essentially unchanged in the PLA/PCL blend whereas those thermal parameters were not detected for the PLA. The disappearance of Tg for the PLA could be associated with the overlapping of the Tm of PCL which fall in the same temperature range. Incorporation of PEG acts as an effective plasticizer and facilities the chain mobility of the polymers in the blend, in particular, the PLA mobility. The Tm and the Tc values for each polymer in the blend were detected including a small melting and crystallization peak at 46.18 °C and −7.72 °C, respectively for the PEG. The Tm of PCL was not influenced by the incorporation of PEG however, the ΔHm dropped further to a value of 12.23 J/g. Incorporation of CEO imparted a significant plasticization effect as also observed through the rheological measurement. It can be seen that the addition of CEO drops the Tg of the PLA/PEG/PCL blend marginally to about -64 °C however, the most significant drop was observed on the 5

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PLA) gets contorted due to the incorporation of ZnO in PLA/PEG/PCL films. A similar finding has been reported earlier by Chieng, Ibrahim, Yunus, and Hussein (2013)) for PLA film embedded with PEG and graphene NPs. 3.7. Surface morphology SEM surface micrographs showed that PLA/PEG/PCL has discernible long thread fibrils oriented in one direction on the fracture surface (Fig. 3). Jain et al. (2010) observed similar findings for the PLA/ PCL blend, and they reported both PLA and PCL are incompatible with each other with phase separation in the blend. The appearance of pits on the surface of the PLA/PCL blend film with a few micro-voids has also been reported by Wu et al. (2014). The small pores appeared in the PLA/PEG/PCL/CEO films whereas the ZnO-loaded films resulted in the larger micro-pores. An increase in the void spaces of PCL/gelatin/ cerium oxide (CeO2) films at a higher loading concentration of CeO2 was reported by Naseri-Nosar et al. (2017), and the authors suggested that the inadequate interphase interactions between NPs and polymer matrix in the film could be the possible reason for those voids. In the PLA/PEG/PCL/CEO/ZnO composite films, denser open micro-pores were visualized. While working with the impregnation of thymol into PLA/PCL films, Wu et al. (2014) observed micro-voids in the blend films, and the voids became larger and more with increasing the thymol concentration. Furthermore, it has been reported that the micro-voids and channels facilitated the release of the antimicrobial agent and improve the microbial inactivation (Liu, Jin, Coffin, & Hicks, 2009).

Fig. 2. FTIR spectra (―PLA/PCL/PEG; ― PLA/PCL/PEG /25% CEO; ― PLA/ PCL/PEG /3% ZnO NPs, and ― PLA/PCL/PEG /3% ZnO NPs/25% CEO) of plasticized PLA/PCL films incorporated with ZnO NPs and CEO.

3.6. FTIR spectroscopy FTIR spectra of PLA/PCL/PEG film shows a characteristic peak at 2868 cm−1 attributed to the stretching vibration of eCH2 of PEG and two small peaks at 2994 and 2945 cm-1, due to the asymmetric and symmetric C–H stretching vibrations of the eCH3 group of PLA, respectively (Fig. 2). The peak observed at 1750 cm-1 appeared in all the composites films ascribed to eC]O stretching vibration of PCL and PLA. The peak at 1181 cm-1 represents the symmetric CeOeC stretching of the PLA ester groups. A small peak observed at 1513 cm−1 owed to the incorporation of CEO, which corresponds to the bending of the aromatic ring CeH bonds (Mulla et al., 2017; Wen et al., 2016). Reinforcement of ZnO did not impart any additional peak in the PLA/ PCL/PEG spectrum as supported by earlier observations for PLA/ZnO nanocomposite films (Huang, Zeng, Wang, & Chen, 2018; Shankar et al., 2018). More importantly, the minor peaks at 2994 cm−1 (attributed to asymmetric CeH stretching vibrations of the eCH3 group of

3.8. Antimicrobial properties The in vitro antimicrobial properties of the composite films were tested against S. aureus and E. coli as illustrated in Fig. 4a. The PLA/ PEG/PCL films did not show any antibacterial inactivation, and the growth of both test organisms increased after an incubation period of 7 days. However, the PLA/PEG/PCL/ZnO films exhibited a marginal inactivation for S. aureus after 24 h incubation, and the inactivation did not improve further. However, about 1 to 1.5 log reduction of S. aureus was detected for PLA/PEG/PCL/CEO and PLA/PEG/PCL/ZnO/CEO films after 24 h which further improved (2–4.5 log) after 7 days

Fig. 3. Micrographs of PLA/PEG/PCL and its incorporation with ZnO and GO NPs and CEO. a) PLA/PCL/PEG b) PLA/PCL/PEG/25% CEO c) PLA/PCL/PEG/3% ZnO NPs, and d) PLA/PCL/PEG/3% ZnO NPs/25% CEO; Magnification: ×200. 6

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compound from the clove oil and the ZnO. A significantly higher antimicrobial activity as shown by the CEO-loaded films could be influenced by the rapid release of the volatiles from the CEO on the surface of the film over the NP-enriched films (Ahmed, Arfat et al., 2018, 2018b). The antimicrobial activity of nanoparticles and essential oils against S. aureus and E. coli has been established earlier (Hammer, Carson, & Riley, 1999; Jones, Ray, Ranjit, & Manna, 2008). The hydrophobic compounds from the essential oil and zinc cations are capable of penetrating through the bacterial cell membrane to rupture the cell structure (Burt, 2004; Tayel et al., 2011). 3.9. Microbial validity of the film with scrambled egg and applicability of the Weibull model The initial counts of E. coli and S. aureus in the inoculated samples was 6.42 and 6.16 log CFU/g, respectively. A moderate reduction of test organisms (≈ 1.3–2 log) found in the egg samples packed in PLA/PEG/ PCL for 21 days. The sample packed in PLA/PCL/PEG/ZnO films showed 5 and 2.5 log reduction for E. coli and S. aureus after 21 days storage (Figs. 4 b and c). These findings are consistent with the observed antibacterial activity of poly(vinylprolidone)/ZnO films employed for liquid egg white packaging (Jin et al., 2009). The antimicrobial activity exhibited by the ZnO-loaded films is believed to be attributed to the penetration of Zn2+ through the cell wall of the microorganisms that finally damaged the cells (Zhang, Ding, Povey, & York, 2008). Additionally, the produced hydrogen peroxide from the ZnO surface acts as an effective oxidizing agent for the inhibition of bacterial growth by damaging the cell membrane of bacteria (Tayel et al., 2011). The growth of the test microorganisms was restricted while the egg samples were packed in PLA/PCL/PEG/CEO films. The counts of S. aureus dropped significantly to 3.20 log CFU/g, and complete inhibition of E. coli was detected after 21 days of storage at refrigerated conditions. A similar drop in the microbial counts was reported by Qin et al. (2015) when mushrooms were packed in PLA/ cinnamaldehyde films. The progression of E. coli and S. aureus was impeded further when the CEO was infused in the PLA/PEG/PCL/ZnO composite films. The complete inhibition of E. coli achieved in the egg sample after 21 days of storages, whereas the microbial counts of S. aureus were reduced to 2.36 log CFU/g at a similar condition. Additionally, the composite films containing both CEO and ZnO achieved the maximum reduction of pathogens, which is believed to be associated with the synergic effect activated by the release of both active compounds of CEO and zinc ions from the composite film, which leads to disrupt the metabolic processes, rupture the bacterial cell wall and finally influenced the death of the cell (Li et al., 2010). The fittings of the Weibull model for the inactivation kinetics of S. aureus and E. coli in different composite packages stored at 4 °C are presented in Table 2. The nonlinear models showed a good fit with the RSE ranging from 0.003 to 0.654 and 0.032 to 0.568 for E.coli and S. aureus, respectively, and a typical adjusted model for E.coli is illustrated in Fig. 4b and c. Although the Weibull model has successfully employed to evaluate microbial inactivation curves in the literature, however, no information is available so far, on antimicrobial packaging materials. The survival curves showed a drop of both E. coli and S. aureus counts during storage time. The p-value of the PLA/PEG/PCL film was less

Fig. 4. (a). in vitro antibacterial activities of composite films after incubation period of 1 and 7 days; and survival curves for the test organisms in scrambled egg samples wrapped with composite films stored at 4 °C for 21 days and applicability of the Weibull equation (b). E. coli and (c). S. aureus.

incubation. For E. coli, 4 and 6 log reduction was noted for PLA/PEG/ PCL/ZnO and PLA/PEG/PCL/CEO packaging, respectively. The complete inhibition of E. coli was found for the PLA/PEG/PCL/ZnO/CEO film which indicates the synergism between eugenol–the active

Table 2 Weibull model parameters and fitting (RSS–RSE) for the inactivation of E. coli and S. aureus inoculated in scrambled egg during storage at 4 °C. E. coli

PLA/PEG/PCL PLA/PEG/PCL/ZnO PLA/PEG/PCL/CEO PLA/PEG/PCL/ZnO/CEO

S. aureus

δ

p

Log10 N0

RSS-RSE

δ

p

Log10 N0

RSS-RSE

10.43 10.17 8.058 8.008

0.71 2.24 1.54 1.51

6.04 6.08 5.43 5.28

0.427–0.654 0.036–0.190 0.071–0.268 1.46·10−5–0.003

5.05 0.421 12.63 12.51

0.538 0.214 1.924 2.395

6.43 6.42 5.88 5.87

0.002–0.040 0.015–0.123 0.013–0.116 0.323–0.568

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than 1, which suddenly reversed (1.51–2.24) for the rest of the films (p > 1) for E. coli, and the curve shapes changed accordingly from concavity to convexity, which accounts for its sharp inactivation capability of the composite films. For S. aureus, the curve shape changed with p-values ranged between 1.924 and 2.395 for the PLA/PEG/PCL/ CEO and PLA/PEG/PCL/ZnO/CEO films. The calculated δ values for E. coli ranged from 8.01 to 10.43, and the lowest δ value obtained for PLA/PEG/PCL/ZnO/CEO indicates the time required for first log reduction is the shortest. However, the trend of δ did not follow for the S. aureus (5.05 to 12.63) where the higher δ values exhibited the highest inactivation. While working with oregano and lemongrass essential oils against Salmonella Enteritidis in ground beef during refrigerated storage, Oliveira et al. (2013) found a decrease of Salmonella counts during storage time. However, the ‘p’ value was less than unity for all treatments, which accounts for its upward concavity. Furthermore, the δ values were much lower than the present work. The differences in the p and δ values in the antimicrobial films could be attributed to the concentration of EO and the release kinetics of the active compound from the film surface to the food materials. These data indicate that the Weibull parameters were more specific to the microorganism rather than the packaging materials.

Journal of Food Science, 75(8), N97–N108. Albert, I., & Mafart, P. (2005). A modified Weibull model for bacterial inactivation. International Journal of Food Microbiology, 100, 197–211. Arfat, Y. A., Ahmed, J., Al Hazza, A., Jacob, H., & Joseph, A. (2017). Comparative effects of untreated and 3-methacryloxypropyltrimethoxysilane treated ZnO nanoparticle reinforcement on properties of polylactide-based nanocomposite films. International Journal of Biological Macromolecules, 101, 1041–1050. ASTM (1995). Standard test method for oxygen gas transmission rate through plastic film and sheeting using a coulimetric sensor. Standard Designation: D3985-95. Annual book of American standard testing methods. Philadelphia, PA: ASTM. Burt, S. (2004). Essential oils: Their antibacterial properties and potential applications in foods—A review. International Journal of Food Microbiology, 94, 223–253. Castro-Mayorgaa, J. L., Fabraa, M. J., Pourrahimib, A. M., Olssonb, R. T., & Lagarona, J. M. (2017). The impact of zinc oxide particle morphology as anantimicrobial and when incorporated inpoly(3-hydroxybutyrate-co-3-hydroxyvalerate)films for food packaging and food contact surfacesapplications. Food Bioproduct Processing, 101, 32–44. Chieng, B. W., Ibrahim, N. A., Yunus, W. M. Z. W., & Hussein, M. Z. (2013). Poly (lactic acid)/poly (ethylene glycol) polymer nanocomposites: Effects of graphene nanoplatelets. Polymers, 6(1), 93–104. Elen, K., Murariud, M., Peeters, R., Dubois, P., Mullens, J., Hardy, A., & Van Bael, M. K. (2011). Towards high-performance biopackaging: Barrier and mechanical properties of dual-action polycaprolactone/zinc oxide nanocomposites. Polymers for Advanced Technologies. Gerard, T., & Budtova, T. (2012). Morphology and molten-state rheology of polylactide and polyhydroxyalkanoate blends. European Polymer Journal, 48, 1110–1117. Hammer, K. A., Carson, C. F., & Riley, T. V. (1999). Antimicrobial activity of essential oils and other plant extracts. Journal of Applied Microbiology, 86(6), 985–990. Huang, X. J., Zeng, X. F., Wang, J. X., & Chen, J. F. (2018). Transparent dispersions of monodispersed ZnO nanoparticles with ultrahigh content and stability for polymer nanocomposite film with excellent optical properties. Industrial & Engineering Chemistry Research, 57(12), 4253–4260. Jain, S., Reddy, M. M., Mohanty, A. K., Misra, M., & Ghosh, A. K. (2010). A new biodegradable flexible composite sheet from poly (lactic acid)/poly (ε‐caprolactone) blends and Micro‐Talc. Macromolecular Materials and Engineering, 295(8), 750–762. Javidi, Z., Hosseini, S. F., & Rezaei, M. (2016). Development of flexible bactericidal films based on poly(lactic acid) and essential oil and its effectiveness to reduce microbial growth of refrigerated rainbow trout. LWT - Food Science and Technology, 72, 251–260. Jones, N., Ray, B., Ranjit, K. T., & Manna, A. C. (2008). Antibacterial activity of ZnO nanoparticle suspensions on a broad spectrum of microorganisms. FEMS Microbiology Letters, 279(1), 71–76. Lee, M., Kim, S. Y., & Park, H. J. (2018). Effect of halloysite nanoclay on the physical, mechanical, and antioxidant properties of chitosan films incorporated with clove essential oil. Food Hydrocolloids, 84, 58–67. Li, W. R., Xie, X. B., Shi, Q. S., Zeng, H. Y., You-Sheng, O. Y., & Chen, Y. B. (2010). Antibacterial activity and mechanism of silver nanoparticles on Escherichia coli. Applied Microbiology and Biotechnology, 85, 1115–1122. Liu, L., Jin, T. Z., Coffin, D. R., & Hicks, K. B. (2009). Preparation of antimicrobial membranes: Coextrusion of poly(lactic acid) and nisaplin in the presence of plasticizers. Journal of Agricultural and Food Chemistry, 57, 8392–8398. Mafart, P., Couvert, O., Gaillard, S., & Leguerinel, I. (2002). On calculating sterility in thermal preservation methods: Application of the Weibull frequency distribution model. International Journal of Food Microbiology, 72, 107–113. Mulla, M., Ahmed, J., Al-Attar, H., Castro-Aguirre, E., Arfat, Y. A., & Auras, R. (2017). Antimicrobial efficacy of clove essential oil infused into chemically modified LLDPE film for chicken meat packaging. Food Control, 73, 663–671. Murariu, M., Doumbia, A., Bonnaud, L., Dechief, A. L., Paint, Y., Ferreira, M., et al. (2011). High-performance polylactide/ZnO nanocomposites designed for films and fibers with special end-use properties. Biomacromolecules, 12(5), 1762–1771. Nair, L. S., & Laurencin, C. T. (2007). Biodegradable polymers as biomaterials. Progress in Polymer Science, 32, 762–798. Naseri-Nosar, M., Farzamfar, S., Sahrapeyma, H., Ghorbani, S., Bastami, F., Vaez, A., et al. (2017). Cerium oxide nanoparticle-containing poly (ε-caprolactone)/gelatin electrospun film as a potential wound dressing material: In vitro and in vivo evaluation. Materials Science and Engineering C, 81, 366–372. Olewnik, E., & Richert, J. (2015). Influence of the compatibilizing agent on permeability and contact angle of composites based on polylactide. Advanced Manufacturing Polymer & Composites Science, 36, 17–25. Oliveira, T. L. C., Soares, R. A., & Piccoli, R. H. (2013). Weibull model to describe antimicrobial kinetics of oregano and lemongrass essential oils against Salmonella Enteritidis in ground beef during refrigerated storage. Meat Science, 93, 645–651. Ostafinska, A., Fortelny, I., Nevoralova, M., Hodan, J., Kredatusova, J., & Slouf, M. (2015). Synergistic effects in mechanical properties of PLA/PCL blends with optimized composition, processing, and morphology. RSC Advances, 5, 98971–98982. Paul, M.-A., Alexandre, M., Degee, P., Henrist, C., Rulmont, A., & Dubois, P. (2003). New nanocomposite materials based on plasticized poly (L-lactide) and organo-modified montmorillonites: Thermal and morphological study. Polymer, 44, 443. Plackett, D. V., Holm, V. K., Johansen, P., Ndoni, S., Nielsen, P. V., Sipilainen‐Malm, T., Södergård, A., & Verstichel, S. (2006). Characterization of l‐polylactide and l‐polylactide–polycaprolactone co‐polymer films for use in cheese‐packaging applications. Packaging Technology and Science: An International Journal, 19(1), 1–24. Qin, Y., Liu, D., Wu, Y., Yuan, M., Li, L., & Yang, J. (2015). Effect of PLA/PCL/cinnamaldehyde antimicrobial packaging on physicochemical and microbial quality of button mushroom (Agaricus bisporus). Postharvest Biology and Technology, 99, 73–79. Qin, Y., Li, W., Liu, D., Yuan, M., & Li, L. (2017). Development of active packaging film

4. Conclusion The active packaging films fabricated by incorporating CEO and ZnO into PLA/PEG/PCL matrix exhibited excellent microbial inactivation for a model food system during 21 days storages at 4 °C. The mechanical rigidity of the composite films at melt was severely lowered by its catalytic degradation effect. The introduction of PCL into PLA/PEG dramatically improved the mechanical strength of the blend. Reinforcement of ZnO and CEO significantly improved the mechanical, structural and barrier properties of the nanocomposite films. Overall, the composite films might be a good candidate for active packaging applications. Further studies are required to estimate Weibull parameters for the composite packaging materials and correlate with the test organisms during the storage. Acknowledgments The authors would like to express their thanks and appreciation to the Kuwait Foundation for the Advancement of Sciences and the Kuwait Institute for Scientific Research for the financial support of the project (Grant number FB 087C). Authors also thankful to Umicore Zinc Chemicals (EverZinc), Belgium for providing ZnO for this research. References Ahmadzadeh, Y., Babaei, A., & Goudarzi, A. (2018). Assessment of localization and degradation of ZnO nano-particles in the PLA/PCL biocompatible blend through a comprehensive rheological characterization. Polymer Degradation and Stability, 158, 136–147. Ahmed, J., Arfat, Y. A., Bher, A., Mulla, M., Jacob, H., & Auras, R. (2018). Active chicken meat packaging based on polylactide films and bimetallic Ag-Cu nanoparticles and essential oil. Journal of Food Science, 83, 1299–1310. Ahmed, J., Hiremath, N., & Jacob, H. (2016). Antimicrobial, rheological and thermal properties of plasticized polylactide films incorporated with essential oils to inhibit Staphylococcus aureus and Campylobacter jejuni. Journal of Food Science, 81, E419–E429. Ahmed, J., Luciano, G., Schizzi, I., Arfat, Y. A., Maggiore, S., & Thai, L. A. (2018). Nonisothermal crystallization behavior, rheological properties and morphology of poly(εcaprolactone)/graphene oxide nanosheets composite films. Thermochimica Acta, 659(10), 96–104. Ahmed, J., Mulla, M. Z., & Arfat, Y. A. (2016). Thermo-mechanical, structural characterization and antibacterial performance of solvent casted polylactide/cinnamon oil composite films. Food Control, 69, 196–204. Ahmed, J., Mulla, M., & Arfat, Y. A. (2017). Application of high-pressure processing and polylactide/cinnamon oil packaging on chicken sample for inactivation and inhibition of Listeria monocytogenes and Salmonella typhimurium, and post-processing film properties. Food Control, 78, 160–168. Ahmed, J., Varshney, S. K., Auras, R., & Hwang, S. W. (2010). Thermal and rheological properties of L-polylactide/polyethylene glycol/silicate nanocomposites films.

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J. Ahmed, et al.

Fabrication of electrospun polylactic acid nanofilm incorporating cinnamon essential oil/β-cyclodextrin inclusion complex for antimicrobial packaging. Food Chemistry, 196, 996–1004. Wu, D., Lin, D., Zhang, J., Zhou, W., Zhang, M., Zhang, Y., et al. (2011). Selective localization of nanofillers: Effect on morphology and crystallization of PLA/PCL blends. Macromolecular Chemistry and Physics, 212, 613–626. Wu, D., Zhang, Y., Zhang, M., & Yu, W. (2009). Selective localization of multi-walled carbon nanotubes in poly(ε-caprolactone)/polylactide blend. Biomacromolecules, 10, 417–424. Wu, Y., Qin, Y., Yuan, M., Li, L., Chen, H., Cao, J., et al. (2014). Characterization of an antimicrobial poly (lactic acid) film prepared with poly (ε‐caprolactone) and thymol for active packaging. Polymers for Advanced Technologies, 25, 948–954. Yahyaoui, G., D´ıaz, A., & Labidi (2016). Development of novel antimicrobial films based on poly(lactic acid) and essential oils. Reactive & Functional Polymers, 109C, 1–8. Zhang, L., Ding, Y., Povey, M., & York, D. (2008). ZnO nanofluids–A potential antibacterial agent. Progress in Natural Science, 18, 939–944.

made from poly (lactic acid) incorporated essential oil. Progress in Organic Coatings, 103, 76–82. Ramos, M., Jiménez, A., Peltzer, M., & Garrigós, M. C. (2014). Development of novel nano-biocomposite antioxidant films based on poly (lactic acid) and thymol for active packaging. Food Chemistry, 162, 149–155. Tayel, A. A., El-Tras, W. F., Moussa, S., El-Baz, A. F., Mahrous, H., Salem, M. F., et al. (2011). Antibacterial action of zinc oxide nanoparticles against foodborne pathogens. Journal of Food Safety, 31, 211–218. Royer, S.-J., FerroÂn, S., Wilson, S. T., & Karl, D. M. (2018). Production of methane and ethylene from plastic in the environment. PloS One, 13(8), e0200574. https://doi. org/10.1371/journal.pone.0200574. Shankar, S., Wang, L. F., & Rhim, J. W. (2018). Incorporation of zinc oxide nanoparticles improved the mechanical, water vapor barrier, uv-light barrier, and antibacterial properties of pla-based nanocomposite films. Materials Science and Engineering C, 93, 289–298. Wen, P., Zhu, D. H., Feng, K., Liu, F. J., Lou, W. Y., Li, N., Zong, M. H., & Wu, H. (2016).

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