Elsevier

LWT

Volume 98, December 2018, Pages 260-267
LWT

Antioxidant and antifungal effects of eugenol incorporated in bionanocomposites of poly(3-hydroxybutyrate)-thermoplastic starch

https://doi.org/10.1016/j.lwt.2018.08.046Get rights and content

Highlights

  • PHB-TPS bionanocomposites films with Eugenol (essential oil) were prepared by extrusion.

  • Bionanocomposites showed higher tensile strength than PHB-TPS blend.

  • DPPH radical scavenging activity and antifungal activity against Botritys cinerea were attributed to eugenol.

  • Bionanocomposites with eugenol could be an interesting alternative as material for food packaging.

Abstract

Traditional food packaging materials (e.g., polypropylene and polyethylene) serve to isolate foods from the environment. For this reason, there is growing interest in developing active food packaging materials that can extend shelf-life and interact with foods, which could also counteract the level of contamination by plastic in the environment using biodegradable polymers as packaging materials.

For this purpose, poly(3-hydroxybutyrate) (PHB)-thermoplastic starch (TPS)/organically modified montmorillonite (OMMT)/eugenol bionanocomposites were prepared by melt blending. Morphological, thermal and mechanical properties were determined by comparing the influence of the eugenol and clay on the PHB-TPS blend and PHB. The X-ray diffraction (XRD) diffractograms and Transmission electron microscopy (TEM) micrographs indicated that the morphology of the bionanocomposites were intercalated-exfoliated. The presence of additives did not affect the decomposition temperature of PHB, but if the melting temperature decreased by approximately 10 °C, the degree of crystallinity increased with respect to PHB. Tensile test indicated that the elastic modulus decreased by 25% for the PHB-TPS (65:35) blend, while for the PHB-TPS (65:35)/OMMT bionanocompuestos increased by 12%, compare to pure PHB. Finally, bionanocomposites with eugenol exhibited antifungal activity against Botritys cinerea and antioxidant activity, as indicated by high percentages of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical removal. This study showed that bionanocomposites with eugenol could be used as food packaging materials.

Introduction

In the recent past, food packaging was only responsible for containing and protecting the food (passive packaging). Currently, people want packaging that has antimicrobial or antioxidant properties (active packaging). These packaging materials interact with food to extend shelf-life and improve quality and safety. Active antioxidant food packaging is a package that allows reduced lipid oxidation, which is one of the processes most important to quality deterioration in food systems because oxidation gives the food an odor and an unusual color. Active antimicrobial packages inhibit the growth of microorganisms, such as fungi or bacteria, and prevent food spoilage. One of the alternatives to antioxidant and antimicrobial packaging is to use essential oils, such as 4-allyl-2-methoxyphenol (eugenol), 2-isopropyl-5-methylphenol (thymol) and 5-Isopropyl-2-methylphenol (carvacrol), which are found in natural products, such as cloves, thyme and oregano, respectively. These compounds are generally recognized as safe by the FDA (American Food and Drug Administration). Currently, essential oils are replacing synthetic compounds used as antimicrobials and antioxidants in the food industry, since the use of synthetic compounds, such as sodium benzoate, nisin (antimicrobials) (Narayanan, Neera, Mallesha, & Ramana, 2013), butyl hydroxytoluene, and hydroxybutylanisol (antioxidants) (Pereira de Abreu, Paseiro Losada, Maroto, & Cruz, 2011) have been restricted due to their possible toxic or carcinogenic effects and because consumers demand natural products.

Eugenol has been used in the food, pharmaceutical, cosmetic and dental industries because of its anti-inflammatory, antioxidant, antifungal and antibacterial properties, which have been tested against a broad spectrum of bacteria, both Gram-negative and Gram-positive (Marchese et al., 2017), and its antifungal properties have been tested against Penicillium (growth in salami) (Cenci et al., 2015) and Aspergillus ochraceus (growth in grains stored) (Hua et al., 2014). Eugenol also has antioxidant properties that have been analyzed by different methods (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), (2,2-Diphenyl-1-picrylhydrazyl) (DPPH), and cupric ion (Cu+2) reducing antioxidant capacity (CUPRAC) (Gülçin, 2011) (Goñi, Gañán, Strumia, & Martini, 2016).

However, the challenge of essential oils is avoiding their rapid release from the film to the food. Different techniques have been studied to avoid its rapid release, such as direct incorporation into the material by mixing (Ramos, Jiménez, Peltzer, & Garrigós, 2012), molding by injection, extrusion, electrospinning, surface coating, or supercritical impregnation with carbon dioxide (Sung, Tin, Tan, & Vikhraman, 2013), and using polymeric nanocomposites (Campos-Requena, Rivas, Pérez, Garrido-Miranda, & Pereira, 2015; Mascheroni, Guillard, Gastaldi, Gontard, & Chalier, 2011). Nanocomposite polymers have advantages compared to other types of active packaging, as several studies have demonstrated that nanocomposites improve barrier properties, which increases the tortuosity factor (De Azeredo, 2013). This phenomenon enables a slow release of components depending on the clay used (Tunç & Duman, 2011) (Campos-Requena et al., 2015).

Nanocomposites are a class of nanostructured hybrid materials formed by the combination of a matrix that can be a biodegradable polymer (bionanocomposites) or a synthetic polymer (nanocomposite) that also has a charge that can be an inorganic/organic solid with at least one of its nanoscale dimensions (Bitinis, Hernandez, Verdejo, & Kenny, 2011). Recently, the environmental impacts of synthetic polymers, such as polypropylene, polyethylene and polyethylene terephthalate, have raised general global concern because these polymers can take years to degrade after being discarded. For this reason, research developed in the packaging industry on biodegradable polymers, especially for use in short-term packaging. Biodegradable polymers can be divided into different categories based on the origin of the raw materials and their manufacturing processes. These categories include i) natural polymers, such as starch, cellulose, and alginate, ii) synthetic biodegradable polymers, such as poly(l-lactide), polycaprolactone, and polyvinyl alcohol, and iii) polymers produced by microbial fermentation, such as polyhydroxybutyrate (PHB) and polyhydroxybutyrate valerate (PHBV) (Rhim, Park, & Ha, 2013). Among the different fillers that exist (carbon nanotube, nanoparticles of copper or silver), the most used are the clays due to their high availability, low cost, significant improvements of the properties of the polymers, and they do not inhibit the biodegradation process. The most widely used clays in the literature include Montmorillonite (MMT), Cloisite and hectorite. MMT is a laminar phyllosilicate that has been widely used with polymers such as low-density polyethylene (LDPE), polypropylene (PP), polyethylene (PE) or high density polyethylene (HDPE) and biodegradable polymers such as starch, polyhydroxybutyrate, poly(lactic acid), polyhydroxybutyrate valerate. In concentrations between 1 and 10% mass, they significantly improve the mechanical properties, such as storage modulus, which increased 85% for PHB nanocomposites with 3% MMT (Panayotidou et al., 2015) or tensile strength that increased from 5.63 to 7.95 MPa with 1% MMT for TPS/PLA (60/49) (Ayana, Suin, & Khatua, 2014) and increased of about 70% for PHBHV with 1 wt% of clay(Akin & Tihminlioglu, 2018). Additionally, PHBHV nanocomposites showed a 25% reduction in water vapor permeability, and PLA nanocomposites showed a 69% reduction in moisture permeability with 10 wt% MMT modified with a quaternary ammonium salt (Tang & Agarwal, 2018).

Few studies have investigated the obtained bionanocomposites with antimicrobial or antioxidant activities through the use of essential oils, and most studies have been carried out with different matrixes, such as alginate (Alboofetileh, Rezaei, Hosseini, & Abdollahi, 2014) agar-cellulose(Atef, Rezaei, & Behrooz, 2015), chitosan (Abdollahi, Rezaei, & Farzi, 2012), polycaprolactone (Sanchez-Garcia, Ocio, Gimenez, & Lagaron, 2008), kappa-carrageenan (Shojaee-Aliabadi et al., 2014) and methylcellulose (Tunç & Duman, 2011). These studies mainly analyze the antibacterial activity of the essential oils and their release over time. To the best of our knowledge, there is only one investigation of bionanocomposites of thermoplastic starch in which the antifungal capacity of a mixture of essential oils was studied (thymol-carvacrol) (Campos-Requena et al., 2017) and another investigation in which the antioxidant capacity of milk thistle in chitosan bionanocomposites was analyzed (Shojaee-Aliabadi et al., 2014). However, neither of these studies included investigation of the antioxidant or antifungal effects of eugenol in bionanocomposites.

Therefore, the main objective of this paper was to obtain bionanocomposites with antifungal and antioxidant properties. Polyhydroxybutyrate (PHB)-thermoplastic starch (TPS) using organically modified clay (OMMT) and eugenol as fillers were obtained by melt mixing in a twin screw extruder. The influence of eugenol and clay on morphological, thermal and mechanical properties and radical scavenging activity were analyzed, as was antifungal activity against Botritys cinerea. These results are significant because they show the great potential that this material could have for fruit, meat and vegetable packaging.

Section snippets

Materials

Pelletized poly(3-hydroxybutyrate) (PHB), Biomer P226, was purchased from Biomer Ltd. (Krailling, Germany). The polymer was dried in an oven at 60 °C for 24 h before use. Corn starch (composed of 25% amylose and 75% amylopectin), eugenol (99%) and technical-grade glycerol were purchased from Sigma-Aldrich (Arlington Heights, Illinois, United States). Organically modified montmorillonite (OMMT) Nanomer I.34TCN and montmorillonite clay surface modified with 25–30 wt %

Morphological characterizations

X-ray diffraction (XRD) and transmission electron microscope (TEM) were the techniques used to observe the morphology of the bionanocomposites. With XRD, angles smaller than 8° were analyzed to observe the clay dispersion in the polymers. Fig. 2 presents a characteristic peak at 4.81° corresponding to clay. Furthermore, PHB, PHB-TPS blend and bionanocomposite diffractograms are shown. For the PHB and PHB-TPS blend no peaks were observed in the range of 2–6° since these samples did not have

Conclusions

Poly(3-hydroxybutyrate) (PHB) thermoplastic starch (TPS) bionanocomposites with eugenol were obtained by melt mixing in a twin-screw extruder. Two concentrations of eugenol, 2.5% and 3% by weight, were used in bionanocomposites, and their properties (morphological, thermal, and mechanical) were compared with pure PHB, a PHB-TPS blend and a bionanocomposite without eugenol. Analysis of the bionanocomposite morphology by TEM and XRD indicated that clay layers were intercalated and exfoliated in

Funding sources

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Acknowledgments

Karla Garrido thanks to scholarship CONICYT21161368 and the Postgraduate School of the University of Concepción.

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