Physical, antioxidant and antimicrobial properties of chitosan films containing Eucalyptus globulus essential oil

https://doi.org/10.1016/j.lwt.2015.12.050Get rights and content

Highlights

  • Chitosan films were prepared with Eucalyptus globulus (EG) essential oil.

  • Incorporation EG into the film decrease moisture content and water-solubility.

  • Chitosan edible films shows a significant antimicrobial and antioxidant activity.

  • Chitosan edible films with EG essential oil could be used as active films.

Abstract

In this work active films from chitosan containing Eucalyptus globulus (EG) essential oil (0, 1, 2, 3 and 4% (v/v)) were developed by casting and solvent-evaporation method. Then, the physical properties, the total phenolic content, the antioxidant and antimicrobial activities of different films were assessed, to define if the chitosan films incorporated with EG essential oil could be used as natural active films for food use. The antioxidant activity was determined with three different analytical assays (DPPH, NO and H2O2). The agar disc diffusion method was used to determine the antimicrobial activity against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans and Candida parapsilosis. In fact, incorporating EG essential oil into chitosan-based films significantly decreases moisture content and water-solubility. These results can be explained by the films microstructure, which was analyzed by scanning electron microscopy. The antioxidant properties proved to be significantly enhanced with increasing EG essential oil concentration. The microbiological assessment confirmed antimicrobial efficiency of chitosan films EG containing essential oil. The mentioned results proved the potential of this original material which could be used as active films due to its excellent antimicrobial and antioxidant activities.

Introduction

Biodegradable films made of polysaccharides, proteins and lipids have currently a variety of advantages over synthetic materials, such as biodegradability, edibility, biocompatibility and environmentally friendly properties (Petersen et al., 1999). These films are loaded with many functional ingredients, such as antioxidants, antimicrobial agents, flavors, spices and colorants which improve the functionality of the packaging materials via adding novel or extra functions (Salmieri & Lacroix, 2006).

Chitosan is a linear polysaccharide of randomly distributed β-(1-4)- linked d-glucosamine and N-acetyl-d-glucosamine, it has been recommended due to its biocompatibility, biodegradability and non-toxicity properties (Guldas, Akpinar-Bayizit, Ozcan and Yilmaz-Ersan, 2010). Chitosan with a high degree of deacetylation (>75%) and an important molecular weight have shown the strongest antibacterial effects in aqueous solutions regardless of the type of acid used for solubilization (No, Park, Lee, & Meyers, 2002). However, the acid used for film preparation significantly affects the film properties. Acetic and formic acid–based films have shown the highest tensile strengths followed by the films prepared with lactic, propionic, and citric acids (Begin & Van Calsteren, 1999). Park, Marsh, and Rhim (2002) confirmed that increasing chitosan molecular weight improved the films strength, but did not significantly affect their water and vapor permeability. Furthermore various additives have been examined for their potential in order to modify chitosan films properties, for example the use of glycerol as plasticizer aiming at decreasing their hydrophilicity (Vargas, Albors, Chiralt, & González-Martínez, 2009). In addition, chitosan offers immense advantages as an edible packaging material owing to its good film-forming properties (Kim et al., 2011, Ruiz-Navajas et al., 2013). However, antimicrobial properties may become inconsiderable when chitosan is in a form of insoluble films (Ouattara, Simard, Piette, Begin, & Holley, 2000). There are several natural ingredients, added to edible films, that present antioxidant or antimicrobial properties such as nisin or lysozyme (Pranoto, Rakshit, & Salokhe, 2005), essential oils (Ruiz-Navajas et al., 2013) or fruit extracts (Genskowsky et al., 2015). Essential oils from plant extracts are natural antimicrobial agents; incorporation of essential oil in edible films may not only enhance the films antimicrobial properties but also reduce water-solubility, vapor-permeability and slow lipid oxidation of the product (Ojagh, Rezaei, Razavi, & Hosseini, 2010).

Eucalyptus species are aromatic and medicinal plants belonging to the Myrtle family. The antimicrobial and antioxidant properties of Eucalyptus species essential oil are widely used in pharmaceutical and cosmetic products, flavoring and preservation of several foods. A number of studies have demonstrated the antimicrobial properties of Eucalyptus essential oils against a wide range of microorganisms (Ait-Ouazzou et al., 2011, Santos et al., 2012). These studies, however, are focused on a few Eucalyptus species, especially Eucalyptus globulus (EG) oil, which has been shown to have a wide spectrum of antimicrobial activity (Pereiraa et al., 2014, Vázquez et al., 2008).

The aim of this study was to evaluate chitosan films incorporated with EG essential oil (1%, 2%, 3% and 4% (v/v)), in order to examine their physical properties, their antioxidant activity and the growth inhibition of some bacterial strains to assess the ability of chitosan films containing EG essential oil to enhance food safety.

Section snippets

Chemicals

Chitosan from shrimp shells (≥75%, deacetylated) was purchased from Sigma–Aldrich Chemical Co. All chemicals were of analytical grade and also purchased from Sigma–Aldrich Chemical Co. (St. LouisMo).

Essential oil extraction from E. globulus

Fresh plant leaves were collected; the leaves were subjected to steam distillation using a Clevenger-type apparatus. Briefly, the plant leaves were completely immersed in water and heated to boiling, after which the essential oil was evaporated together with water vapor and finally collected after

Chemical composition of the EG essential oil

The analytical data of major compounds in EG essential oil were identified by GC–MS and the results are shown Table 1 p-Cymene was a predominant component and accounted for 18.18% of the total peak area. The other components were Methyl eugenol (8.83%), 4-Terpinenol (8.45%), s-Methyl 3-methylbutanethioate (7.26%), γ-Terpinene (5.12%), 1,8-cineole (3.16%), spathulenol (2.98%), 1,8-Menthadien-4-ol (2.36%), α-phellandrene epoxide (2.46%), 1,8-Menthadien-4-ol (2.36%), cis-3-Hexenol (1.95%), Thymol

Conclusion

Chitosan is a promising biopolymer for active food packaging. These results showed that chitosan-based films containing EG essential oil could be used as active films due to its law affinity to water and excellent in vitro antimicrobial and antioxidant activities. Incorporation of EG essential oil in films has decrease moisture content, water-solubility and enhanced the antioxidant and antimicrobial properties which are important in food packaging applications. Edible films made from chitosan

Acknowledgments

This work was supported by a grant from Tunisian Ministry of Higher Education and Scientific Research.

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