Document Type : Research Article
Authors
Faculty of Food Science & Technology, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran.
Abstract
Introduction: The edible films and coatings had remarkable growth in recent years to increase the shelf life and to enhance food quality, stability, and safety and expected to have an important impact on the food market in the following years. In addition, these matrices can be used as carriers of antimicrobials to minimize the risk of foodborne contamination by pathogens and inhibit the development of spoiler microbes. Antimicrobial packaging is a type of active packaging that provides the continuous migration of antimicrobial components to the surface of the foods. Chitosan is a linear copolymer of β-1, 4-linked D-glucosamine and N-acetyl-d-glucosamine. It is a cationic polysaccharide for food packaging applications, due to its unique characteristics of films, including excellent oxygen barrier properties, good mechanical properties, nontoxicity and good antimicrobial activity. Eucalyptus is a plant native from Australia and the Myrtasya family that includes about 900 species and sub-species. There is abundant scientific evidence regarding the efficacy of different species Myrtasya as the antibacterial and antifungal compounds used in health products, and food industry. Using natural antimicrobials are interesting strategies for reducing the use of chemical additives in the food industry. Essential oils (EOs) are defined as a mixture of volatile water insoluble substances to be incorporated into the edible films due to exhibit antimicrobial effects. Moreover, evaluation EOs on the physical, optical and structural properties of the resulting film is also important. Therefore, the aims of this work were to determine the effect Eucalyptus globulus essential oil on antibacterial properties (2) to determine the antimicrobial activity of chitosan based films containing Eucalyptus globulus essential oil against S. aureus, B. cereus, E. coli and S. intertidis.
Materials and methods: The foodborne microbial strains were prepared from Persian Type Culture Collection. The essential oil was analyzed by gas chromatography (GC) (Thermoquest 2000, UK). In this study, the antimicrobial activity of Eucalyptus globulus essential oils (EGOs) was evaluated against two gram positive (S. aureus and B. cereus) and two gram negative (E. coli and S. intertidis) bacteria by the agar diffusion technique and microdilution test. The effect of EGO was evaluated in liquid media and vaporous phase too. Chitosan solution were prepared by dissolving 1.5 % (W/V) of chitosan in aqueous solution containing 0.7% (V/V) of acetic acid under a magnetic stirrer at 40°C until chitosan was completely dissolved. Glycerol as plasticizer (10% weight of chitosan powder) was added to the solution and stirred for 10 minutes. The EGO with concentrations of 0.5, 1 and 1.5% v/v was added to the solution and was stirred for 5 minutes. The film forming solutions using a homogenizer (Heidolph, Germany) were homogenized with 12000 rpm for 4 min, then degassed for 5 min and 25 ml were cast on a 10 cm diameter petri dish. After drying the film in the oven at 38°C for 24 h, they were peeled from the plate surface and were evaluated. The antimicrobial activity of the films was evaluated in contact with liquid and vaporous media.
Results and discussion: Minimum inhibition concentration for gram negative (E. coli, S. enteritidis) and gram positive (B. cerus and S. aureus) bacteria showed 3.125 and 1.562 µg/l respectively. The inhibition zone for gram positive bacteria was bigger than gram negatives. The effect of EGO on bacteria based on Log reduction value (LRV) of S. aerus > B. cerus > E. coli> S. enteritidis. Thses results confirmed that gram positive bacteria were more sensitive to inhibition by plant essential oils than the gram-negative bacteria. Our results showed that chitosan film containing 1 and 1.5 % essential oil was able to reduce the density of bacteria. The Log reduction value of chitosan bioactive film was increased by increasing the concentration of E. globulus essential oil than 0.5 to 1.5 % in liquid media. The results of this work had demonstrated that chitosan bioactive film containing 1.5% EGO can be used an effective antimicrobial film for food packaging in direct contact.
Conclusion: Chitosan is a good biopolymer for active food packaging. The result of this study showed that chitosan films containing EGO could be used as active films due to enhanced the antimicrobial properties which are important in food packaging applications. Films containing essential oil had unique properties that are useful for coating of perishable foods such as fish and poultry.
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