Development and Characterization of Antimicrobial Food Coatings Based on Chitosan and Essential Oils

The objectives of this research were (1) to evaluate antimicrobial effects of essential oils incorporated in chitosan edible films against Listeria monocytogenes and Escherichia coli O157:H7, (2) to evaluate effectiveness of the films on a meat product, (3) to characterize physical properties of chitosan films enriched with essential oils, and (4) to determine whether the addition of oregano essential oil to bologna can influence consumer liking of the product.

Anise, basil, coriander, and oregano essential oils were tested for antimicrobial activity by paper disc diffusion test with concentration of 1 to 24 ml/disc. Chitosan films incorporated with those essential oils with concentration of 1 to 3 % (3 to 9 ml/disc) were tested for antimicrobial property by film disc diffusion test. Oregano essential oil – chitosan films were applied on thick bologna slices to determine antimicrobial efficacy on a real food product. Solvent extraction and GC/MS analysis were performed to identify and quantify the dominant compounds in oregano essential oil incorporated into the chitosan films before and after application on bologna. Physico–chemical properties of oregano essential oil enriched chitosan films were characterized for thickness, water vapor permeability (WVP), puncture strength, tensile strength, and elongation. The influence of additional oregano EO (45 ppm and 90 ppm) to bologna slices on consumer liking was tested with computerized hedonic scales and just about right scale.

Results showed that oregano essential oil exhibited the strongest antimicrobial activity towards L. monocytogenes and E. coli O157:H7 compared to other tested essential oils (oregano >> coriander > basil > anise). Although both tested pathogens were affected, Listeria monocytogenes appeared to be more sensitive to oregano essential oil than Escherichia coli O157:H7. Application of pure chitosan films reduced pathogen counts on meat product (bologna) from 1 to 3 logs and chitosan films enriched with 1 and 2 % oregano essential oil were sufficient for 4 logs reduction of L. monocytogenes and E. coli O157:H7 on bologna slices stored at 10 °C for 5 days. Results of physico–chemical tests showed that addition of oregano essential oil to chitosan films resulted in increased thickness, higher elasticity, reduced puncture and tensile strength, and lower WVP. Application of the films on bologna resulted in increased thickness, higher WVP, higher elasticity, and reduced puncture and tensile strength of the films. Bologna slices covered with chitosan films with 1 % oregano essential oil and stored 5 days at 10 ^oC absorbed 60 ppm of the EO. Addition of 45 ppm oregano EO did not affect the consuming liking of the product compared to control.