Antimicrobial Activity of a Pullulan-Caraway Essential Oil Coating on Reduction of Food Microorganisms and Quality in Fresh Baby Carrot

摘要

This research evaluated the antimicrobial efficacy of pullulan films containing caraway essential oil (CEO). The films were prepared from a 10% of pullulan, containing from 0.12% to 10.0% of CEO. The composition of the CEO was analyzed with the use of gas chromatography. The antimicrobial activity of the CEO was evaluated with the method of serial microdilutions, and the films containing CEO-with the agar diffusion method against selected Gram-negative, Gram-positive bacteria, and fungi. The structure of the film surface and its cross-section were analyzed using a scanning electron microscope (SEM). Analyses were also carried out to determine the efficacy of a pullulan coating with 10% CEO on baby carrots experimentally inoculated with Salmonella enteritidis, Staphylococcus aureus, Saccharomyces cerevisiae, or Aspergillus niger and stored at a room temperature for 7 d. At a concentration of 0.12%, CEO inhibited the growth of all the tested microorganisms. Pullulan films containing 8% to 10% of CEO were active against all tested microorganisms. Populations of S. aureus on carrot samples were reduced by approximately 3 log CFU/g, while those of A. niger and S. cerevisiae by, respectively, 5 and 4 log CFU/g, after 7 d of storage. S. enteritidis was the most resistant among the tested species, since it was not significantly reduced after 7 d of storage. At the end of storage, samples treated with pullulan-caraway oil coating maintained better visual acceptability than control samples. Results of this study suggest the feasibility of applying a pullulan film with incorporated CEO to extend the microbiological stability of minimally processed foods.