Access Type

Open Access Thesis

Date of Award

January 2014

Degree Type

Thesis

Degree Name

M.S.

Department

Nutrition and Food Science

First Advisor

Yifan Zhang

Abstract

The objective of this study was to evaluate the antimicrobial activity of essential oil emulsions against food borne pathogenic bacteria and determine potential applications. The oils used for this study were cinnamon, oregano, clove, thyme, rosemary, sage, bergamot, nutmeg, lemon grass and bay. Oil in water emulsions were prepared using Tween 80 as an emulsifying agent, with a stock oil concentration in the emulsions of 20,000 ppm. Essential oil emulsions were individually screened against E. coli (ATCC 25922), E. coli (ATCC 700927), L. monocytogens (ATCC 19115), L. innocua (ATCC 33090) and S. Typhimurium (ATCC 19585) using the broth micro dilution method. Cinnamon showed the highest antimicrobial efficacy against all test organisms, as determined by the minimum inhibitory concentration (MIC). Oregano had the second highest efficacy, while the other oils did not exhibit high antimicrobial

activities. To determine synergistic effect of the emulsions, combinations were tested using checkerboard method. The only synergism observed was between cinnamon and oregano against

E. coli (ATCC 700927) and L. innocua (ATCC 33090) and also between cinnamon and clove towards L. innocua (ATCC 33090). All other combinations were additive or indifferent in nature

to the test organisms. To determine antimicrobial activity of the essential oils on food, chicken pieces were inoculated with the bacteria standardized in CAMHB, and consequently treated with

a twofold concentration of the individual in vitro MIC of the EOs that expressed synergism. The pieces were placed in 60 mm dishes and stored under refrigeration at 4ºC. Samples were prepared for day 0, day 1, day 3 and day 6 for each bacterial treatment.Cinnamon in comparison to control showed Log reduction of E. coli (ATCC 25922), E. coli (ATCC 700927), L. monocytogens (ATCC 19115), L. innocua (ATCC 33090) and S. Typhimurium (ATCC 19585)

by 2.885, 3.39, 3.275, 4.29 and 3.06. While oregano reduced E. coli (ATCC 25922) and E. coli (ATCC 700927) by 3.21 and 3.53 Log. All bacterial species showed significant reduction (p < 0.05) in comparison to control samples. These results suggest that essential oil emulsions have the potential to be used as antimicrobial agents for enhancing food safety.

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