Karina Walker

Date of Graduation

2015

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Agricultural and Resource Economics

Committee Chair

Kristen E Matak

Committee Co-Chair

Jacek Jaczynski

Committee Member

Litha Sivanandan

Abstract

The development of natural antimicrobials for foods is of increasing interest as consumers' desire for more natural foods continues to rise. Organic acids and citrus essential oils (EOs) are natural, generally regarded as safe substances that are known to possess antimicrobial properties. In-vitro tests of natural antimicrobials against a range of bacteria are required in order to determine their feasibility for food applications. The objective of this study was to determine the antimicrobial activity of citrus essential oils and organic acids against Salmonella Baildon, Salmonella Enteritidis, Salmonella Typhimurium (ATCC 14028) and three strains of Listeria monocytogenes (ATCC 19115, ATCC 15313, ATCC 13932). Disk diffusion assays and minimum inhibitory concentrations (MIC) were determined to assess the antimicrobial activity of lemon, lime and mandarin essential oils and acetic, citric and lactic acids. Results showed that lime had the greatest combined average zone of inhibition for Salmonella serotypes (11.5 mm; p<0.05) while lime and lemon produced the largest average zones for Listeria spp. (17.4mm, 17.0mm; p<0.05). Acetic acid and lactic acid were most effective at inhibiting Listeria spp. (15.2mm, 14.0mm; p0.05). Lime EO exhibited a MIC of 2.5 and 5% for L. monocytogenes 15313 and L. monocytogenes 19115, respectively. Acetic and lactic acids had the lowest MICs for Listeria spp., ranging from 0.078- 0.313%. The Salmonella were most sensitive to acetic acid with MICs ranging from 0.078-0.156%. Checkerboard dilution assays of lime EO and acetic acid were used to assess their combined antimicrobial activity against L. monocytogenes 19115 and S. Typhimurium. An additive antimicrobial effect was demonstrated against Listeria when lime EO and acetic acid were combined. Further research is needed in order to test their in vivo antimicrobial abilities.

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