Date of Award

1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

School of Nutrition and Food Sciences

First Advisor

Douglas L. Marshall

Abstract

The objective of this study was to evaluate the antimicrobial properties of glycerol monolaurate (monolaurin) either alone or in combination with organic acids against Listeria monocytogenes in model broth or food. The minimal inhibitory concentration (MIC) of monolaurin was reduced by decreasing the pH value of the medium. The contribution of temperature to monolaurin effectiveness showed that lethal effects of monolaurin increased at higher temperatures and lower pH values, whereas, bacteriostatic effects on growth increased as temperature and pH decreased. The inhibitory effect of ethanol on the growth of L. monocytogenes was slight up to 2.5% ethanol, but was significant in the presence of 5% ethanol. When monolaurin was combined with ethanol, MIC value of the combination was not changed compared to that of the most active single compound alone. MIC value was lower when monolaurin was combined with lactic acid. Synergistic effects were observed when monolaurin was combined with acetic, benzoic, or lactic acid, whereas, there was little interaction when monolaurin was combined with citric acid or ethanol. Planktonic cells exposed to 50 or 100 $\mu$g/ml monolaurin were much more sensitive than were adherent cells, while 1-d adherent cells on stainless steel exposed to 50 or 100 $\mu$g/ml monolaurin were more sensitive than 7-d adherent cells in tryptic soy broth or diluted tryptic soy broth. However, the inactivation effect on those cells significantly increased (P $<$ 0.05) when 50 or 100 $\mu$g/ml monolaurin was combined with 1% acetic acid. Heat effects on planktonic cells, 1-d, or 7-d adherent cells at 55$\sp\circ$C were lower, but inactivation was more enhanced at 65$\sp\circ$C. However, planktonic cells, 1-d, or 7-d adherent cells exposed to 50 or 100 $\mu$g/ml monolaurin at 65$\sp\circ$C were completely inactivated. Air-, vacuum-, or modified atmosphere-package effects combined with 200 $\mu$g/ml monolaurin or 0.5% lactic acid on crawfish tail meat inoculated with 10$\sp3$ cells/g of L. monocytogenes at 4$\sp\circ$C were not different (P $>$ 0.05) compared with controls. However, each package containing crawfish tail meat treated with 200 $\mu$g/g monolaurin combined with 0.5% lactic acid significantly enhanced (P $<$ 0.05) the inhibitory effect. Results indicate that 200 $\mu$g/ml monolaurin, 0.5% lactic acid, and MAP had the greatest potential to inhibit growth of the bacterium.

Pages

192

DOI

10.31390/gradschool_disstheses.5537

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