Masters Theses


Yobouet Dje

Date of Award


Degree Type


Degree Name

Master of Science


Food Science and Technology

Major Professor

P. Michael Davidson

Committee Members

F.A. Draughon, M.J. Riemann


Listeria has been recognized as a human and animal pathogen for over 50 years. Recent foodborne listeriosis outbreaks (Fleming et al., 1985; James et al., 1985) have given an increasing importance to this bacterium. To date, a majority of listeriosis outbreaks have been associated with dairy products. However, there is increasing evidence that meat and poultry products are major sources of this organism. Recovery of the pathogen in meat processing plants and in meat products (Johnson, 1988; Cox et al., 1989; Genigeorgis et al., 1989; Farber et al., 1989) are tangible reasons to believe that both raw and ready-to-eat meat products are susceptible to contamination. A recent study by the Centers for Disease Control (CDC) (Schwartz et al., 1988) emphasized this point. Based upon epidemiological data, the CDC reported that consumption of chicken and raw hot dogs was associated with sporadic listeriosis.

The primary method used for the prevention of growth of pathogens in foods is low temperature storage (refrigeration). However, due to its psychrotrophic nature, L. monocytoqenes is able to grow relatively rapidly at 4-7°C. It is therefore desirable to have post-process safeguards which would prevent the proliferation of Listeria and other foodborne pathogens during refrigerated storage or temperature abuse. The most effective method of controlling microorganisms in these circumstances is the use of antimicrobial agents. Additives such as sodium chloride, organic acids and their salts, sulfites and sodium nitrite have been used as food preservatives for centuries. However, very little research has been done on the control of Listeria in meat products.

The antimicrobial action against bacteria of esters of p-hydroxybenzoic acid is well established. However, their effect on Listeria was not recognized until a recent study by Payne et al. (1989). They determined the minimum inhibitory concentration (MIC) of methyl and propyl parabens for Listeria and found that propyl paraben inhibited L. monocytogenes in a model milk system at 4°C (Payne et al., 1989).

This study was undertaken in order to determine the effect of methyl paraben, propyl paraben and sodium lactate on Listeria monocytogenes Scott A and ERM, when inoculated into salt brine and model meat systems at 4°C, 24°C and 35°C.

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