Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

School of Nutrition and Food Sciences

First Advisor

Douglas L. Marshall

Abstract

The generation time of L. monocytogenes was calculated to be 72.2, 28.5, 17.01, and 6.9 h on crawfish tail meat held at 0, 4, 6, and 12$\sp\circ$C, respectively. Potassium sorbate (PS) (0.3%) spray treatments on crawfish held at 4$\sp\circ$C, extended the lag phase of the bacterium. However, once exponential growth began, a generation time not significantly different (P $>$ 0.05) than that of untreated crawfish was observed. Samples sprayed with 0.3% citric acid (CA) and held at 4$\sp\circ$C supported growth of the bacterium equally well as that of untreated samples. Thermal inactivation of L. monocytogenes using a three neck reactionary flask method yielded D$\sb{55,60,65}$ values of 10.23, 1.98, and 0.19 min, respectively. A z value of 5.5$\sp\circ$C was calculated. Polybag and cellulose casing methodology yielded significantly higher (P $\ge$ 0.05) D$\sb{60}$ values of 4.68 and 3.84 respectively, for the bacterium. D$\sb{60}$ values for L. monocytogenes decreased as the percent lactic acid (LA) spray treatments levels were increased. Increasing sensitivity to heat with LA was not solely due to a reduction of pH. D$\sb{60}$ values for the bacterium on samples packed in air, O$\sb2$, CO$\sb2$, or N$\sb2$ were not significantly different (P $>$ 0.05), however, D$\sb{60}$ of samples packed under O$\sb2$ were lowest. Generation times for heat damaged L. monocytogenes on crawfish meat stored at 4$\sp\circ$C and packed under air, O$\sb2$, CO$\sb2$, or N$\sb2$ was determined. Twenty percent of the cell population was damaged when thermally treated at 60$\sp\circ$C for 12.5 min. The bacterium consistently grew slowest in CO$\sb2$ and O$\sb2$. Samples receiving a treatment of 1% LA, packaging under either of the 4 different atmospheres, and storage at 4$\sp\circ$C, were lethal to the bacterium. These studies indicate that post-packaging heat treatments of 60$\sp\circ$C or greater in the presence of CO$\sb2$ or O$\sb2$, and the addition of 1% LA sprays, would be detrimental to the survival of L. monocytogenes on crawfish meat.

Pages

119

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