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<OL> <LI> To evaluate the extent to which levulinate, the acid anion of levulinic acid (4-oxypentanoic acid), inhibits growth of Listeria monocytogenes in ready-to-eat meat products as compared to lactate and acetate. <LI> To establish the impact of levulinate on the sensory acceptability of ready-to-eat meat products. <LI> To investigate the mechanisms by which internal accumulation of levulinate, lactate, and acetate inhibits growth of Listeria.
NON-TECHNICAL SUMMARY: Listeria is pathogen of significant concern to the food industry, especially those industry segments producing ready-to-eat products such as processed meats and dairy products. This study will validate practical use of levulinate as an antilisterial additive for ready-to-eat meat products, and investigate the cellular mechanism(s) for the susceptibility of Listeria. to levulinate and two other important organic acid anions, lactate and acetate.
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APPROACH: This project will utilize a combination of applied and fundamental studies to validate the practical use of levulinate as an antilisterial additive for RTE meat products, and to investigate the cellular mechanism(s) for the susceptibility of Listeria sp. to levulinate, lactate, and acetate. Experiments for objective 1 will validate the use of levulinate as an antilisterial additive in comparison to the industry standards of lactate and diacetate. Ready-to-eat meat products (bologna and restructured turkey breast) will be manufactured to contain 0% organic acid salt (negative control), 1.0, 2.0 3.0% (wt/wt of formulation) of sodium levulinate (test additive), and 2% sodium lactate or 0.125% sodium diacetate (positive controls as allowed by USDA and reflecting current industry practice). The salts will be added directly to the bologna and restructured turkey breast during chopping and tumbling, respectively. L. monocytogenes will be inoculated on the surface of sliced meat products, and Listeria growth followed during anaerobic storage at 4 and 10 degrees C. The antilisterial effects of different additives will be compared by statistical ANOVA. Experiments for objective 2 will employ sensory analysis to determine if levulinate effects acceptability of bologna and restructured turkey breast. Members of a consumer taste panel will be asked to evaluate their overall liking of bologna and restructured turkey breast containing 0% organic acid salt (negative control), 1.0, 2.0 or 3.0% (wt/wt of formulation) of sodium levulinate (test samples), and 2% sodium lactate or 0.125% sodium diacetate. Evaluations will be recorded using a hedonic scale of 1 to 9, with 1 = strongly dislike, 5 = neither like nor dislike, and 9 = strongly like. The sensory effects of different additives will be compared by statistical ANOVA. Experiments for Objective 3 will investigate the mechanism(s) by which in internal accumulation of organic acid anions inhibits growth of Listeria. Listeria will be cultured in the presence of each lactate, acetate, and levulinate when external pH = 5.8 and external acid anion concentration = 3 mM, and when external pH = 6.5 and external acid anion concentration = 15 mM. In our preliminary studies, these conditions resulted in varied inhibition of growth by the different acids even though internal accumulation of anion was predicted to be similar for both conditions. This suggested that the internal accumulation of different organic acids inhibits growth by different mechanisms. To identify these mechanisms, we will follow bacterial growth and metabolism including measurement of internal pH, internal concentration of acid anion and efflux of anions, internal glutamate and potassium levels, internal ATP concentrations, and methionine biosynthesis.