Date of Graduation

5-2012

Document Type

Thesis

Degree Name

Master of Science in Food Science (MS)

Degree Level

Graduate

Department

Food Science

Advisor

Philip G. Crandall

Committee Member

Navam S. Hettiarachchy

Second Committee Member

Frank Millet

Third Committee Member

Steven C. Ricke

Keywords

Biological sciences, Attachment, Bio-sanitizer, Lactic acid bateria, Listeria monocytogenes

Abstract

Listeria monocytogenes an important foodborne pathogen that continues to be a serious problem for the food industry. This pathogen contaminates food primarily during post-harvest in the food-processing environment. Its ecology in the food-processing environment is not well understood but previous research has demonstrated the ability of L. monocytogenes to survive on food contact surfaces after cleaning and disinfection. The current study explored the attachment of three lactic acid bacteria (LAB) strains, Lactobacillus animalis , Lb. amylovorus and Pediococcus acidilactici , their combination in a cocktail, and their influence to prevent the attachment of L. monocytogenes at room temperature by examining their cell surface hydrophobicity, total carbohydrates production and adherence capability to stainless steel coupons made from a deli slicer. Subsequently, the study evaluated the influence of L. innocua on the attachment of L. monocytogenes on stainless steel, and on aluminum surfaces. The hydrophobicity tests were performed according to microbial adhesion to solvent (MATS). Extracellular carbohydrates were quantified using a colorimetric method. Based on these tests, Lb. animalis exhibited the greatest hydrophobicity (26.3 %) and its adherence increased sharply from 24 to 72 hr, whereas Lb. amylovorus yielded the lowest hydrophobicity 3.86 % and was only weakly adherent. P. acidilactici with a hydrophobicity of 10.1 % adhered strongly. The attached LAB strains produced significantly (P < 0.05) higher total carbohydrates than their planktonic counterparts, which is an important characteristic for attachment. Three separate conditions, LAB first, LAB and L. monocytogenes concurrently and L. monocytogenes inoculated first then LAB, were simulated to evaluate the ability of the LAB cocktail (10 8 CFU/ml) to competitively exclude L. monocytogenes (103 CFU/ml) on the surface of the stainless coupons. In all the three comparisons, the LAB cocktail was able to reduce the attachment of L. monocytogenes significantly (P < 0.05). Thus, the LAB cocktail indicated attachment on stainless steel and bacteriostatic activity against L. monocytogenes attached on stainless steel. These properties may be used in manufacturing a bio-sanitizer geared to prevent the formation L. monocytogenes biofilm on food contact surfaces. Preliminary data showed L. innocua had a positive effect on the attachment of L. monocytogenes on stainless steel or aluminum surfaces.

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