Author

Yao Chen

Date of Award:

5-2014

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Agricultural Systems Technology and Education

Advisor/Chair:

Marie K. Walsh

Abstract

Listeria monocytogenes leads to severe health problems and is the third leading cause of death among the major 5 pathogens. A synthesized novel sugar ester, lactose monolaurate (LML), has antimicrobial properties against Listeria monocytogenes. The minimum bactericidal concentration (MBC) of LML is less than 5 mg/mL (9.5 mM) in growth media. To determine which moiety of LML dominates in its bacteriostatic activities, the antibacterial effect of lactose, lauric acid and Tween 20 were tested. Lactose has no inhibition effect on Listeria. Lauric acid and Tween 20 had some antimicrobial effect (3.48 and 1.59 log reduction respectively), but did not have a bactericidal effect as LML did. To determine the antibacterial effect of LML on L. monocytogenes a 5-strain cocktail of L. monocytogenes with an initial concentration of approximately 5 log CFU/mL was incubated in milk, yogurt and cottage cheese. The effects were determined via plate counts after 24-hour incubation at 37°C. LML had at least a 4 log reduction and killed all the bacteria at 5 mg/mL in fat-free milk, fat-free drinkable yogurt, 1% fat drinkable yogurt, and fat-free cottage cheese. LML also showed bacteriostatic effect in low-fat milk, whole milk, 1.5% fat drinkable yogurt, and 2% fat cottage cheese with a log reduction varying from 3.54 to 4.35. These tests showed that the antibacterial effect of LML was related to the fat content of the dairy products as well as temperature. LML only inhibited Listeria at room temperature (37°C) and showed no inhibitive effects at refrigeration temperature (4°C). LML can inhibit the viable but nonculturable state of Listeria monocytogenes for up to 6 weeks at room temperature.

Included in

Food Science Commons

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