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USE OF AQUEOUS DISPERSIONS OF SDS MICELLES TO REMOVE BACTERIAL CONTAMINATION FROM FRESH PRODUCE AND FOOD CONTACT SURFACES
Title
USE OF AQUEOUS DISPERSIONS OF SDS MICELLES TO REMOVE BACTERIAL CONTAMINATION FROM FRESH PRODUCE AND FOOD CONTACT SURFACES
Creator
Han, Yibin
Date
2013-04-30, 2013-05
Description
The current trend of increased consumption of fresh produce has coincided with an increase in foodborne illness resulting from fresh produce...
Show moreThe current trend of increased consumption of fresh produce has coincided with an increase in foodborne illness resulting from fresh produce consumption, which in turn has increased the amount of research directed at understanding the interactions between microbial pathogens and fresh produce. This dissertation examines the removal and inactivation of Escherichia coli O157:H7 and E. coli K12 from Romaine lettuce leaves and a model hydrophobic surface (polyvinyl chloride, PVC) using a nanofluid (a fluid containing nanometer-sized particles - in this case, sodium dodecyl sulfate, SDS) and its combinations with organic acids. A novel mechanism previously proposed by Wasan and Nikolov (D. T. Wasan & Nikolov, 2003) was used as the basis to explore the removal of bacteria from these surfaces by the aqueous dispersion of SDS micelles, and to explain how SDS plus levulinic acid at pH<3 improves inactivation of these bacteria. Examination of the bactericidal effect of levulinic acid, SDS, and their combination on E. coli O157:H7 attached to Romaine lettuce leaves revealed that using levulinic acid or SDS alone cannot effectively wash the bacterial cells from the surface or cause inactivation. However, combining them increased the effectiveness of the solution. The most effective combination of SDS plus acid for bacteria removal and inactivation among those we tested was found to be 0.06 mol/L SDS + 0.25 mol/L levulinic acid. This combination, which has a pH of 2.9, inactivated more than 5.2-log E. coli O157:H7 on a leaf surface, and similar results were achieved for E. coli K12 on a leaf surface, and for both E. coli O157:H7 and E. coli K12 on the surface of PVC. Surface and interface measurements, including x surface tension and contact angle, of washing solutions indicated that solutions containing SDS had a lower work of adhesion than those without the surfactant, which shows that a significant role of SDS in the inactivation mechanism is a weakening of the forces of attraction between the bacteria and the surface being cleaned. Our experiments also confirm that SDS likely plays a secondary role which depends on the solution pH. When the presence of an organic acid lowers the pH of the washing solution to below 2.6, the surface charge of E. coli O157:H7 changes from negative to positive (the pH is lower than the bacteria’s isoelectric point). In this case, we hypothesize that negatively-charged SDS molecules attach to the cells’ surfaces and inactivate the bacteria. This work provides additional insight into the complex nature of bacterial detachment from solid surfaces. Our work with aqueous dispersions of SDS micelles indicates how and why bacterial inactivation is increased through a combination treatment of SDS and an organic acid.
M.S. in Food Safety and Technology, May 2013
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