The cross-contamination of foods, especially raw fish and seafood products, is an important food safety problem. Seafood products can be cross-contaminated at the working environment, when food contact surfaces (e.g. processing equipment, utensils, knives, etc) bear a high number of microorganisms. In addition, raw seafood products can become contaminated when food handlers do not follow good manufacturing practices. Another important source of cross-contamination can be the ice in contact with raw seafood products and the water from this melted ice. Since ice is extensively used as a preservation method, ice prepared with safe sanitizers could be a promising alternative to reduce the potential for cross-contamination from raw fish and seafood products.
The first part of this thesis (Chapter 2) reports an investigation on the stability (melting rate) of ice prepared with neutral electrolyzed water (NEW) and PRO-SAN® sanitizers and compared them with the stability of ice prepared with tap water. This first part also evaluated the efficacy of the sanitized ice in reducing the natural microbial burden on whole fish samples and in the ice used to store the fish. In addition, the efficacy of sanitized ice in reducing Escherichia coli K-12, Listeria innocua and Pseudomonas putida populations on Tilapia fish fillet samples and in storage ice was alsoevaluated. This was done by enumerating each bacterial species on the fish fillet and in the water from the melted ice at 12 and 24 hour intervals.
This study found that sanitizing the ice did not affect its stability when compare with the control. Also, this study revealed that ice prepared with PRO-SAN® was effective in reducing the natural microflora washed off from the whole fish in both the water from the melted ice and in the ice that was in contact with the fish. In addition, this study found that ice prepared with PRO-SAN® and the NEW sanitizers had the ability to produce at least a 4 log reduction in E. coli, L. innocua and P. putida populations in the water collected when the ice melted. However, the overall reductions in the bacterial species on the fish fillet samples stored on sanitized ice were not different than the reductions obtained for the ice prepared with tap water.
The second part of this thesis (Chapter 3) reports an investigation of the mechanisms used by PRO-SAN® and the NEW sanitizers to cause injury to the cells of E. coli K-12 and L. innocua. This was done by examining the bacterial cells using the transmission electron microscopic technique. The transmission electron microscope (TEM) images showed that the sanitizers altered the cell wall, internal membrane of E. coli and L. innocua. The results obtained for L. innocua revealed that this bacterium was more resistant to the bactericidal action of the NEW and PRO-SAN® sanitizers. This second part of this thesis confirmed that the mechanism used by various sanitizers against target microorganisms can be studied and understood using TEM.