Transportation is central to the global food and feed supply chain. Thus issues of safety, especially cross contamination with pathogens during food transit should be important in food handling operations. A large proportion of the worlds’ food cargo is moved using intermodal cargo containers, either with refrigerated units or otherwise. Foodborne pathogenic disease outbreaks have caused havoc including loss of lives, permanent morbidity, ailments with high costs of treatment and even collapse of businesses in various parts of the wold. With transportation needed in so many stages of the food chain, its role in food safety cannot be ignored.
Unfortunately not much effort has been put, scientifically, into understanding the role of the various features of the transportation links in food cross contamination (compared to studies for homes, processing factories and farm yards). The PhD project has attempted to shed light on containerized food transport and some of its important attributes as regards hygiene and cross contamination. The overall aim of the study was to ‘identify possible microbial hazards and ways of cross contamination during containerized transportation of foods and to identify means to prevent the attachment, establishment and survival of pathogenic microorganisms on both biotic and abiotic surfaces relevant for containerized transport’.
This thesis begins with a review of the literature to guide the reader into some important aspects of the project. Important pathogens involved in foodborne disease outbreaks and their use in the present study have been discussed. Both Gram negative and Gram positive bacteria have been used in various experiments. The history of containerized transportation and its revolutionary role in the world of commerce is also briefly traced. With regards to transporting of food cargo, the design features of standard cargo containers (reefers) were examined from a hygienic perspective with special focus on the materials used as linings for the interior and other structures that may be considered incidental food contact surfaces. Bacteria cross contamination scenarios involving both biotic and abiotic surfaces alongside the factors affecting the process have been briefly discussed. Cleaning and disinfection scenarios in related food hygiene environments have been looked into in the literature as well.
The experimental work was in several phases. Firstly, the attachment and detachment of bacteria pathogens on container lining materials and apple (food) surfaces were investigated in the absence and presence of food residue. The number of attached cells for the two organisms studied, Escherichia coli and Salmonella Typhimurium, was negatively correlated with hydrophobicity of the three surface studied – aluminium, stainless steel and fibre re-enforced plastic (FRP). The presence of residue caused a reduction in the hydrophobicity of the materials in addition to reducing the number of attached cells. However attached cells were significantly more difficult to detach or wash-off in presence of residue. The presence of chicken residue also caused a reduction or increase in cells attaching to apple surfaces depending on the scenario.
The use of UV-radiation in assessing the cleanliness of surfaces was also investigated. This was done to understand the role of selected wavelengths and the type of surface material on the sensitivity of detecting various food residues on the surfaces. Wavelengths in the 365-445 nm regions consistently illuminated both plant and animal food residue to different extents; the optimal wavelength differed for various residues depending on the surface material. The need to select the right lamp/wavelength especially for environments with composite materials such as is the case for most cargo containers in use today was thus highlighted and discussed.
An evaluation of how practical common cleaning and disinfecting agents are was made with a view to assessing both their corrosive tendencies and effectiveness in inactivating selected test organisms. Assays were performed on bacteria in suspension as well bacteria dried onto coupons of the three test surfaces mentioned above. Peracetic acid was found to be the most practical and effective of the agents tested as it inactivated all pathogens tested at typical in-use concentrations, in addition to having the least corrosive effect. It is also known to breakdown readily in the environment. A usability index combining data from disinfection efficacy assays and corrosion tests provided a useful way of choosing the right disinfectant for containers having linings composed of diverse materials.
Experiments were also conducted to understand the various (micro)-environmental factors that are critical in the survival and transfer of pathogens under transit conditions. This involved exposure of test bacteria dried onto the test surfaces, to various controlled condition sets. The results showed that the relative humidity (RH), presence of food residue, surface type, temperature and the atmosphere that pathogens on container lining surfaces are exposed to during food cargo transit all affect their survival in the transportation scenarios studied. The presence of residue resulted in significantly higher survival levels of all the pathogens under all the conditions on all surfaces. The specific atmosphere in the enclosures affected survival, but in a more species-specific fashion; the Gram negative bacteria survived at significantly higher levels in modified atmosphere (MA; 2% O2, 6% CO2 and 92% N2) than in atmospheric air. Initial experiments were done to the test the hypothesis that pathogens exposed to transportation conditions may express changes in virulence and transfer characteristics. As not much data was obtained due to some setbacks and time limitations, only the hypothesis and supporting literature are discussed in the text with perspectives for its consideration in future work.
This project has demonstrated the need for good hygienic design of the containers, beginning with choice of construction materials (linings) as well as the need for prompt and effective removal, cleaning and disinfection of residue and pathogens from incidental food contact surfaces in the containers. Measures such as instituting and enforcing HACCP based programs for the container handling operations will also prove useful in reducing cross contamination in containerized food transport.