Finding optimal photosensitisers for the decontamination of foods by the photodynamic effect.

A new method for sanitation based on the photodynamic effect is introduced. Photosensitisers are compounds that generate cytotoxic oxygen species and free radicals after excitation with appropriate visible light. The cell killing efficacy is due to their chemical structure, to the actual environment and therefore also to their degree of aggregation. As has been shown, photosensitisers bound to the cell wall or incorporated into the cells are very effective cytotoxic agents after illumination. Even singlet oxygen generated in the gas phase surrounding the micro-organisms effectively kills cells. Especially membrane components are the targets of the photodynamic effect. Membrane disintegration is observed soon after illumination. The food contaminants under investigation are Bacillus subtilis, Bacillus cereus, forming endospores, Staphylococcus aureus, forming a wide range of agressins, exotoxins and enterotoxins, all gram positive micro-organisms, Escherichia coli, a hygiene indicator, and the yeasts Saccharomyces cerevisiae, Kloeckera javanica, Rhodotorula mucilaginosa, a blue and a pink pigmented isolate from foods. We investigated the capacity of several photosensitisers to induce the phototoxic effect towards those micro-organisms following excitation by visible light.