| Author: | Chan, Kai-leung |
| Title: | Photodynamic inactivation of foodborne microorganisms |
| Degree: | M.Sc. |
| Year: | 2007 |
| Subject: | Hong Kong Polytechnic University -- Dissertations. Food -- Microbiology. Food -- Analysis. Photosensitizing compounds. |
| Department: | Department of Health Technology and Informatics |
| Pages: | x, 74 leaves : ill. (chiefly col.) ; 30 cm. |
| Language: | English |
| Abstract: | Aims: This project aims to explore the photodynamic inactivation potential of two different photosensitizers, PS-Tricyclic (PS-3) and PS-Tetrapyrrole (PS-4) by halogen lamp towards three selected foodborae microorganisms, Staphylococcus aureus, Salmonella, and Bacillus cereus; and one food safety indicator microorganism (for faecal contamination) Escherichia coli. As well as to study the effects of two different light sources (halogen and tungsten lamps) on the photodynamic inactivation of PS-3 and PS-4 at 4 oC against the above named microorganisms. Moreover, the effects of temperature on photodynamic inactivation of two photosensitizers were investigated. In addition, the possibilities of applications for photodynamic inactivation on food surface disinfection were explored. Methods: Three selected foodbome microorganisms, Staphylococcus aureus. Salmonella, and Bacillus cereus; and one food safety indicator microorganism, Escherichia coli were treated with PS-3 and PS-4, for photodynamic inactivation under different drug concentrations and light doses including halogen lamp versus tungsten lamp. Viability was evaluated by monitoring the bacterial colony forming ability. Known concentrations of the proposed organisms were sprayed on four different food samples (BBQ pork inoculated with Staphylococcus aureus, cold cut-sausage inoculated with Bacillus cereus, salad inoculated with Salmonella, and Sashimi inoculated with Escherichia coli); after photodynamic inactivation treatment on food surface and in PBS suspensions, the survival organisms were enumerated and compared to the control sample. Results: All the isolates were successfully photoinactivated by the PS-3 and PS-4. The degree of photodynamic inactivation was dependent on the drug concentrations and the light doses for the strains of Staphylococcus aureus, Bacillus cereus, Salmonella, and Escherichia coli isolates. The photodynamic activities of PS-3 (2.66mM, 115J/cm2) at 4 oC under halogen lamp irradiation exhibited 1.9 logs killing for Staphylococcus aureus, 1.6 logs killing for Bacillus cereus, 1.3 logs killing for Salmonella, and 1.4 logs killing for Escherichia coli. For PS-4 (1.38mM, H5J/cm2) at 4 oC under halogen lamp irradiation, it exhibited 3.0 logs killing for Staphylococcus aureus and Bacillus cereus, 1.6 logs killing for Salmonella, and 1.7 logs killing for Escherichia coli. For food surface disinfection, PS-3 (2.66mM, 115J/cm2) at 4 oC under halogen lamp irradiation exhibited 0.7 logs killing for Staphylococcus aureus and Bacillus cereus, 0.3 logs killing for Salmonella, and 0.4 logs killing for Escherichia coli. For PS-4 (1.38mM, 115J/cm2) at 4 oC under halogen lamp irradiation, exhibited 1.6 logs killing for Staphylococcus aureus and Bacillus cereus, 0.8 logs killing for Salmonella and Escherichia coli, Photodynamic inactivation of PS-3 (2.66mM, 115J/cm2) and PS-4 (1.38mM, 115J/cm2) were varied at different irradiation temperatures. Comparing the photodynamic inactivation efficacy of low irradiation temperature (4 oC) and high irradiation temperatures (26 oC and 29 oC), the killing effects at 4 oC were obviously higher than that of at 26 oC and 29 oC. Additionally, the results showed that photodynamic inactivation process was found to be light sources dependent. Halogen and tungsten filament lamps showed different photodynamic inactivation activity under the same energy output. Halogen lamp was found to possess higher photodynamic inactivation efficiency. Conclusion: These results indicated that PS-3 and PS-4 may represent useful alternatives over conventional antimicrobial treatment of selective isolates. |
| Rights: | All rights reserved |
| Access: | restricted access |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| b23056009.pdf | For All Users (off-campus access for PolyU Staff & Students only) | 2.88 MB | Adobe PDF | View/Open |
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