Novel approach to the microbial decontamination of strawberries: chlorophyllin-based photosensitization.

AIMS: This study is focused on the possibility to control microbial contamination of strawberries by chlorophyllin (Na-Chl)-based photosensitization. Moreover, photosensitization-induced effects on key quality attributes of treated strawberries was evaluated. METHODS AND RESULTS: Strawberries were inoculated with Listeria monocytogenes ATC(L3) C 7644, soaked in 1mmol l(-1) Na-Chl for 5 min and illuminated for 30 min with visible light (λ = 400 nm, energy density 12 mW cm(-2) ). Results indicated that the decontamination of strawberries using photosensitization was 98% compared to control sample. Naturally occurring yeasts/microfungi and mesophiles were inhibited by 86 and 97%, respectively. The shelf life of treated strawberries was extended by 2 days. The total antioxidant activity of treated strawberries increased by 19%. No impact on the amount of phenols, anthocyanins or surface colour was detected. CONCLUSIONS: Photosensitization may be an effective, nonthermal and environmentally friendly microbial decontamination technique which expands the shelf life of strawberries without any negative impact on antioxidant activity, and phenols, anthocyanins or colour formation. SIGNIFICANCE AND IMPACT OF THE STUDY: Experimental data support the idea that Na-Chl-based photosensitization can be a useful tool for the future development of nonthermal food preservation technology.

Inactivation of Bacillus cereus by Na-chlorophyllin-based photosensitization on the surface of packaging.

AIMS: This study was focused on the possibility to inactivate food-borne pathogen Bacillus cereus by Na-chlorophyllin (Na-Chl)-based photosensitization in vitro and after attachment to the surface of packaging material. METHODS AND RESULTS: Bacillus cereus in vitro or attached to the packaging was incubated with Na-Chl (7·5×10(-8) to 7·5×10(-5) mol l(-1) ) for 2-60min in phosphate buffer saline. Photosensitization was performed by illuminating cells under a light with a λ of 400nm and an energy density of 20mW cm(-2) . The illumination time varied 0-5min and subsequently the total energy dose was 0-6J cm(-2) . The results show that B. cereus vegetative cells in vitro or attached to the surface of packaging after incubation with 7·5×10(-7) mol l(-1) Na-Chl and following illumination were inactivated by 7log. The photoinactivation of B. cereus spores in vitro by 4log required higher (7·5×10(-6) mol l(-1) ) Na-Chl concentration. Decontamination of packaging material from attached spores by photosensitization reached 5log at 7·5×10(-5) mol l(-1) Na-Chl concentration. Comparative analysis of different packaging decontamination treatments indicates that washing with water can diminish pathogen population on the surface by <1log, 100ppm Na-hypochlorite reduces the pathogens about 1·7log and 200ppm Na-hypochlorite by 2·2log. Meanwhile, Na-Chl-based photosensitization reduces bacteria on the surface by 4·2 orders of magnitude. CONCLUSIONS: Food-borne pathogen B. cereus could be effectively inactivated (7log) by Na-Chl-based photosensitization in vitro and on the surface of packaging material. Spores are more resistant than vegetative cells to photosensitization-based inactivation. Comparison of different surface decontamination treatments indicates that Na-Chl-based photosensitization is much more effective antibacterial tool than washing with water or 200ppm Na-hypochlorite. SIGNIFICANCE AND IMPACT OF THE STUDY: Our data support the idea that Na-Chl-based photosensitization has great potential for future application as an environment-friendly, nonthermal surface decontamination technique.

Inactivation of food pathogen Bacillus cereus by photosensitization in vitro and on the surface of packaging material.

AIMS: The study was focused on the possibility to inactivate food pathogen Bacillus cereus by 5-aminolevulinic acid (ALA) - based photosensitization in vitro and after adhesion on the surface of packaging material. METHODS AND RESULTS: Bacillus cereus was incubated with ALA (3-7.5 mmol l(-1)) for 5-60 min in different environment (PBS, packaging material and wheat grains) and afterwards illuminated with visible light. The light source used for illumination emitted light at lambda = 400 nm with energy density at the position of the cells, 20 mW cm(-2). The illumination time varied from 0 to 20 min, and subsequently a total energy dose was between 0 and 24 J cm(-2). The obtained results indicate that B. cereus after the incubation with 3-7.5 mmol l(-1) ALA produces suitable amounts of endogenous photosensitizers. Following illumination, micro-organism inactivated even by 6.3 log. The inactivation of B. cereus after adhesion on the surface of food packaging by photosensitization reached 4 log. It is important to note that spores of B. cereus were susceptible to this treatment as well; 3.7-log inactivation in vitro and 2.7-log inactivation on the surface of packaging material were achieved at certain experimental conditions. CONCLUSIONS: Vegetative cells and spores of Gram-positive food pathogen B. cereus were effectively inactivated by ALA-based photosensitization in vitro. Moreover, the significant inactivation of B. cereus adhered on the surface of packaging material was observed. It was shown that photosensitization-based inactivation of B. cereus depended on the total light dose (illumination time) as well as on the amount of endogenous porphyrins (initial ALA concentration, time of incubation with ALA). SIGNIFICANCE AND IMPACT OF THE STUDY: Our previous data, as well as the one obtained in this study, support the idea that photosensitization with its high selectivity, antimicrobial efficiency and nonthermal nature could serve in the future for the development of completely safe, nonthermal surface decontamination and food preservation techniques.