Egle Paskeviciute

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.

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.

Inactivation of several strains of Listeria monocytogenes attached to the surface of packaging material by Na-Chlorophyllin-based photosensitization

This study was focused on the possibility to inactivate thermosensitive Listeria monocytogenes ATC(L3)C 7644 and thermoresistant 56 Ly strain by Na-Chlorophyllin (Na-Chl)-based photosensitization in vitro and on the surface of packaging. Comparative analysis of antimicrobial efficiency of photosensitization with conventional surface cleaning was performed. Data indicate that both Listeria strains, after incubation with Na-Chl and following illumination (λ=400nm, 20mWcm(-2)), were inactivated by 7 log in vitro. This treatment cleaned both Listeria strains from packaging surfaces. Comparative analysis indicates that washing with water diminishes pathogens by less than 1 log, 200ppm Na-hypochlorite by 1.7 log, Na-Chl-based photosensitization by 4.5 log. Listeria biofilms were totally removed from the surface by photosensitization at higher photosensitizer concentrations and longer incubation times. In conclusion, both strains of L. monocytogenes can be effectively inactivated by photosensitization in vitro and on the surface of packaging. Listeria biofilms are susceptible to this treatment as well. Comparison of different surface decontamination treatments reveals that photosensitization is much more effective against both Listeria strains than washing with water or 200ppm Na-hypochlorite. Our data support the idea that Na-Chl-based photosensitization is an effective antimicrobial tool which may serve in the future for the development of human and environmentally friendly surface decontamination techniques.

Photosensitization-based inactivation of food pathogen Listeria monocytogenes in vitro and on the surface of packaging material.

The study was focused on the susceptibility of Listeria monocytogenes ATCL3C 7644 cells and biofilms to non-thermal antimicrobial treatment - photosensitization in vitro and after adhesion to the surface of packaging material. L. monocytogenes was incubated with 5-aminolevulinic acid (ALA) (7.5 mM) for 0-2h and illuminated with visible light. The LED-based light source used for the illumination emitted light lambda=400 nm with energy density 20 mW/cm(2). The illumination time varied 0-20 min, and a total light dose reached 0-24 J/cm(2). The obtained data indicate that L. monocytogenes produces endogenous porphyrins after incubation with 7.5mM ALA. Subsequent illumination of cells remarkably inactivates (4 log) them in vitro. Photosensitization diminished population of Listeria cells adhered onto the packaging material by 3.7 log and inactivated bacterial biofilms by 3.1 log. It was shown that antimicrobial efficiency of photosensitization depended on the illumination time, incubation with ALA time as well as on the used ALA concentration. In conclusion, cells and biofilms of L. monocytogenes ATCL3C 7644 can be effectively inactivated by ALA-based photosensitization in the solution as well as adhered onto the surface of packaging material. Obtained data support the idea, that photosensitization as non-thermal and effective antimicrobial treatment has potential to develop into environmentally safe, surface decontamination technique.

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.

Microbial control of food-related surfaces: Na-Chlorophyllin-based photosensitization.

The aim of this study was to evaluate efficiency of photosensitization as surface sanitation alternative using model systems when food pathogens, their spores and biofilms were attached to the food-related surface (polyolefine). In addition it was important to compare antibacterial efficiency of Na-Chlorophyllin (Na-Chl)-based photosensitization with conventional sanitizers. Obtained results indicate that Bacilluscereus ATCC 12826 and Listeriamonocytogenes ATCC 7644 as well as their thermoresistant strains B.cereus SV90 and L.monocytogenes 56LY were effectively inactivated (7 log) by Na-Chl-based photosensitization in vitro. Inactivation rate of thermoresistant strains was slower. The number of attached to the surface B.cereus ATCC 12826 and L.monocytogenes ATCC 7644 was reduced from 4-4.5 log to 0 log after photosensitization treatment. To achieve adequate inactivation of thermoresistant strains the higher Na-Chl concentration and longer illumination times had to be used. Comparison of different surface decontamination treatments reveal that photosensitization is much more effective against all surface-attached B.cereus and L.monocytogenes strains than washing with water or 200 ppm Na-hypochlorite. It is important to note, that surface-attached B.cereus spores and L.monocytogenes biofilms can be eliminated from it by photosensitization as well. Our data support the idea that Na-Chlorophyllin-based photosensitization has high antibacterial potential which may serve in the future for the development of human and environment friendly, non-thermal surface decontamination technique.

Towards better microbial safety of fresh produce: Chlorophyllin-based photosensitization for microbial control of foodborne pathogens on cherry tomatoes

The aim of this study is to evaluate the antimicrobial efficiency of Chlorophyllin-based photosensitization for microbial control of cherry tomatoes. Chlorophyllin-based photosensitization (1.5 × 10-4 M, 3 J/cm2) significantly (2.4 log) reduced the population of naturally distributed surface attached various mesophilic bacteria (microbiota) on tomatoes. Moreover, the population of thermoresistant strains of food pathogens Bacillus cereus and Listeria monocytogenes inoculated on tomatoes was reduced by 1.5 log and 1.6 log respectively after this treatment. Conventional washing with water reduced the population of Listeria on tomato by 0.6 log and Bacillus by 0.8 log. In comparison, hypochlorite treatment reduced Listeria on tomatoes by 1.4 log and Bacillus by 1.6 log. The regrowth of mesophilic bacteria and thermoresistant Listeria on the surface of tomatoes after photosensitization was delayed for 28 days and 14 days respectively. Moreover, photosensitization did not induce harmful effects on main parameter of nutritional quality of tomatoes, i.e. antioxidant activity of tomatoes remained unchanged (27.5 mM Fe2+/kg). Eventually, this treatment did not induce visible thermal effects in fruit matrix and prolonged the shelf-life of tomatoes by 4 days. In our opinion, chlorophyllin-based photosensitization has a huge potential as alternative to not-chemical food preservation technology, saving water and energy. In addition, fast development of light emitting diodes (LEDs) and light sources based on LED technologies make this treatment low cost, environmentally friendly and easy to maintain.