title: Effective photosensitization-based inactivation of Gram (-) food pathogens and molds using the chlorophyllin-chitosan complex: towards photoactive edible coatings to preserve strawberries.
abstract: This study is focused on the novel approaches to enhance the inactivation of the Gram (-) food pathogen Salmonella enterica and harmful molds in vitro and on the surface of strawberries using the chlorophyllin-chitosan complex. Salmonella enterica (∼1 × 10(7) CFU mL(-1)) was incubated with chlorophyllin 1.5 × 10(-5) M (Chl, food additive), chitosan 0.1% (CHS, food supplement) or the chlorophyllin-chitosan complex (1.5 × 10(-5) M Chl-0.1% CHS) and illuminated with visible light (λ = 405 nm, light dose 38 J cm(-2)) in vitro. Chlorophyllin (Chl)-based photosensitization inactivated Salmonella just by 1.8 log. Chitosan (CHS) alone incubated for 2 h with Salmonella reduced viability 2.15 log, whereas photoactivated Chl-CHS diminished bacterial viability by 7 log. SEM images indicate that the Chl-CHS complex under these experimental conditions covered the entire bacterial surface. Significant cell membrane disintegration was the main lethal injury induced in Gram (-) bacteria by this treatment. Analysis of strawberry decontamination from surface-inoculated Salmonella indicated that photoactivated Chl-CHS (1.5 × 10(-5) M Chl-0.1% CHS, 30 min incubation, light dose 38 J cm(-2)) coatings diminished the pathogen population on the surface of strawberries by 2.2 log. Decontamination of strawberries from naturally distributed yeasts/molds revealed that chitosan alone reduced the population of yeasts/molds just by 0.4 log, Chl-based photosensitization just by 0.9 log, whereas photoactivated Chl-CHS coatings reduced yeasts/molds on the surface of strawberries by 1.4 log. Electron paramagnetic resonance spectroscopy confirmed that no additional photosensitization-induced free radicals have been found in the strawberry matrix. Visual quality (color, texture) of the treated strawberries was not affected either. In conclusion, photoactive Chl-CHS exhibited strong antimicrobial action against more resistant to photosensitization Gram (-) Salmonella enterica in comparison with Gram (+) bacteria in vitro. It reduced significantly the viability of strawberry surface-attached yeasts/molds and inoculated Salmonella without any negative impact on the visual quality of berries. Experimental data support the idea that photoactivated Chl-CHS can be a useful tool for the future development of edible photoactive antimicrobial coatings which can preserve strawberries and prolong their shelf-life according to requirements of "clean green technology".
authors.affiliation: Vilnius University, Institute of Applied Research, Sauletekio 10, 10223, Vilnius, Lithuania. Zivile.Luksiene@tmi.vu.lt.
authors.forename: Irina
authors.initials: I
authors.lastname: Buchovec
authors.forename: Viktorija
authors.initials: V
authors.lastname: Lukseviciute
authors.forename: Arunas
authors.initials: A
authors.lastname: Marsalka
authors.forename: Ignas
authors.initials: I
authors.lastname: Reklaitis
authors.forename: Zivile
authors.initials: Z
authors.lastname: Luksiene
mesh_terms: D048271:Chitosan / Q000737:chemistry*; D002735:Chlorophyllides / Q000737:chemistry*; D003666:Decontamination / Q000379:methods; D004578:Electron Spin Resonance Spectroscopy; D005516:Food Microbiology; D031985:Fragaria / Q000382:microbiology*; D005658:Fungi / Q000528:radiation effects*; D008027:Light; D019779:Salmonella enterica / Q000528:radiation effects*; D013050:Spectrometry, Fluorescence
chemical_list: D002735:Chlorophyllides; D048271:Chitosan; C007020:chlorophyllin