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. 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. 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. Experimental data support the idea that Na-Chl-based photosensitization can be a useful tool for the future development of nonthermal food preservation technology.

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 × 10⁷ 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”.