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".

Photodynamic inactivation of foodborne bacteria by eosin Y

“…Recently, curcumin mediated photodynamic action could inactivate Vibrio parahaemolyticus in oysters and improve the shelf-life Wu et al 2016). In addition, photosensitization provided a novel approach for decontaminating fruits and vegetables (Luksiene and Paskeviciute 2011;Aponiene et al 2015;Buchovec et al 2016).…”

Efficacy of photoactivated curcumin to decontaminate food surfaces under blue light emitting diode

“…Visible LED illumination with or without exogenous photosensitizers has been reported to exhibit antibacterial effects on various pathogenic bacteria (Kim, Tang, Bang, & Yuk, 2017;Luksiene, Pe ciulyte, Jurkoniene, & Puras, 2005;Maclean et al, 2009;Nitzan, Salmon-Divon, Shporen, & Malik, 2004). Nevertheless, the inactivation of bacteria on the surface of foods or solids by visible LED light was relatively limited (Buchovec, Lukseviciute, Marsalka, Reklaitis, & Luksiene, 2016;Kim, Tang, et al, 2017;Murdoch et al, 2012). Buchovec et al (2016) combining chlorophyllin-chitosan complex and a 405 nm LED light source was able to reduce about 7.0 log cfu/ml of Salmonella enterica in liquid suspension.…”

Perspectives and Trends in the Application of Photodynamic Inactivation for Microbiological Food Safety

“…Illumination was performed from the top and the bottom using 405 nm LEDs, with the intensities on the top end and the bottom end of the strawberries being 10 and 11 mW/cm 2 , respectively. A dose of 38 J/cm 2 caused approximately a 2 log CFU/g reduction in the population of the pathogen and nearly a 1.5 log CFU/g reduction in the total yeasts and molds (Buchovec, Lukseviciute, Marsalka, Reklaitis, & Luksiene, ).…”

“…might prevent the contamination of not only the packaging material but through controlled release, also the packaged food. In addition to the use of edible Chl-Chs coatings discussed previously (Buchovec et al, 2016), studies in clinical medicine have demonstrated the feasibility of using erythrosine-loaded chitosan nanoparticles and porphyrin-loaded cellulose nanocrystals for inactivating several pathogenic bacteria (Carpenter, Feese, Sadeghifar, Argyropoulos, & Ghiladi, 2012;Chen, Chen, & Tsai, 2012). Food choices are significantly influenced by sensory attributes, an important example of which is color.…”