Inactivation of food pathogenBacillus cereusby photosensitizationin vitroand on the surface of packaging material

Abstract

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. 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. 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). 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.