Effective inactivation of food pathogens Listeria monocytogenes and Salmonella enterica by combined treatment of hypericin-based photosensitization and high power pulsed light.

AIMS: The aim of this study was to evaluate the inactivation efficiency of Listeria monocytogenes ATC(L3) C 7644 and Salmonella enterica serovar Typhimurium strain DS88 by combined treatment of hypericin (Hyp)-based photosensitization and high power pulsed light (HPPL). METHODS AND RESULTS: Cells were incubated with Hyp (1 × 10(-5) or 1 × 10(-7) mol l(-1)) in PBS and illuminated with a light λ = 585 nm. For the combined treatment, bacteria were, after photosensitization, exposed to 350 pulses of HPPL (UV light dose = 0·023 J cm(-2)). Fluorescence measurements were performed to evaluate optimal time for cell-Hyp interaction. Results indicate that Hyp tends to bind both Listeria and Salmonella. After photosensitization treatment, Listeria population was reduced 7 log, whereas Salmonella was inactivated just 1 log. Electron photomicrograps of Salmonella and Listeria confirmed that photosensitization induced total collapse of the Listeria cell wall, but not that of Salmonella. After combined photosensitization-HPPL treatment, the population of Listeria was diminished by 7 log and Salmonella by 6·7 log. CONCLUSIONS: Listeria can be effectively inactivated by Hyp-based photosensitization (7 log), whereas Salmonella is more resistant to photosensitization and can be inactivated just by 1 log in vitro. Combined treatment of photosensitization and pulsed light inactivates effectively (6·7-7 log) both the Gram-positive and the more resistant to photosensitization Gram-negative bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: A new approach to combat Gram-positive and Gram-negative bacteria is proposed, combining photosensitization with high power pulsed light.

Advanced high-power pulsed light device to decontaminate food from pathogens: effects on Salmonella typhimurium viability in vitro.

AIMS: The aim of this study was to construct an advanced high-power pulsed light device for decontamination of food matrix and to evaluate its antibacterial efficiency. Key parameters of constructed device-emitted light spectrum, pulse duration, pulse power density, frequency of pulses, dependence of emitted spectrum on input voltage, irradiation homogenicity, possible thermal effects as well as antimicrobial efficiency were evaluated. METHODS AND RESULTS: Antimicrobial efficiency of high-power pulsed light technique was demonstrated and evaluated by two independent methods - spread plate and Miles-Misra method. Viability of Salmonella typhimurium as function of a given light dose (number of pulses) and pulse frequency was examined. According to the data obtained, viability of Salmonella typhimurium reduced by 7 log order after 100 light pulses with power density 133 W cm(-2). In addition, data indicate, that the pulse frequency did not influence the outcome of pathogen inactivation in the region 1-5 Hz. Moreover, no hyperthermic effect was detected during irradiation even after 500 pulses on all shelves with different distance from light source and subsequently different pulse power density (0-252 W cm(-2)). CONCLUSION: Newly constructed high-power pulsed light technique is effective nonthermal tool for inactivation of Salmonella typhimurium even by 7 log order in vitro. SIGNIFICANCE AND IMPACT OF THE STUDY: Novel advanced high-power pulsed light device can be a useful tool for development of nonthermal food decontamination technologies.

Implementation of diffractive optical element in four-wave mixing scheme for ex situ characterization of hydride vapor phase epitaxy-grown GaN layers.

A holographic beam splitter has been integrated into a picosecond four-wave mixing (FWM) scheme. This modification significantly simplified the procedure of dynamic grating recording, thus making the FWM technique an easy-to-use tool for the holographic characterization of wide band gap materials. The novel FWM scheme was applied for characterization of hydride vapor phase epitaxy-grown undoped GaN layers of different thickness. It allowed the determination of carrier lifetime, diffusion coefficient, and carrier diffusion length by optical means, as well as the study of carrier recombination peculiarities with respect to dislocation and excess carrier density.

Evaluation of photoelectric processes in photorefractive crystals via the exposure characteristics of light diffraction.

We demonstrate a novel way to analyse carrier recombination and transport processes in photorefractive semiconductors via the exposure characteristics of light induced diffraction. The results of a picosecond four-wave mixing on free carrier gratings in semi-insulating GaAs crystals at various grating periods and modulation depths of a light interference pattern are discussed. The role of a deep-trap recharging in carrier diffusion and recombination is sensitively revealed through a feedback effect of a space-charge field to non-equilibrium carrier transport.