Aims:  Salmonellosis is one of the most common foodborne diseases in the world. The aim of this study was to evaluate the antibacterial efficiency of 5‐aminolevulinic acid (ALA) based photosensitization against one of food pathogens Salmonella enterica. Methods and Results:  Salmonella enterica was incubated with ALA (7·5 mmol l−1) for 1–4 h and afterwards illuminated with visible light. The light source used for illumination of S. enterica emitted light λ = 400 nm with energy density 20 mW cm−2. The illumination time varied from 0 to 20 min and subsequently a total energy dose reached 0–24 J cm−2. The data obtained indicate that S. enterica is able to produce endogenous photosensitizer PpIX when incubated with ALA. Remarkable inactivation of micro‐organisms can be achieved (6 log) after photosensitization. It is obvious that photosensitization‐based inactivation of S. enterica depends on illumination as well as incubation with ALA time. Conclusion:  ALA‐based photosensitization can be an effective tool against multi‐drug resistant Gram‐negative bacteria S. enterica serovar Typhimurium. Significance and Impact of the Study:  Experimental data and mathematical evaluations support the idea that ALA‐based photosensitization can be a useful tool for the development of nonthermal food preservation technology in future.

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The aim of this study was to develop modern light technology (photosensitization) for non-thermal decontamination of different surfaces including food. For this purpose a light emitting diode (LED) based light source was constructed. The highpower LEDs (mfr Seoul Semiconductors) with peak wavelength at 400 nm were mounted within the prototype of light source. Antimicrobial action of aminolevulinic acid-based photosensitization was evaluated using three pathogenic bacteria (Bacillus, Listeria, and Salmonella) usually distributed on the surface of food. Pathogen inactivation by almost 6-7 orders of magnitude was achieved by ALA-based photosensitization. We suggest mathematical description for kinetics of the bacteria number within inactivation process, which is in good agreement with experimental data. Theoretical analysis of the experimental data helps in revealing the optimal conditions for food decontamination process.

We report on the investigation of electroluminescence (EL) modulation depth as a function of photon energy in a high-power double-heterojunction AlGaInP light-emitting diode (LED). At low frequencies, the modulation spectrum exhibits the features as follows: (i) a dip at the photon energy close to the EL spectrum peak; (ii) an almost wavelength-independent modulation enhancement in the long-wavelength wing of the EL spectrum; and (iii) a linear increase of the modulation depth with photon energy in the short-wavelength wing of the EL spectrum. With increasing modulation frequency, these features diminish but do not disappear. A model, which quantitatively accounts for the experimental data has been introduced. At low frequencies, the spectral modulation features are due mainly to the modulation of EL efficiency, bandgap energy and the carrier distribution function caused by the oscillation of junction temperature. In the high-frequency limit when the oscillation of junction temperature fades, the spectral modulation features can be understood in terms of asymmetrical EL band broadening due to athermal many-body effects. The investigation of spectrally resolved EL modulation was shown to be applicable for the estimation of small (∼0.1 K) junction temperature oscillation and thermal relaxation time constants of LEDs emitting due to band-to-band recombination of free carriers.

The forward voltage, series resistance, and junction conductivity of commercial high-power InGaN light-emitting diodes (LEDs) were investigated as a function of aging time. A gradual decrease of series resistance with a rate of about −1%/1000 h was revealed in InGaN LEDs within first ∼9,600 hours of aging under ordinary conditions (nominal forward current 350 mA, junction temperature 350 K), whereas the characteristic energy of tunnel injection exhibited a decrease with a rate of about −0.1%/1000 h. The observed aging effects were attributed to continuous post-fabrication self-annealing of the p-type cladding layer and to the variation of the localized-state density in the active layer of the LED chips.