Pulsed light as a non-thermal technology for food decontamination

Pulsed light (PL) has been proposed as a non-thermal food preservation strategy due to its effectiveness in inhibiting microbial growth and degrading mycotoxins by the production of oxygen and nitrogen radical species that oxidize cell membranes, inhibit DNA synthesis, and change the chemical structure of mycotoxins reducing their toxicity. Being an emerging technology, its effect on many food matrices is still under evaluation. Therefore, a thorough investigation of its potential against a broad spectrum of microorganisms and mycotoxins becomes necessary. The present study aims to explore possible application strategies of PL on two different food products: cold-smoked salmon and lupin beans. In the former, the study focuses on the effectiveness of PL against a foodborne pathogen, Listeria monocytogenes; in the latter, the detoxification of phomopsin-A (PHO-A), a mycotoxin responsible of severe animal diseases and potentially harmful for humans, was evaluated. Different PL treatments, measured in terms of combinations of energy, treatment time, number of bursts, and frequency, were applied by using a Xenon X-1100 pulsed light system on cold-smoked salmon fillets inoculated with the foodborne pathogen Listeria monocytogenes, and on lupin beans inoculated by a PHO-A-producing, phytopathogenic fungus, Diaporte toxica. The antilisterial efficacy of PL was evaluated by microbiological analysis on selective medium. Instead, the efficacy of PL in reducing mycotoxin concentration in lupin beans was evaluated by PHO-A quantification using SPE extraction followed by UHPLC-MS/MS analysis. Results showed great antibacterial activity against L. monocytogenes, with a significant load reduction in all the evaluated treatments and a maximum reduction of 1 log CFU g-1, when using 30 pulses, 230.0 J energy, 0.333 Hz frequency. Remarkably, increased pulsed light dose did not enhance the load reduction. Concerning the mycotoxin degradation, also in this case PL showed an activity in all the tested parameters combinations, but PHO-A reduction did not show a regular trend; in fact, the highest treatment intensities did not increase reduction. The best result was achieved by the use of the following parameters: 240 pulses, 230.0 J energy, frequency of 0.333 Hz. In conclusion, results highlighted a good potential of PL for both decontamination of cold-smoked salmon from L. monocytogenes and detoxification of PHO-A from lupin beans. Therefore, the great potential of PL as a novel decontamination technology has been demonstrated. Notably, in all cases, an increased intensity of the treatment did not produce an enhancement of the effectiveness. This parameter is of paramount importance for the application of PL treatments to food matrices, indicating that a tailor-made process should be developed and applied based on the substrate. Moreover, a thorough investigation of the treatment target is vital for large-scale applications, since bacteria, fungi and mycotoxins demonstrated relevant differences in the effects of PL treatments.