Survival and growth of Listeria innocua treated by pulsed light technology: Impact of post-treatment temperature and illumination conditions

Inactivation of Listeria innocua by pulsed light (PL) was evaluated at different post-treatment temperature and illumination conditions. The impact of post-PL-treatment temperature on L. innocua culturability was evaluated for cells cultured at 37 °C (optimal growth temperature) and 4 °C (classical refrigerated food temperature). For both culture conditions, significant higher reductions (up to 3 log) were observed after post-PL-treatment temperature of 4 °C than of 37 °C. Contrarily, L. innocua culturability after PL treatment increased up to 2.2 log in presence of daylight illumination in comparison to dark storage. This photorepair mechanism was quickly activated reaching the maximum photoreactivation level after only 30 min of illumination. Moreover, photorepair capacity was rapidly reduced by increasing the time in darkness from PL treatment to samples illumination, being completely lost after time in darkness equal or greater than 5 h. According to these findings, the combination of PL with post-treatment temperature of 4 °C has a synergistic effect on the inactivation of L. innocua, whereas post-treatment daylight illumination has an antagonic effect on PL antimicrobial efficacy. Post-PL-treatment temperature and illumination conditions could be thereby considered important environmental factors to activate, inhibit or control the repair and/or growth of L. innocua survivors after PL treatment.