Influence of processing parameters on the pulsed-light inactivation of Penicillium expansum in apple juice

The objective of this study was to evaluate the efficiency of pulsed light treatments on the inactivation of Penicillium expansum inoculated in apple juice. Different critical processing parameters, namely fluence (0.2 and 0.4 J/cm2 per pulse), number of pulses (5, 10, 15, 20, 30 and 40 flashes applied from opposite product sides), depth of the juice layer (6, 8, 10 mm) and inoculation level (2.3 × 104 CFU/mL and 3 × 105 CFU/mL) were studied regarding their effect on microbial inactivation. Moulds inactivation increased with increasing number of pulses and fluence. Treatments led to microbial reductions of up to 3.76 log CFU/mL. Inactivation levels achieved with treatments performed on thin layers of juice (6 mm) were substantially higher than those observed after applying the same treatments on deeper layers of 8 or 10 mm. As well, P. expansum inactivation in juice samples with lower initial counts was greater than in samples with higher counts. Minor changes were noticed after PL treatments regarding juice pH and soluble solids; however, apple juice colour slightly darkened after applying and overall fluence of 32 J/cm2 (40 pulses of 0.4 J/cm2 from both upper and bottom sides). The obtained results suggest that PL-technology can be applied to efficiently reduce P. expansum counts in apple juice while maintaining the product quality.