Improved process for decontamination of whey by a continuous flow-through pulsed light system

The effect of a continuous flow-through pulsed light (PL) system on the inactivation of Listeria innocua was evaluated in different liquid substrates: distilled water, whey, diluted whey and skimmed whey. Reductions in L. innocua counts increased with number of pulses and total fluence. For similar total fluence, treatments consisting of a higher number of pulses but lower voltage were more effective in L. innocua inactivation due to a higher probability to expose cells to the incident light. Microbial inactivation by PL depended on the quantity of light transmitted in the range 230–290 nm by liquid substrates. Regardless of the limited effectiveness of PL for decontamination of whey, its shelf life during storage at 4 °C was extended by at least 7 days. In order to improve the antimicrobial effectiveness of PL, this treatment could be carried out at mild processing temperatures (60 °C), which was shown to exhibit a synergistic effect on the inactivation of L. innocua. This combined process appears as a promising technique to decontaminate complex substrates such as whey or to reduce the intensity of individual treatments to achieve the required level of microbial inactivation.