Pulsed Light Inactivation of Salmonella Enteritidis on Almond Surfaces

Introduction: Almonds often are consumed raw and were the source of two outbreaks of Salmonella in 2001 and 2004. Several technologies like propylene oxide fumigation have been developed to reduce pathogens on almonds, but these have drawbacks such as hazardous chemical residues, deterioration of flavor and nutritional components, etc. Pulsed light, an emerging nonthermal technology, is proving to be effective against a myriad of microorganisms and food matrices without adversely affecting the food quality. Therefore, it shows great promise to be applied effectively for Salmonella inactivation on almond surfaces.

Purpose: To investigate the effect of pulsed light on the survival of a predetermined population of Salmonella Enteritidis(PT30), spot inoculated on the surface of almonds.

Methods: Spot-inoculated samples were exposed to pulsed light at a rate of 3 pulses/sec, for 10, 30 and 60 sec at a distance of 14.1, 16.6, and 19.2 cm from the central axis of the lamp. Samples were also intermittently treated for 60 sec with 10-sec treatment followed by a 3-min cooling period. The surviving population was enumerated.

Results: A maximum inactivation of 3.36 ± 0.19 log CFU/almond was obtained after a 30 sec exposure to pulsed light at a distance of 14.1 cm away from the lamp axis. Even a 10 sec treatment resulted in 2.88 ± 0.21 log CFU/almond reduction at 14.1 cm from the lamp axis. As expected, microbial inactivation decreased as the distance increased with reductions of 3.36 ± 0.19, 1.76 ± 0.09, 1.25 ± 0.04, and log CFU/almond were obtained at 14.1, 16.6 and 19.2 cm, respectively. Intermittent treatment of samples (10-sec treatment followed by 3-min cooling for 60 sec) resulted in up to 1.02-log CFU/almond increase in the microbial reduction depending upon the distance from the lamp housing.

Significance: Results clearly indicate that pulsed light is effective as a surface decontamination technology for inactivation of Salmonella on almond surfaces.