Laser Labeling of Valencia Oranges Does Not Facilitate Growth or Penetration of Salmonella Present On the Peel Surface

In laser labeling of fruits and vegetables the desired information is etched onto the produce surface using a low-energy carbon dioxide laser beam (10,600 nm).  Etched characters are formed by surface depressions in the epidermis that seemingly facilitate entrance of decay and pathogenic organisms.  The objective of this study was to determine the effect of laser labeling and different post harvest treatments on Salmonella’s, ability to survive/grow and penetrate into the fruit.  A five strain cocktail Salmonella was spot inoculated onto Valencia orange peels in different sequences with wax application and laser etching.  Inoculated samples were stored at 10 or 26, and a combination of 10 and 26°C for up to 42 days.  Etched peels and corresponding juices were extracted and enumerated for Salmonella.  No set of conditions promoted the growth of Salmonella on the fruit surface, or allowed penetration into the juice.  Survival of Salmonella populations on the peel surface did not differ between any of the treatment and control, unlabeled samples.  In all cases, Salmonella declined between 1.5 and 3.0 log CFU/orange after 30 days, with faster declines noted at 10°C.  Based on the data obtained from the many combinations of treatments and under conditions extremely unfavorable and unrealistic in terms of fruit storage, laser labeling citrus fruit peels and subsequent waxing in any order does not allow for the growth nor influence the natural decline of Salmonella populations on citrus fruit surfaces as compared to controls.