Salmonella not influenced by natural-light labelling

The objective, from the study supported by Sunkist, Inc. and Durand-Wayland, was to determine if differences in Salmonella survival and/or growth on orange peel surfaces exist between non-light labelled oranges and natural-light labelled.

For in natural-light labelling of fruits and vegetables, information is etched onto the produce surface using a low-energy carbon dioxide laser beam.

Supporters of the technology claim that traceability can be improved by the permanent labelling of individual produce items.

It offers an alternative to price look-up (PLU) stickers that are often used to identify products.

Alternative techs​

Concerns had been raised about increased risk of contamination due to the use of etching. We spoke to Greg Drouillard, last year, about the tech​.    

The consistent similarities between treatments at all temperatures and the congruencies between treatments and controls indicate that the perforations created by the natural-light labelling did not modify the survival ability of Salmonella, said ​Danyluk et al.

A five-strain cocktail of Salmonella was spot inoculated onto Valencia orange with wax and natural-light etching and samples were stored at 10, 26 °C, or combinations of both, for up to 42 days.

Etched peels and juices were extracted from whole oranges following storage and enumerated for Salmonella.​ No set of conditions involving natural-light labelling promoted growth on the fruit surface or resulted in detection from the juice of sound fruit.

Salmonella survival​

Survival of Salmonella populations on the peel surface did not differ between any of the treatment and control samples. The pathogen declined between 1.5 and 3.0 log CFU/orange after 30 days, with faster decline noted at 10 °C.

The lack of juice contamination and Salmonella growth was by applying a worst case scenario where it was inoculated onto the open peel disruptions between labelling and waxing.

Valencia oranges were shipped overnight from Sunkist to the University of Florida's research facilities located at the Citrus Research and Education Center in Lake Alfred, Florida, USA.

Fruit were individually placed on a plastic ring with the orange surface 10cm apart from the natural-light source. All fruit were labelled using a maximum energy level of 0.578 W per character with a time of exposure of 35 μs and a duty cycle of 25%.

“​Based on the data obtained from all treatments and under conditions extremely unfavourable and unrealistic in terms of fruit storage, natural-light labelling citrus fruit peels and subsequent waxing in any order did not allow for the growth or influence the natural decline of Salmonella​ populations on citrus fruit surfaces, or movement into juices, as compared to controls​,” said the researchers.

Source: Food Control, volume 34 issue 2 December 2013 pages 398-403

Online ahead of print, DOI: 10.1016/j.foodcont.2013.04.036​

“Growth or penetration of Salmonella into citrus fruit is not facilitated by natural-light labels​”

Authors: Michelle D. Danyluk, Loretta M. Friedrich, Preeti Sood, Ed Etxeberria