Introduction: Pathogens can be present in fruits and vegetables because of contamination events occurred in the field or during processing (cross contamination or recontamination). However, due to both the low pathogens incidence and sampling limitations, little is known about how bacteria are distributed or which concentration and prevalence levels are given in the final product.
Purpose: To study the effect of cross contamination during processing on the spread of Salmonella in processed fresh apples.
Methods: A commercial process of packaged fresh apples was simulated at lab-scale. To simulate a natural contamination, one apple was spot-inoculated with Salmonella and introduced into a lot of 30 apples which were consequently processed according to the following steps: overnight storage (4 °C), washing, pre-dry on sponges, air-dry and packaging in plastic bag. After processing, all processed apples, sponges and wash water were sampled and analyzed for Salmonella. The experiments were carried out using two inoculums levels in the initially contaminated apples: high (8 log CFU/apple) and low (5 log CFU/apple) level.
Results: Salmonella counts after the storage step at 4 °C dropped >2 log CFU/apple. At high inoculum level, all processed apples, sponges and wash water were positive for Salmonella. At low contamination level, only the initially inoculated sample was positive while the rest of processed apples were found negative after a standard enrichment method. Even though no cross contamination occurred at low inoculums level, Salmonella was found in wash water (1/2) and sponges (3/4). Based on generated data, a stochastic model was derived to be used to validate and optimize sampling plans.
Significance: This information can be relevant to establish and develop effective sampling plans and food safety criteria.