Purpose: The log reduction and cross-contamination potential of an attenuated Salmonella enterica sv. Typhimurium was assessed on oranges during passage through a pilot immersion and high pressure wash line.
Methods: Oranges were spray-inoculated under field conditions with attenuated Salmonella Typhimurium (~6 log CFU/orange). Oranges were harvested three days post-inoculation, separated into groups (n = 30) and immersed in water (21°C), 200 ppm free chlorine (pH 7.0, 21°C and 26°C), or combined chlorine and 1.0% sodium bicarbonate (pH 8.0, 26°C). Additional samples (n = 30) were treated with a high pressure wash (150 psi) containing the same disinfectants or a combined high pressure wash and immersion treatment. Following disinfection, oranges passed through a wax cabinet and dryer at 49°C (2 min residence time). Individual fruit were quantified and enriched for Salmonella. Additionally, a mix of inoculated (n = 185) and uninoculated (n = 110) oranges were passed through the high pressure wash line (200 ppm free chlorine, 1.0% sodium bicarbonate) to assess cross-contamination.
Results: At harvest, oranges contained 2.70 log CFU/orange of Salmonella, with post-treatment reductions of 1.12 - 1.45 log CFU/orange. 76.7-86.7% of samples were positive for Salmonella following immersion treatments, while the high pressure wash with disinfectants resulted in 43.4 - 60% positive samples. The combined high pressure wash and immersion treatment was the most effective, with 33.3% of samples positive. In the cross-contamination study, 45.9% of inoculated oranges remained positive post-disinfection, while 4.5% of uninoculated oranges became contaminated during treatment.
Significance: The sequential chemical and mechanical wash-line treatments significantly reduced the surface-adhering populations of applied Salmonella indicating a substantial log-reduction may be achieved. However, low numbers of persistent Salmonella indicate continual improvements in wash-line design and process controls would be prudent in full commercial handling.