Sanitizer Efficacy against Salmonella during Simulated Commercial Packing of Tomatoes

Introduction:  During tomato packing chemical sanitizers are usually added to the dump tank water to minimize cross-contamination.  However, the efficacy of sanitizers continues to be questioned.

Purpose: This study assessed the ability of three commonly used commercial sanitizers to reduce Salmonellapopulations on tomatoes, in wash water and on equipment surfaces using a pilot-scale processing line.

Methods:  Five sanitizer treatments - 40 ppm peroxyacetic acid (Tsunami 100, Ecolab, St. Paul, MN), 40 ppm mixed peracid (Tsunami 200, Ecolab) and 40 ppm free chlorine from XY-12 (Ecolab) at pH 7.8 or pH 6.0 (adjusted with SmartWash (SW) or citric acid (CA)) were evaluated in triplicate for efficacy against Salmonella Typhimurium LT2 (avirulent) on 25 lbs (11.3 kg) of dip-inoculated tomatoes (~6 log CFU/g)  that were washed for 2 min in a 3.3-m dump tank equipped with two overhead spray jets and then dried on a 0.4-m × 1.5-m polyethylene roller conveyor with sanitizer-free water serving as the control. Two tomatoes (~500 g) and individual water samples (400 ml) were collected at 15-sec intervals during washing with ten dump tank (100 cm²), four water tank (100 cm²) and six roller conveyor (350 cm²) surface samples collected after washing using Kimwipes^®. All samples were appropriately neutralized, hand-rubbed/stomached, diluted and surface-plated on trypticase soy agar containing 0.6% yeast extract, 0.05% ferric ammonium citrate and 0.03% sodium thiosulfate with or without membrane filtration to enumerate Salmonella.

Results:  All sanitizer treatments were more effective (P < 0.05) than the water control with XY-12 + CA yielding a significantly greater (P < 0.05) reduction for Salmonella on tomatoes (3.16 log CFU/g) as compared to Tsunami 100 (2.53 log CFU/g), Tsunami 200 (2.49 log CFU/g), XY-12 (2.10 log CFU/g) and XY-12 + SW (1.98 log CFU/g). The same five sanitizers yielded Salmonella population of -2.18, 0.62, 0.12, -1.66 and -2.26 log CFU/ml in the dump-tank water after washing. The water control yielded a Salmonella transfer rate of 94.1% for the dump tank water and 0.003, 0.002 and 0.001% for surfaces of the dump tank, water tank and roller conveyor after processing with all equipment samples negative for Salmonellawhen sanitizers were used during processing.      

Significance:  All sanitizers were able to prevent cross-contamination after washing with XY-12 + CA most effective against Salmonella on tomatoes. However, additional steps, including acidification of dump tank water containing chlorine-based sanitizers, are still needed to better ensure end product safety.