Effect of Sanitizers on the Survival of Lactobacillus plantarum and Salmonella spp. on Surface Inoculated, Hydrocooled Strawberries

Introduction: Forced-air-cooling is typically employed to cool strawberries to 3-4°C immediately after harvest. Hydrocooling in the presence of a sanitizer offers a faster and more uniform cooling of the berries, although the risk of cross-contamination has not been evaluated.

Purpose: This study examined the growth and survival of Salmonella (human pathogen) and Lactobacillus plantarum (proposed surrogate for Salmonella) on forced-air-cooled and hydrocooled strawberries. The second phase of this study compared the effect of sanitizers on Salmonella and Lactobacillussurvival on surface inoculated strawberries subjected to hydrocooling.

Methods: Intact strawberries inoculated with Lactobacillus (10⁷ cfu/berry) were subjected to a) forced-air-cooling at 2°C for 90 min or b) hydrocooling in water (2-5°C) containing three different sanitizers, 100 ppm HOCl, chlorine dioxide (5 ppm) or peroxyacetic acid (80 ppm). Similarly, berries inoculated with Salmonella (10⁷cfu/berry) were also forced-air-cooled or hydrocooled in water containing 100 or 200 ppm HOCl. The microbial populations were enumerated on multiple days post-treatment, and the experiments were performed in triplicate (n=9).

Results: The survival of both Lactobacillus and Salmonella were significantly lower (p ≤ 0.05) on hydrocooled berries, compared to forced-air-cooled or untreated strawberries. Lactobacillus survival was significantly lower when the berries were treated with HOCl or peroxyacetic acid. The concentration of active chlorine (100 or 200 ppm) did not significantly (p ≤ 0.05) affect Salmonellasurvival on strawberries.

Significance: Hydrocooling significantly reduced Lactobacillus and Salmonella survival on inoculated intact strawberries compared to forced-air-cooling. Bacterial populations were significantly lower when a sanitizer was added to the hydrocooling solution.