Efficacy of Sanitizers Approved for Organic Use against Salmonella enterica on Organic Leafy Greens

Introduction: Consumption of organic produce has been increasing in recent years. Salmonella is one of the pathogens of concern for the produce industry because of its association with foodborne illness outbreaks from fresh produce. Post-harvest sanitizing is an effective method to reduce microbial contamination in fresh produce.

Purpose: The objective of this study was to compare the efficacy of various sanitizers approved for organic use against Salmonella Newport on four types of organic leafy greens−Romaine and iceberg lettuce, and mature and baby spinach.

Methods: The sanitizers tested included 3% hydrogen peroxide, formulations of chlorine dioxide (CD), calcium hypochlorite (CH), and a mixture of peroxyacetic acid and hydrogen peroxide (PAH). The concentrations of the working solutions were determined according to the manufacturer’s directions (CD at 11 ppm, CH at 100 and 200 ppm, and PAH at 85 and 200 ppm). Water was used as a control. Leafy green samples were washed and dip inoculated in 10⁶ CFU/ml Salmonella Newport culture. Samples were dried in biohood for 1 hour, and then immersed in various concentrations of sanitizers for 2 min. After storage at 4 °C for 0, 1 and 3 days, samples were taken for enumeration of survivors.

Results: After sanitizer treatments, there were 0.5-1.6 log additional reductions of Salmonella compared to water treatment (P < 0.05) at day 0. The sanitizer solutions containing 200 ppm PAH and 200 ppm CH showed the best reductions on all types of organic leafy greens at day 0 (0.9-1.6 logs). There was a slight increase (<0.4 logs) in reductions of Salmonella population by day 1 and 3, for both water and sanitizer treatments. In general, the sanitizer treatments were more effective on iceberg lettuce than on other leafy greens.

Significance: The results from this study could provide organic leafy green industry with more options to select sanitizers for post-harvest treatments.