The efficacy of sodium acid sulfate on controlling Listeria monocytogenes on apples in a water system with organic matter

During fresh apple packing, wash water in the dump tank and flume systems is reused during daily production, resulting in high levels of organic matter in the wash water. This study evaluated the antimicrobial efficacy of sodium acid sulfate (SAS), a Generally Recognized as Safe compound, against Listeria monocytogenes on fresh apples in a water system with high organic load. SAS at 1.0% reduced L. monocytogenes population in water with 1000 ppm chemical oxygen demand (COD) by more than 5.0 Log10 CFU/ml in 5 min, 2.0–3.0% SAS reduced L. monocytogenes to undetectable levels (10 CFU/ml) within 2 min regardless of organic levels. When applied on apples, a 2-min wash with SAS at 1.0, 1.5, 2.0, and 3.0% reduced L. monocytogenes by ~1.3, 1.9, 2.3, and 3.0 Log10 CFU/apple in clean water, respectively. High organic load in wash water up to 4000 ppm COD had no impact on the bactericidal effect of SAS against L. monocytogenes on fresh apples regardless of SAS concentrations. Shortening the contact time from 2 min to 30 s significantly reduced the antimicrobial efficacy of 25 ppm chlorine and 1.0–2.0% SAS but not that of 3.0% SAS. In addition, SAS at 1.0% demonstrated a better efficacy than 25 ppm chlorine in reducing fruit-to-water cross-contamination regardless of organic matter. SAS also showed a comparable efficacy as 25 ppm chlorine in reducing fruit-to-fruit cross-contamination in water with organic matter. The collective data indicate that SAS, as an enviroment-friendly compound, has the potential to be used as an alternative antimicrobial washing aid in dump tank process water intervention in apple packing facilities.