In-Plant Validation of Postharvest Water Sanitation Practices to Prevent Cross-Contamination in Michigan Commercial Apple Packinghouses

Recirculated postharvest water systems play a critical role in produce packinghouse operations, but are also recognized as potential points for microbial cross-contamination. To evaluate the effectiveness of current commercial practices, an in-plant validation study was conducted across three Michigan apple packinghouses during routine operations. Microbial [aerobic plate count (APC), Enterobacteriaceae (EB), total coliforms (TCs), and generic Escherichia coli (EC)] and physicochemical (turbidity, pH, temperature, and sanitizer concentration) parameters were monitored in flume water (159 samples) and on apples (255 samples) over water hold times of up to 80 h. Microbial levels in flume water and on apples were plated onto Petrifilm. Differences in physicochemical parameters and indicator concentrations by location and time were assessed for both water and apples. Flume systems exhibited considerable variability in sanitizer concentrations relative to targets (e.g., Packinghouse A peroxyacetic acid target 75 ppm, ranged 15-180 ppm, mean 69.1 ± 48.8 ppm) and consistent increases in turbidity over time (e.g., Packinghouse B: 18.3 NTU at 0 h to 52.4 NTU at 55.5 h). Generic E. coli was infrequently detected [4/255 (1.6%) apples and 2/159 (1.3%) water samples], limiting its utility as an indicator for postharvest water quality in these apple systems. APC, EB, and TC levels in both water and on apples were consistently lower in Packinghouse C compared to Packinghouses A and B. No statistically significant differences in APC (5.04 log CFU/apple; p = 0.06-0.60), EB (3.47 log CFU/apple; p = 0.06-0.37), or TC (3.34 log CFU/apple; 0.32-0.48) levels were observed on apples before and after flume systems, indicating that cross-contamination was effectively managed. Microbial reductions were not achieved, further supporting that postharvest washing, even with sanitizers, should not be considered a reduction step. Commercial operating conditions in the studied apple packinghouses were sufficient to prevent cross-contamination. Individual packinghouse should validate their systems to understand the effectiveness of postharvest water management as a process control.