T1-04 Dynamic Changes in Water Quality and Microbial Survival during Commercial Fresh-cut Produce Wash Operation

Monday, July 10, 2017: 9:15 AM
Room 15 (Tampa Convention Center)
Yaguang Luo , U.S. Department of Agriculture–ARS , Beltsville , MD
Bin Zhou , U.S. Department of Agriculture–ARS , Beltsville , MD
Boce Zhang , U.S. Department of Agriculture–ARS , Beltsville , MD
Xiangwu Nou , U.S. Department of Agriculture–ARS , Beltsville , MD
Sam Van Haute , University of Maryland , College Park , MD
Ellen Turner , U.S. Department of Agriculture–ARS , Beltsville , MD
Zi Teng , University of Maryland , College Park , MD
Qin Wang , University of Maryland , College Park , MD
Patricia Millner , USDA ARS Environmental Microbial and Food Safety Laboratory , Beltsville , MD
Introduction: Determining minimal, effective free chlorine (FC) concentration for preventing pathogen survival and cross-contamination is critical for developing science- and risk-based food safety practices.

Purpose: This study investigated the correlation between dynamic FC concentrations and bacterial survival under commercial fresh-cut produce wash operations.

Methods: Chopped romaine lettuce, shredded iceberg lettuce, and diced cabbage were washed in a two-flume system under typical commercial fresh-cut processing conditions. Targeted FC concentrations and pH levels were maintained using sodium hypochlorite and a phosphoric acid-based solution, respectively, via an automated control system. Wash water was sampled every 30 minutes and assayed for chemical oxygen demand (COD), turbidity, total dissolved solids (TDS), and FC. Bacterial survival was determined by plating aliquots of neutralized water samples on APC Petrifilms™.

 Results: Significant increases in COD, turbidity, and TDS were observed over time, with more rapid increases during wash of diced cabbage. Combined chlorine concentration increased consistently over time; FC concentration fluctuated, as impacted by the rate of chlorine replenishment, cut product loading, and water replenishment. Bacterial survival in wash water correlated with FC concentration. With FC below approximately 10 mg/liter, increasing FC concentration resulted in sharp declines in the frequency and population of surviving bacteria detected. Further increases in FC concentration resulted in most total aerobic bacterial count being reduced to below the detection limit (50 CFU/100 ml); there were a few sporadic positive samples with low cell counts.

Significance: Results showed that maintaining at least 10 mg/liter FC in wash water contributes significantly to reduced survival of culturable aerobic bacteria. Tests with culturable, indigenous aerobic bacteria in produce wash conditions are valuable for commercial operations, since inoculating produce with human pathogens or even non-pathogenic surrogates during commercial operations is not feasible given the inherent food safety risks.