Evaluation of the microbial safety and quality of Louisiana strawberries after flooding

Abstract

Adverse weather such as flooding affects Louisiana strawberry production. Floodwater is an ideal medium for the growth of foodborne pathogens and may cause contamination of soil, water, and fresh produce. To evaluate the microbial safety of strawberries after flooding, four flooding scenarios were investigated. Five raised beds were exposed to a simulated flood event. Treatments included High Flood High Contamination (HFHC), High Flood Low Contamination (HFLC), Low Flood High Contamination (LFHC), Low Flood Low Contamination (LFLC) and a Control (C). High flood groups (HF) were exposed to 890 L of floodwater where strawberries were fully submerged, while low flood groups (LF) were exposed to 600 L of floodwater where strawberries did not come into direct contact with the floodwater. Three strains of generic Escherichia coli were spiked into the floodwater to establish a baseline population of approximately 106 colony forming units per liter (CFU/L) (high contamination) and 102 CFU/L (low contamination). Strawberry plants in all treatments were flooded for 4 h until floodwater receded. Strawberries were harvested when mature and sampled during shelf-life at 4 °C at 0, 48, 96, and 144 h. Soil samples were collected in the field every 48 h for one week. Even though the generic E. coli was not detected (<10 CFU/g) in strawberry samples, it was detected in soil samples within 96 h after flooding. In soil samples, generic E. coli was higher in HFHC samples (1.6 log CFU/g) compared to HFLC samples (1.1 log CFU/g) at harvest. Additionally, 1.0 to 2.8 log CFU/g of coliform were present in the strawberries and soil at 0, 48, 96, and 144 h in all treatment beds.