Food Safety and Flooded Vegetable Fields

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

In produce fields that are flooded, another consideration for growers is food safety. The following is a good article on the subject from Steve Reiners at Cornell University.

FLOODS AND FOOD SAFETY
There are two types of flooding. The first is more typical and occurs after a heavy downpour when fields become saturated and water pools on the soil surface. This type of flooding can reduce yields and even kill plants but usually will not result in contamination of produce with human pathogens.

The second type of flooding is more severe and seen less often. Standing water in fields that is runoff from stream/river overflows will more likely be contaminated with human pathogens. Unless flooding was light and there is no danger of bacterial contamination from floodwater, do not use fruits and vegetables that were ready for harvest at the time of flooding. Some fruits and vegetables are more susceptible than others to bacterial contamination.

Leafy vegetables (such as lettuce, cabbage, mustard, kale, collards, spinach, and Swiss chard) along with strawberries are more likely to be contaminated. Silt and other contaminants may be imbedded in the leaves, petioles, stems, or other natural openings of fleshy structures and can be difficult to remove. Do not use if mature when flooded.

Root, bulb, and tuber crops such as beets, carrots, radishes, turnips, onions, and potatoes are less susceptible to bacterial contamination. Produce with a protected fruit or impervious outer skin such as peas, melons, eggplant, sweet corn, or winter squash may be contaminated on the surface.

It is extremely important that produce be properly washed to reduce contamination.

To control postharvest losses, it is recommended that produce be washed in chlorinated water before storage or shipping (see table below). The wash temperature should be about 10°F warmer than the produce temperature to ensure that decay organisms are not sucked into the tissue. Since chlorine is most effective at a slightly acidic pH, it is important that wash water is buffered to adjust the pH to between 6 and 7.

Chlorine in the wash water is often inactivated when the wash water becomes dirty. Use filtering devices to remove soil and organic material, and check the chlorine concentration often. Produce should be subjected to the chlorinated wash from one to ten minutes. After it is removed, allow it to drain for several minutes before packing. NOTE: Leafy vegetables at or near harvest that were flooded with stream/river overflows should not be harvested or consumed. Chlorinated wash water will not eliminate likely human pathogens on their surface.

Amount of sodium hypochlorite to add to wash water for 50-150 PPM dilution.

Target ppm

ml/L

tsp/5 gal

cup/50 gal

Sodium Hypochlorite, 5.25%

50

1.0

3.66

0.75

75

1.4

5.5

1

100

1.9

7.25

1.5

125

2.4

9

2

150

2.9

11

2.25

Sodium Hypochlorite, 12.75%

50

0.4

1.5

0.33

75

0.6

2.25

0.5

100

0.8

3

0.66

125

1.0

3.75

0.8

150

1.2

4.5

1

 

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