Food Safety for Leafy Greens

Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

With fall vegetable season approaching, cabbage, collards, kale, mustard, turnips, lettuce, Chinese cabbage, and other leafy greens will be harvested. The following are some considerations in the production, harvest and handling of leafy greens from the Southern Regional Fresh Produce Food Safety Training Program.

Many leafy greens (including cabbage, collards, kale, mustard, turnips, lettuce, and Asian greens) are cut by hand and packed directly in the field for the fresh market. Cabbage also may be cut by hand, loaded into a bulk container, such as a field wagon, and hauled to a packing shed for trimming, grading and packaging. Field sanitation practices are very important to reduce the spread of disease among plants and to prevent the possibility of contamination by microorganisms that are pathogenic (cause illness) to humans.

The principal food safety hazard from leafy greens is microbial contamination. Ensuring the safety of raw leafy greens begins with preventing hazards in the field.

Grazing animals on or near crop land can introduce bacteria harmful to humans into the soil. Growers should ensure that land has not been used for animal husbandry and that it is not close to animal feedlots or water runoff from grazing lands.

Incompletely composted organic fertilizers (manures in particular) may contain bacteria harmful to humans from animal or human feces. If organic fertilizers are used, they must be properly and completely composted so pathogens are not present. To avoid potential for contamination, raw manures should not be used for the production of leafy greens within that growing season, even if incorporated before planting.

Natural surface water (e.g., ditch, stream, pond) provides enough organic matter to support the growth of bacterial pathogens. It may be used with caution for irrigation but should be tested for the presence of the bacterium Escherichia coli (E. coli), which is an indicator of fecal contamination. Well water is less likely to harbor human pathogens but still should be analyzed for contamination.

Overhead irrigation is more likely to spread contamination to above-ground plant parts than is root-zone irrigation. Growers should document how water is stored, if animals are confined nearby, and if water is potable (safe to drink).

Hand-harvesting also may lead to pathogen contamination if field workers practice poor hygiene. Field crews must be trained and monitored regarding personal hygiene practices, and portable bathrooms and hand washing facilities must be provided at convenient locations in the field. The same personal hygiene precautions apply to family operations. Frequent hand washing is a key and provisions need to be made to be able to wash hands in the field.

Hand-harvesting using knives can wound produce, encouraging contamination from the soil. Knives should be routinely sanitized to keep disease inoculum from building on their surfaces and infecting sound cabbage heads or leafy greens. For best protection, place buckets of sanitizing agents at the ends of selected rows in the field. This will allow workers to sanitize their knives at regular intervals and reduce disease buildup over the course of the production day. Fresh sanitizer should be introduced throughout the work day. Routine knife sanitation is also critical for smaller farms using family labor.

Containers for harvesting fresh produce should be washed with detergent prior to use. After detergent cleaning, field bins, buckets, baskets, wheel barrows, etc., should be sanitized by using a very strong sodium hypochlorite solution dispensed from a high pressure sprayer. This should be repeated each harvest day. If wagons or trucks are used, the same procedure should be followed.

Leafy greens may be cleaned in sanitized water (75 to 100 ppm free chlorine) before marketing. Direct field-packing of boxed leaves or heads also may be done, without washing. It is critical to make sure that no dirt has contaminated the greens if doing field packing and to pack into clean boxes or containers.

Ice used to cool and preserve quality during transit can be a source of contamination. Steps should be taken to minimize ice exposure to workers, soil, and airborne dust.

If water is used in cleaning and cooling it should be chlorinated at a concentration of 75 to 100 ppm of free chlorine. Chlorination can be accomplished using a gas injection system, adding bleach, or using calcium hypochlorite tablets. Chlorination levels in the water should be monitored frequently during operation, through the use of a chlorine test kit. Water pH should be maintained between 6.5 and 7.5 to avoid having to use excess chlorine and in order to maintain recommended free chlorine levels. Excessive use of chlorine causes gassing off (which can lead to objectionable chlorine odor, irritation of workers’ skin, corrosion of equipment, and increased sanitation cost).

Information reprinted in part from “Good Agricultural Practices for the Production and Handling of Cabbage and Leafy Greens” by William C. Hurst and Darbie Granberry, Food Science and Horticultural Science Departments, University of Georgia, Athens, Georgia. This is a factsheet from the Southern Regional Fresh Produce Food Safety Training Program. Information in italics is from Gordon Johnson, Extension Agriculture Agent, UD, Kent County.

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