Research conducted at Oregon State University’s Malheur County experiment station has shown that E. coli contamination is not a risk in furrow- or drip-irrigated bulb onions.
The research began last year after the U.S. Food and Drug Administration released a proposed produce safety rule that would limit the amount of generic E. coli bacteria that can be present in irrigation water.
This year’s trial is much larger and researchers expect it will confirm last year’s findings, which showed bulb onions pose no risk of E. coli contamination, regardless of how they are irrigated and regardless of the water quality.
Researchers even enriched some of the water with extremely high levels of generic E. coli by using runoff water from a pasture. Still, there was no trace of bacteria when the onions were ready for packing.
“By the time we packed them out, the numbers were all zero,” said Clint Shock, director of the Malheur experiment station.
There were traces of E. coli present on the outside of some onion bulbs when they were pulled out of the soil and left on the ground to dry. But after they were cured in the field — all bulb onions in this area go through that process — and ready for packing, no E. coli was present on any of the onions.
“The results of last year showed that the bacteria died off really rapidly after they were lifted, and cured in the field,” Shock said. “And we didn’t have any generic E. coli at all on any of the onions when we packed them out.”
E. coli levels for soils and onions were recorded during growing, harvesting and processing conditions. At no time was E. coli ever detected inside of any of the onions.