A new study, conducted at the University of California, has found that when spinach is contaminated with bacteria, some 90 per cent of the bacteria remain on leaves after washing and packing. The reason for this is because the rinsing process conducted by many manufacturers is not very effective. If the bacteria are pathogenic then they can cause food poisoning and thus present a risk to public health.
Scientists working at the university’s Bourns College of Engineering found that the disinfectant applied to the rinse water only rarely makes contact with the leaves of spinach. Although the study was carried out on one vegetable — spinach — the findings are generally applicable to all pre-packaged and washed vegetables.
That said, the particular shape of spinach contributes to the unevenness of the disinfection process. According to the research note: “because of the varied topography of the spinach leaf nearly 15 percent of the leaf surface may reach concentrations as low as 1,000 times that of the bleach disinfectant being used to rinse it.”
To highlight the issue, researchers deliberately inoculated the bacterium Escherichia coli to spinach leaves, then subjected samples of the vegetable to a standard wash and bleach process, and then enumerated the surviving organisms.
The ineffectiveness of the process means that bacteria can survive and continue to grow; moreover, the way that the packaged food is handled means that bacteria can readily spread across the entire vegetable mass.
Commenting on the study, Doug Sider, medical director of communicable disease prevention and control for Public Health Ontario, told the Toronto Star pre-washing “doesn’t necessarily mean pathogen-reduction to a point where we judge there is little of no risk of transmission.”
The new research was recently presented at the 250th American Chemical Society National Meeting & Exposition, which took place in August 2015. The presentation was delivered by Nichola M. Kinsinger and Sharon Walker. The two plan to report the findings to a peer reviewed journal in the near future.
In the meantime, for spinach sold int he U.S. at least, the general advice is to rinse it even if it is sold as pre-packaged and pre-washed.
