none of these make any difference when you're buying greens, because they are all contaminated.
according to the most recent consumer report, packaged leafy greens that were tested had bacteria that are "common indicators of poor sanitation and fecal contamination, in some cases, at rather high levels."
you can read the actual report here: http://www.consumerreports.org/cro/index.htm
but you might be a little bit lazy, which is why you buy pre-packaged leafy greens, so i'll break it down for you.
right now in the united states there is no feeral standard for "indicator bacteria" in salad greens although there are standards for beef, milk, and drinking water. because we get a lot of salad greens from the united states, this is something that we might want to be concerned about.
the suggested unacceptable level would be about 10,000 or more of "colony forming units per gram".
with that guideline in mind, let's look at the results of the tests:
- 39 percent of samples exceeded 10,000 CFUs (or another similar measure) per gram for total coliforms and 23 percent for Enteroccocus, the levels industry consultants deemed unacceptable.
- 2 percent of samples exceeded French and 5 percent Brazilian standards for fecal coliform bacteria.
- Many packages containing spinach, and packages which were one to five days from their use-by date, had higher bacterial levels. Packages six to eight days from their use-by date generally fared better.
- Whether the greens came in a clamshell or bag, included "baby" greens, or were organic made no difference in bacteria levels.
- Brands for which there were more than four samples, including national brands Dole, Earthbound Farm Organic, and Fresh Express, plus regional and store brands, had at least one package with relatively high levels of total coliforms or Enteroccocus.
translation: you have to wash your salad/leafy greens before you eat them. rinsing them off won't really wash away any bacteria but it can get rid of "residual soil" which could contain bacteria and other fecal-related nasty things.
or, better yet, buy whole heads of lettuce and fresh spinach. yes, they also have some residual soil on them but they don't have to go through the same packaging process as the bagged stuff=less dirty hands on yo' lettuce.