From Hillel Academy, Spinach for Science Fair by Stacey Dresner:
In her project, “Quantitative Analysis of Bacterial Growth on Packaged Salads and Effect on Antibiotic Resistance and Nutrient Content,” Kaili [Janette] investigated several varieties of bagged salad greens.
She tested the bagged greens for bacteria content, and found “extensive growth of bacteria within 24 hours in the fresh “unwashed” samples.”
“I found the highest percents of bacteria in dark, leafy varieties such as spinach and Mediterranean” showing “a correlation between high levels of iron and high levels of bacteria.”
She washed the samples using different cleaning techniques n cleaning with sterile water, cooking with boiling water for five minutes, and using commercial cleaning rinse n water with a pinch of bleach. The only method that killed most of the bacteria was the commercial rinse. The others did not really inhibit bacterial growth.
“On all of bagged salads, it is printed that you do not need to wash before use,” she said. “I learned never to trust that phrase.”