I am looking for a product that you put on lettuce to keep if from turning brown. I used to work in a hospital and we used to put this stuff on the lettuce to keep it from turning brown and keep it ...
I believe there is a product called stay-fresh, which is a potato whitener that also works on lettuce. I would not recomend this chemical as it leaves a very peculiar taste. To make your lettuce fresh , soak in cold water, then drain well. It will not take away the brown color but it will be more crisp.Also use a salad spinner to remove most of the excess water and your lettuce will last longer.
Potato whitener is a combination of Sodium bisulfite and citric acid. bisulfite is used to preserve wine to prevent oxidation. When I was young some 20 years ago, the restuarant I worked in would soak lettuce in potatoe whitener and it would be crisp and look fresh several weeks later.
I have no idea what type of health risk it has other than to those with sulfite sensitivity.