Do Not Use Special Plastic Knives and Simply Tear the Salad to Prevent Browning.
You’ve probably seen serrated plastic knives to prevent lettuce and other foods darken too quickly after slicing. Cook’s Illustrated found that they did work, but were probably not worth the money.
In their experiment, they sliced romaine lettuce and iceberg lettuce using three different knives (one stainless steel, the other high carbon steel, and a special plastic salad knife), and tore the leaves by hand. Two weeks later, the torn lettuce was the last to brown around the edges, compared to 12 days before browning with metal knives and 13 days before browning with a plastic knife.
Save drawer space and tear up the salad if you want to extend its life:
To extend the life of the salad by a day or two, try to pluck it by hand. Tearing allows leaves to break along natural fault lines, destroying fewer cells and reducing premature darkening.
However, if you are so inclined, you can make your own plastic salad knife . WonderHowTo is discovering that plastic and ceramic knives do slow the browning of other foods like avocados and apples, so it might be worth the investment or DIY effort.
Salad Knives | Illustrated chef