Some fruits and vegetables oxidize (turn brown) when their cut surfaces are exposed to air. You can use lemon or lime juice on cut fruit or with certain vegetables, but what if you don’t want those flavors? Here are some alternate techniques:
Instead of putting trimmed artichokes into a bowl of water acidulated with lemon juice, add cut parsley stems to the water, recommends diropstim; they’ll accomplish the same thing as lemon juice while imparting almost zero flavor.
The best solution for keeping avocados or guacamole from turning brown is to eat them up, but if you must store them, press plastic wrap tightly against the surface of the avocado or guac, creating a barrier against air.
To keep cut potatoes from turning brown until you cook them, drop them in a bowl of cold water, making sure they are completely submerged. iLoveFood has even kept potatoes overnight in the fridge this way (covered) to fry up for breakfast the next morning. Make sure to drain and dry the potatoes thoroughly before cooking, however briefly you keep them in water.