It's believed that to keep artichokes from darkening, they must be stored in lemon water as soon as they are cut and then also cooked in lemon water. Are both steps really essential? And will vinegar work just as well?
When the cell walls of artichokes (as well as avocados, apples, and potatoes) are cut or crushed, enzymes in their tissues are exposed to the air and react with polyphenols, producing black- or brown-colored pigments that mar their appearance. Contact with an acid will slow the rate of this browning. We found that vinegar (which is high in acetic acid) and parsley (which is high in ascorbic acid) each minimized darkening when added to cooking water. However, lemon juice proved more effective than either of these substances. This is because lemon juice contains both citric and ascorbic acids, which together not only slow the enzymatic reaction but also limit its activity in the first place.
As for whether soaking cut artichokes in lemon juice before cooking is also necessary to prevent them from browning, the answer is no. Since browning occurs only on surfaces where the tissues are ruptured, the acid’s impact is limited to cut areas during a precooking soak. Adding lemon juice to the cooking water is far more important, as many more cells of the artichoke will burst in the boiling water, potentially creating browning throughout the vegetable.