Wikipedia says this:
Sodium bicarbonate was sometimes used in cooking green vegetables, as it gives them a bright green colour—which has been described as artificial-looking—due to its reacting with chlorophyll to produce chlorophyllin.[17] However, this tends to affect taste, texture and nutritional content, and is no longer common.[18]
Baking soda is still used to soften pulses (peas, beans) before and during cooking, as in the traditional British mushy peas recipe for soaking the peas. The main effect of sodium bicarbonate is to modify the pH of the soaking solution and cooking water, that in turn softens the hard external shell, reduces cooking times and may alter the percentage of nutrients in the dish, its flavour and consistence.[19]
Baking soda may react with acids in food, including vitamin C (L-ascorbic acid).
It is used in Asian and Latin American cuisine to tenderize meats. It is also used in breading, such as for fried foods, to enhance crispness and allow passages for steam to escape, so the breading is not blown off during cooking.