Acids

acids a large group of substances essential to the working of the body and widespread in food. The scientific definition of an acid is a substance that dissolves in water to release hydrogen ions, dissolves metals releasing hydrogen gas, and reacts with a base to form a salt. All these properties are relevant to food.

First, the release of hydrogen ions—that is, hydrogen atoms with a positive electrical charge—means that acids tend to remove oxygen from other substances, and combine it with the hydrogen to form water. Oxygen tends to spoil foods (see, for example, fats and oils), so acids act as preservatives, as in pickles and some fermented foods such as sauerkraut and yoghurt.