Why Does Red Cabbage Change Colour When Cooked?

Chemistry is just not about chemicals in laboratories. It is present in everything that we do in our daily life and also in our kitchens. When we cook this red cabbage, the cabbage changes its colour. Have you wondered how that happens? Let’s find out what happens when red cabbage is cooked.

Red cabbage is one of many fruits and vegetables that contain a class of reddish purple pigments called anthocyanins, which is responsible for its colour. Anthocyanins are a type of flavonoid pigment that are responsible for the red, purple and blue colours in most plants, leaves, flowers and fruits. These pigments have a tendency to change colour when mixed with alkaline or acidic ingredients.

Anthocyanins consist of many carbon rings onto which hydrogens are attached. This particular chemical formation allows these molecules to take on two forms. In one form, a hydrogen atom present is attached to the exterior and in the other form it is not. Acidic ingredients are characterized by having more hydrogen atoms (H+) than hydroxyl groups (OH-) so when exposed to acid, anthocyanins grab a hydrogen atom and turns red in colour. In alkaline conditions where there are no excess hydrogen atoms, the molecule appears blue or green in colour.

Anthocyanin turns red in acidic conditions when the pH is less than seven. It is not uncommon for apples or lemon juice to be part of braised red cabbage recipes because they help maintain the its red colour. Common acidic ingredients used in cooking include: 1) Vinegar 2) Lemon juice 3) Citric acid 4) Fruits and fruit juices.

Even baked goods, which frequently use baking soda or baking powder as a leavening agent can discolour fruits and vegetables like red cabbage. An understanding of simple cabbage chemistry will now allows you to adjust the pH of a recipe in order to prevent undesirable discolouration of the food item.

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