Everyday Chemistry - 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. Let's find out what happens when red cabbage is cooked.

Why is the cabbage red in colour?

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.

How does the change in colour occur?

Red cabbage contains at least thirty-six of the over 300 different anthocyanins that exist. These pigment molecules are stored in the cells of the red cabbage leaf. When exposed to heat during cooking, the cells containing anthocyanins burst open and cause the water-soluble colour pigments to bleed into the surrounding liquid. This is why there is immediate colour change in the cabbage and the cooking water.

Anthocyanins pigments are sensitive to changes in pH

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.

Can I minimize / enhance the colour changes in red cabbage?

Yes, this can be done with the help of certain kitchen ingredients. 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.