Riboflavin is also known as Vitamin B2, and is a necessary substance for the maintenance of a healthy body. It occurs in many manufactured foods, as well as soft drinks. It plays an important part in how the body metabolises certain things, such as fat, carbohydrate and protein. Riboflavin occurs naturally in a range of foodstuffs, including mushrooms, cheese, almonds, leafy vegetables and kidneys. It also occurs in many commercially manufactured soft drinks.
Riboflavin's main purpose, as far as food and drink manufacture is concerned, is to add colour. The jars of B vitamins that you might see in your local pharmacy are given their orange color by riboflavin. It is used as an orange/red coloring in food and drinks, and has been given the E number E101 in Europe.
As riboflavin can also have some health benefits, it is often used as a food supplement. It can be found in items like baby food, breakfast cereals, energy drinks and some other kinds of soft drinks, processed cheeses and factory-produced sauces. It does, however, possess poor water solubility, so riboflavin-5'-phosphate (E101a) has been produced and is also used in some food stuffs.
The urine of healthy people always contains a percentage of riboflavin, which means people can be susceptible to deficiencies. Deficiency in this vitamin is usually associated with deficiencies in other vitamins too, though. Symptoms of deficiency can include a dry throat, dry, cracked lips and mouth ulcers. This is relatively rare though, and can be mitigated against by making sure enough of the vitamin is included in a healthy diet.
Asparagus, bananas and milk are all good sources of riboflavin. The vitamin is destroyed by ultra-violet light though, so milk in clear glass bottles will have less of the vitamin present. Eating a varied diet with plenty of fresh fruit, vegetables and high quality meat will keep riboflavin levels sufficiently high in most people.