Riboflavin (E101), also known as Vitamin B2, is an easily absorbed, water-soluble micronutrient with a key role in maintaining human health. Like the other B vitamins, it supports energy production by aiding in the metabolising of fats, carbohydrates and proteins. Vitamin B2 is also required for red blood cell formation and respiration, antibody production, and for regulating human growth and reproduction. It is essential for healthy skin, nails, hair growth and general good health, including regulating thyroid activity.

Riboflavin also helps in the prevention or treatment of many types of eye disorders, including some cases of cataracts. It may assist bloodshot, itching or burning eyes and abnormal sensitivity to light.

Milk, cheese, leafy green vegetables, liver and yeast are good sources of Vitamin B2, but exposure to light will destroy the Riboflavin in these natural sources. Any excess is excreted in the urine but as the human body does not store Riboflavin it is thought deficiency is common.

In processed foods it is very likely to be GM as it can be produced synthetically using genetically modified Bacillus subtilis, altered to both increase the bacteria production of riboflavin and to introduce an antibiotic (ampicillin) resistance marker.

Riboflavin is yellow or orange-yellow in colour and in addition to being used as a food colouring it is also used to fortify some foods. It can be found in such foods as baby foods, breakfast cereals, sauces, processed cheese, fruit drinks and vitamin-enriched milk products as well as being widely used in vitamin supplements.

It is difficult to incorporate Riboflavin into many liquid products as it has poor solubility. Hence the requirement for E101a Riboflavin-5'-Phosphate, a more expensive but more soluble form of Riboflavin.