What it is
E101 is riboflavin (vitamin B2), a yellow-orange water-soluble vitamin. Modern food-grade riboflavin is produced by microbial fermentation of plant sugars.
Why it matters
Used as both a colour and a nutritional supplement in cereals, baby foods, sauces, soft drinks, and processed cheese alternatives.
What to do
Always vegan in modern production. The closely-related E101a (riboflavin 5'-phosphate) is also vegan.