Explain the Occurrence of vitamin B₂

Vitamin B₂ (riboflavin) occurs in nature almost exclusively in a combined form i.e. esterified with phosphoric acid as riboflavin-5'-phosphoric acid ester. Vitamin B₂ occurs in a combined form in any plant and animal cell - yeasts, wheat, white bread, rye bread, fruits, nuts, spinach, cabbage, milk, cheese, egg yolk, fish, meat, rice bran, potatoes and others.