Simplify the following text for a Grade 4 native English-speaking person.
Original: It is difficult to incorporate riboflavin into many liquid products because it has poor solubility in water , hence the requirement for riboflavin-5 ' - phosphate ( E101a ) , a more expensive but more soluble form of riboflavin . Riboflavin is generally stable during the heat processing and normal cooking of foods if light is excluded .
Simplified: These foods have a lot of riboflavin .