Five- and six-carbon atom unsaturated acids have an important role, mostly in cheesy and fruity flavors. For example, trans-2-hexenoic acid (FEMA# 3169, CAS# 13419-69-7) (F-1)—which occurs in apple, banana, grape, strawberry, beer, wine, pork and tea—has a cheesy, fatty, herbal, warm odor, and is applied to cheesy, berry and fruity flavoringsa.
The most important 5–7 carbon atom unsaturated carboxylic acids can be seen in F-2.