Terpenes are hydrocarbon compounds that give many fruits their characteristic aroma. Citrus fruits owe most of their peel fragrance to a terpene called limonene, and mangoes get their resinous, sweet smell from terpenes like terpinolene and alpha-pinene. Fruits such as banana, guava, sapota and custard apple rely mostly on esters and other volatiles for their flavour instead. So citrus fruits and mango are the terpene flavoured pair.