Free Volatile Terpenoids in Ponkan Mandarin Pulp: Changes during Shelf Life and Pathways of Formation and Transformation

ABSTRACT For Ponkan mandarin, a highly popular citrus fruit, the maintenance and improvement of its aroma are of practical interest, but the formation and transformations of its aroma compounds, especially terpenoids, are still not well understood. This work investigated the key free volatile terpenoids in ripe Ponkan mandarin pulp (PMP) during shelf life, quantifying their dynamic changes and examining their formation and transformation mechanisms to elucidate the underlying metabolic pathways. Fifteen free volatile terpenoids were identified from PMP. Three terpenoids were found in PMP for the first time, that is, 1,4‐dimethyl‐4‐acetyl‐1‐cyclohexene, 6‐camphenone and nootkatone. The contents of linalool, α‐terpineol, citronellol and ( E )‐nerol decreased steadily over time, whereas the contents of D‐limonene, 6‐camphenone, trans ‐carveol, carvone and β‐damascenone were the highest after storage for 1 week. The following interconversions between the aroma terpenoids in PMP were confirmed: D‐limonene, from linalool, terpinen‐4‐ol, α‐terpineol, carveol, citronellol, L‐carvone, ( Z )‐nerol, piperitone and L‐perillal; α‐terpineol, from linalool, ( Z )‐nerol and D‐limonene; linalool, from citronellol, ( Z )‐nerol and α‐terpineol; ( E )‐nerol, from linalool; terpinen‐4‐ol, from L‐perillal, citronellol and α‐terpineol; piperitone, from terpinen‐4‐ol; carveol, from D‐limonene; carvone, from carveol. The formation and transformation of these terpenoids mainly involved the rearrangements of carbocations and the redox reactions of intermediates.