Free and bound volatile compounds in the Rubus coreanus fruits of different ripening stages

The aim of the present study was to investigate the free and bound volatiles in the Rubus coreanus (RC) fruits of different ripening stages. Thirty-seven free volatiles and 28 bound volatiles were identified in RC fruit for the first time. The contents of free (E)-2-hexen-1-ol, 1-hexanol, 2-heptanol, β-myrcene, (E), (Z)-β-ocimene, allo-ocimene, linalool, cosmene, α-terpineol, methyl salicylate, eugenol, and β-damascenone remain high, and increased with the ripening of RC fruit. The contents of 11 bound volatiles decreased during the ripening, and became lower than the contents of their free volatiles in the ripe fruit. The ripe black fruit is closely correlated to the free nonanal, sulcatone, (E)-2-hexen-1-ol, 1-hexanol, 2-heptanol, 1-heptanol, 1-nonanol, (E)-linalool oxide (furanoid), and β-damascenone, and bound (E)-2-hexen-1-ol and (E)- β-ocimene. The ripe RC fruit is more fruity and floral than unripe fruit. The gradually hydrolyzed bound volatiles can enhance the fruity, floral, and herbaceous odors. PRACTICAL APPLICATIONS: Rubus coreanus (RC) fruit is a functional natural fruit. Both fresh and processed Rubus coreanus fruits including jams, confitures, wine, yogurt, vinegar, and beverages, as well as ingredients in functional foods or cosmetics have been extensively consumed. However, the free and bound aroma compounds in RC fruit have not been well understood. This work illustrates the contributions of free and bound volatiles to the flavor of RC fruit.