# Profiling Taste and Aroma Compound Metabolism during Apricot Fruit Development and Ripening
## 2 Results
### Changes in Aroma Volatiles during Development and Ripening  
A total of 46 aroma compounds were identified, including eight aldehydes, five alcohols, seven esters, five norisoprenoids, eight lactones, ten terpenes and six acids (Table S2). Among them, 18 aroma compounds, including three aldehydes (hexanal, (Z)-3-hexenal, (_E_,_Z_)-2,6-nonadienal), three apocarotenoids (\(\beta\)-damascenone, \(\beta\)-ionone, dihydro-\(\beta\)-ionone), five lactones (\(\gamma\)-octalactone, \(\delta\)-octalactone, \(\gamma\)-decalactone, \(\delta\)-decalactone, \(\gamma\)-dodecalactone), five terpen (\(\beta\)-myrcene, inalool, \(\alpha\)-terpineol, geraniol, limonene) and two esters (hexyl acetate, (Z)-3-hexenyl acetate), were the major aroma compounds in apricots by odor activity values (OVA) method. The OVAs of these 18 aroma compounds were more than 1 (Table 2). \(\gamma\)-decalactone was the highest OVA compound in all cultivars tested, it ranged from 145 to 319 with the highest OVA in LT peel. \(\beta\)-ionone was the second major aroma compound in apricot fruit tested. It ranged from 40 to 506. The OVA of \(\beta\)-ionone in LT and BX were 4.65-16.09 times greater than those in other cultivars. \(\gamma\)-dodecalactone was the third major aroma compound and it ranged from 37.21 to 160 with the highest level in LT peel. High OVAs of \(\beta\)-damascenone (180) and hexyl acetate (183), (_E_,_Z_)-2,6-nonadienal (319), and \(\alpha\)-terpineol (103) were found in DX, whereas high OVAs of \(\beta\)-ionone (506), \(\gamma\)-dodecalactone (160), \(\gamma\)-decalactone (319) and hexyl acetate (183) was found in LT. Significantly higher OVAs were observed in peels than pulps for all cultivars tested. Changes in 18 major aroma compounds during the whole development period are given in Figure 5. The contents of hexanal, (_Z_)-3-hexenal and (_E_,_Z_)-2,6-nonadienal decreased rapidly throughout the whole development period (Figure 5a). The total aldehydes decreased from 1170 to 47.8 \(\mu\)g/kg FW. Significantly higher aldehydes were observed in peels than in pulps. As the most abundant aroma compounds in apricot, the contents of \(\beta\)-damascenone, \(\beta\)-ionone and dihydro-\(\beta\)-ionone increased dramatically during fruit ripening, especially the major apocarotenoids. The content of \(\beta\)-ionone increased from 155 to 1875 \(\mu\)g/kg FW in peels and from 30 to 1026 \(\mu\)g/kg FW in pulps of all cultivars tested. It is very interesting that the content of \(\beta\)-ionone, dihydro-\(\beta\)-ionone and total apocarotenoids in LT and BX were significantly higher than those in other cultivars, especially the \(\beta\)-ionone. Similarly, the contents of apocarotenoids in peels were significantly higher than those in the pulps of cultivars tested. Lactones were the second most abundant aroma compounds, and \(\gamma\)-decalactone was the predominant lactone, it ranged from 17.14 to 350.71 \(\mu\)g/kg FW in peels and 5-277.14 \(\mu\)g/kg FW in pulps, respectively. BX had the highest \(\gamma\)-decalactone in cultivars tested. Total lactones also increased rapidly during the ripening period. Conversely, \(\beta\)-myrcene, linalool, \(\alpha\)-terpineol, geraniol and limonene all decreased through the ripening period. Linalool was the predominant terpene in these fruits, and it decreased from 987 to 122 \(\mu\)g/kg FW in peels and from 356 to 45 \(\mu\)g/kg FW in pulps during the whole development period. DX had the highest level of linalool and total terpen during fruit ripening. Two major esters, hexyl acetate and (_Z_)-3-hexenyl acetate, increased during the whole development period, especially as the predominant, ester hexyl acetate increased from 13 to 365 \(\mu\)g/kg FW in peels and 3 to 76 \(\mu\)g/kg FW in pulps, respectively. LT peel had the highest level of total esters. The contents of total aldehydes and terpen in all cultivars decreased rapidly during fruit development and ripening, while the contents of total lactones and apocarotenoids kept increasing during this period (Figure 5b).