3.4 Volatile compounds of Qingjinju seed oils
The volatile compounds of the Qingjinju seed oils are described in Table 4. The primary volatile compound classes in the Qingjinju seed oils were esters, aldehydes, hydrocarbons, acids, and alcohols, which agrees with results reported by Kalua el al48. The identity and relative concentrations of volatile compounds were significantly different between oils produced by the different extraction techniques, similar to results reported by Moreno et al.21 A total of 43 volatile compounds were identified in SPO, 42 in SO, and 44 in SCO. The greatest number of compounds in both SPO and SCO were aldehydes, containing 16 and 13, respectively. In SO, the largest number of compounds in SO were hydrocarbons (18). Regardless of the extraction method, seven volatile compounds were observed: 2-methylaminobenzoic acid methyl ester, 2-methylaminobenzoic acid ethyl ester, (E )-2-heptenal, (E ,E )-2,4-heptadienal, (E ,E )-2,4-decadienal, 2,4-decadienal, and n -hexadecanoic acid. These compounds accounted for 40.52%, 46.19%, and 54.76% of the total volatile compounds in SPO, SO, and SCO, respectively. These appear to be the primarily volatile compounds of the Qingjinju seed oils.
The relative contents of volatile compounds in SPO were esters (30.28%), aldehydes (22.61%), and hydrocarbons (26.32%). The volatile compounds in SO were primarily comprised of hydrocarbons (43.74%), esters (25.79%), and aldehydes (19.91%). The volatile compounds in SCO were primarily composed of esters (32.55%), aldehydes (30.95%), and alcohols (12.91%). The relative content of limonene was 13.4 times higher in SPO (24.49%) than SCO, while no limonene was detected in SO. The relative content of limonene could therefore be used as a characteristic indicator to determine the extraction method. The relative contents of octane and 2,2,4,6,6-pentamethylheptane were 9.73% and 9.75% in SO, but were absent from SPO and SCO. These two volatile compounds may be exogenously supplied by the solvent used during the extraction process. Whether these two volatile compounds are indicative of the solvent extraction technique requires further evaluation.