# Compositional Analysis and Aroma Evaluation of Feijoa Essential Oils from New Zealand
## 2 Results and Discussion
### Aroma Active Compounds in Feijoa Essential Oil  
Further to the compositional analysis of the essential oils from the four feijoa cultivars, the aroma active compounds of the essential oils were identified using the HS-SPME-GC-O-MS and they were characterized with aroma description and intensity. Due to the solvent free and non-destructive nature of the samples [39], the technique of HS-SPME is widely employed in the detection of aromatic volatile compounds in various matrixes [40; 41; 42]. As a result, a total of 97 compounds were detected by SPME-GC-MS (Table 1, compounds marked with *). A few compounds that were discovered by GC-MS liquid injection were not detected. These compounds were either at extremely low concentrations or had a high boiling point. In particular, the compounds with a retention index (RI) larger than 1847 (after No. 131 in Table 1) were not extracted by SPME. Similar findings from [PERSON], [PERSON] and [PERSON] [42] working on agarwood essential oil were observed. To the contrary, two compounds, 3-octanyl acetate and \(\beta\)-selinene, were only detected by SPME-GC-MS, which could be due to the fact that SPME concentrates volatile compounds, enabling the detection of the compounds at trace amounts [39]. Therefore, a total of 160 compounds were detected in feijoa essential oils by both GC-MS and SPME-GC-MS and 90 of them were reported for the first time. As shown in Table 2, 24 aroma active compounds consisting of eight esters, eight terpen, three alcohols, two ketones, and three unknown compounds were identified by olfactory tests. The four chemical groups were also major compositional classes in feijoa essential oil (Figure 3). The most important aroma active compound, which was consistently detected with'strong' intensity (aroma intensity \(>\) 4) in the four essential oils, was the 'fresh and minty' \(\alpha\)-terpineol. Other major aroma contributors, with an average intensity above 3 in all essential oils, were the 'fresh and fruity' ethyl benzoate, the 'honey-like' (\(Z\))-3-hexenyl hexanoate, the 'floral' linalool, the 'fruity and peach-like' (\(E\))-geraniol, the 'bitter and herbal' 2-undecanone, the'mushroom-like' 3-octanone, the'sweet and herbal' \(\alpha\)-cubebene, the'sweet, herbal, and floral' germacrene D, and two of the unknown compounds identified with the 'bitter and pungent' and the 'fruity and honey-like' notes (RI of 1153 and 1367, respectively, in Table 1). However, the essential oils from the four feijoa cultivars were found to consist of various aroma active compounds. The 'banana-like' (\(Z\))-3-hexenyl acetate was only detected in the Apollo and Wiki Tu essential oils, the 'fresh and minty' (\(4E\),\(6Z\))-allo-ocimene were not perceived in the Apollo and Unique essential oils, and the'sweet and herbal' (\(E\))-\(\beta\)-ocimene and the'mushroom-like' \(\beta\)-ocimene were not present in the Apollo and Unique essential oil, respectively. Thus, these compounds could be used to differentiate essential oils from different feijoa cultivars. Furthermore, the perceived aroma intensity of each compound also differed among the essential oils from the four cultivars. Some aroma active compounds were found to be specifically important in one or more cultivars. The 'feijoa-like' methyl benzoate and the'metallic' \(\beta\)-myrcene were dominant aromatic compounds; both scored the highest aroma intensity in Apollo essential oils. The two compounds were also among the principle aromatic compounds in the Wiki Tu essential oil (aroma intensity at 3.67 and 4.33, respectively). Methyl benzoate was previously reported to be responsible for the characteristic 'feijoa-like' aroma [16], which is consistent with our olfactory result. The 'herbal' \(\delta\)-cadinence contributed greatly to the aroma of the Opal Star essential oil (aroma intensity of 4.33) and also played an important role in the aroma of the Unique and Wiki Tu essential oil (aroma intensity at 3.33 and 3.67 respectively), while it was only detected to be 'weak' in the Apollo essential oil.