## 2 Results and Discussion  
### Discrimination of Different Flower Stages by Electronic Nose  
_C. odorata_ flowers were selected on the basis of their botanical characteristics to evaluate floral volatile polymorphisms according to different development stages: bud, display-petal, initial-flowering,full-flowering, end-flowering, wilted-flower, and dried flower stages [12] (Figure 1). To discriminate the different flower stages better, an electronic nose was coupled with discriminant factor analysis (DFA) [13,14] to classify the aroma emitted by _C. odorata_ flowers. The process was conducted by using signals corresponding to four repeated exposures of each stage, as shown in Figure 2. The DFA score plot in Figure 2 shows that the electronic nose effectively discriminates each of the different flower stages of _C. odorata_. The first two discriminant factors, DF1 (81.16%) and DF2 (16.36%), explain 97.52% of total system variance. DFA is as valid as the multivariate statistical model if the percentage of recognition is higher than 90% [14]. In this case, the percentage of recognition was 97.52% (maximum 100%), which indicates that a certain degree of discrimination was achieved. For instance, the initial-flowering, full-flowering, and end-flowering stages were clearly distinguishable from one group to another, although a small overlap was observed between the bud and display-petal stages. These results show that the odors emitted at different stages of _C. odorata_ flower development evidently differed. As [PERSON] and [PERSON] [13] suggested, electronic nose analysis based on botanical characteristics is a useful technique to discriminate flower aromas at different stages. Analysis of C. odorata Floral Volatile Polymorphism by Headspace-Solid Phase Microextraction-Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS)  
Previous researchers [7; 8; 9; 10] have extensively investigated the volatile compositions of essential oils from _C. odorata_ flower by using the hydrodistillation method [10; 15]. However, distillation has several disadvantages, including time consumption, and loss of target compounds because of thermal degradation [16; 17; 18; 19; 20]. Studies on the volatile compounds present at different stages of _C. odorata_ flower development have never been conducted elsewhere. Therefore, the volatile compounds in _C. odorata_ flowers were analyzed by using HS-SPME coupled with GC-MS. Table 1 shows the 92 components identified over the flower-life. These components include 47 hydrocarbons, 17 esters, 14 alcohols, seven aldehydes, two phenols, 1 acid, three ketones, and one ether. In accordance with the report by [PERSON] _et al._[9], [PERSON] and [PERSON] [3], the total profile of the volatile compounds in all studied stages reveals the predominance of hydrocarbons, esters, alcohols, and aldehydes (Figure 3). Of these 92 compounds, 11 were particularly identified in the full-flowering stage on the basis of 15 AFNOR (ISO 3063: 2004 (E)). This finding is considered as characteristic of ylang-ylang essential oil. Additionally, volatile compositions varied considerably among the seven life-flower stages of _C. odorata_ flowers. The mean Bray-Curtis similarity (_BCS_) value was 52.45% \(\pm\) 11.61% (range: 32.84%-77.34%, \(n\) = 21 comparisons, Table 2). The full-flowering stage was more similar to the initial-flowering stage (\(BCS\) = 59.68%) than to the dried flower stage (\(BCS\) = 42.63%), and was largely dissimilar to the wilted-flower stage (\(BCS\) = 35.02%). As regards the comparison among the studied stages, 10 volatiles among the total volatile constituents notably existed in all life-flower stages, whereas 11 more volatile compounds were present in four of the seven stages. The results showed low similarity among the seven stages, although several constitutes [\(\alpha\)-cadinol, farnesol isomer \(a\), nerolidol, \(\alpha\)-pinene, _etc._] were exclusively identified in different stages. The pattern may indicate a relatively high volatile diversity variation at a full life-flower scale.