## 3 Results and Discussion
### Building a Formulation as RM for the Rancid Defect  
Figure 4 shows the chromatogram of a rancid VOO (Md = 9.5) in which relevant compounds were identified. To build a RM for this defect, the initial formulation (R1, Table 4) was prepared with the main markers of a rancid perception that were selected as \"primary compounds\" (hexanal, nonanal, Table 2) [18; 22; 37; 38]. The dilution of these two compounds alone (600 mg/kg and 80 mg/kg for hexanal and nonanal respectively) produced a chemical perception far from actual VOOs, and was qualified as \"chemical\" or \"non-natural\" by assessors. Consequently, as in the formulations for winey-vinegary defect, this formulation also required addition of a \"green base aroma\". In the initial formulation, _E_-2-hexenal was excluded from the compounds producing the green perception, since their aroma was distinctly perceived as green almond, and only two volatiles, 1-hexanol and _E_-3-hexen-1-ol, were added at 20 mg/kg and 40 mg/kg, respectively, to reproduce the green aroma. However, aldehydes, which are the main markers of the rancid perception because their concentrations mainly result from oxidation processes [39], are also associated with a green-fruity sensory note when they are present at low  
concentrations; hexanal is the paradigm. This simple fact means that if the concentration of aldehydes reaches the olfactory receptors of assessors at low concentrations, due to the dispersion of molecules in air, they will firstly perceive a green odor that can be followed by a rancid one once the concentration increases with time. The duality of aroma characteristics of hexanal under different concentrations and air flow rates was shown in a previous study in which assessors reported both rancid and green aroma [30]. Thus, R1 was qualified by most assessors as green aroma ending with a slight rancid perception (Table 4). Furthermore, it was observed that, at the same concentration, the prevalence of green or rancid perception greatly depended on the assessors, who repeatedly noted one of the two types of aroma when they smelled the formulation in repeated experiments. This observation pointed out a subjective dependence, which obliged us to reconsider the initial formulation to provide an aroma that the assessors defined as unquestionably rancid. As a first approach for the reformulation, the combination of hexanal and nonanal to emulate rancid aroma was studied by sensory assessment of two dilutions at 600 mg/kg and 6000 mg/kg of both compounds individually. When hexanal was presented to assessors at 600 mg/kg, its aroma was \begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **Sensory Descriptors** & **Code** \\ \hline
600 & 80 & 20 & 40 & - & - & - & - & Green aroma ending with slight rancid sensory notes & R1 \\
100 & - & 100 & 100 & 600 & 600 & 600 & Rancid but slightly green as well, a little sweet, undesirable & R2 \\
50 & - & 50 & 50 & 50 & 600 & 600 & Rancid but slightly green, rancid but a little sweet & R3 \\
35 & - & 35 & 35 & 35 & 600 & 600 & 600 & Slight green, slightly rancid, sweet, ripe fruity, rancid nuts, rancid aftertaste & R4 \\
600 & - & 1.5 & 1.5 & 1.5 & 600 & 600 & Rancid intensely rancid, nuts & R5 \\
600 & - & 1.5 & 1.5 & 1.5 & - & 363 & 420 & Intensely rancid, nuts, seeds & R6 * \\ \hline \end{tabular}
\end{table} 
Table 4: Main formulations (volatile compounds and concentrations in mg/kg) emulating rancid aroma in VOO that resulted from Modified Simplex Procedure and evaluated by a set of assessors about their eligibility as possible RM. Note: **1**, hexanal; **2**, nonanal; **3**, 1-hexenol; **4**, _E_-3-hexen-1-ol; **5**, _E_-2-hexenal; **6**, \(E\),_E_-2,4-hexadien; **7**, \(E\),_E_-2,4-decadienal; **8**, _E_-2-decadien; * pentanoic acid (500 mg/kg) and hexanoic acid (500 mg/kg) were added to the formulation. Figure 4: Chromatogram of a VOO qualified with an intensity (median of the defect) of 9.5 of the rancid aroma defect.